Song Fu

Song Fu
Tsinghua University | TH · Department of Engineering Mechanics

Doctor of Philosophy

About

259
Publications
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3,008
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Publications

Publications (259)
Article
Full-text available
The objective of this work is to investigate linear modal and algebraic instability in Poiseuille flows with fluids close to their vapour-liquid critical point. Close to this critical point, the ideal gas assumption does not hold and large non-ideal fluid behaviours occur. As a representative non-ideal fluid, we consider supercritical carbon dioxid...
Preprint
The stability of hypersonic flows along a streamwise corner is studied here with bi-global stability theory for freestream Mach numbers 4.5 and 6.0. The steady laminar base flows are obtained by solving the corresponding self-similar solution for the corner plane and are in good agreement with direct numerical simulation. The base flow exhibits a p...
Article
The Vortex-Induced Vibration (VIV) hydrokinetic energy converter can be used to harvest low-speed ocean current energy. In order to match the nonlinear resonance response in VIV, the nonlinear damping model is proposed. A two-way CFD numerical model is developed to simulate the VIV responses. The nonlinear damping model (Ct=Cmax(Vt/Vmax)n) contains...
Preprint
Full-text available
Data-driven turbulence modeling studies have reached such a stage that the fundamental framework is basically settled, but several essential issues remain that strongly affect the performance, including accuracy, smoothness, and generalization capacity. Two problems are studied in the current research: (1) the processing of the Reynolds stress tens...
Article
Full-text available
It is commonly known that riblets with sharper tip generally have better turbulent drag reduction capacity, which, however, poses great challenges for manufacturing and makes the riblets vulnerable to tip erosion. In this study, we show that a scalloped riblet which is not as sharp in the tip as corresponding triangular riblet with same height-widt...
Article
An efficient gas-kinetic scheme with fourth-order accuracy in both space and time is developed for the Navier-Stokes equations on triangular meshes. The scheme combines an efficient correction procedure via reconstruction (CPR) framework with a robust gas-kinetic flux formula, which computes both the flux and its time-derivative. The availability o...
Article
The vortex induced vibration (VIV) energy converter is a novel device to extract hydrokinetic energy from ocean currents. The flow velocity near the sea level is relatively higher, which makes ocean surface currents more exploitable. However, due to the influence from free surface (such as wave impact, etc.), the total system damping of the convert...
Article
A spanwise traveling wave, generated by blowing and suction at walls, is applied in direct numerical simulations to reduce the drag in a fully developed turbulent channel flow with Reτ≈180. The wave traveling direction reverses periodically to induce a spanwise motion of the flow near the wall, similar to that from spanwise wall oscillations. Such...
Article
Full-text available
Abstract The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities. In this work, the oblique-mode breakdown, as one of the most available transition mechanisms, is studied using the nonlinear parabolized stability equations (NPSE) with co...
Article
Noise-interference suppression and data-processing acceleration are crucial to aeroacoustic measurements with phased array in wind tunnels. In this paper, we develop a "multi-window" beamforming algorithm that recursively processes data based on an array-acquisition model. This spatial filtering algorithm is derived from the Kalman filter theory fo...
Article
Uvulopalatopharyngoplasty (UPPP) is a widely accepted surgery to treat patients with obstructive sleep apnea. However, the outcomes of surgery are variable and not satisfactory in many cases. To explore the key factors that influence outcomes of surgery from perspectives of upper airway stability using computational fluid dynamics methods, three-di...
Article
A novel bio-inspired V-shaped layout is proposed to enhance energy conversion performance for VIV hydrokinetic energy converters. The layout method is inspired by wild geese flying in a V-formation. In this paper, 2-dimensional RANS equations with the SST k-ω turbulence model are used to simulate the VIV responses at various distances. The numerica...
Article
In this work, the stability of Mach 20 flows past a 6 deg wedge in thermal–chemical nonequilibrium (TCNE) is studied by means of linear parabolized stability equations (PSEs) in combination with advanced thermodynamic and transport models. First, verifications are performed against existing numerical results in the literature. Good agreement is ach...
Article
Compared to the widely studied linear instabilities, the nonlinear analyses of the high-enthalpy and hypersonic boundary-layer transition had received much less attention. In this work, secondary instabilities of high-enthalpy boundary layers are studied to highlight the impacts of thermal–chemical nonequilibrium (TCNE). The numerical tools adopted...
