Article
Mechanics
T. O. Jelly, A. Ramani, B. Nugroho, N. Hutchins, A. Busse
Summary: The study reveals that ESy can strongly affect the roughness drag penalty, especially for low-ESx surfaces. Additionally, it is observed that specific low-ESy surfaces may result in reduced levels of outer-layer similarity in both mean flow and turbulence statistics, attributed to inadequate scale separation between the outer length scale and the in-plane spanwise roughness wavelength.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Fan Mo, Qiang Li, Likun Zhang, Zhenxun Gao
Summary: This paper investigates the method of generating inflow turbulence based on turbulence fluctuation library (TFL) in direct numerical simulation (DNS) of the hypersonic turbulent boundary layer (TBL). The application of the TFL method to the DNS of a supersonic TBL shows successful development to the target TBL downstream, despite significant differences in freestream between the TFL and the target TBL. New thermodynamic fluctuations scaling laws are derived to address the defects of the current TFL method under hypersonic TBL, resulting in more rational and accurate scaling laws. The study also highlights the importance of matching the friction Reynolds number (Re-tau) between the TFL and the target TBL in determining the length of recovery distance.
Article
Mechanics
A. Rouhi, M. K. Fu, D. Chandran, A. Zampiron, A. J. Smits, I. Marusic
Summary: Turbulent drag reduction through streamwise travelling waves is investigated over a wide range of Reynolds numbers. Wall-resolved large-eddy simulations are conducted to examine how the frequency and wavenumber of the travelling wave influence the drag reduction. The study finds that the level of turbulence attenuation, and hence drag reduction, changes with the near-wall Stokes layer protrusion height. A range of frequencies is identified where the Stokes layer attenuates turbulence and increases the drag reduction, while outside this range, the strong Stokes shear strain leads to a drop in drag reduction.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Computer Science, Interdisciplinary Applications
Philipp Bahavar, Claus Wagner
Summary: Condensation is an important aspect in flow applications, and simulating the gas phase and tracking the deposition rates of condensate droplets can capture the effects of surface droplets on the flow while reducing computational costs.
COMPUTERS & FLUIDS
(2024)
Article
Mechanics
Xiao-Ping Chen, Deng-Song Huang, Shuo Zhao, Chen-Shao Zhu
Summary: This study conducts direct numerical simulations to investigate the influence of compressibility effects on turbulent statistics and large-scale structures in temporally evolving turbulent channel flows with a weak spanwise rotation. The results show that compressibility has some impact on the turbulent statistics distributions, but many asymmetric characteristics still exist.
Article
Mechanics
Soham Prajapati, Sreevatsa Anantharamu, Krishnan Mahesh
Summary: This study investigates the vibrational acoustic response of an elastic plate in a turbulent channel using direct numerical simulation. Different plate boundary conditions and materials result in variations in the displacement and pressure spectra, as well as the deformation patterns of soft and stiff plates.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
S. V. Mahmoodi-Jezeh, Bing-Chen Wang
Summary: The study investigates turbulent heat transfer in ribbed square ducts with three different blockage ratios using direct numerical simulation (DNS). The presence of ribs and confinement of the duct lead to organized secondary flows that interact intensely with the rib elements and sidewalls, significantly impacting momentum and thermal energy transport. The research reveals that both drag and heat transfer coefficients are highly sensitive to rib height, with increased rib height strengthening turbulent mixing and heat transfer on the windward face.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2021)
Article
Mechanics
Yi Huang, Liang Wang, Song Fu
Summary: By applying a spanwise traveling wave generated by blowing and suction at walls, drag reduction in fully developed turbulent channel flow can be achieved. The drag reduction mechanism is strongly related to pressure-strain correlations, with reduced wall-normal strain rate and pressure-strain correlation being the main causes.
Article
Mechanics
Yong Ji, Jie Yao, Fazle Hussain, Xi Chen
Summary: Investigation on vorticity transport in turbulent channels under large-scale active drag control reveals the significant contribution of vorticity fluctuations to frictional drag, with random and coherent components playing different roles in drag reduction. Analysis suggests that suppressing random spanwise-vorticity transport is crucial for more effective drag reduction.
