The theory of interaction between wave and basic flow

This paper investigates the interaction between transient wave and non-stationary and non-conservative basic flow. An interaction equation is derived from the zonally symmetric and non-hydrostatic primitive equations in Cartesian coordinates by using the Momentum-Casimir method. In the derivation, it is assumed that the transient disturbances satisfy the linear perturbation equations and the basic states are non-conservative and slowly vary in time and space. The diabatic heating composed of basic-state heating and perturbation heating is also introduced. Since the theory of wave-flow interaction is constructed in non-hydrostatic and ageostrophic dynamical framework, it is applicable to diagnosing the interaction between the meso-scale convective system in front and the background flow. It follows from the local interaction equation that the local tendency of pseudomomentum wave-activity density depends on the combination of the perturbation flux divergence second-order in disturbance amplitude, the local change of basic-state pseudomomentum density, the basic-state flux divergence and the forcing effect of diabatic heating. Furthermore, the tendency of pseudomomentum wave-activity density is opposite to that of basic-state pseudomomentum density. The globally integrated basic-state pseudomomentum equation and wave-activity equation reveal that the global development of basic-state pseudomomentum is only dominated by the basic-state diabatic heating while it is the forcing effect of total diabatic heating from which the global evolution of pseudomomentum wave activity results. Therefore, the interaction between the transient wave and the non-stationary and non-conservative basic flow is realized in virtue of the basic-state diabatic heating.

RELATIONSHIPS BETWEEN DIFFERENT TROPICAL CONVECTIVE ACTIVITIES AND LOW FREQUENCY WAVE－MEAN FLOW INTERACTIONS

Based on ECMWF objective analysis data, and with use of Batterworth bandpass-filtered skill and diagnostic analysis method, the interaction characteristics of low frequency wave and mean flow in midlatitudes during the winter years of 1983 / 1984 and 1986 / 1987 have been studied in this paper. The main results point out the important role of the tropical convective activity on the above mentioned interaction process.

The Propagation and Transport Effect of Planetary Waves in the Northern Hemisphere Winter

Based on the transformed Eulerian-mean equations, the dynamics of planetary waves are discussed. Both observations and simulations indicate that in the Northern Hemisphere winter there are two waveguides for the meridional propagation of quasi-stationary planetary waves. One is the high latitude waveguide, and the other is the low latitude waveguide. These results are in good agreement with theoretical analysis. Moreover, the convergence of EP flux indicates that the stratospheric sudden warming is the result of anomalous planetary wave propagation along the high latitude waveguide and its interaction with mean flows. The tropical quasi-biennial oscillation (QBO) winds, which represent one significant variation of zonal flow in the lower stratosphere at low latitudes, can influence the low latitude waveguide of planetary wave propagation. Our results of the wave-mean flow coupled model show that these tropical winds can also modulate the high latitude waveguide significantly in the case of wave-mean flow interaction.The transport effect of planetary waves on ozone is also analyzed. The residual mean circulation forced by planetary waves indicates that there is strong transport circulation for the dissipative planetary waves. Under the forcing of northward eddy heat transport, a positive transport circulation can result which rises at low latitudes and sinks at high latitudes. At the same time, the modification of planetary wave propagation by the equatorial QBO winds is shown to have an important impact on the transport circulation. The model results indicate that the meridional transport is amplified during the easterly phase of the QBO. This mechanism may explain the interannual variability of ozone in the stratosphere at high latitudes.

A NOTE ON THE INTERACTIONS OF ELEMENTARY WAVES FOR THE AR TRAFFIC FLOW MODEL WITHOUT VACUUM

In this note, we consider the interactions of elementary waves for the traffic flow model proposed by Aw and Rascle when the vacuum is not involved. The solutions are obtained constructively and globally when the initial data consist of three pieces of constant states. Furthermore, it can be found that the Riemann solutions are stable with respect to such small perturbations of the initial data in this particular situation by investigating the limits of the solutions as the perturbed parameter ε goes to zero.