Article
Full-text available
We propose an image-based flow decomposition developed from the two-dimensional (2-D) tensor empirical wavelet transform (EWT) (Gilles, IEEE Trans. Signal Process., vol. 61, 2013, pp. 3999-4010). The idea is to decompose the instantaneous flow data, or their visualisation, adaptively according to the averaged Fourier supports for the identification...
Preprint
Full-text available
A highly efficient gas-kinetic scheme with fourth-order accuracy in both space and time is developed for the Navier-Stokes equations on triangular meshes. The scheme combines an efficient correction procedure via reconstruction (CPR) framework with a robust gas-kinetic flux formula, which computes both the flux and its time-derivative. The availabi...
Preprint
Data-driven turbulence modeling has been considered an effective method for improving the prediction accuracy of Reynolds-averaged Navier-Stokes equations. Related studies aimed to solve the discrepancy of traditional turbulence modeling by acquiring specific patterns from high-fidelity data through machine learning methods, such as artificial neur...
Article
Data-driven turbulence modeling has been considered an effective method for improving the prediction accuracy of Reynolds-averaged Navier–Stokes equations. Related studies aimed to solve the discrepancy of traditional turbulence modeling by acquiring specific patterns from high-fidelity data through machine learning methods, such as artificial neur...
Article
The research on hypersonic boundary layer transition is a recent focal point in fluid dynamics. One of the effective numerical methods for transition study is the high-order shock-fitting method, which is especially suitable for dealing with shock-related interactions and removing post-shock oscillations as compared with shock-capturing methods. Cu...
Article
As a novel passive flow control device, a ring-shaped Karman-vortex generator (KVG) is employed to alleviate the severe flow separation of a conical diffuser with a total divergence angle of 36∘ at a Re=1.0×104. The baseline diffuser and 18 controlled schemes with different KVG sizes and location combinations are studied by an implicit large-eddy s...
Article
Full-text available
Small-scale roughness elements or imperfections are inevitable over the surface of a flight vehicle. The aerodynamics of these small-scale structures is difficult to predict but may play an important role in the design of a flight vehicle at high speed. The forward-facing step is a typical type of roughness element. Many experiments have been condu...
Preprint
Full-text available
We propose an image-based flow decomposition developed from the two-dimensional (2D) tensor empirical wavelet transform (EWT) (Gilles 2013). The idea is to decompose the instantaneous flow data, or its visualisation, adaptively according to the averaged Fourier supports for the identification of spatially localised structures. The resulting EWT mod...
Article
Implicit large-eddy simulation is employed to simulate the flow in an asymmetric plane diffuser at Re=9000. Flow separation exists near the throat and evolves to large-scale, unsteady separation in the expansion section and the downstream region. An unconventional flow control method, namely, a cylindrical Karman-vortex generator (KVG) with differe...
Article
The research on hypersonic boundary layer transition is a recent focal point in aerodynamics. For the so-called 'natural transition', where the level of environment disturbance is low, stability analysis has been proved to be a helpful technique in studying evolution of disturbances. On the other hand, temperatures in hypersonic boundary layer incr...
Chapter
Full-text available
This study deals with numerical prediction through Improved-Delayed-Detached-Eddy Simulation of the separating-reattaching flow over a backward-facing step and the manipulated flow with harmonic actuation for investigating the mechanism of reattaching acceleration. The predicted base flow agrees well with the experimental results in terms of both t...
Article
Full-text available
It is well known that hypersonic boundary-layer transition is sensitive to a surface roughness since the roughness may either trigger an early transition or delay the transition. Hypersonic transition is still poorly understood as there are a very limited number of studies in the literature. In the present work, we conduct a computational study on...
Article
The flight velocity effect on a cold jet flow is numerically predicted by the improved delayed detached eddy simulation (IDDES) with a modification to the grid length scale, mainly focusing on the near-field flows and intermittency properties in the jet centerline region. First, the modification in IDDES is validated using three meshes and availabl...
Article
Full-text available
The secondary instabilities of stationary cross-flow vortices in a Mach 6 swept wing flow are studied using Floquet theory. High-frequency secondary instability modes of ‘y’ mode on top of stationary cross-flow vortices, and ‘z’ mode concentrating on the shoulder of the stationary cross-flow vortex are found. The most unstable secondary instability...
Chapter
Full-text available
High-temperature effects need to be considered for a better design of hypersonic and reentry vehicles. They affect both the boundary layer flow and its flow transition, whose primary stages can be investigated through modal stability analysis. In this work, physical and numerical tools for high-temperature flows are presented and the efficiency of...
