Faculty Profiles - Suzuki Hiroki

Attempt to quantify the impact of seasonal air density variation on operating tip-speed ratio of small wind turbines Reviewed

Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2090/1/012145/pdf

Hiroki Suzuki, Yutaka Hasegawa, O.D. Afolabi Oluwasola, Shinsuke Mochizuki

Journal of Physics: Conference Series 2090 ( 1 ) 012144 - (8 pages) 2021.12

Authorship：Lead author,　Corresponding author Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

<title>Abstract</title>
This study presents the impact of seasonal variation in air density on the operating tip-speed ratio of small wind turbines. The air density, which varies depending on the temperature, atmospheric pressure, and relative humidity, has an annual amplitude of about 5% in Tokyo, Japan. This study quantified this impact using the rotational speed equation of motion in a small wind turbine informed by previous work. This governing equation has been simplified by expanding the aerodynamic torque coefficient profile for a wind turbine rotor to the tip-speed ratio. Furthermore, this governing equation is simplified by using nondimensional forms of the air density, inflow wind velocity, and rotational speed with their characteristic values. In this study, the generator’s load is set to be constant based on a previous analysis of a small wind turbine. By considering the equilibrium between the aerodynamic torque and the load torque of the governing equation at the optimum tip-speed ratio, the impact of the variation in the air density on the operating tip-speed ratio was expressed using a simple mathematical form. As shown in this derived form, the operating tip-speed ratio was found to be less sensitive to a variation in air density than that in inflow wind velocity.

DOI： 10.1088/1742-6596/2090/1/012144

Numerical simulation of viscosity/implicit large-eddy steady turbulence with the Reynolds number dependency Reviewed

Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2090/1/012144/pdf

Simplified numerical modeling of rotational speed response for a small wind turbine Reviewed

(peer-reviewed) Proceedings of the International Conference on Power Engineering 2021 (ICOPE-2021) paper No.0130 - (4 pages) 2021.10

Naoyuki Iwata, Hiroki Suzuki, Shinsuke Mochizuki

Journal of Physics: Conference Series 2047 ( 1 ) 012007 - (7 pages) 2021.10

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

<title>Abstract</title>
This study presents a numerical analysis that models small scale turbulence using numerical viscosity or implicit large-eddy simulation (LES). The motivation for focusing on these models is that the sub-grid scale components of LES are assumed to have a sufficiently high Reynolds number turbulence. The Reynolds number dependence of steady isotropic turbulence is used to validate the present analysis. Here, this dependency ranges from low to high Reynolds numbers. The results of this analysis are validated by comparing them with those of direct numerical simulation. The donor cell method and quick method are used as schemes of the numerical viscosity. Analysis based on the numerical viscosity can give accurate turbulent kinetic energy values at high Reynolds numbers and implicit LES at low Reynolds numbers. However, these models did not accurately predict static pressure fluctuations. These results were discussed by visualizing the large-scale turbulent structures.

DOI： 10.1088/1742-6596/2047/1/012007

Effects of spatial resolution anisotropy on viscous terms using isotropic steady turbulence numerical analysis Reviewed

Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2047/1/012007/pdf

Riku Hirabayashi, Hiroki Suzuki, Shinsuke Mochizuki

Journal of Physics: Conference Series 2047 ( 1 ) 012008 - (7 pages) 2021.10

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

<title>Abstract</title>
This study presents the effects of spatial resolution anisotropy on an isotropic turbulence field. Here, this turbulence field is steady. In order to set the anisotropy of the spatial resolution, the accuracy order of the viscosity terms is set to be anisotropic. The convection and viscosity terms are discretized using the second-order or fourth-order central difference schemes. The Reynolds number dependence of the turbulence statistics is used to examine this influence. The effects of resolution anisotropy on the small-scale turbulent field obtained by longitudinal derivatives as well as large-scale turbulent fields are small. On the other hand, the small-scale turbulent field obtained by lateral derivatives is significantly affected by the anisotropy of resolution in the low Reynolds number condition.

DOI： 10.1088/1742-6596/2047/1/012008

Effect of the kinetic energy conservation error on unsteady/steady isotropic turbulence: a numerical simulation study Reviewed

Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2047/1/012008/pdf

Shinnosuke Nakamura, Hiroki Suzuki, Shinsuke Mochizuki

Journal of Physics: Conference Series 2047 ( 1 ) (8 pages) - 012009 2021.10

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

<title>Abstract</title>
This study presents the effects of the conservation error of turbulent kinetic energy on the isotropic turbulence field. Here, the present research focuses on the effects on the unsteady turbulence field in addition to the steady field. This unsteady turbulence field is given by changing the magnitude of the external forcing term using a linear forcing scheme with a sinusoidal function. The conservation error is caused by using the Crank-Nicolson method, which is an implicit time integration method. This result is examined by comparing those with the results with negligible conservation error using the fourth-order Runge-Kutta scheme. For this unsteady turbulence, the period and amplitude of the external forcing term are changed as computational conditions. In contrast to steady turbulence, unsteady turbulence is shown to be affected by turbulent kinetic energy conservation error. These effects are significant when the period is short and the amplitude is large.

