Experimental study of vortex flow about low aspect ratio wings and circular cones at M = 2

Characteristic of the flow about wings of low aspect ratio with subsonic leading edges and bodies of revolution at angles of attack is the formation of spiral vortices as a result of rolling-up of the transverse flow, which separates near the wing leading edge and on the lateral generator of the body. The vortices, concentrated in a pair of free vortex cores, interact with the boundary layer, causing a complex flow pattern on the surface of the model in question.There are several methods which make it possible to study the flow about the model. Pickups may be used to measure the pressure field or the velocity field near the model. This technique has found wide application and was used for studying the flow pattern about wings and bodies of revolution at both subsonic and supersonic speeds (see, for example, [1–4]). However, this method is very tedious and, in addition, the probes always introduce disturbances into the flow, particularly for supersonic speeds.A visual picture of the vortex flow may be obtained in a towing basin by adding to the water metal powder in the suspended state, or by introducing filaments of colored liquid [1, 5].The vapor screen [6] and smoke [3] methods are also used for flow visualization.The boundary layer flow on the model may be studied with the aid of oil or evaporting coatings. These methods have been used in [1, 7] to study flow about wings and in [8] to study flow about circular cones.According to the studies presented in [9] of an electric discharge with the application of high voltage to electrodes located in an air stream, a stable glow occurs as a result of the prebreakdown discharge.The properties of the prebreakdown discharge have been used by the authors of the present paper to study visually the vortex flows (high voltage electric discharge method). This technique was used to obtain the trajectories of the vortex trails for low aspect ratio wings and circular cones mounted at various angles of attack in a stream with Mach number M=2 and Reynolds number R=0.9·10⁶.In conclusion the author wishes to thank B. V. Kalachev, R. V. Bertyn, and E. D. Korolev for assistance in carrying out the experiments.     

Hypersonic flow past ducted blunt bodies of revolution

Chernyi [1, 2] has examined the problem of hypersonic flow past a ducted cone with sharp leading edge. In the following we present an analysis of the characteristic features of this problem in the case of a blunt leading edge. We use hypersonic theory for flow past slender bodies with nose blunting of relatively small dimensions [1, 3, 4], based on replacing the nose by a concentrated force and use of the nonsteady analogy. It has been shown in [4, 5] that within the framework of this theory the effect of the violation of the law of plane sections and also the effect of the chemical and physical transformations of the gas in the high-entropy layer is qualitatively equivalent to a change in the drag coefficient of the nose. This approach makes it possible to establish useful similarity laws. The development of these ideas in the direction of the study of the flow structure behind the bow shock wave and analysis of the parameters defining this structure is given in [6–8] in which, in particular, the role of the entropy distribution with respect to the streamlines in the transitional section between the nose and the side surface was clarified and the important practical empirical result was established that this distribution is universal for noses of any form for given flow conditions. In the following these results are extended to blunt bodies of revolution with a duct in the nose. We examine the flow region which is external to the duct under the assumption that the external flow regime corresponds to maximum flow rate through the duct. A characteristic feature of the problem is associated with the additional characteristic linear dimension r₀, which determines the gas mass lost through the duct.     

Method of calculating supersonic three-dimensional flow past smooth bodies

A method is suggested in [1] for calculating supersonic flow past smooth bodies that uses an analytic approximation of the gasdynamic functions on layers and the method of characteristics for calculating the flow parameters at the nodes of a fixed grid. In the present paper this method is discussed for three-dimensional flows of a perfect gas in general form for cylindrical and spherical coordinate systems; relations are presented for calculating the flow parameters at the layer nodes, results are given for the calculation of the flow for specific bodies, and results are shown for a numerical analysis of the suggested method. Three-dimensional steady flows with plane symmetry are considered. In the relations presented in the article all geometric quantities are referred to the characteristic dimension L, the velocity components u, v, w and the sonic velocitya are referred to the characteristic velocity W, the density is referred to the density of the free stream, and the pressure p is referred to w².     

Longitudinal oscillations of bodies of revolution and flow at supersonic velocities

The method of aerodynamic derivatives [1–3] can be used for the investigation of the flow around a body executing oscillations with a small amplitude. The characteristics of the flow are expressed in the form of functions which are determined from the solution of the linearized equations of gasdynamics and describe the flow pattern with adequate accuracy. The present article is devoted to the discussion of the results of solution of the general nonstationary problem in nonlinear formulation. Supersonic flows around a hemisphere and a cylindrical front end executing arbitrary harmonic oscillations along the axis of symmetry or experiencing the corresponding oscillations of the flow (turbulent atmosphere) are discussed as examples. The effect of the nonlinearity on the flow pattern is demonstrated for different Strouhal numbers. The results are compared with those of the linear theory and with the results obtained from the solution of the corresponding stationary problems. The solution is obtained by using the characteristic method in form [4].     

Experimental modeling of three-dimensional modes of hypersonic flow past cylindrically-blunted bodies

Several sets of experimental studies of the structure of transverse hypersonic flow past blunt bodies (cylinder and truncated wedge) and heat transfer on them are performed in the UT-1M shock tube of the Central Aerohydrodynamics Institute. The purpose of the investigation was to obtain three-dimensional modes of hypersonic flow past the nose surfaces of blunt bodies in an artificially disturbed and nominally uniform flows. The controlled disturbances in the freestream were produced by thin threads pulled over the nozzle exit. In the experiment the flow was visualized using the Töpler method and the heat flux distribution over the cylinder was measured using luminescent temperature transformers. The experiments show that both the flow and the heat transfer in the vicinity of the cylinder nose are very sensitive to vortex disturbances in the oncoming hypersonic flow. In a nominally uniform flow (M_∞ = 8 and Re_∞ = 3160–11670) a steady three-dimensional mode of flow past the nose surface of a blunt wedge could be obtained in the form of a single vortex pair.     

