Investigation of the supersonic flow around a pointed elliptical cone at an angle of attack

The picture of ideal gas flow around cones at zero and low angles of attack has been well studied by using approximate methods [1], and results for high angles of attack have been obtained mainly numerically [2–7]. At high angles of attack it is sensible to examine inviscid flow only up to some generator on the downwind side of the cone at which boundary-layer separation occurs. Hence, the domain where the flow can be considered inviscid yields the main contribution to the magnitude of the aerodynamic forces and the heat fluxes [5, 9]. A picture of the supersonic flow around a pointed elliptical cone is obtained in this paper by the numerical solution of the gasdynamics equations. The whole flow domain is computed at low angles of attack while the solution at high angles is obtained in a domain bounded by some surface of three-dimensional type [10]. The dependence of the flow parameters on the angle of attack is studied when the shock is attached to the cone apex. In contrast to a circular cone, at low angles of attack two spreading lines occur on the surface of an elliptical cone, to which the maximum pressure corresponds. As the angle of attack increases, these lines come together and merge at a certain time. At high angles of attack the flow picture is analogous to a circular cone with a pressure maximum in the plane of symmetry.     

Asymmetric vortices flow over slender body and its active control at high angle of attack

The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area. This paper attempts to provide an update state of art to the investigations on the fields of forebody asymmetric vortices. This review emphasizes the correlation between micro-perturbation on the model nose and its response and evolution behaviors of the asymmetric vortices. The critical issues are discussed, which include the formation and evolution mechanism of asymmetric multi-vortices; main behaviors of asymmetric vortices flow including its deterministic feature and vortices flow structure; the evolution and development of asymmetric vortices under the perturbation on the model nose; forebody vortex active control especially discussed micro-perturbation active control concept and technique in more detail. However present understanding in this area is still very limited and this paper tries to identify the key unknown problems in the concluding remarks. The project supported by the National Natural Science Foundation of China (10172017), Aeronautical Science Foundation of China (02A51048) and Foundation of National Key Laboratory of Aerodynamic Design and Research (51462020504HK0101)     

Stall control at high angle of attack with plasma sheet actuators

We analyzed the modifications of the airflow around an NACA 0015 airfoil when the flow was perturbed with electrohydrodynamic forces. The actuation was produced with a plasma sheet device (PSD) consisting in two bare electrodes flush mounted on the surface of the wing profile operated to obtain a discharge contouring the body in the inter-electrode space. We analyze the influence of different parameters of the actuation (frequency, input power, electrodes position) on the aerodynamic performance of the airfoil, basing our study on measurements of the surface pressure distribution and of the flow fields with particle image velocimetry technique. The experiments indicated that at moderate Reynolds numbers (150,000 < Re < 333,000) and at high angles of attack, steady or periodic actuations enabled large improvement of the lift and drag/lift aerodynamic coefficients by reattaching the flow along the extrados. However, to attain the same results steady actuations required larger power consumption. When exciting the flow with a moderate value of non-dimensional power coefficient (ratio of electric power flow with the kinetic power flow), a frequency of excitation produced a peak on the coefficients that evaluate the airfoil performance. This peak in terms of a non-dimensional frequency was close to 0.4 and can be associated to an optimal frequency of excitation. However, our work indicates that this peak is not constant for all stalled flow conditions and should be analyzed considering scale factors that take into account the ratio of the length where the forcing acts and the cord length.     

Vibrations of slender bodies at high angle of attack in supersonic flow

The method of curved bodies [1] is extended to the case of arbitrary angle of attack within the framework of the law of plane sections [2].     

平板大攻角绕流升力和阻力系数的计算

二维平板或二维对称薄翼型大攻角绕流升力和阻力系数与攻角之间存在的函数关系一般用数据表格的形式给出。本文根据垂直平板绕流阻力实验数据和对称薄翼型全攻角绕流实验数据,分析得到了平板大攻角绕流总压力及其升力分量和阻力分量系数的近似计算公式。结果表明：平板总压力系数约等于攻角正弦值的2倍;总压力的阻力分量系数约等于攻角正弦值平方的2倍;升力分量系数约为攻角2倍的正弦值。计算结果与两组试验数据具有较好的一致性。     

Input-output reduced-order modeling of unsteady flow over an airfoil at a high angle of attack based on dynamic mode decomposition with control

Due to the damage caused by stall flutter, the investigation and modeling of the flow over a wind turbine airfoil at high angles of attack are essential. Dynamic mode decomposition (DMD) and dynamic mode decomposition with control (DMDc) are used to analyze unsteady flow and identify the intrinsic dynamics. The DMDc algorithm is found to have an identification problem when the spatial dimension of the training data is larger than the number of snapshots. IDMDc, a variant algorithm based on reduced dimension data, is introduced to identify the precise intrinsic dynamics. DMD, DMDc and IDMDc are all used to decompose the data for unsteady flow over the S809 airfoil that are obtained by numerical simulations. The DMD results show that the dominant feature of a static airfoil is the adjacent shedding vortices in the wake. For an oscillating airfoil, the DMDc results may fail to consider the effect of the input and have an identification problem. IDMDc can alleviate this problem. The dominant IDMDc modes show that the intrinsic flow for the oscillating case is similar to the unsteady flow over the static airfoil. Moreover, the input–output model identified by IDMDc can give better predictions for different oscillating cases than the identified DMDc model.     

