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Mechanism of three-dimensional boundary-layer receptivity

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Applied Mathematics and Mechanics(English Edition) 2017年第9期38卷 1213-1224页

作者： luyu SHEN changgen lu School of Marine Sciences Nanjing University of Information Science&TechnologyNanjing 210044China

Boundary-layer receptivity is always a hot issue in laminar-turbulent tran- sition. Most actual laminar-turbulent transitions belong to three-dimensional flows. An infinite back-swept fiat-plate boundary layer is a typical three-dimensionalflow. Study of its receptivity is important both in theory and applications. In this paper, a free- stream turbulence model is established. A modified fourth-order Runge-Kutta scheme is used for time marching, and compact finite difference schemes are used for space dis- cretization/ On these bases, whether unsteady cross-flow vortices can be excited in the three-dimensional boundary layer （the infinite back-swept flat-plate boundary layer） by free-stream turbulence is studied numerically. If so, effects of the level and the direc- tion of free-stream turbulence on the three^dimensional boundary-layer receptivity are further studied. Differences of the three-dimensional boundary-layer receptivity are then discussed by considering the non-parallel effect, influence of the leading-edge stagnation point of the flat plate, and variation of the back-swept angle separately. Intensive studies on the ＇three-dimensional boundary-layer receptivity will benefit the development of the hydrodynamic stability theory, and provide a theoretical basis for prediction and control of laminar-turbulent transition.

关键词： receptivity three-dimensional boundary layer free-stream turbulence

Local receptivity in non-parallel boundary layer

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Applied Mathematics and Mechanics(English Edition) 2016年第7期37卷 929-940页

作者： luyu SHEN changgen lu College of Atmospheric Science Nanjing University of Information Science and Technology School of Marine Science Nanjing University of Information Science and Technology

The research on boundary-layer receptivity is the key issue for the laminarturbulent transition prediction in fluid mechanics. Many of the previous studies for local receptivity are on the basis of the parallel flow assumption which cannot accurately reflect the real physics. To overcome this disadvantage, local receptivity in the non-parallel boundary layer is studied in this paper by the direct numerical simulation （DNS）. The difference between the non-parallel and parallel boundary layers on local receptivity is investigated. In addition, the effects of the disturbance frequency, the roughness location, and the multiple roughness elements on receptivity are also determined. Besides, the relations of receptivity with the amplitude of free-stream turbulence （FST）, with the roughness height, and with the roughness length are ascertained as well. The Tollmien- Schlichting （T-S） wave packets are excited in the non-parallel boundary layer under the interaction of the FST and the localized wall roughness. A group of T-S waves are separated by the fast Fourier transform. The obtained results are in accordance with Dietz＇s measurements, Wu＇s theoretical calculations, and the linear stability theory （LST）.

关键词： receptivity non-parallel boundary layer free-stream turbulence (FST),wall roughness

Leading-edge receptivity of boundary layer to three-dimensional free-stream turbulence

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Applied Mathematics and Mechanics(English Edition) 2019年第6期40卷 851-860页

作者： luyu SHEN changgen lu Xiaoqing ZHU School of Marine Sciences Nanjing University of Information Science & Technology

The laminar-turbulent transition has always been a hot topic of fluid mechanics. Receptivity is the initial stage and plays a crucial role in the entire transition process. The previous studies of receptivity focus on external disturbances such as sound waves and vortices in the free stream, whereas those on the leading-edge receptivity to the three-dimensional free-stream turbulence (FST), which is more general in the nature, are rarely reported. In consideration of this, this work is devoted to investigating the receptivity process of three-dimensional Tollmien-Schlichting (T-S) wave packets excited by the three-dimensional FST in a flat-plate boundary layer numerically. The relations between the leading-edge receptivity and the turbulence intensity are established, and the influence of the FST directions on the propagation directions and group velocities of the excited T-S wave packets is studied. Moreover, the leading-edge receptivity to the anisotropic FST is also studied. This parametric investigation can contribute to the prediction of laminar-turbulent transition.

