Jian Fang

• PhD
• Principal Scientist at Science and Technology Facilities Council

We analyze the energy flux in compressible turbulence by generalizing the exact decomposition recently proposed by Johnson (Phys. Rev. Lett., vol. 124, 2020. 104501) to study incompressible turbulent flows. This allows us to characterize the effect of dilatational motion on the inter-scale energy transfer in three-dimensional compressible turbulenc...

This paper presents the development and validation of a Magnetohydrodynamics (MHD) module integrated into the Xcompact3d framework, an open-source high-order finite-difference suite of solvers designed to study turbulent flows on supercomputers. Leveraging the Fast Fourier Transform library already implemented in Xcompact3d, alongside sixth-order c...

Cavities are a common design feature that can be used to house sensitive instruments, such as optical sensors, and manage the local flow environment, e.g. wheel wells to retract landing gear. However, cavities can also be a source of flow disturbance creating unsteady flow oscillations and increasing drag. In this work, we are investigating hyperso...

This video illustrates the interaction between turbulence and a hydrogen flame. Turbulence fluctuations disrupt the combustion, by stretching and bending the flame surface and altering the chemical reaction inside the reaction zone. In the meantime, the high temperature of the combustion products caused by the heat released from the flame dampens t...

The existence of a large-scale non-equilibrium dissipation law (Cε∼Reλ−15/14) has been well documented through various experiments conducted on grid-generated turbulent wake flows. In our previous studies, we have successfully demonstrated the coexistence of a rapid non-equilibrium dissipation law (Cε∼Reλ−2) before the large-scale counterpart in ho...

In this work, supersonic premixed H2/air combustion stabilised by a cavity flame-holder in a model scramjet combustor with a Mach 1.5 inflow is studied via direct numerical simulations. By applying turbulent and laminar inlet condition separately, we compare the flame stabilisation characteristics between these two cases to study the effect of infl...

Data-driven modeling has contributed significantly to the field of computational fluid dynamics (CFD), but integrating machine-learning (ML) models into a CFD workflow still remains to be a challenging task. In this paper, we introduce an interface library for the deployment of ML models in CFD codes. The library supports multiple ML backends with...

A bounded normalization method is proposed to improve the extrapolation capability of the recently developed iterative ML- based turbulence modeling framework (Liu et al., 2021), whose performance degrades when the Reynolds number is beyond the training range. The bounded normalization method constrains the input feature into a finite range, and th...

A Mach 1.5 non-reactive flow in a cavity-stabilized combustor of a model scramjet is studied via a direct-numerical simulation approach, and the analysis is focused on the interaction among boundary layer, free shear-layer above the cavity and shock wave. It is found that the impingement of the free shear-layer on the aft wall of the cavity leads t...

Direct numerical simulations of a turbulent channel flow developing over convergent–divergent (C–D) riblets at a Reynolds number of Reb=2800 are presented. It is found that, with a fixed normalized riblet height of h+=5, as the ratio of the riblet spacing and the height, s/h, increases from 2 to 10, the strength of the large-scale secondary flow mo...

A hybrid scheme is developed for direct numerical simulations of hypersonic flows over a blunt body. The scheme switches to the first-order AUSMPW+ scheme near the bow shock to provide sufficient dissipation to handle the carbuncle phenomenon. In the smooth part of the computational domain, a sixth-order central scheme with an eighth-order low-pass...

In this paper, the effect of the secondary flow induced by convergent-divergent riblets in supersonic turbulent boundary layers over a 24 o compression ramp at Mach number 2.9 is studied via direct numerical simulation. Two riblet cases with the wavelength Λ being 1.1 δ and 1.65 δ are conducted to examine their impact on the secondary rolling motio...

A neural-networks predictor library has been developed to deploy machine learning (ML) models into computational fluid dynamics (CFD) codes. The pointer-to-implementation strategy is adopted to isolate the implementation details in order to simplify the implementation to CFD solvers. The library provides simplified model-managing functions by encap...

