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Investigations of an enclosed annular rotor-stator system with LES method

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Science China(Physics,Mechanics & Astronomy) 2018年第11期61卷 50-60页

作者： Zhe Jiao song fu School of Aerospace Engineering Tsinghua University

In this study, the flows in an enclosed annular rotor-stator system with the Reynolds number ranging from 0.75×105 to 3.75×105 and an aspect ratio of 36.5 are investigated using the LES method. Few studies have explored such a rotor-stator system with this aspect ratio and the flow structure on the rotor side. The mean flow structure varies from a torsional Couette type to a Batchelor type as the Reynolds number increases. The onset of the instability in the B?dewadt layer adjacent to the stator is delayed,whereas it is promoted in the Ekman layer adjacent to the rotor. Both the layers demonstrate rich spiral structures. Turbulent spirals are observed to occur at the rotor disk side that also generates TS-wave-like(Tollmien-Schlichting) structures between adjacent spiral arms. further, the turbulence at the stator is complex and interesting. Statistically, the turbulence is highly anisotropic near both the rotating and nonrotating disks, which is depicted by the Reynolds stresses.

关键词： rotating flow rotor-stator system large eddy simulation anisotropic turbulence Ekman-B6dewadt layers

Forward-facing steps induced transition in a subsonic boundary layer

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Science China(Physics,Mechanics & Astronomy) 2017年第10期60卷 34-44页

作者： Hui Zhu song fu School of Aerospace Engineering Tsinghua University Beijing 100084 China

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 to streamwise vortices upstream of the step. It is observed that these small-scale streamwise structures interact with the step and hairpin vortices are quickly developed after the step leading to flow transition in the boundary layer.

关键词： forward-facing steps boundary layer transitional flow

Numerical investigation of separation-induced transition in a lowpressure turbine cascade in a low-disturbance environment

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Science China(Physics,Mechanics & Astronomy) 2020年第6期63卷 66-82页

作者： Si-Ya Jiang song fu School of Aerospace Engineering Tsinghua UniversityBeijing 100084China

In this paper,the separation-induced transition in an LPT(low-pressure turbine)cascade is investigated at low Reynolds number with DNS(direct numerical simulation).The transition process is accurately predicted giving good agreements between the DNS and experimental *** illustrate the secondary instability of separation-induced transition in a low-disturbance environment,the results are comprehensively analyzed in both Fourier space and physical *** is illustrated that the effect of hyperbolic instability dominates around the saddle point of hyperbolic *** instability mechanism is responsible for the emergence of the streamwise vortices in the braid *** and intensified because of the“stretching”effect of the background flow,these vortices become the most noticeable characteristic of the flow *** modes of small spanwise wavelength are excited in the braid region,so as some low-frequency *** elliptical instability plays a minor role than hyperbolic *** is also observed that the fundamental mode with a larger spanwise wavelength is unstable in the vortex core which is associated with the deformation of the vortex core via elliptical *** is no convincing evidence for the existence of subharmonic instability.

关键词： separation direct numerical simulation transition to turbulence

Floquet analysis of fundamental,subharmonic and detuned secondary instabilities of Grtler vortices

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Science China(Physics,Mechanics & Astronomy) 2014年第3期57卷 555-561页

作者： REN Jie fu song School of Aerospace Engineering Tsinghua University

Nonlinear parabolized stability equations are employed in this work to investigate the nonlinear development of the G6rtler insta- bility up to the saturation stage. The perturbed boundary layer is highly inflectional both in the normalwise and spanwise directions and receptive to the secondary instabilities. The Floquet theory is applied to solve the fundamental, subharmonic and detuned secondary instabilities. With the Gortler-vortices-distorted base flow, two classes of secondary disturbances, i.e. odd modes and even modes, are identified according to the eigenfunctions of the disturbances. These modes may result in different patterns in the late stages of the transition process. Li and Malik [ 1 ] have shown the sinuous and varicose types of breakdown originating from the odd and even modes. The current study focuses on the four most amplified modes termed the even modes I ＆ Ⅱ and odd modes I ＆ lI. Odd mode II was missing in the work of Li and Malik [1] probably due to their inviscid simplifeation. The detuned modes are confirmed to be less amplifed than the fundamental （for the odd mode I） and subharmonic modes （for even modes I ＆ II and the odd mode II）.

关键词： Goirtler vortices secondary instability Floquet theory

Analysis of flow structures in supersonic plane mixing layers using the POD method

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Science China(Physics,Mechanics & Astronomy) 2008年第5期51卷 541-558页

作者： YANG Qin fu song School of Aerospace Tsinghua UniversityBeijing 100084China

The proper orthogonal decomposition(POD) method was applied to analyzing the database obtained from the direct numerical simulation(DNS) of supersonic plane mixing *** effect of different forms of the inner products in the POD method was *** was observed that the mean flow contributes to a predominant part of the total flow energy,and the energy spectrum of the turbulence fluctuations covers a wide range of POD *** patterns of leading(high energy) POD modes reveal that the flow structures exhibit spanwise counter rotating rolls,as well as oblique *** flow patterns are insensitive to the velocity of the *** the convective Mach number increases,the energy spectrum be-comes wider,the leading POD modes contain more complicated structures,and the flow becomes more chaotic.