DOI： 10.1088/1742-6596/2047/1/012009

Time-series observation of the effects of kinetic energy conservation error on isotropic and anisotropic steady incompressible turbulence Reviewed

Other Link： https://iopscience.iop.org/article/10.1088/1742-6596/2047/1/012009/pdf

Visualization of intermittency of low-Reynolds-number anisotropic steady incompressible turbulence using implicit/SGS-model-based large-eddy simulation Reviewed

Journal of Physics: Conferense Series 1983 012041 - (8 pages) 2021.8

Ryoma Honda, Hiroki Suzuki, Shinsuke Mochizuki

Journal of Physics: Conference Series 1978 ( 1 ) 012026 - (7 pages) 2021.7

Scalar structures around the mixing interface of a thermal mixing layer in multiscale-generated decaying turbulent flows visualized using DNS database Reviewed

Shotaro Jomura, Hiroki Suzuki, Shinsuke Mochizuki, Yasuhiko Sakai

Journal of Physics: Conference Series 1978 ( 1 ) 012012 - (7 pages) 2021.7

Reynolds Number Dependency of Small Scale Structures in Steady Anisotropic Turbulence Produced by Implicit Large-Eddy Simulation Reviewed

Mayuka Oshibuchi, Hiroki Suzuki, Shinsuke Mochizuki

Journal of Physics: Conference Series 1978 012021 - (8 pages) 2021.7

Autocorrelation Function for Estimating Static Pressure Fluctuation Intensity in Incompressible Homogeneous Turbulence under an Intermediate Reynolds Number Reviewed

Hiroki Suzuki, Shinsuke Mochizuki, Yutaka Hasegawa

Journal of Physics: Conference Series 1978 ( 1 ) 012002 - (8 pages) 2021.7

An experimental study on the equilibrium boundary layer subjected to favourable pressure gradient (Effect of pressure gradient on law of the wall) Reviewed

Yudai Hikita, Hiroki Suzuki, Takatsugu Kameda, Shinsuke Mochizuki

Transactions of the JSME 87 ( 894 ) 20-00394 - 00394 2021.1

Reduced Conservation Error of Kinetic Energy using a Runge-Kutta Algorithm with Reduced Numerical Dissipation Reviewed

Hiroki Suzuki, Koudai Hasebe, Yutaka Hasegawa, Tatsuo Ushijima

Journal of Physics: Conference Series 1633 012021 - (9 pages) 2020.9

Simple Scheme generating an Axisymmetrically Anisotropic Initial Flow of Incompressible Turbulence using a Normal Random Number Vector Reviewed

Hiroki Suzuki, Koudai Hasebe, Yutaka Hasegawa, Tatsuo Ushijima, Shinsuke Mochizuki

Journal of Physics: Conference Series 1592 012004 - (8 pages) 2020.9

Second-Order Kinetic Energy-Conservative Analysis of Incompressible Turbulence under a Collocated Grid System Reviewed

Hiroki Suzuki, Yutaka Hasegawa, Masaya Watanabe, Tatsuo Ushijima, Shinsuke Mochizuki

Journal of Physics: Conference Series 1633 012063 - (9 pages) 2020.9

Small Transparent Prism for the Cross-Sectional Visualization for a Turbulent Scalar Mixing Layer using a Water-Channel PLIF Method Reviewed

Ryota Ukai, Hiroki Suzuki, Shinsuke Mochizuki, Yasuhiko Sakai

Journal of Physics: Conference Series 1592 012001 - (7 pages) 2020.9

Verification of the Numerical Analysis Using a Collocated Grid System Directly Solving the Quasi-Inviscid Incompressible Flow around a Symmetric Airfoil Reviewed

Hiroki Suzuki, Masaya Watanabe, Yutaka Hasegawa, Shinsuke Mochizuki

Journal of Physics: Conference Series 1633 012028 - (10 pages) 2020.9

Influence of Order Enhancement of the Runge-Kutta Method on Low-order Turbulence Statistics of Incompressible Wall Turbulence under a Second-order Central Difference Scheme Reviewed

Shotaro Jomura, Hiroki Suzuki, Yutaka Hasegawa, Shinnosuke Matsuo, Shinsuke Mochizuki

Journal of Physics: Conference Series 1592 012095 - (9 pages) 2020.9

Quasi-Analytical Solutions of a Turbulence-Modeling Equation on the Robustness of Decaying Homogeneous Turbulence Reviewed

Hiroki Suzuki, Shinsuke Mochizuki, Yutaka Hasegawa

Advances in Mechanical Engineering 12 ( 2 ) 1 - 13 2020.2

Simple Analytical Solutions of One-Equation Modelling for Steady/Decaying Homogeneous Turbulence sensitized to Small Strain Reviewed

Hiroki Suzuki, Shinsuke Mochizuki, Yutaka Hasegawa

Journal of Physics: Conference Series 1324 012063 - (8 pages) 2019.10

Simple Mean-Error Estimation of a Recalibration Scheme for Constant-Temperature Anemometry Measurements Reviewed

Hiroki Suzuki, Yoshiaki Shikata, Shinsuke Mochizuki, Yutaka Hasegawa

Journal of Physics: Conference Series 1324 012062 - (7 pages) 2019.10

Monte-Carlo Simulation Study for Uncertainty Evaluation in Turbulent Statistics Obtained by Constant-Temperature Anemometry Reviewed

Kenji Fujita, Hiroki Suzuki, Shinsuke Mochizuki

Journal of Physics: Conference Series 1324 012068 - (8 pages) 2019.10

Turbulence-Model Validation of Wind-Tunnel-Blockage Effects on the Grid-Generated Turbulence Reviewed

Naru Itamura, Hiroki Suzuki, Shinsuke Mochizuki

Proceedings of the 7th Joint Conference on Renewable Energy and Nanotechnology (JCREN2018) Paper IN_03 - (4 pages) 2018.12

Energy Transport Mechanisms in the Outer Layer of the Turbulent Boundary Layer Subjected to Favourable Pressure Gradient Reviewed

Suyako Mizukami, Hiroki Suzuki, Shinsuke Mochizuki

Proceedings of the 7th Joint Conference on Renewable Energy and Nanotechnology (JCREN2018) Paper IN_04 - (4 pages) 2018.12

Numerical Simulation Study on the Incompressible Decaying Turbulent Flows Affected by the Divergence of the Viscous Terms Reviewed