关键词： leading-edge receptivity free-stream turbulence (FST) boundary layer three-dimensional Tollmien-Schlichting (T-S) wave

A High-Order Numerical Method to Study Three-Dimensional Hydrodynamics in a Natural River

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Advances in Applied Mathematics and Mechanics 2015年第2期7卷 180-195页

作者： luyu Shen changgen lu Weiguo Wu Shifeng Xue College of Marine Sciences Nanjing University of Information Science and TechnologyNanjing 210044China College of Atmospheric Sciences Nanjing University of Information Science and TechnologyNanjing 210044China Department of Engineering Mechanics China University of PetroleumDongying 266555China

A high-order numerical method for three-dimensional hydrodynamics is *** present method applies high-order compact schemes in space and a Runge-Kutta scheme in time to solve the Reynolds-averaged Navier-Stokes equations with the k-ǫturbulence model in an orthogonal curvilinear coordinate *** ad-dition,a two-dimensional equation is derived from the depth-averaged momentum equations to predict the water *** proposed method isﬁrst validated by its application to simulateﬂow in a 180◦curved laboratoryﬂ*** is found that the simulated results agree with measurements and are better than those from SIMPLEC *** the method is applied to study three-dimensional hydrodynamics in a natural river,and the simulated results are in accordance with measurements.

关键词： Compact scheme three-dimensional hydrodynamics k-ǫturbulence model orthog-onal curvilinear coordinate system Runge-Kutta scheme

INTERACTION BETWEEN COHERENT STRUCTURES IN WALL REGION OF A TURBULENT BOUNDARY LAYER

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Transactions of Nanjing University of Aeronautics and Astronautics 2001年第Z1期18卷 82-86页

作者： lu changgen(Hohai University Nanjing 210098,P.R.China) Hohai University Nanjing 210098 P. R. China

Using the idea of general resonant triad of the hydrodynamic stability, the theoretical models for coherent structures in the wall region of a turbulent boundary layer is proposed. The interaction between coherent structures in the wall region of a turbulent boundary layer is studied by combining the compact finite differences of high numerical accuracy and the Fourier spectral hybrid method for solving the three dimensional Navier Stokes equations. In this method, the third order mixed explicit implicit scheme is employed for the time integration. The fifth order upwind compact finite difference schemes for the nonlinear convection terms in the physical space, and the sixth order center compact schemes for the derivatives in spectral space are descried, respectively. The fourth order compact schemes satisfied by the velocities and pressure in spectral space is derived. As an application, the method is implemented to the wall region of a turbulent boundary to study the interaction between coherent structures. It is found that the numerical results are satisfactory.

关键词： interaction coherent structure turbulent boundary layer compact finite difference

Large eddies induced by local impulse at wall of boundary layer with pressure gradients

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Progress in Natural Science:Materials International 2008年第7期18卷 873-878页

作者： changgen lu a,b,*, Weidong Caob, Yanmei Zhang b, Jintao Pengb a College of Atmospheric Science, Nanjing University of Information Science & Technology, Nanjing 210044, China b College of Environmental Science and Engineering, Hohai University, Nanjing 210098, China College of Atmospheric Science Nanjing University of Information Science & Technology Nanjing 210044 China College of Environmental Science and Engineering Hohai University Nanjing 210098 China

Large eddies induced by local impulse at the wall with pressure gradients in the boundary layer was studied by direct numerical sim- ulations. The results show that the amplitude evolution, the high and low speed stripes, the formation of streamwise vortices, the ejection and sweeping, inflexions and distortion at the mean velocity profiles, as well as other characteristics, are consistent with the experimental and other numerical results. It is also found that large eddies are easy to be excited with adverse pressure gradient in the boundary layer, and the growth of amplitudes, formation of streamwise vortices and the influencing area etc., are much larger than those with favorable pressure gradient in the boundary layer. In contrast, large eddies are hardly to be induced through local impulse disturbance at the wall with favorable pressure gradients in the boundary layer.

关键词： Boundary layer Pressure gradients Impulse Large eddies

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近壁湍流相干结构演化机理的研究

空气动力学学报 1999年第3期17卷 351-355页

作者：陆昌根南京航空航天大学六系南京210016

从流动稳定性理论中的共振三波出发，提出了近壁湍流相干结构的理论模型，采用紧致有限差分和Ｆｏｕｒｉｅｒ谱展开相结合的方法对近壁湍流相干结构进行了数值模拟。结果表明，在小初始幅值下，单个相干结构不容易被激发；仅在相当大... 详细信息

从流动稳定性理论中的共振三波出发，提出了近壁湍流相干结构的理论模型，采用紧致有限差分和Ｆｏｕｒｉｅｒ谱展开相结合的方法对近壁湍流相干结构进行了数值模拟。结果表明，在小初始幅值下，单个相干结构不容易被激发；仅在相当大的初始幅值下，它可能被激发增长起来；该结论与文献［１］的结果吻合。另外，非对称单个相干结构比对称单个相干结构更容易增长。

关键词：相干结构数值模拟共振三波近壁湍流