Nose micro-blowing for asymmetric vortices control on blunt-nose slender body at high angle of attack

The asymmetric vortices over blunt-nose slender body at high angles of attack result in random side force. In this paper, a nose micro-blowing technology is used to control the asymmetric flow. Pressure measurement and particle image velocimetry(PIV) experiments are conducted in a low-speed wind tunnel to research effects of jet flow rate on asymmetric vortices over blunt-nose slender body. The angle of attack of the model is fixed at 50?and the Reynolds number for the experiments is 1.6×10~5 based on diameter of aftbody. A blow hole(5 mm in diameter) on the nose is processed at circumferential angle θ_b= 90?and meridian angle γ_b= 20?with jet momentum ratio C_μ ranging from 5.30×10~(-7) to1.19×10~(-4). Tests are made under two kinds of perturbations. One is called single perturbation with only blow hole and the other is called combined perturbation consists of blow hole and additional granules set on nose. The results show that whether the model has the single perturbation or the combined one,the sectional side force of x/D = 3 varies in the same direction with the increasement of C_μ and remains stable when C_μ is greater than 3.29×10~(-6). But the stable force values are different according to various perturbations. The fact proves that the size and direction of the side force of blunt-nose slender body can be controlled by the nose micro-blowing.     

Permeable plate at angle of attack in steady flow of a viscous fluid

An approximate solution is presented for the problem of the resistance of a permeable plate of widthl at an angle of attack in a steady plane flow of an incompressible viscous fluid for the case of both small and very large Reynolds numbers with different permeability laws. The results obtained in the case of large Reynolds numbers are compared with the corresponding results for flow past plane rod grids.     

Supersonic flow past a star-shaped body without symmetry planes at angle of attack

The author's solution [2] for the flow past a star-shaped body without symmetry planes is generalized. It is shown that in this case also the vector of the resultant force is situated in the plane of the angle of attack (there is no lateral force). The twisting moment acted on the star-shaped body is calculated.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 164–173, May–June, 1993.     

Investigation of the control of the flow around a wing using mini-flaps

The flow around an airfoil with a mini-flap mounted on the lower or upper wing surface is investigated. The results are obtained by measuring the pressure distribution over the airfoil surface and the forces acting on it for Mach and Reynolds numbers M = 0.1?0.8 and Re = (0.6?3.8) × 10⁶. It is shown that, as distinct from known devices such as Gurney flaps, blunt trailing edge, etc., for controlling the flow in the vicinity of the trailing edge of an airfoil, a mini-flap mounted on the undersurface produces gas flow from the upper to the lower surface around a sharp edge. In this case the flow pattern is considerably affected not only near the trailing edge but also over the entire airfoil. The pressure redistribution over the airfoil makes it possible to increase or decrease the wing lift. Thanks to the low hinge moment, the mini-flap can serve as an effective means of low-inertia control of the flow around a wing.     

Super-twisting sliding mode control for aircraft at high angle of attack based on finite-time extended state observer

Nonlinear Dynamics - This paper proposes a finite-time decoupling control strategy for aircraft with thrust vector at high angle of attack maneuver. Firstly, the nonlinear mathematical model of the...     

Passive control of the flow around a square cylinder using porous media

The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two‐dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier–Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd.     

Three-dimensional boundary layer and vortex wake over a cone at high angle of attack: study of asymmetries

An experimental investigation of the flow over a one at a large angle of attack is reported. First, the study was focused on the wall shear stress measurement, including the localization of the separation. Secondly, the mean flow field in the whole wake of the cone was measured, as well as the velocity fluctuations. Results indicate that the separation and the fluctuations are asymmetrical in a certain way, whereas the mean flow field is approximately symmetrical. Finally, the different parts of the flow can be easily determined using vorticity calculations.List of symbols C vortex core - D diffusion coefficient for the polarographic solution - D cone diameter for the rotation plane of the electrochemical probes - D separation point - F function F (sin ) = (K ₁-K ₂)/(K ₁+K ₂) - G function G(sin ) = (K ₁+K ₂)/(K ₁+K ₂)( = 90dg) - g bidimensional gain of the electrochemical probe (constant for each probe) - K ₁, K ₂ mass transfer coefficients for differential probes - Re _x Reynolds number based on the X length, and relative to the forward upstream velocity - wall velocity gradient vector - S wall velocity gradient modulus - S enclosing saddle point - S _x azimuthal component of the wall velocity gradient (perpendicular to a generator) - S _z longitudinal component of the wall velocity gradient (along a generator) - U mean value of the forward upstream velocity - U _i component number i of the velocity vector in the (X, Y, Z) coordinates - X, Y, Z cone cartesian coordinates - non-dimensional cone cartesian coordinates (relative to D) Greek symbols incidence (part 1) angle between the wall velocity gradient and the neutral axis of the electrochemical probe (except part 1) - _r relative incidence /0 _c - velocity circulation - wavelength of the laser beam - kinematic viscosity - azimuthal angle - _c cone semi-apex angle     

Turbulent flow of a fluid in the neighborhood of the trailing edge of a plate at zero angle of attack

The laminar flow regime of an incompressible fluid at the trailing edge of a plate was studied by Stewartson and Messiter [1, 2] by means of the method of matched asymptotic expansions. In. the present paper, this method is used to analyze the same problem, but in the case of turbulent flow in the boundary layer and the wake. A system of linear equations of elliptic type with variable coefficients is obtained for the averaged values of the flow parameters in the main part of the boundary layer and the wake that is responsible for the change in the displacement thickness. A solution of this system is constructed by the Fourier method in the case of a power law of the velocity in front of the interaction region.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 17–23, November–December, 1983.