Kazunobu Nomura, Hiroki Suzuki, Shinsuke Mochizuki

Proceedings of the 7th Joint Conference on Renewable Energy and Nanotechnology (JCREN2018) Paper IN_01 - (4 pages) 2018.12

Numerical Study on the Low Reynolds Number Steady Incompressible Turbulence due to Isotropic/Anisotropic Forcing Reviewed

Shotaro Jomura, Hiroki Suzuki, Shinsuke Mochizuki

Proceedings of the 7th Joint Conference on Renewable Energy and Nanotechnology (JCREN2018) Paper IN_02 - (4 pages) 2018.12

Numerical-Based Theoretical Analysis on the Decay of Homogeneous Turbulence affected by Small Strain based on Constant and Linear Strain Variations Reviewed

Hiroki Suzuki, Kenji Fujita, Shinsuke Mochizuki, Yutaka Hasegawa

Journal of Physics: Conference Series 1053 012039 - (7 pages) 2018.8

Numerical Investigation on the Sensitivity of Turbulence Statistics to Small Velocity Variations in Grid-Generated Turbulence based on k-ε model Reviewed

Yoshiaki Shikata, Hiroki Suzuki, Shinsuke Mochizuki

Advanced Experimental Mechanics 3 78 - 85 2018.8

Shear stress vector measurement using a circular sublayer plate with multiple pressure taps Reviewed

Dan Hua, Hiroki Suzuki, Shinsuke Mochizuki

AIAA Journal 56 ( 6 ) 2138 - 2144 2018

Local Wall Shear Stress Measurement with a Rectangular Plate Submerged in the Sublayer Reviewed

Hua Dan, Hiroki Suzuki, Shinsuke Mochizuki

Extended Abstracts of the Ninth JSME-KSME Thermal and Fluids Engineering Conference TFEC9-1021 - (5 pages) 2017.10

Validation Scheme for Effects of Wind-tunnel Blockage for Spatially Varying Acceleration Parameter Reviewed

Hiroki Suzuki, Kenji Fujita, Shinsuke Mochizuki

Advanced Experimental Mechanics 2 53 - 58 2017.8

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：The Japanese Society for Experimental Mechanics

<p>We have been studying a validation scheme for the effects of wind-tunnel blockage on grid-generated turbulence. The focus is the effects of the streamwise variation of the acceleration parameter characterizing the fluid acceleration. First, a method is used for calculating the value of the acceleration parameter from the profile of the streamwise mean velocity. Then, a validation scheme based on the spatially varying acceleration parameter is derived. This derived validation scheme builds on the standard k-ε model. The effects of the streamwise variation of the acceleration parameter are found to be somewhat large. Also, the decay exponent of grid-generated turbulence is sensitive to the streamwise variation of the acceleration parameter.</p>

DOI： 10.11395/aem.2.0_53

Validation Scheme for Small Effect of Wind Tunnel Blockage on Decaying Grid-Generated Turbulence Reviewed

Local Wall Shear Stress Measurements with a Thin Plate Submerged in the Sublayer in Wall Turbulent Flows Reviewed

Hua Dan, Hiroki Suzuki, Shinsuke Mochizuki

Experiments in Fluids 58 124 - (11 pages) 2017.8

Numerical investigation using an exact solution of the effects of non-solenoidality of the viscous terms on the incompressible flow Reviewed

Hiroki Suzuki, Shingo Hattori, Shinsuke Mochizuki

Journal of Fluid Science and Technology 12 ( 1 ) 16-00257 - (13 pages) 2017

Simple Model of Decay of Homogeneous Turbulence Affected by Weak Fluid Acceleration Reviewed

Hiroki Suzuki, Shinsuke Mochizuki

Proceedings of the 20th Australasian Fluid Mechanics Conference Paper No.411 - (4 pages) 2016.12

Basis Study on the Output-Voltage Variation of Constant-Temperature Anemometry at Freestream Velocity Reviewed

Hiroki Suzuki, Shingo Hattori, Shinsuke Mochizuki, Yutaka Hasegawa

Advanced Experimental Mechanics 1 36 - 41 2016.8

Effect of Fluid Acceleration due to Area Reduction of a Wind Tunnel on Temporally and Spatially Decaying Grid Turbulence Reviewed

Hiroki Suzuki, Shinnosuke Matsuo, Shinsuke Mochizuki, Yutaka Hasegawa

Advanced Experimental Mechanics 1 15 - 22 2016.8

Hiroki Suzuki, Shinsuke Mochizuki, Yutaka Hasegawa

Journal of Fluid Science and Technology 11 ( 3 ) 16-00195 - (13 pages) 2016.7

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers, JSME

<p>This paper proposes a validation scheme for the effect of wind tunnel blockage on decaying grid-generated turbulence. This validation scheme was derived from the governing equations of the k-∈ model. Analytical solutions for the validation scheme were derived by introducing a model of the difference between the rate of change of the effect of fluid acceleration on the turbulent kinetic energy and that of the effect on its dissipation. The derived solutions include a decay exponent that excludes the acceleration effect, a parameter characterizing the acceleration, the initial anisotropy, and the model coefficient of the k-∈ model, and can be quantified by parameters which can be known. The physical meaning of the model was clarified. The derived solutions and model were confirmed to be accurate through numerical simulation. An equation for the decay exponent, which is also affected by the fluid acceleration, was developed using the derived solutions. This scheme was applied to the examination of the reduced fluid acceleration effect in a moderate-sized wind tunnel to measure the grid-generated turbulence. The fluid acceleration effect in the wind tunnel was confirmed to be small using the derived equations. The decay characteristics of the grid-generated turbulence in the wind tunnel were measured and were found to agree with those obtained in previous experiments.</p>

DOI： 10.1299/jfst.2016jfst0012

Research of electric power regeneration using automotive cooling fan (Influence of wind turbine on air resistance through vehicle cooling system) Reviewed