Article
Full-text available
Background noise is inevitable when sensor arrays are used for aeroacoustic measurements in wind tunnels. The direct removal of background noise, however, would affect the measurement accuracy. In particular, the existing array signal processing algorithms are either invalid or inefficient for removing the noise that is coherent with the signal of...
Chapter
Several vortex identification methods along with a newly proposed \(\Omega \) method are examined in the Burgers vortex and the Sullivan vortex. Of particular interest is the physical meaning of the parameter, especially the thresholds. While all the methods are capable of capturing precise vortex boundaries in these two analytical vortices, only t...
Article
Full-text available
Purpose The purpose of the paper is to propose some modifications to the SIMPLE (semi-implicit method for pressure-linked equations) algorithm. These modifications can ensure the numerical robustness and optimize computational efficiency. They remarkably promote the ability of the SIMPLE algorithm for incompressible DNS (direct numerical simulatio...
Article
This paper investigates the potential use of dielectric-barrier-discharge (DBD) plasma actuators to control the crossflow instability of the boundary layer on a 45° swept NLF-0415 airfoil at −4∘ angle of attack.The disturbance evolution is resolved using nonlinear parabolized stability equations (NPSEs). Actuators are mounted near the leading edge...
Article
Full-text available
The new mode of instability found by Tunney et al. [24] is studied with viscous stability theory in this article. When the high-speed boundary layer is subject to certain values of favorable pressure gradient and wall heating, a new mode becomes unstable due to the appearance of the streamwise velocity overshoot (U(y) > U ∞) in the base flow. The p...
Preprint
Full-text available
The new mode of instability found by Tunney et al. is studied with viscous stability theory in this article. When the high-speed boundary layer is subject to certain values of favorable pressure gradient and wall heating, a new mode becomes unstable due to the appearance of the streamwise velocity overshoot ($U(y)>U_\infty$) in the base flow. The p...
Article
The spectrum of a hypersonic three-dimensional boundary layer at Mach 6 is investigated with linear stability theory. It is shown that the three-dimensional wave of Mode S of discrete spectrum can be excited by the slow acoustic wave of continuous spectrum near the leading edge, and Mode S can evolve into the unstable traveling wave of crossflow mo...
Article
Full-text available
Space vehicle in atmosphere travels mostly at supersonic speed and generates a very strong bow shockwave around its blunt nose. Oblique shock and conical separated flow zone generated by a forward disk-tip spike significantly reduce the drag by reducing the high pressure area on the blunt nose. This study employs improved delayed detached eddy simu...
Article
The implicit large eddy simulation method is applied in a riblet drag reduction study of a low-speed airfoil. The numerical method is tested by a channel flow with streamwise riblets installed on one side. The mean velocity profile, root mean square of velocity and Reynolds shear stress match well with reference direct numerical simulation data. Ne...
Article
Full-text available
A space vehicle in atmosphere travels mostly at supersonic speed and generates a very strong bow shock wave around its blunt nose. This causes a large high-pressure area at the front nose surface accompanied with high temperature. It suggests high-pressure drag and high risk of heat shield failure. Oblique shock and conical separated flow zone gene...
Chapter
Full-text available
In this study, Improved Delayed Detached-Eddy Simulations (IDDES) were conducted for active flow control with a harmonic actuation on a backward-facing step (BFS) and pulsed blowing on a NACA0015 airfoil for reattachment and separation controls. By using Dynamic Mode Decomposition, the characteristic physical modes of the unexcited flow have been e...
Chapter
Based on the extended BGK equation, the gas-kinetic scheme (GKS) is developed for fine simulation of high-Reynolds-number turbulence. With the help of existing hybrid RANS/LES models to approximate the effective relaxation time, two extended schemes, GKS-DES/IDDES are constructed and show good performances in typical turbulent flow around a cylinde...
Chapter
The rod-airfoil subjected to a forced oscillation was numerically studied using the Improved Delayed Detached Eddy Simulation (IDDES) method. The freestream flow Mach number is 0.21 and Reynolds number based on the rod diameter is 48000. The transversely oscillating motion of the rod-airfoil changes the flow properties dramatically, compared to the...
Article
A third-order accurate gas-kinetic scheme based on the correction procedure via reconstruction (CPR) framework is developed for the Euler and Navier–Stokes equations on triangular meshes. The scheme combines the accuracy and efficiency of the CPR formulation with the multidimensional characteristics and robustness of the gas-kinetic flux solver. Co...