Gao's interacting shear flows( ISF) theory and its inferences and their applications

Gao＇s viscous/in-viscid interacting shear flows （ISF） theory, proposed by professor Gao Zhi in Institute of Mechanics, China Academy of Science, and its inferences and their applications in computational fluid dynamics （CFD） are reviewed and some subjects worthy to be studied are pro- posed in this paper. The flow-field and motion law of ISF, mathematics definition of strong viscous shear layer flow in ISF, ISF equations, wall-surface compatibility criteria （Gao＇s criteria ）, space scale variety law of strong viscous shear layer reveals flow mechanism and local space small scale triggered by strong interaction that cause some abnormal severe local pneumatic heating phenomenon in hypersonic flow. Gao＇s ISF theory was used in near wall flow, free ISF flow simulation and design of computing grids, Gao＇s wall-surface criteria were used to verify calculation reliability and accuracy of near wall flows, ISF theory approximate analytical result of shock waves-boundary layer interac- tion and ISF equations were used to obtain the numerical exact solution of local area flow （ such as stationary point flow）. Some new subjects, such as, improving near-wall turbulent models according to the turbulent flow simulation satisfying the wall-criteria and illustrating relation between grid-con- vergence based on the wall criteria and other convergence tactics, are suggested. The necessity of applying Gao＇s ISF theory and wall criteria is revealed. Difficulties and importance of hypersonic vis- cous/in-viscid interaction phenomenon were also emphasized.

NON-LINEAR WATER WAVES ON SHEARING FLOWS

This article is devoted to the study of the propagations of the non- linear water waves on the shear flows. Assuming μ = kh is small and ε/μ~2 ～ 0 (1), and the base flow is uniformly sheared, the modified Boussinesq equation is obtained. We calculate propagations of the single sohtary wave with vorticity Γ = 0, >0 and <0. The influences of the vorticity are manifested. At the end examples of the interactions of two solitary waves, moving in opposite and the same directions, are given. Besides the phase shift, there also occur second wavelets after head-on collision.

Vortex Rossby Waves in Asymmetric Basic Flow of Typhoons

Wave ray theory is employed to study features of propagation pathways（rays） of vortex Rossby waves in typhoons with asymmetric basic flow, where the tangential asymmetric basic flow is constructed by superimposing the wavenumber-1 perturbation flow on the symmetric basic flow, and the radial basic flow is derived from the non-divergence equation. Results show that, in a certain distance, the influences of the asymmetry in the basic flow on group velocities and slopes of rays of vortex Rossby waves are mainly concentrated near the radius of maximum wind（RMW）, whereas it decreases outside the RMW. The distributions of radial and tangential group velocities of the vortex Rossby waves in the asymmetric basic flow are closely related to the azimuth location of the maximum speed of the asymmetric basic flow, and the importance of radial and tangential basic flow on the group velocities would change with radius. In addition, the stronger asymmetry in the basic flow always corresponds to faster outward energy propagation of vortex Rossby waves. In short, the group velocities, and thereby the wave energy propagation and vortex Rossby wave ray slope in typhoons, would be changed by the asymmetry of the basic flow.

Effects of Topography and Current on Horizontal Irrotational Waves in Shallow Water

Based on the Boussinesq assumption, derived are couple equations of free surface elevation and horizontal velocities for horizontal irrotational flow, and analytical expressions of the corresponding pressure and vertical velocity. After the free surface elevation and horizontal velocity at a certain depth are obtained by numerical method, the pressure and vertical velocity distributions can be obtained by simple calculation. The dispersion at different depths is the same at the O (epsilon) approximation. The wave amplitude will decrease with increasing time due to viscosity, but it will increase due to the matching of viscosity and the bed slope, thus, flow is unstable. Numerical or analytical results show that the wave amplitude, velocity and length will increase as the current increases along the wave direction. but the amplitude will increase, and the wave velocity and length will decrease as the water depth decreases.