Other Link： https://jlc.jst.go.jp/DN/JLC/20023288926?from=CiNii

Shinsuke Mochizuki, Hiroki Suzuki, Hitoshi Tokunaga, Takatsugu Kameda

Proceedings of the 5th International Conference on Jets, Wakes and Separated Flows (ICJWSF2015) 185 ( 1 ) 317 - 324 2016

Mixing and diffusion in regular/fractal grid turbulence

Yasuhiko Sakai, Koji Nagata, Hiroki Suzuki, Yasumasa Ito

CISM International Centre for Mechanical Sciences, Courses and Lectures 568 17 - 73 2016

Research of Electric Power Regeneration using Automotive Cooling Fan (Improvement of Fan Efficiency by Diffuser) Reviewed

Yoshitaka Wagayama, Shinichi Oda, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima

Proceedings of the International Symposium on EcoTopia Science 2015 Paper No. 1035 - (1 page) 2015.12

Study on Pitch Motion Optimization of Wing-Stroke Wind Turbine Reviewed

Hironori Nakano, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima

Proceedings of the International Symposium on EcoTopia Science 2015 Paper No. 1028 - (1 page) 2015.12

A Small Wind Tunnel with Lower Fluid Acceleration Reviewed

Shinnosuke Matsuo, Hiroki Suzuki, Yutaka Hasegawa, Tatsuo Ushijima, Shinsuke Mochizuki

Proceedings of the 10th International Symposium on Advanced Science and Technology in Experimental Mechanics Paper No.A111 - (6 pages) 2015.11

Fundamental Study on the Temporal Variation of CTA Calibration Curves Reviewed

Hiroki Suzuki, Shinsuke Mochizuki, Yutaka Hasegawa

Proceedings of the 10th International Symposium on Advanced Science and Technology in Experimental Mechanics Paper No.A112 - (6 pages) 2015.11

Shinichi Oda, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima, Hideki Ooya

Transactions of the JSME (in Japanese) 81 ( 830 ) 14-00169 - (16 pages) 2015.9

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

This work aims at developing a new fan-turbine that operates as a cooling fan at a low vehicle speed and operates as a wind turbine at a high vehicle speed to generate electric power. The present paper reports the influence of a wind turbine on air resistance through a vehicle cooling system. We have developed a method to measure air resistance by using a general-purpose facility and the following results have been provided. The wind turbine operation reduces air resistance through the cooling system and regenerates electric power simultaneously. Furthermore we have confirmed the influence of the wind turbine on air resistance through the vehicle cooling system by using a CFD analysis.

DOI： 10.1299/transjsme.14-00691

Research of electric power regeneration using automotive cooling fan (Enhancement of wind turbine power by installing high solidity rotor on vehicle) Reviewed

Shinichi Oda, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima, Hideki Ooya

Transactions of the JSME (in Japanese) 81 ( 829 ) 15-00042 - (12 pages) 2015.8

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

This work aims at developing a new cooling fan for vehicle engine. This fan can operate as a cooling fan at low vehicle speed. At high vehicle speed, however, the fan is rarely used as a cooling fan. Therefore the fan can be used as a wind turbine, which generates electric power. In the previous report we had confirmed the effect of S-Shaped blade profile on the wind turbine efficiency by CFD analysis and the experiments. The present paper reports the enhancement of wind turbine power by installing high solidity rotor on a vehicle. High solidity rotor can increase the wind turbine efficiency and receive more input power due to the increased rate of the rotor resistance to the total resistance through the cooling system, although the air flow rate through the system decreases. We confirmed by the estimation and the actual vehicle test that the high solidity rotor can regenerate more electric power than the original low solidity rotor.

DOI： 10.1299/transjsme.15-00042

Development of a PIV System and a Measurement of Grid-Generated Turbulence

Research of electric power regeneration using automotive cooling fan (Improvement of wind turbine efficiency by high solidity rotor) Reviewed

Shinichi Oda, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima

Transactions of the JSME (in Japanese) 81 ( 827 ) 15-00069 2015.7

SUZUKI Hiroki, NAGATA Koji, SAKAI Yasuhiko

Journal of the Visualization Society of Japan 35 ( 139 ) 29 - 34 2015

Language：English Publisher：The Visualization Society of Japan

We develop a PIV system and validate it by measuring a grid-generated turbulence. We first show the background of this research before we approach the development of the system, and then, we describe the newly developed PIV system. We also describe an interpolation method, which we introduce into the PIV system, which notably decreases the uncertainty of PIV measurement. Then, we apply the PIV system to measurement of a grid-generated turbulent flow, and validate the PIV system by measuring the flow. First, an instantaneous flow field and basic characteristics of the flow are shown. Then, the energy decay of velocity fluctuation in the flow is shown, and coefficients of the decay law of the intensity are measured. Measuring the energy dissipation of the flow, we measure the value of these coefficients. The agreement of these coefficient values with those of previous experiments validates the PIV measurement.

DOI： 10.3154/jvs.35.139_29

DNS Study on the Development of Boundary Layer with Heat Transfer under the Effects of External and Internal Disturbances Reviewed

On Deviation of Operated Tip Speed Ratio of Small Wind Turbine due to Effect of Air Density Variation Reviewed

Hiroki Suzuki, Yutaka Hasegawa, Tatsuo Ushijima

Proceedings of National Symposium on Wind Engineering 23 103 - 108 2014.12

Research of electric power regeneration using automotive cooling fan (Improvement of wind turbine efficiency by changing blade profile) Reviewed

Shinichi Oda, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo UshijimaSHIJIMA

Transactions of the JSME (in Japanese) 80 ( 819 ) FE0315 - (11 pages) 2014.12

Improvement of Rotor Configuration for Achievement of Automotive Fan-Turbine System Reviewed