A hybrid scheme is developed for direct numerical simulations of hypersonicflows over a blunt body. The scheme switches to the first-order AUSMPW+ scheme near the bow shock to provide sufficient dissipationto handle the carbuncle phenomenon. In the smooth part of the computationaldomain, a sixth-order central scheme with an eighth-orderlow-pass fil...

We derive from first principles analytic relations for the second- and third-order moments of $\boldsymbol{\mathsf{m}}$ , the spatial gradient of fluid velocity $\boldsymbol{u}$ , $\boldsymbol{\mathsf{m}} = \nabla \boldsymbol{u}$ , in compressible turbulence, which generalize known relations in incompressible flows. These relations, although derive...

Direct numerical simulations are undertaken to examine the impact of C-D riblets on the shock wave/boundary layer interaction and the feasibility of using them to mitigate flow separation. Over the riblet section, a large-scale secondary roll mode is produced by C-D riblets with the downwelling motion occurring around the diverging region and upwel...

A new Direct Numerical Simulation (DNS) code HAMISH with Adaptive Mesh Refinement (AMR) has been developed to simulate compressible reacting flow in a computationally economical manner. The focus is on problems where high gradients of temperature, density and species mass fraction remain localised, for example within the interior structure of flame...

We derive from first principles analytic relations for the second and third order moments of the velocity gradient mij = dui/dxj in compressible turbulence, which generalize known relations in incompressible flows. These relations, although derived for homogeneous flows, hold approximately for a mixing layer. We also discuss how to apply these rela...

Direct numerical simulations of a turbulent channel flow developing over convergent–divergent (C–D) riblets are performed at a Reynolds number of Reb = 2800, based on the half channel height δ and the bulk velocity. To gain an in-depth understanding of the origin of the drag generated by C–D riblets, a drag decomposition method is derived from kine...

Machine-learning (ML) techniques provide a new and encouraging perspective for constructing turbulence models for Reynolds-averaged Navier-Stokes (RANS) simulations. In this study, an iterative ML-RANS computational framework is proposed that combines an ML algorithm with transport equations of a conventional turbulence model. This framework mainta...

Some shock-wave/turbulent-boundary-layer interaction (SWTBLI) flows typical to supersonic and hypersonic vehicles have been investigated by using direct-numerical simulation (DNS) and large-eddy simulation (LES) approaches. The developed seventh-order low-dissipation monotonicity-preserving (MP7-LD) scheme has presented its advantage in capturing s...

Many recent laboratory experiments and numerical simulations support a non-equilibrium dissipation scaling in decaying turbulence before it reaches an equilibrium state. By analyzing a direct numerical simulation (DNS) database of a transitional boundary-layer flow, we show that the transition region and the non-equilibrium turbulence region, which...

The mechanism of turbulence amplification in shock-wave/boundary layer interactions is reviewed, and a new turbulence amplification mechanism is proposed based on the analysis of data from direct numerical simulation of an oblique shock-wave/flat-plate boundary layer interaction at Mach 2.25. In the upstream part of the interaction zone, the amplif...

The spike flow is often observed around the lead-edge of a blade in an axial compressor cascade, which would lead to the sudden expansion and pressure diffusion. A strong spike flow might create a local separation bubble near the leading-edge and even trigger the boundary layer transition immediately (Walraevens and Cumpsty in J. Turbomach 117:115-...

A planar duct flow configuration with a cross-flow injected from a longitudinal slit close to the upper wall of the duct is studied by using a direct numerical simulation approach to explore the underlying flow mechanism in relation to the tip-leakage vortex (TLV), which is one of the most important flow phenomena in turbomachinery. Major character...

The aerodynamic performance of the blade determines the power and load characteristics of a wind turbine. In this paper, numerical research of the active deformation of an airfoil with equal thickness camber line was carried out, which shows the great potential of this active flow control method to improve the flow field. The NACA0012 is taken as t...

A framework of machine-learning (ML) based turbulence modeling for Reynolds-averaged Navier-Stokes (RANS) equations is developed to close the Reynolds stress term in the RANS equations. Several principles for turbulence modeling using ML techniques are discussed, including the effectiveness of the closure term and sufficiency of input variables for...