Observed Solar Cycle Variation of the Stratospheric QBO Generated in the Mesosphere and Amplified by Upward Propagating Waves

With an analysis of zonal wind observations over 40 years, Salby and Callaghan [1] showed that the Quasi-biennial Oscillation (QBO) at 20 km is modulated by 11-year solar cycle (SC) variations from about 12 to 20 m/s (Figure 2). The observations are reproduced qualitatively in a study with the 3D Numerical Spectral Model, which shows that the SC effect of the stratospheric QBO is produced by dynamical downward coupling originating in the mesosphere. In this modeling study, the SC period is taken to be 10 years, and a realistic heat source is applied varying exponentially with altitude: 0.2%, surface;2%, 50 km;20%, 100 km and above. The numerical results show that the variable solar radiation in the mesosphere around 65 km generates a hemispheric symmetric Equatorial Annual Oscillation (EAO), which is modulated by relatively large SC variations. Under the influence of wave mean flow interactions, the EAO propagates into the lower atmosphere and is the dynamical source or pacemaker for the large SC modulation of the QBO. The numerical results show that the upward propagating small-scale gravity waves from the troposphere amplify the SC modulations of the QBO and EAO in the stratosphere, part of the SC mechanism. The zonal winds of the equatorial QBO and EAO produce through the meridional circulation measurable SC variations in the temperature of the stratosphere and troposphere at high latitudes. Analysis of NCEP temperature and zonal wind data (1958 to 2006) provides observational evidence of the EAO with SC variations around 11 years.

激波/湍流边界层干扰中的自适应控制技术

从激波/湍流边界层干扰机理以及流动控制的迫切需求入手,从自适应涡流发生器、自适应鼓包、自适应微射流以及自适应次流循环四个方面对激波/湍流边界层干扰中的自适应控制技术研究进展进行了总结。分析认为,结合AI技术发展自适应流动控制技术,加速控制方式智能化,可作为新一代高超声速飞行器宽速域飞行的重要技术手段。具体来说,就是通过调节外加激励对高超声速飞行器不同区域实现局部流动加/减速、气动热防护、气动控制等功能,根据流场参数建立控制反馈回路,自适应调整局部流场结构,以满足工程实际需求。

北半球夏季急流遥相关:进展与展望

急流遥相关是沿急流波导传播的准静止行星尺度波列,在大气环流的维持和演变中有重要作用,其异常活动常伴随极端天气气候事件的发生。研究急流遥相关在不同时间尺度的变异特征和机理不仅可以加深对大气环流变化规律的理解,还可以为相应时间尺度上的天气预报、气候预测乃至气候预估提供科学依据。根据波导的性质,北半球夏季的急流波导可以分为以正压效应为主要维持机制的副热带急流波导和以斜压效应为维持机制的极锋急流波导。本文聚焦夏季急流遥相关活动最为活跃的欧亚大陆地区,在回顾急流遥相关理论的基础上,简要总结了近年来关于夏季副热带急流遥相关和极锋急流遥相关的形成条件、动力机制、气候影响和未来变化的研究进展,并展望了一些未来值得继续深入研究的问题。

不同截面形状淹没水平柱体上波浪力数值模拟研究

基于黏性流理论,采用有限体积法,考虑多种波浪参数和截面形状,计算淹没水平柱体在波浪作用下的受力.通过受力分解和局部流场特征分析,探究了波浪参数和截面形状对柱体受力的影响.结果表明,3种不同截面形状柱体受力主要由惯性力主导,柱体的淹没体积更大程度地决定了柱体所受波浪力的大小.在相同宽高比条件下,矩形柱淹没体积最大,其次是曲边矩形柱,最小的是椭圆柱.因此,综合考虑3种截面形状淹没水平柱体,矩形柱所受波浪力最大,椭圆柱所受波浪力最小,且随着宽高比的增大逐渐减小.