Shinichi Oda, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima

Proceedings of the Grand Renewable Energy 2014 International Conference and Exhibition Paper No. O-Wd-15-2 - (4 pages) 2014.7

A 3D Navier-Stokes Simulation under Staggered/Collocated Grids with High-Kinetic-Energy-Conservation Reviewed

Hiroki Suzuki, Shinnosuke Matsuo, Masaya Watanabe, Yutaka Hasegawa, Tatsuo Ushijima

Proceedings of the Grand Renewable Energy 2014 International Conference and Exhibition Paper No. P-Wd-2-22 - (3 pages) 2014.7

Effects of Blade Aspect Ratio on Aerodynamic Performance of Turbine Blade in Wing-Stroke Motion Reviewed

Hironori Nakano, Noriyuki Tanimura, Yutaka Hasegawa, Hiroki Suzuki, Tatsuo Ushijima

Proceedings of the Grand Renewable Energy 2014 International Conference and Exhibition Paper No. P-Wd-1-33 - (4 pages) 2014.7

Study of Tower Effects on Rotor Characteristics of Horizontal Axis Wind Turbine Reviewed

Noriyuki Tanimura, Yutaka Hasegawa, Hiroki Suzuki, Fumiya Hara, Tatsuo Ushijima

Proceedings of the Grand Renewable Energy 2014 International Conference and Exhibition Paper No. P-Wd-1-22 - (4 pages) 2014.7

Development and Application of a Navier-Stokes Simulation Code with High- Kinetic-Energy-Conservation Reviewed

Hiroki Suzuki, Shinnosuke Matsuo, Yutaka Hasegawa, Tatsuo Ushijima

Proceedings of the Grand Renewable Energy 2014 International Conference and Exhibition Paper No. O-Wd-1-2 - (3 pages) 2014.7

A study on effects of temporally varying/ fluctuating noises on statistical profiles measured by means of PLIF method (Development of prediction formulas of the effects, and validation by high-Sc-number scalar mixing layer in grid turbulence) Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Yutaka Hasegawa, Tatsuo Ushijima

Transactions of the JSME (in Japanese) 80 ( 813 ) FE0114 2014.5

Development of turbulence behind the single square grid Reviewed

Yi Zhou, Kouji Nagata, Yasuhiko Sakai, Hiroki Suzuki, Yasumasa Ito, Osamu Terashima, Toshiyuki Hayase

Physics of Fluids 26 ( 4 ) 045102 - (17 pages) 2014.4

Shuang XIA, Yasumasa Ito, Koji Nagata, Yasuhiko Sakai, Hiroki Suzuki, Osamu Terashima, Toshiyuki Hayase

Journal of Fluid Science and Technology 9 ( 1 ) JFST0005 - (13 pages) 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

The effects of external and internal disturbances on the development of boundary layer with heat transfer are investigated by means of direct numerical simulation (DNS) based on the finite difference scheme. The fractional step method is used to solve the governing equations. The external disturbance is generated by a regular turbulence-generating grid, while the internal disturbance is generated by a tripping object mounted on the wall. In order to clarify the momentum and heat transfer mechanism in a boundary layer under these effects, the instantaneous and statistical characteristics of velocity and temperature fields are presented and discussed along with their interactions. The results show that the boundary layer in the case with grid turbulence becomes turbulent even though the Reynolds number based on the momentum thickness is low. On the other hand, in the case with the tripping object, only low-amplitude fluctuations are generated in the vicinity of the tripping object and the boundary layer does not fully developed. The grid increases the skin friction and enhances heat transfer more significantly than the tripping object. It is also found that strong strain in the viscous sublayer, which is induced by the vortical motion in the buffer layer, contributes to the enhancement of heat transfer.

DOI： 10.1299/jfst.2014jfst0005

Direct Numerical Simulation of Grid-Generated Turbulence (Analysis on Invariants and Rotta Model) Reviewed

Relevance of turbulence behind the single square grid to turbulence generated by regular- and multiscale-grids Reviewed

Yi Zhou, Kouji Nagata, Yasuhiko Sakai, Hiroki Suzuki, Yasumasa Ito, Osamu Terashima, Toshiyuki Hayase

Physics of Fluids 26 ( 7 ) 075105 - (22 pages) 2014

Study on Blade Elasticity Influence on Blade Load Characteristics of NREL Turbine Reviewed

Fumiya Hara, Yutaka Hasegawa, Noriyuki Tanimura, Hiroki Suzuki, Tatsuo Ushijima

Proceedings of the International Symposium on EcoTopia Science 2013 Paper No. 1063 - (1 page) 2013.12

Numerical Study of Dynamic Inflow Effects on Aerodynamic Response of HAWT Rotor Reviewed

Yuta Taniguchi, Yutaka Hasegawa, Noriyuki Tanimura, Hiroki Suzuki, Tatsuo Ushijima

Proceedings of the International Symposium on EcoTopia Science 2013 Paper No. 1034 - (1 page) 2013.12

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase, Yutaka Hasegawa, Tatsuo Ushijima

Transactions of the Japan Society of Mechanical Engineering Series B (in Japanese) 79 ( 807 ) 2363 - 2374 2013.11

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

The aim of this study is to address the essential features of experimental decaying grid-generated turbulence. Specifically, this study has focused on invariants of grid turbulence in the downstream region and Rotta model by means of direct numerical simulation based on the finite difference method. The mesh Reynolds number defined by the mesh size of the grid M, streamwise mean velocity and kinematic viscosity is 2; 500. Streamwise computational domain size is 112 M. The result shows that u²_oL⁴ is nearly constant such that u²_oL⁴ ∝ X^0:08 in the far downstream region, where X = x/M - x_o/M, x is the streamwise distance from the grid and x_o is the virtual origin. Rotta model is applicable in the region holding u²_oL⁴ = constant, and value of the Rotta constant is almost 1. The value can be well estimated by an estimation method introduced by previous experiments.