关键词： coherent structure compressible mixing layer POD low-dimensional model

Research of the rapid pressure-strain correlation model in the rapid distortion limit

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Science China(Physics,Mechanics & Astronomy) 2008年第9期51卷 1380-1389页

作者： HUANG SiYuan fu song Department of Engineering Mechanics Tsinghua UniversityBeijing 100084China

Even though a number of rapid pressure-strain models have been suggested and successfully tested for different flow situations by various authors,the model proposals still exhibit some apparent deficiencies when subjected to the flows with rapid distortion. From Mansour's relatively straightforward rapid distortion analysis,if an initially anisotropic flow undergoes a purely rapid rotation,the anisotropy measures will exhibit the behavior of the damped oscillations. Within the current framework of modeling the rapid pressure-strain correlation,i.e.,the models based on the assumption that the M-tensor for the rapid pressure-strain term is expand-able in the Reynolds-stress anisotropy tensor alone,all the model predictions fail to give the damped oscillations in the turbulence anisotropy. In the case of initially isotropic turbulence subjected to rapid distortion,Sj?gren and Johansson showed that all the existing rapid pressure-strain models would deliver the identical path in the anisotropy-invariant map for both homogeneous plane strain and shear flows. The rapid distortion analysis shows two distinct curves reflecting different flow physics. In this work,we try to present a possible way to create a system that can overcome these deficiencies with the aid of the rapid distortion theory (RDT).

关键词： Reynolds-Stress turbulence Model rapid pressure-strain correlation rapid distortion theory

Modelling flow transition in a hypersonic boundary layer with Reynolds-averaged Navier-Stokes approach

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Science China(Physics,Mechanics & Astronomy) 2009年第5期52卷 768-774页

作者： WANG Liang fu song School of Aerospace Tsinghua UniversityBeijing 100084China

Based on Reynolds-averaged Navier-Stokes approach,a laminar-turbulence transition model is proposed in this study that takes into account the effects of different instability modes associated with the variations in Mach numbers of compressible boundary layer *** model is based on k-ω-γ three-equation eddy-viscosity concept with k representing the fluctuating kinetic energy,ωthe specific dissipation rate and the intermittency factorγ.The particular features of the model are that:1)k includes the non-turbulent,as well as turbulent fluctuations;2)a transport equation for the intermittency factorγis proposed here with a source term set to trigger the transition onset;3)through the introduction of a new length scale normal to wall,the present model employs the local variables only avoiding the use of the integral parameters,like the boundary layer thicknessδ,which are often cost-ineffective with the modern CFD(Computational Fluid Dynamics)methods;4)in the fully turbulent region,the model retreats to the well-known k-ωSST(Shear Stress Transport)*** model is validated with a number of available experiments on boundary layer transitions including the incompressible,supersonic and hypersonic flows past flat plates,straight/flared cones at zero incidences,*** is demonstrated that the present model can be successfully applied to the engineering calculations of a variety of aerodynamic flow transition.

关键词： hypersonic boundary-layer transition turbulence model intermittency factor

Competition of the multiple Grtler modes in hypersonic boundary layer flows

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Science China(Physics,Mechanics & Astronomy) 2014年第6期57卷 1178-1193页

作者： REN Jie fu song School of Aerospace Engineering Tsinghua University

Competition of multiple Gortler modes in hypersonic boundary layer flows are investigated with the local and marching methods. The wall-layer mode （mode W） and the trapped-layer mode （mode T） both occur in the compressible boundary layer where there exists a temperature adjustment layer near the upper edge. The mode T has the largest growth rate at a lower Gortler number while the mode W dominates at larger G/Srtler numbers. These two modes are both responsible for the flow transition in the hypersonic flows especially when Gortler number is in the high value range in which the crossover of these two modes takes place. Such high Gortler numbers are virtually far beyond the neutral regime. The nonparallel base flows, therefore, cease to influence the stability behavior of the Gortler modes. The effects of the Mach number on the multiple Gortler modes are studied within a chosen Mach number of 0.95, 2, 4 and 6. When the flow Mach number is sufficiently large, e.g., Ma ≥4, the growth rate crossover of the mode T and mode W occurs both in the conventional G-β map as well as on the route downstream for a fixed wavelength disturbance. Four particular regions （Region T, T-W, W-T and W） around the crossover point are highlighted with the marching analysis and the result matches that of the local analysis. The initial disturbance of a normal mode maintains the shape in its corresponding dominating region while a shape-transformation occurs outside this region.

关键词： Gortler vortices linear stability theory multiple modes local analysis marching analysis

Detached-eddy simulation of supersonic flow past a spike-tipped blunt nose

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Chinese Journal of Aeronautics 2018年第9期31卷 1815-1821页

作者： Yuan XUE Liang WANG song fu School of Aerospace Engineering Tsinghua University

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 simulation to investigate the characteristic flow structures around a spike-tipped blunt nose at Mach number of 3 and Reynolds number（based on the blunt-body diameter） of 2.72x10;. The calculated time-averaged quantities agree well with experimental data. Characteristic frequencies in different flow regions are extracted using fast Fourier transform. It is found that two distinct instability modes exist: oscillation mode and pulsation mode. The former is related to the foreshock/turbulence interaction with nondimensional frequency at around 0.004. The latter corresponds to the interaction between turbulence and shock structures around the blunt nose, with a typical coherent structure shedding frequency at 0.092.

关键词： Detached-eddy simulation Drag reduction Oscillation mode Pulsation mode Spike-tipped blunt vehicle Supersonic flow