Article
Full-text available
The present study conducted improved delayed detached-eddy simulations of actively controlled flows with a harmonic actuation on a backward-facing step and pulsed blowing on a pitching airfoil for reattachment and separation controls. Spectra analyses based on the unexcited flowfield data were carried out by using dynamic mode decomposition to iden...
Article
Full-text available
An efficient Bayesian uncertainty quantification approach is proposed, which combines the adaptive high dimensional model representation technique (HDMR) and stochastic collocation (SC) method based generalized polynomial chaos (gPC) to construct the surrogate for sampling procedure in Bayesian calibration step. Specifically, the adaptive HDMR tech...
Article
Full-text available
A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the local boundary-layer thickness. The Reynolds number based on the step height is 720. Inlet disturbances are introduced giving rise t...
Article
Purpose The purpose of this paper is to numerically investigate the mildly separated flow phenomena on a near-stall NACA0015 airfoil, by using Detached-Eddy Simulation (DES) type methods. It includes a comparison of different choices of underlying Reynolds-averaged Navier –Stokes model as well as subgrid-scale stress model in Large-Eddy simulation...
Article
The formation and evolution of wingtip vortex system generated from three wing configurations are simulated with the improved delayed detached eddy simulation (IDDES) method. Numerical results show that each layout produces an interacting wingtip vortex system. These three corresponding vortical interactions are, respectively, the interaction betwe...
Article
Full-text available
Turbulent boundary layer control (TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities, which have improved the understanding of the flow structures of turbulence. Advances in micro-electronic technology have enabled the fabrication of active device systems...
Article
Full-text available
Sensitivity analyses and non-linear parabolized stability equations are solved to provide a computational assessment of the potential use of a Dielectric Barrier Discharge (DBD) plasma actuator for a prolonging laminar region in swept Hiemenz flow. The derivative of the kinetic energy with respect to the body force is deduced, and its components in...
Article
In this article, a series of simulations of a rotating disk system with air cooling is introduced. These simulations are performed with the realizable k-ε eddy-viscosity model. Computational results illustrate the effect of the cooling air and disk rotation on the temperature of the disk surface. The maximum rotating disk speed reaches about 78300...
Article
In this study, a series of numerical experiments are performed on supersonic/hypersonic flows over an adiabatic flat plate with transitionally and fully rough surfaces. The Mach numbers simulated are 4, 5, 6, and 7; the flight heights considered are 20, 24, 28, 32, and 36 km. First, a modified roughness correction is proposed and validated with the...
Article
Flows at over a cavity with different leading-edge sawtooth spoilers were numerically studied using improved delayed detached-eddy simulation based on the two-equation shear stress transport model, coupled with the adaptive dissipation scheme. Transonic flow past M219 cavity was chosen as the validation case for numerical methods and mesh convergen...
Conference Paper
A high performance parallel algorithm for UGKS is developed to simulate three-dimensional flows internal and external on arbitrary grid system. The physical domain and velocity domain are divided into different blocks and distributed according to the two-dimensional Cartesian topology with intra-communicators in physical domain for data exchange an...
Article
Full-text available
Purpose – The purpose of this paper is to investigate the characteristic flow structures behind a backward-facing step. With better understanding of unsteady features, effective control practice with harmonic actuation is illustrated. Design/methodology/approach – The present study employs Improved Delayed Detached Eddy Simulation to resolve flow...
Article
Stabilization of two-dimensional disturbances in hypersonic boundary layer flows by finite-amplitude streaks is investigated using nonlinear parabolized stability equations. The boundary-layer flows at Mach numbers 4.5 and 6.0 are studied in which both first and second modes are supported. The streaks considered here are driven either by the so-cal...
Conference Paper
Full-text available
The flow structures behind a backward-facing step were investigated numerically by IDDES (Improved Delayed Detached Eddy Simulation) method. The time- and spanwise-averaged quantities agreed well with experimental data. We then applied cross-correlation functions of velocity fluctuations to resolve the scales of vortices. The vortex passing frequen...
Chapter
Two advanced DES (detached eddy simulation) methods, delayed-DES (DDES) and improved-delayed DES (IDDES), are the two wide-used RANS-LES (Reynolds averaged Navier-Stokes and large eddy simulation) hybrid methods. They are applied to accurately simulate the unsteady complex turbulent flows at high Reynolds numbers with a wide Mach number range from...