DOI： 10.1299/kikaib.79.2363

Analysis of Flow Characteristics of Turbulent Plane Jets Based on Velocity and Scalar Fields Using DNS Reviewed

DNS of Channel Flow with Two-Scale Surface Roughness on One Wall Reviewed

Hiroki Suzuki, Richard J. Perkins

Proceedings of the 14th European Turbulence Conference Paper No. 115 - (2 pages) 2013.9

Study on the Effects of Grid-Generated Turbulence on the Initial Growth of Turbulent Boundary Layer by Direct Numerical Simulation Reviewed

S. Xia, Y. Ito, K. Nagata, Y. Sakai, H. Suzuki, O. Terashima, T. Hayase

Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows paper No. 1169 - (4 pages) 2013.9

Direct Numerical Simulation of Single-Square Grid-Generated Turbulence Reviewed

Y. Zhou, K. Nagata, Y. Sakai, H. Suzuki, Y. Ito, O. Terashima, T. Hayase

Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows paper No. 1102 - (5 pages) 2013.9

Effects of Initial Condition on Coherent Structure and Evolution of Turbulent Plane Jets Reviewed

N. Wu, Y. Sakai, K. Nagata, H. Suzuki, O. Terashima, T. Hayase

Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows paper No. 1010 - (6 pages) 2013.9

Measurement of Axial Turbulent Scalar Flux of High Sc/Low Re Round Jet Using Line Scan Camera Reviewed

Hiroshi Nishiyama, Tatsuo Ushijima, Hiroki Suzuki, Yutaka Hasegawa

Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows Paper No. 1193 - (5 pages) 2013.9

Development and Quantitative Validation of a Numerical Code Using Highly Energy-Conservative Scheme Reviewed

Masaya Watanabe, Hiroki Suzuki, Yutaka Hasegawa, Tatsuo Ushijima

Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows Paper No. 1170 - (4 pages) 2013.9

DNS Study on Pressure Characteristics of Fractal- Generated Turbulence Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase, Yutaka Hasegawa, Tatsuo Ushijima

Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows Paper No. 1109 - (4 pages) 2013.9

Nannan Wu, Yasuhiko Sakai, Kouji Nagata, Hiroki Suzuki, Osamu Terashima, Toshiyuki Hayase

Journal of Fluid Science and Technology 8 ( 3 ) 247 - 261 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Turbulent plane jets are prototypical free shear flows on which fundamental research can expand the overall understanding of turbulent flows. In this study, flow characteristics of the turbulent plane jets are studied by means of direct numerical simulation (DNS) based on the finite difference method. The effects of the initial conditions at the jet exit (i.e. Reynolds number and velocity profile) on the spatial development of velocity and scalar fields are mainly investigated. Meanwhile the instantaneous coherent structures, based on the Q-criterion and the local minimum of pressure, are presented. The results suggest that the plane jet flow with the higher Re (=U_bd/ν : U_b is the bulk mean velocity at the jet exit, d is the slot width, and ν is the kinematic viscosity) and the parabola velocity profile at the jet exit will correspond to the shorter potential core, furthermore, the lower Re and the parabola velocity profile will strengthen the decay of the mean field in the process of flow transition to full turbulence. The flow self-similarity will be achieved at shorter streamwise distance from the jet exit for the higher Re and the parabola velocity profile at the jet exit. Moreover, the dependency of coherent structures on the initial Reynolds number is remarkable, especially in the flow development region, but the change of initial velocity profile at the jet exit hardly acts on the scale of coherent structures. It is also observed that the scalar field is more sensitive to changes of initial conditions than the velocity field.

DOI： 10.1299/jfst.8.247

Wind Tunnel Experiments on the Spatial Development of Fractal-Grid Turbulence (2nd Report, Measurements of Turbulent Kinetic Energy Transport by Using I- and X-Type Hot-Wire Probes) Reviewed

DNS on Multiscale- Generated Grid Turbulence Using Classical Grid Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase, Yutaka Hasegawa, Tatsuo Ushijima

Proceedings of the 8th International Symposium on Turbulence and Shear Flow Phenomena Paper No. HOM1E - (6 pages) 2013.8

Fractal analysis of turbulent mixing in fractal-generated turbulence by planar laser-induced fluorescence Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Yutaka Hasegawa

Physica Scripta 88 ( 155 ) 014062 - (5 pages) 2013.7

An Attempt to Improve Accuracy of PIV Using an Interpolation Method Reviewed

Hiroki Suzuki, Tatsuo Ushijima, Yutaka Hasegawa, Kouji Nagata, Yasuhiko Sakai

Proceedings of the 12th Asian Symposium on Visualization Paper No.218 - (4 pages) 2013.5

Visualization of turbulent reactive jet by using direct numerical simulation Reviewed

Tomoaki Watanabe, Yasuhiko Sakai, Kouji Nagata, Osamu Terashima, Hiroki Suzuki, Toshiyuki Hayase, Yasumasa Ito

International Journal of Modeling, Simulation, and Scientific Computing 4 ( SUPPL.1 ) 1341001 - (16 pages) 2013

INABA Takuto, NAGATA Kouji, SAKAI Yasuhiko, SUZUKI Hiroyuki, TERASHIMA Osamu, SUZUKI Hiroki

Transaction of the Japan Society of Mechanical Engineering Series B 79 ( 804 ) 1476 - 1488 2013

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Spatial development of a turbulent field generated by a multiscale, fractal-grid is investigated in a wind tunnel. A square type (i.e., fractal elements with square shapes) fractal grid is placed at the inlet of the test section. The Reynolds number based on the length of the biggest grid bar is set to 5900. The spatial developments of cross-sectional profiles of turbulent kinetic energy K, dissipation rate of K, ε, and the advection, production, triple-correlation transport, pressure transport and viscous diffusion terms in the transport equation of K are measured by using a hot wire anemometer. The results show that in the upstream region, turbulence produced by the biggest grid bar is transported to the central and outward regions by the triple-correlation term T. In the decay region, there is low turbulence production downstream of the interior of the biggest grid bar, which is mainly transported outward rather than to the central region by T. The advection term is large and positive in the decay region whereas the pressure transport and the viscous diffusion terms are very small in the decay region.