This work presents a converged framework of Machine-Learning Assisted Turbulence Modeling (MLATM). Our objective is to develop a turbulence model directly learning from high fidelity data (DNS/LES) with eddy-viscosity hypothesis induced. First, the target machine-learning quantity is discussed in order to avoid the ill-conditioning problem of RANS...

Non-equilibrium turbulence phenomena have raised great interests in recent years. Significant efforts have been devoted to non-equilibrium turbulence properties in canonical flows, e.g., grid turbulence, turbulent wakes, and homogeneous isotropic turbulence (HIT). The non-equilibrium turbulence in non-canonical flows, however, has rarely been studi...

An implicit large-eddy simulation is carried out to study turbulent boundary-layer separation from a backward-facing rounded ramp with active wall actuation control. This method, called spanwise alternating distributed strips control, is imposed onto the flat plate surface upstream of a rounded ramp by alternatively applying out-of-phase control an...

The effect of spanwise alternatively distributed strips (SADS) control on turbulent flow in a plane channel has been studied by direct numerical simulations to investigate the characteristics of large-scale streamwise vortices (LSSVs) induced by small-scale active wall actuation, and their potential in suppressing flow separation. SADS control is r...

Direct numerical simulations of turbulent flow in a plane channel using spanwise alternatively distributed strips (SADS) are performed to investigate the characteristics of large-scale streamwise vortices (LSSVs) induced by small-scale active wall actuations, and their role in suppressing flow separation. SADS control is obtained by alternatively a...

Shock wave boundary layer interaction is an ubiquitous and important phenomenon in supersonic and hypersonic flow scheme. In this paper, a Mach 2.5 supersonic boundary layer impinged by an oblique shock wave and its control using Micro Vortex Generator (MVG) is studied by large-Eddy Simulation (LES). A high order cut-cell immersed boundary method c...

Three-dimensional shock wave/turbulent-boundary-layer interaction of a hypersonic flow passing a single fin mounted on a flat plate at a Mach number of five and unit Reynolds number 3.7×107 was conducted by a large-eddy simulation approach. The performed large-eddy simulation has demonstrated good agreement with experimental data in terms of mean f...

We show by direct numerical simulations (DNSs) that in different types of isotropic turbulence, the fourth-order statistical invariants have approximately a linear relation, which can be represented by a straight line in the phase plane, passing two extreme states: the Gaussian state and the restricted Euler state. Also, each DNS case corresponds t...

Large-eddy simulation (LES) of an oblique shock-wave generated by an 8° sharp wedge impinging onto a spatially-developing Mach 2.3 turbulent boundary layer and their interactions has been carried out in this study. The Reynolds number based on the incoming flow property and the boundary layer displacement thickness at the impinging point without sh...

The efficiency and mechanism of an active control device “SparkJet” and its application in shock-induced separation control are studied using large-eddy simulation in this paper. The base flow is the interaction of an oblique shock-wave generated by 8° wedge and a spatially-developing Ma=2.3 turbulent boundary layer. The Reynolds number based on th...

In numerical simulations, “isotropic” turbulent flows are always generated by using periodic conditions. We show that these periodic conditions mathematically lead to large-scale anisotropy which can be about of the mean values, and thus prevent existing post-processing results from being accurate. A decomposition method by employing spherical harm...

Large-Eddy Simulation (LES) of shock-wave/boundary layer interactions (SWBLI) with SparkJet control technique is carried out in this paper. The base flow is an oblique shock-wave generated by an 8°wedge impinging onto a spatially-developing Mach 2.3 turbulent boundary layer. The numerical approaches are validated by comparing the LES predictions of...

The M = 2.9 supersonic turbulent flows over a tandem expansion-compression corner configuration with a sharp deflection angle of 25◦ at three Reynolds numbers Reδ = 20 000, 40 000, and 80 000 were studied by using direct numerical simulation. The flow statistics were validated against available experimental measurements and other numerical predicti...

The three-dimension (3D) shock-wave/turbulent boundary layer interaction (SWTBLI) raised from a hypersonic flow passing a single-fin at Mach 5 is investigated i by using LES. The performed LES has demonstrated very good agreements with available experimental data [1] in terms of the mean flowfield structure, the surface pressure and as well as the...