基于两相流流固耦合方法的两栖火炮水上射击稳定性分析

两栖火炮水上射击稳定性是一个涉及两种流场与两栖火炮相互作用的复杂问题。此前的研究往往将该问题中的流场作用简化为弹簧-扭簧系统,这样的简化模型会导致两栖火炮水上射击稳定性的预测精确度不足。文章通过两相流流固耦合方法详细研究了两栖火炮受到海面风浪作用产生的摇荡。仿真结果表明,两栖火炮在3、4级风浪环境中具有较好的稳定性,同等级风浪环境下不同的车体朝向角将对两栖火炮稳定性产生较大影响。

Analysis of the Oscillatory Flows of Multiple Shock Waves in a Constant Area Duct

The oscillatory response of multiple shock waves to downstream perturbations in a supersonic flow is studied numerically in a rectangular duct.Multiple shock waves are formed inside the duct at a shock Mach number of 1.75.The duct has an exit height of H,and the effect of duct resonance on multiple shock oscillations is investigated by attaching exit ducts of lengths 0H,50H,and 150H.The downstream disturbance frequency varied from 10 Hz to 200 Hz to explore the oscillation characteristics of the multiple shock waves.The oscillatory response of shock waves under self-excited and forced oscillation conditions are analyzed in terms of wall static pressure,shock train leading-edge location,shock train length,and the size of the separation bubble.The extent of the initial shock location increases with an increase in exit duct length for the self-excited oscillation condition.The analysis of the shock train leading edge and the spectral analysis of wall static pressure variations are conducted.The variation in the shock train length is analyzed using the pressure ratio method for self-excited as well as forced oscillations.The RMS amplitude of the normalized shock train length(ζ_(ST))increases with an increase in the exit duct length for the self-excited oscillation condition.When the downstream perturbation frequency is increased,ζ_(ST)is decreased for exit duct configurations.For all exit duct designs and downstream forcing frequencies,the size of the separation bubble grows and shrinks during the shock oscillations,demonstrating the dependence on duct resonance and forced oscillations.

基于膨胀波效应的高超声速进气道肩部流动分离控制研究

为改善高超声速进气道唇口激波/附面层干扰诱导的肩部流动分离,从膨胀波及激波理论出发,推导出了膨胀波效应影响下的斜激波附面层干扰理论公式,获得了影响斜激波诱导分离的主要因素:膨胀角梯度、激波角及波前马赫数。在此基础上,开展了膨胀波效应影响下的流动分离控制研究,给出了膨胀波效应影响下斜激波诱导分离的判别及预测方法。结果表明:增大激波入射点处膨胀角梯度,可以显著减小甚至消除肩部流动分离;随着激波角增大,激波强度及逆压力梯度增加,分离区尺寸显著增大。而波前马赫数对分离区尺寸的影响不显著;在进口马赫数3.57~5.18,唇罩角度6°~10°范围内,当激波入射点处逆压比梯度小于250 m^(-1)时,斜激波诱导的流动分离消失,可为改善超声速/高超声速进气道内流道流动分离提供技术支撑。

压缩拐角强激波边界层干扰直接数值模拟研究

激波/湍流边界层干扰是高超声速飞行中常见的流动现象,平板-压缩拐角存在于飞行器进气道、翼舵等,是研究激波/湍流边界层干扰的标准构型。采用直接数值模拟方法研究了马赫数6.0、40°压缩拐角的高超声速强激波/湍流边界层干扰问题。在上游湍流边界层内,近壁流动以高低速条带结构为主;当流动进入干扰区后,流向条带消失,同时形成具有三维特征的流动结构。在强激波作用下,分离长度超过10个边界层厚度。流动再附后,壁面摩阻、压力及其脉动峰值分别达到上游湍流边界层的8.9、36和124倍。干扰区内湍动能强度显著增加,其峰值是边界层峰值的6.4倍。研究发现激波运动、分离剪切层是湍动能强度增加的主要原因。