DOI： 10.1299/kikaib.79.1476

Wind Tunnel Experiments on the Spatial Development of Fractal-Grid Turbulence (1st Report, Measurements of Fundamental Turbulence Properties by Using an I-Type Hot-Wire Probe) Reviewed

NAGATA Kouji, TERASHIMA Osamu

Transaction of the Japan Society of Mechanical Engineering Series B 79 ( 798 ) 115 - 125 2013

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Spatial development of a turbulent field generated by a multiscale, fractal-grid is investigated in a wind tunnel. A square type (i.e., fractal elements with square shapes) fractal grid is placed at the inlet of the test section. The Reynolds numbers based on the length of the biggest grid bar are set to 5900 and 11400. Turbulent characteristics in the downstream region of the grid are measured by using a hot wire anemometer. The results on the centerline statistics are compared with those in the previous experiments at the same Reynolds numbers. The results on the centerline statistics generally agree with the previous measurements despite the difference in the size of the test sections used. The spatial developments of cross-sectional profiles are also measured. It is found that the non-uniformity in the mean velocity field almost disappear in the downstream direction, although the non-uniformities of higher-order statistics are still observed even in the far downstream region. In the entire cross section of the tunnel, the ratio of the integral length scale L_u to the Taylor microscale λ hardly changes in the decay region of the rms velocity. These results will provide useful information in clarifying the non Richardson-Kolmogorov cascade process in the fractal-generated turbulence found in the previous measurement (Mazellier and Vassilicos, Physics of Fluids, Vol. 22, 075101 2010).

DOI： 10.1299/kikaib.79.115

Experimental Study on the Mixing of High-Schmidt-Number Scalar in Regular/Fractal Grid Turbulence Reviewed

Turbulence structure and turbulence kinetic energy transport in multiscale/fractal-generated turbulence Reviewed

Kouji Nagata, Yasuhiko Sakai, Takuto Inaba, Hiroki Suzuki, Osamu Terashima, Hiroyuki Suzuki

Physics of Fluids 25 ( 6 ) 065102 - (26 pages) 2013

NAGATA Kouji, TERASHIMA Osamu, ITO Yasumasa

Transaction of the Japan Society of Mechanical Engineering Series B 79 ( 799 ) 304 - 316 2013

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

High-Schmidt-number scalar mixing layers in a turbulent flow generated by regular and fractal grids are investigated by means of experiments using particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) technique. The Reynolds number based on the mesh size is 2,500. Rhodamine B is used as a fluorescent dye. The Schmidt number is about 2,100. The flow is separated into upper and lower layers by a splitter plate installed upstream of the grids; thus, the turbulent scalar mixing layers develop downstream of the grids. The results show that fractal grid turbulence has stronger turbulence intensity than that in regular grid turbulence. The decay exponent of turbulence intensity, n, is n = 1.21 for the regular grid and n = 1.40 for the fractal grid. The eddy diffusivity for mass in fractal grid turbulence is approximately four times larger than that in regular grid turbulence. The scalar dissipation in fractal grid turbulence is smaller than that in regular grid turbulence. Finally, it is concluded that turbulent scalar mixing is more enhanced by the fractal grid than by the regular grid.

DOI： 10.1299/kikaib.79.304

Effects of the Cylinder Wake in a Freestream on Statistical Properties of a Turbulent Boundary Layer Reviewed

NAGATA Kouji, TERASHIMA Osamu

Transaction of the Japan Society of Mechanical Engineering Series B 79 ( 799 ) 291 - 303 2013

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Effects of the cylinder wake in a freestream on statistical properties of a turbulent boundary layer over a flat plate are investigated by means of wind tunnel experiments. The cylinder is set horizontally over the flat plate and the interactions between its wake and the zero-pressure-gradient turbulent boundary layer are investigated. Instantaneous velocity is measured by using hot wire anemometry. The bursting events are detected by the variable interval time average (VITA) technique. The results show that the time-averaged mean velocity in the inner layer with the cylinder wake coincides with that without the cylinder wake. However, turbulence intensities normalized by the inner parameters are suppressed by the cylinder wake. It is found that the peak value of the velocity fluctuation during the sweep phase in the bursting event is increased by the cylinder wake.

DOI： 10.1299/kikaib.79.291

Investigation of Eddy Diffusivity in a Reactive Plane Jet by using Direct Numerical Simulation Reviewed

Quantitative visualization of high-Schmidt-number turbulent mixing in grid turbulence by means of PLIF Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai

Journal of Visualization 15 ( 2 ) 109 - 117 2012.5

Tomoaki Watanabe, Yasuhiko Sakai, Kouji Nagata, Osamu Terashima, Yasumasa Ito, Hiroki Suzuki, Toshiyuki Hayase

Communications in Computer and Information Science 323 CCIS ( PART 1 ) 144 - 150 2012

Improved PIV analysis using an interpolation technique (analysis on improvement effects of the fourier interpolation using quasi particle-images) Reviewed

Hiroki Suzukib, Kouji Nagata, Yasuhiko Sakai, Yutaka Hasegawa

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 78 ( 790 ) 1248 - 1259 2012

Quantitative Visualization of High-Schmidt-Number Scalar Mixing in Grid Turbulence Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai

Proceedings of the 11th Asian Symposium on Visualization Paper No. ASV11-04-05 - (8 pages) 2011.6