LES of hypersonic flow passing a 3D single-fin at Mach 5 and Re ∞ =3.7×10 7 /m was conducted using a newly developed 7 th-order low-dissipation monotonicity-preserving NS solver with dynamic Smagorinsky subgrid model. The simulation captures salient flow phenome such as shock systems, flow separation structures, and turbulence characteristics. It w...

Direct numerical simulations (DNS) of Mach = 2.9 supersonic turbulent boundary layers with spanwise wall oscillation (SWO) are conducted to investigate the turbulent heat transport mechanism and its relation with the turbulent momentum transport. The turbulent coherent structures are suppressed by SWO and the drag is reduced. Although the velocity...

The three-dimensional (3D) shock wave/turbulent boundary layer interaction (SWTBLI) of a hypersonic flow passing a single-fin placed on a flat-plate at Mach 5 and Re=3.7×10 7 /m is conducted by the large-eddy simulation (LES) approach. A newly developed in-house LES code is used that applies the seventh-order low-dissipation monotonicity-preserving...

The influence of numerical dissipation on direct numerical simulation (DNS) of decaying isotropic turbulence and turbulent channel flow is investigated respectively by using the seventh-order low-dissipation monotonicity-preserving (MP7-LD) scheme with different levels of bandwidth dissipation. It is found that for both benchmark test cases, small-...

The influence of numerical dissipation on direct numerical simulation (DNS) of decaying isotropic turbulence and turbulent channel flow is investigated respectively by using the seventh-order low-dissipation monotonicity-preserving (MP7-LD) scheme with different levels of bandwidth dissipation. It is found that for both benchmark test cases, small-...

It is of great significance to improve the accuracy of turbulence models in shock wave/boundary layer interaction flow. The relationship between the pressure gradient, as well as the shear layer, and the development of turbulent kinetic energy in impinging shock-wave/turbulent boundary layer interaction flow at Mach 2.25 is analyzed based on the da...

This paper presents an optimized low-dissipation monotonicity-preserving (MP-LD) scheme for numerical simulations of high-speed turbulent flows with shock waves. By using the bandwidth dissipation optimization method (BDOM), the linear dissipation of the original MP scheme of Suresh and Huynh (J. Comput. Phys. 136, 83–99, 1997) is significantly red...

A high-order low-dissipative monotonicity-preserving (MP-LD) scheme for numerical simulations of turbulent flows with shock waves is proposed in the present paper. Both the linear and nonlinear parts of MP-LD scheme are optimized by using the bandwidth dissipation optimization method and the shock sensor of Ducros et al. (1999) respectively. In com...

Large eddy simulation (LES) of low Mach number compressible turbulent channel flow with spanwise wall oscillation (SWO) is carried out. The flow field is analyzed with emphases laid on the heat transport as well as its relation with momentum transport. When turbulent coherent structures are suppressed by SWO, the turbulent transports are significan...

The large eddy simulation (LES) of compressible turbulent channel flow controlled by active spanwise wall fluctuations (ASWF) is carried out in this paper. Heat transport and its relation with the momentum transport are paid with great attentions. In all the flow cases of present study, the changes of temperature fluctuation, heat transport and tem...

The influences of the modification of turbulent coherent structures on temperature field and heat transfer in turbulent channel flow are studied using large eddy simulation (LES) of compressible turbulent channel flows with spanwise wall oscillation (SWO). The reliability of the LES on such problems is proved by the comparisons of the drag reductio...

The influences of the modification of turbulent coherent structures on temperature field and heat transfer in a compressible turbulent channel flow with spanwise wall oscillation (SWO) are studied using large eddy simulation (LES). The reliability of the LES on such problems is proved by the comparisons of the drag reduction data with those in othe...

Cylinder pressure probes deliver biased data in measuring flow with trans… verse velocity gradient. Numerical and experimental simulations were contrived to investigate this error. The results show that the effect of velocity gradient is to introduce an angle bias and make the measured velocity magnitude greater. Correlations between the angle bias...