基于弹簧—阻尼理论的海上变电站动力特性研究

近年来,随着海上风电的迅速发展,海上变电站的建设也逐渐兴起。然而,错综复杂、瞬息万变的海洋环境对变电站的安全性和稳定性提出了严峻的挑战,因此有必要加强对变电站分析和研究的重视。为了提高变电站数值模型分析的效率,研究以海上风电场变电站为中心,采用ABAQUS建立了实体土有限元模型和基于弹簧—阻尼理论的有限元模型,以模拟桩土相互作用。随后进行了模态分析、风浪流响应分析和地震响应分析研究。研究结果表明:使用两种模型进行模态分析得出的振型非常相似,频率误差小于5%。此外,在承受风和波流荷载时,两种模型得出的变电站结构响应具有显著的一致性。在地震荷载作用下,两个模型中样本点位移时程曲线的相位频率与测量数据非常接近。值得注意的是,基于弹簧—阻尼理论的模型计算出的振幅与地震波测量数据更为接近。此外,弹簧—阻尼理论方法还大大提高了计算效率。

Nonlinear Dynamic Behaviors of A Floating Structure in Focused Waves

Floating structures are commonly seen in coastal and offshore engineering. They are often subjected to extreme waves and, therefore, their nonlinear dynamic behaviors are of great concern. In this paper, an in-house CFD code is developed to investigate the accurate prediction of nonlinear dynamic behaviors of a two-dimensional（2-D） box-shaped floating structure in focused waves. Computations are performed by an enhanced Constrained Interpolation Profile（CIP）-based Cartesian grid model, in which a more accurate VOF（Volume of Fluid） method, the THINC/SW scheme（THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A focusing wave theory is used for the focused wave generation. The wave component of constant steepness is chosen. Comparisons between predictions and physical measurements show good agreement including body motions and free surface profiles. Although the overall agreement is good, some discrepancies are observed for impact pressure on the superstructure due to water on deck. The effect of grid resolution on the results is checked. With a fine grid, no obvious improvement is seen in the global body motions and impact pressures due to water on deck. It is concluded that highly nonlinear phenomena, such as distorted free surface, large-amplitude body motions, and violent impact flow, have been predicted successfully.

The Propagation of Wave Packets and Its Relationship with the Subtropical Jet over Southern China in January 2008

The propagation of wave packets and its relationship with the subtropical jet was investigated for the period 26 29 January 2008 over southern China using ECMWF Interim re-analysis data. Wave packets propagated from the north to the south side of an upper front with eastward development along the upper front during this period. Due to the eastward development of propagation, the acceleration of geostrophic westerly winds shifted eastward along the front. There were two primary sources of the propagation of wave packets at around 30°N. The first was the temperature inversion layer below 500 hPa, and the second was baroclinic zones located along the polarward flank of the subtropical jet in the middle and upper troposphere. Most wave packets propagated horizontally from the baroclinic zones and then converged on the zero meridional gradients of zonal winds.

Study on Internal Supersonic Flows with Pseudo-shock Wave Using Liquid Crystal Flow Visualization Method

The flow visualization technique using shear-sensitive liquid crystal is applied to the investigation of a Mach 2 internal supersonic flow with pseudo-shock wave （PSW） in a pressure-vacuum supersonic wind tunnel. It provides qualitative information mainly concerning the overall flow structure, such as the turbulent boundary layer separation, reattachment locations and the dimensionalities of the flow. Besides, it can also give understanding of the surface streamlines, vortices in separation region and the corner effect of duct flow. Two kinds of crystals with different viscosities are used in experiments to analyze the viscosity effect. Results are compared with schlieren picture, confirming the effectiveness of liquid crystal in flow-visualization.