An experimental study on turbulent mixing of high-Schmidt-number scalar in grid turbulence by means of PIV and PLIF Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Ryota Ukai

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 ( D ) 3763 - 3767 2011

DNS on a spatially developing grid turbulence Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase

(全文査読付) Proceedings of the 13th European Turbulence Conference 318 032043 - (5 pages) 2011

Statistical properties of a turbulent boundary layer affected by grid-generated turbulence (analysis of spatial development by means of direct numerical simulation) Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 77 ( 775 ) 737 - 748 2011

Direct Numerical Simulation on Turbulence Structures in a Transition Process of a Spatially Developing Turbulent Plane Jet Reviewed

Hiroki Suzuki, Yasuhiko Sakai, Kouji Nagata, Daisuke Sugimoto

Proceedings of the 3rd International Conference on Jets, Wakes, and Separated Flows CD-ROM - (6 pages) 2010.9

Direct Numerical Simulation of Regular and Fractal-Grid Turbulence Using the Immersed Boundary Method and Fully Conservative Higher Order Finite-Difference Schemes Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase

International Review of Physics 4 ( 2 ) 83 - 90 2010.4

S0502-1-1 A DNS study on spatial structure of a turbulent plane jet

SUGIMOTO Daisuke, SUZUKI Hiroki, SAKAI Yasuhiko, NAGATA Kouji

The proceedings of the JSME annual meeting 2010 143 - 144 2010

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

Spatial structures of a turbulent plane jet are investigated by the direct numerical simulation (DNS) based on the finite difference method. Reynolds number is 1500. Special care has been paid to the boundary condition to reproduce proper entrainments. In this study, we focused on the pressure fluctuations, velocity gradient tensors, and rate-of-rotation tensors in the transition region of the jet, which are difficult to measure.

DOI： 10.1299/jsmemecjo.2010.2.0_143

S0502-7-4 On statistical properties of turbulent boundary layers affected by free-stream turbulence

TSUKUDA Saori, SUZUKI Hiroki, KITAYAMA Tomoyuki, NAGATA Kouji, SAKAI Yasuhiko

The proceedings of the JSME annual meeting 2010 217 - 218 2010

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

The effects of free-steam turbulence on a turbulent boundary layer are experimentally investigated by using a wind tunnel. For the case with free stream turbulence, turbulence-generating grid is placed upstream of the leading end of a flat plate, on which turbulent boundary layer is developed. The Reynolds number based on the momentum thickness is Re_θ=2990 for the case with and without grid turbulence. Instantaneous streamwise velocity is measured using a hot-wire anemometry with an inhouse I-type probe. The effects of free-stream turbulence on statistical properties of the turbulent boundary layer are discussed.

DOI： 10.1299/jsmemecjo.2010.2.0_217

S0502-7-3 Experimental Analysis of High-Schmidt-Number Scalar Mixing by means of High-Accuracy PLIF Technique

UKAI Ryota, SUZUKI Hiroki, NAGATA Kouji, SAKAI Yasuhiko

The proceedings of the JSME annual meeting 2010 215 - 216 2010

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

High-Schmidt-number scalar mixing layers in the grid turbulence are experimentally investigated in a water channel by means of the planar laser induced fluorescence (PLIF) technique and the time-resolved particle image velocimetry (PIV). A biplane square grid and a fractal square grid are used to generate turbulence. The Reynolds number based on the effective mesh size and mean velocity is 2,500 in both flows. Fluorescent dye (Rhodamine B; Schmidt number is about 2,100) is homogeneously premixed only in the upper stream, and therefore, the scalar mixing layer with an initial step profile develops downstream of the grid. Various turbulence quantities are evaluated and comparisons are made between turbulence and scalar fields generated by the regular and fractal grids.

DOI： 10.1299/jsmemecjo.2010.2.0_215

Direct numerical simulation of fractal-grid generated turbulence using an immersed boundary method and high accuracy finite-difference schemes Reviewed

Direct numerical simulation of turbulent mixing in regular and fractal grid turbulence Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase

Physica Scripta T T142 2010

Turbulence structure of multiscale generated turbulence by fractal grids and scalar transfer mechanism (2nd report, DNS on the influence of grid parameters on homogeneity, isotropy and intermittency) Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 ( 772 ) 2024 - 2031 2010

The image correction method for PLIF measurements of high-schmidt-number scalar transfer (Nonmetric corrections for temporospatial variation of laser intensity and time variation of fluorescence quantum yield) Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Ryota Ukai

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 ( 770 ) 1543 - 1551 2010

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase

Transaction of the Japan Society for Mathematical Science (in Japanese) 11 ( 1 ) 33 - 38 2009.12

Turbulence Structure of Multiscale Generated Turbulence by Fractal Grids and Scalar Transfer Mechanism : 1st Report, DNS on the Effect of Fractal Shapes on Turbulent Flow Field Reviewed

Hiroki Suzuki, Kouji Nagata, Yasuhiko Sakai, Toshiyuki Hayase, Takashi Kubo

Transactions of the Japan Society of Mechanical Engineering Series B (in Japanese) 75 ( 755 ) 1387 - 1394 2009.7

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Turbulence characteristics in the spatially developing fractal-generated turbulence are investigated by means of the direct numerical simulation (DNS). Three kinds of fractal grids, namely, cross, I and square types, are numerically constructed using the immersed boundary method. The results show that fractal grids generate high turbulence intensities compared with the classical grid turbulence using a biplane square mesh grid at the same mesh Reynolds number. Among the three types, the fractal square grid is the best to generate nearly homogeneous and isotropic turbulence in the far downstream decaying region. The integral length scale in the fractal generated turbulence remains approximately constant in the decaying region, whereas it grows downstream in the classical grid turbulence. These results are in good agreement with the previous experiments.

DOI： 10.1299/kikaib.75.755_1387