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Secondary instability control of compressible flow by suction for a swept wing

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Science China(Physics,Mechanics & Astronomy) 2011年第11期54卷 2040-2052页

作者： XU GuoLiang xiao zhixiang FU Song School of Aerospace Tsinghua University Beijing 100084 China

The crossflow instability of a three-dimensional boundary layer is a main factor affecting the transition around the *** three-dimensional boundary layer flow affected by the saturated crossflow vortex is very sensitive to the high frequency disturbances,which foreshadows that the swept wing flow transition will *** primary instability of the compressible flow over a swept wing is investigated with nonlinear parabolized stability equations (NPSE).The Floquet theory is then applied to the analysis of the influence of localized steady suction on the secondary instability of crossflow *** results show that suction can significantly suppress the growth of the crossflow mode as well as the secondary instability modes.

关键词： boundary layer suction crossflow instability secondary instability

Analysis of the secondary instability of the incompressible flows over a swept wing

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Science China(Physics,Mechanics & Astronomy) 2011年第4期54卷 724-736页

作者： XU GuoLiang xiao zhixiang FU Song School of Aerospace Engineering Tsinghua University Beijing 100084 China

The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition over a *** this report,the primary instability of the incompressible flow over a swept wing is investigated by solving nonlinear parabolized stability equations (NPSE).The Floquet theory is applied to study the dependence of the secondary and high-frequency instabilities on curvature,Reynolds number and angle of swept (AOS).The computational results show that the curvature in the present case has no significant effect on the secondary *** is generally believed that the secondary instability growth rate increases with the magnitude of the nonlinear mode of crossflow ***,at a certain state,when the Reynolds number is 3.2 million,we find that the secondary instability growth rate becomes smaller even when the magnitude of the nonlinear mode of the crossflow vortex is *** effect of the angle of swept at 35,45 and 55 degrees,respectively,is also studied in the framework of the secondary linear stability *** angles of swept tend to decrease the spanwise spacing of the crossflow vortices,which correspondingly helps the stimulation of 'z' mode.

关键词： crossflow instability secondary instability curvature angle of swept

Numerical investigation of unsteady vortex breakdown past 80°/65° double-delta wing

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Chinese Journal of Aeronautics 2014年第3期27卷 521-530页

作者： Liu Jian Sun Haisheng Liu Zhitao xiao zhixiang State Key Laboratory of Aerodynamics China Aerodynamics Research and Development Center School of Aerospace Tsinghua University

An improved delayed detached eddy simulation （IDDES） method based on the k-x-SST （shear stress transport） turbulence model was applied to predict the unsteady vortex breakdown past an 80o/65o double-delta wing （DDW）, where the angles of attack （AOAs） range from 30° to 40°. Firstly, the IDDES model and the relative numerical methods were validated by simulating the massively separated flow around an NACA0021 straight wing at the AOA of 60°. The fluctuation properties of the lift and pressure coefficients were analyzed and compared with the available measurements. For the DDW case, the computations were compared with such mea-surements as the mean lift, drag, pitching moment, pressure coefficients and breakdown locations. Furthermore, the unsteady properties were investigated in detail, such as the frequencies of force and moments, pressure fluctuation on the upper surface, typical vortex breakdown patterns at three moments, and the distributions of kinetic turbulence energy at a stream wise section. Two dominated modes are observed, in which their Strouhal numbers are 1.0 at the AOAs of 30°, 32° and 34° and 0.7 at the AOAs of 36o, 38° and 40°. The breakdown vortex always moves upstream and downstream and its types change alternatively. Furthermore, the vortex can be identified as breakdown or not through the mean pressure, root mean square of pressure, or even through correlation analysis.