Article
Engineering, Aerospace
Qiang Liu, Zhenbing Luo, Lin Wang, Guohua Tu, Xiong Deng, Yan Zhou
Summary: Direct numerical simulations were conducted on a spatially developing Ma 2.25 supersonic turbulent boundary layer with streamwise-striped wall blowing for turbulence drag reduction. It was found that despite weak control amplitudes, SSB can result in drag reduction effects. Analysis using compressible Renard-Deck decomposition revealed that the spatial growth term is mainly responsible for turbulence drag reduction.
AEROSPACE SCIENCE AND TECHNOLOGY
(2021)
Article
Mechanics
S. Mahmoodi-Jezeh, Bing-Chen Wang
Summary: This study investigates the impact of inclined or V-shaped ribs on turbulent flow in a square duct, revealing significant differences in flow physics between the two ribbed duct cases. The research analyzes the near-wall turbulence structures and momentum transfer, highlighting the sensitivity of turbulence field to rib geometry and boundary layers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
M. Ziefuss, N. Karimi, A. Mehdizadeh
Summary: Heat transfer modeling is crucial for the design and optimization of thermal-fluid systems, but existing models face challenges in predicting second order statistics. By using advanced turbulent heat flux models, this research aims to predict turbulent thermal fields of fluids with different Pr numbers in wall-bounded shear flows, showing that the explicit framework may address current model shortcomings. Additionally, the study highlights the importance of thermal time scale in accurately predicting thermal fields and statistical quantities of fluids with different Pr numbers.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2021)
Article
Mechanics
Hualin Xiao, Kun Luo, Tai Jin, Haiou Wang, Jiangkuan Xing, Jianren Fan
Summary: Direct numerical simulations were conducted to investigate flow and flame structures, as well as transport mechanisms of turbulent kinetic energy and enstrophy in non-premixed swirling fuel-rich/fuel-lean flames within a high-pressure model gas turbine combustor. The study analyzed the behavior of turbulence state in swirling flows, TKE budgets, and enstrophy dynamics, revealing the significant influence of combustion on flow characteristics, predominantly in fuel-lean flames. Combustion led to the suppression of transport effects and the enhancement of baroclinic torque in swirling non-premixed flames.
Article
Mechanics
A. Yakeno
Summary: This study investigated the drag-reduction mechanism of spanwise wall oscillation in a turbulent channel, finding that oscillation affected the optimal energy growth of streak modes and enhanced the growth of tilted-streak modes under longer oscillation periods. The transition of optimal perturbations under oscillation showed that spanwise Stokes layer shear played a more significant role in modification than the spanwise velocity did. A new drag-reduction performance estimation model was proposed based on streak formation modification under oscillation, which restrained energy transfer to streamwise vortices via a tilting delay.
Article
Mechanics
XianXu Yuan, YaLu Fu, JianQiang Chen, Ming Yu, PengXin Liu
Summary: In this study, the effects of spanwise-oriented grooves on the kinetic and thermodynamic statistics in a supersonic turbulent channel flow were investigated using direct numerical simulations. The results showed that these grooves induced compressive and expansive waves that traveled across the channel and influenced the distribution of vortices and streaks. These waves enhanced the fluctuations in temperature, density, and pressure, and also altered the correlations between velocity and temperature.
Article
Mathematics, Applied
Feng Liu, Le Fang, Jian Fang
Summary: Recent studies have shown that in transitional boundary-layer flow, there are different streamwise zones for the transition region and non-equilibrium turbulence region, exhibiting different non-equilibrium scalings. Additionally, in the wall-normal direction, the viscous sublayer, log layer, and outer layer exhibit non-equilibrium phenomena distinct from other types of turbulence. These findings are expected to inform the modeling of various non-equilibrium turbulent flows.
APPLIED MATHEMATICS AND MECHANICS-ENGLISH EDITION
(2021)
Article
Mechanics
Tongbiao Guo, Jian Fang, Shan Zhong, Charles Moulinec
Summary: Direct numerical simulations were performed to investigate the influence of secondary flow motions on the drag generated by convergent-divergent (C-D) riblets in a turbulent channel flow. It was found that the intensity of the secondary flow motion increased with the wavelength of the riblets, peaking at a wavelength equal to the half channel height. The increase in drag was dominated by the turbulent kinetic energy production and viscous dissipation wake component. The work of the Reynolds shear stresses and dispersive stresses played important roles in the increase in drag at different wavelengths.