关键词： Computationalaerodynamics Double-delta wing Improved delayed detachededdy simulation Spiral vortex shedding Unsteady vortex breakdown

Numerical investigation of an advanced aircraft model during pitching motion at high incidence

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Science China(Technological Sciences) 2016年第2期59卷 276-288页

作者： LIU Jian SUN HaiSheng HUANG Yong JIANG Yong xiao zhixiang School of Aerospace Engineering Tsinghua University Beijing 100084 China China Aerodynamics Research and Development Center Mianyang 621000 China

An unsteady Reynolds averaged Navier–Stokes(URANS) method combined with a rigid dynamic mesh technique was developed to simulate unsteady flows around complex configurations during pitching motion. First, a test case with the NACA0012 airfoil was selected to validate the numerical methods and our in-house codes. Then, we evaluated the unsteady flows around an advanced aircraft model during harmonic pitching motion at high incidence. The effects of pitching motion on the hysteresis of aerodynamic force, the evolution of the leading-edge vortex, and the distribution of pressure on the model's surface were analyzed in detail. The roles of several significant parameters such as the reduced frequency and pitching amplitude were revealed. Several conclusions were found: pitching motion would delay the initiation of the leading-edge vortex, strengthen the vorticity, postpone the occurrence of vortex breakdown, and weaken the massively separated flows, thus causing additional aerodynamic force. Two categories of critical reduced frequency have been found, which divide the influence of reduced frequency on aerodynamic force into three stages, called the linear increasing range, slowly increasing range, and constant range. The first-order phase lag between the aerodynamic force and the incidence is a constant that is independent of the amplitude when the reduced frequency is sufficiently high. A scaled maximum value of C_L is proposed; it depends only on the reduced frequency(instead of the amplitude), and increases linearly when the reduced frequency is sufficiently low.

关键词： pitching motion hysteresis critical reduced frequency phase lag scaled maximum of CL

Simulation of shock wave buffet and its suppression on an OAT15A supercritical airfoil by IDDES

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Science China(Physics,Mechanics & Astronomy) 2012年第2期55卷 260-271页

作者： HUANG JingBo xiao zhixiang LIU Jian FU Song School of Aerospace Engineering Tsinghua UniversityBeijing 100084China China Aerodynamics Research&Development Center Mianyang 621000China

In the present paper,extremely unsteady shock wave buffet induced by strong shock wave/boundary-layer interactions (SWBLI) on the upper surface of an OAT15A supercritical airfoil at Mach number of 0.73 and angle of attack of 3.5 degrees is first numerically simulated by IDDES,one of the most advanced RANS/LES hybrid *** results imply that conventional URANS methods are unable to effectively predict the buffet phenomenon on the wing surface;IDDES,which involves more flow physics,predicted buffet *** complex flow phenomena are predicted and demonstrated,such as periodical oscillations of shock wave in the streamwise direction,strong shear layer detached from the shock wave due to SWBLI and plenty of small scale structures broken down by the shear layer instability and in the *** root mean square (RMS) of fluctuating pressure coefficients and streamwise range of shock wave oscillation reasonably agree with experimental ***,two vortex generators (VG) both with an inclination angle of 30 degrees to the main flow directions are mounted in front of the shock wave region on the upper surface to suppress shock wave *** results show that shock wave buffet can be significantly suppressed by VGs,the RMS level of pressure in the buffet region is effectively reduced,and averaged shock wave position is obviously pushed downstream,resulting in increased total lift.

关键词： supercritical airfoil vortex generator shock wave buffet

Studies of the unsteady supersonic base flows around three afterbodies

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Acta Mechanica Sinica 2009年第4期25卷 471-479页

作者： zhixiang xiao Song Fu School of Aerospace Engineering,Tsinghua University, 100084 Beijing, China School of Aerospace Engineering Tsinghua University Beijing China

Unsteady supersonic base flows around three afterbodies, cylindrical （Cy）, boattailed （BT） and three-step （MS）, are investigated in this paper. Reynolds-averaged Navier-Stokes （RANS） and two RANS/LES （large-eddy simulation） hybrid methods, detached eddy simulation （DES） and delayed-DES （DDES）, are used to predict the base flow characteristics around the baseline Cy afterbody. All the RANS and hybrid methods are based on the two-equation SST （shear-stress transport） model with compressible corrections （CC）. According to the comparison of measurements, both DES and DDES can produce more satisfactory results than RANS. RANS can only present the ＂stable＂ flow pat- terns, while the hybrid methods can demonstrate unsteady flow structures. DDES and DES results are little different from one another although the latter exhibits better agreement with the experiment. DES is taken to investigate the 5° BT and three-step afterbodies. The mean flow data and the instantaneous turbulent coherent structures are compared against available measurements.

关键词： Cylindrical Boattailed and three-stepafterbodies DES and DDES Unsteady flow

Can the tropical storms originated from the Bay of Bengal impact the precipitation and soil moisture over the Tibetan Plateau?

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Science China Earth Sciences 2015年第5期58卷 915-928页

作者： xiao zhixiang DUAN AnMin State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atmospheric Physics Chinese Academy of Sciences College of Earth Science University of Chinese Academy of Sciences Key Laboratory of Meteorological Disaster of Ministry of Education Nanjing University of Information Science and Technology

This study investigates the impacts of tropical storms originated from the Bay of Bengal(BOBTSs) on the precipitation and soil moisture over the Tibetan Plateau(TP) in April–June(AMJ) and September–December(SOND) during 1981–2011 based on the best track dataset provided by Joint Typhoon Warning Centre(JTWC). Results indicate that there are about 1.35 BOBTSs influence the TP in each year and most of them occurred in May and October, and the BOBTSs in AMJ influence the TP with larger extension and higher latitudes than those in SOND. The maximum regional precipitation induced by the BOBTSs accounts for more than 50% for the total precipitation in the corresponding month and about 20% for the season. Further analysis reveals that the surface soil moisture anomalies induced by the BOBTSs can persist only 20–25 days in AMJ, and the case is also true for the snow depth in SOND. Numerical simulations by using the regional climate model of Weather Research and Forecasting(WRF) suggest that the soil moisture anomalies in the sub-surface can last 2 months whereas for the surface it can persist only about 20 days, which agrees well with the observation analysis. Overall, the effect of the preceding BOBTSs on the snow depth and soil moisture anomalies over the TP cannot maintain to summer, and there is no robust connection between the BOBTSs and summer precipitation anomalies in East China. Moreover, since the mid-1990 s, the spring rainfall induced by the BOBTSs over the TP seems to be enhanced to a certain degree because of the intensified BOBTSs.

关键词： tropical storms Bay of Bengal the Tibetan Plateau soil moisture snow depth WRF

Prediction of separation flows around a 6:1 prolate spheroid using RANS/LES hybrid approaches

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Acta Mechanica Sinica 2007年第4期23卷 369-382页

作者： zhixiang xiao Yufei Zhang Jingbo Huang Haixin Chen Song Fu School of Aerospace Engineering,Tsinghua University,Beijing 100084,China School of Aerospace Engineering Tsinghua University Beijing China

This paper presents hybrid Reynolds-averaged Navier-Stokes （RANS） and large-eddy-simulation （LES） methods for the separated flows at high angles of attack around a 6：1 prolate spheroid. The RANS/LES hybrid meth- ods studied in this work include the detached eddy simulation （DES） based on Spalart-Allmaras （S-A）, Menter＇s k-ω shear-stress-transport （SST） and k-o9 with weakly nonlinear eddy viscosity formulation （Wilcox-Durbin＋, WD＋） models and the zonalANS/LES methods based on the SST and WD＋ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower-upper symmetric-Gauss-Seidel with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting for the effect on grids and fundamental turbulence models, is obtained for the separation flows.

关键词： RANS/LES hybrid methods DES Zonal-RANS/LES Weakly nonlinear correction

Numerical studies of reverse flows controlled by undulating leading edge

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Science China(Physics,Mechanics & Astronomy) 2019年第7期62卷 95-107页

作者： Biao Wang Jian Liu QiBing Li YunJun Yang zhixiang xiao School of Aerospace Tsinghua University China Academy of Aerospace Aerodynamics

The improved delayed detached-eddy simulation(IDDES) method is used to simulate the reverse flows past an NACA0012 airfoil at medium(10°) and large(30°) angles of attack. The numerical results of the baseline configuration are compared with the available measurements. The effects of the undulating leading edge with four different amplitudes are compared and analyzed at angle of attack of 10°. Based on these analyses, the amplitude of A/C=0.04 yields the best performance. Compared with the uncontrolled case, the performances of the undulating leading edge are greatly improved with reducing of the aerodynamic fluctuations. Furthermore, the mechanisms of performance are explored by comparing the local flow structures near the undulations.

关键词： IDDES method reverse flow flow control undulating leading edge