Article
Mechanics
Tongbiao Guo, Jian Fang, Ji Zhang, Xinliang Li
Summary: In this paper, the impact of convergent-divergent riblets on a supersonic turbulent boundary layer is examined using direct numerical simulations. The riblets induce spanwise heterogeneity and successfully reduce the area of the separation zone.
Article
Computer Science, Interdisciplinary Applications
R. S. Cant, U. Ahmed, J. Fang, N. Chakarborty, G. Nivarti, C. Moulinec, D. R. Emerson
Summary: In this paper, a new Direct Numerical Simulation (DNS) code called HAMISH with Adaptive Mesh Refinement (AMR) is developed to simulate compressible reacting flow in a computationally economical manner. The code is based on an unstructured finite-volume approach and utilizes a Runge-Kutta algorithm for time-stepping. It demonstrates high parallel efficiency and is capable of capturing sharp gradients and dynamically refining the mesh based on flow physics. Various test cases are conducted to showcase the key capabilities of HAMISH.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Mechanics
P-F Yang, J. Fang, L. Fang, A. Pumir, H. Xu
Summary: We derive analytic relations for the second- and third-order moments of the spatial gradient of fluid velocity in compressible turbulence. These relations generalize known relations in incompressible flows and can be approximately applied in a mixing layer. We also discuss the experimental determination of these moments for isotropic compressible turbulence.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Tongbiao Guo, Jian Fang, Ji Zhang, Xinliang Li
Summary: In this study, the effect of secondary flow induced by riblets on supersonic turbulent boundary layers over a compression ramp is investigated. The results show that the secondary flow leads to an increase in the size and intensity of the rolling motion, contributing to the increase of mean momentum flux and turbulent fluctuations. The separation area is also reduced by the presence of riblets, and the frequency of low-frequency motion is higher in the presence of riblets compared to the baseline case.
Article
Thermodynamics
Xingxing Chen, Jian Fang, Charles Moulinec, David R. R. Emerson
Summary: A hybrid scheme is developed for direct numerical simulations of hypersonic flows over a blunt body. The scheme provides sufficient dissipation to handle the carbuncle phenomenon and high spatial accuracy to resolve turbulence. Results show that the hybrid scheme can obtain smooth and accurate predictions of laminar and turbulent hypersonic flows over a blunt body.
FLOW TURBULENCE AND COMBUSTION
(2023)
Article
Thermodynamics
Tongbiao Guo, Jian Fang, Shan Zhong, Charles Moulinec
Summary: This study presents direct numerical simulations of turbulent channel flow developing over convergent-divergent (C-D) riblets. The intensity of the large-scale secondary flow motion generated by the C-D riblets peaks at a ratio of riblet spacing and height of 4. Compared to smooth walls, the turbulent activities and energy level significantly increase in the presence of C-D riblets, resulting in a higher drag. There is a direct correlation between the amount of drag and the intensity of the secondary flow.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Computer Science, Interdisciplinary Applications
Weishuo Liu, Jian Fang, Stefano Rolfo, Charles Moulinec, David R. Emerson
Summary: A bounded normalization method is proposed to improve the extrapolation capability of an iterative ML based turbulence modeling framework when the Reynolds number is beyond the training range. The method constrains the input feature and re-normalizes the learning target with the eddy viscosity from a traditional turbulence model. Tests in channel flows and a spatially developing boundary layer demonstrate improved performance and favorable accuracy.
COMPUTERS & FLUIDS
(2023)
Article
Mechanics
Jian Fang, Xi Deng, Zhi X. Chen
Summary: A Mach 1.5 non-reactive flow in a cavity-stabilized combustor of a model scramjet was studied via direct-numerical simulation, with focus on the interaction among boundary layer, free shear-layer above the cavity and shock wave. Impingement of the free shear-layer on the aft wall of the cavity leads to strong turbulence, high pressure, and compression waves. The analysis reveals that shear production amplifies turbulence in the core of the shear-layer, while deceleration production has a significant impact above the aft wall of the cavity and around the shock interaction points.