Investigation of supersonic radiative flow past bodies at low altitudes

The radiative heat transfer problem for bodies traveling through the earth's atmosphere, as formulated in [1, 3], is considered in the case of low altitudes, i.e., for high gas densities and optical thicknesses in the shock layer. These factors require the use of improved methods of calculation.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 182–184, May–June, 1991.     

Experimental study of flow past a square cylinder at high Reynolds numbers

 Measurements of two-components of velocity in the wake of a square cylinder using a hot-wire anemometer are reported. Two Reynolds numbers, namely 8700 and 17,625, have been considered. The measurements were carried out in a low-speed, low-turbulence wind tunnel. Benchmark experiments at much lower Reynolds numbers show good agreement between the present experiments and published results. At higher Reynolds numbers, the experimental data reveal anticipated trends in terms of wake recovery and turbulence decay. Both velocity and velocity fluctuations show symmetry about the wake axis. The experimental data have been compared with the large eddy simulation (LES) calculation reported by Wang et al. [University of Illinois at Urbana – Champaign (1996) Report CFD 96-03] and LDV measurements of Lyn et al. [J Fluid Mech (1995) 304: 285–319]. The agreement among the three sets is generally acceptable in terms of the time-averaged velocity components, but not the velocity fluctuations. The turbulence fluctuations in the present experiments are seen to be lower than in the referred work. The differences have been traced to factors such as the aspect ratio, blockage ratio and upstream turbulence. Experiments with increased upstream turbulence did show a reduction in the discrepancy between the present experiments and the published data. An assessment of the experimental data in terms of physical mechanisms revealed that (a) streamwise normal stresses were correlated with the vortex centers, and (b) the turbulence kinetic energy profiles are similar to the turbulence shear stress. Spectral analysis of the velocity signals was carried out in the present work. Energy transfer from the mean flow to the streamwise velocity fluctuation was confirmed in the near wake. A redistribution of the kinetic energy between the streamwise and transverse components of velocity over a longer distance downstream was subsequently observed. Received: 17 May 1999/Accepted: 29 December 1999     

Experimental investigation of supersonic flow past blunt bodies with strong distributed injection

The entry of bodies into planetary atmospheres at high supersonic velocities is accompanied by intense evaporation of the surface due to radiative heat fluxes. A series of problems involving the conduction of investigations of such kind has been proposed by Petrov. In [1], in particular, the entry of a meteorite into an atmosphere was examined. The gasdynamic aspects of this problem have been approximately simulated by many authors by intense injection of gas in theoretical, e.g., [2–5], and experimental [6, 7] studies. The theoretical studies were based on two-layer [3, 4] or three-layer [5] schemes of gas flow between the shock wave and the surface of the body. The aim of the present work was an experimental investigation of the interaction of injection with a counter supersonic flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 84–95, May–June, 1978.     

Recent progress on the study of asymmetric vortex flow over slender bodies

The investigations of forebody vortex flow and its flow control have great importance in both academic field and engineering application areas. A large number of papers and many review papers have been published. However in this research field of forebody asymmetric vortices, three problems such as tip perturbation effect, Reynolds number effect and flow instability are less studied and thus not understood completely. So many researches are still working on the issues in recent years. The present paper attempts to provide a review of recent research progress on first two problems. The first problem is mainly concerned with how the vortex flow evolves after tip perturbation; how to solve the problem of repeatability and reproducibility of wind tunnel testing data; how to develop a conception of active flow control technique with tip perturbation based on the study of vortex flow response to tip perturbation. For the second problem one is mainly concerned that how the asymmetric vortices are developed with the increase of Reynolds number; how to classify the vortex flow patterns in different Reynolds number regimes; how to develop an appropriate boundary layer transition technique to simulate flows at high Reynolds number in the convention wind tunnels. Finally, some important ques- tions that deserve answers are proposed in the concluding remarks.     

Experimental study of nonlinear processes in a swept-wing boundary layer at the mach number M=2

Results of experiments aimed at studying the linear and nonlinear stages of the development of natural disturbances in the boundary layer on a swept wing at supersonic velocities are presented. The experiments are performed on a swept wing model with a lens-shaped airfoil, leading-edge sweep angle of 45°, and relative thickness of 3%. The disturbances in the flow are recorded by a constant-temperature hot-wire anemometer. For determining the nonlinear interaction of disturbances, the kurtosis and skewness are estimated for experimentally obtained distributions of the oscillating signal over the streamwise coordinate or along the normal to the surface. The disturbances are found to increase in the frequency range from 8 to 35 kHz in the region of their linear development, whereas enhancement of high-frequency disturbances is observed in the region of their nonlinear evolution. It is demonstrated that the growth of disturbances in the high-frequency spectral range (f > 35 kHz) is caused by the secondary instability.     

Aerodynamic characteristics of star-shaped bodies at Mach numbers M = 3–5

The results are given of an experimental investigation into the aerodynamic characteristics of star-shaped bodies with flat faces at Mach numbers M = 3–5 and angles of attack = 0–12 ° for different numbers of points of the star and different inner radii at the midsection. It is established that the star-shaped bodies have a much lower total drag than bodies of revolution of equivalent length and midsection area.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 88–93, July–August, 1981.     

Experimental study of the induced flow birefringence of a suspension of rigid particles at the transition from Couette flow to Taylor vortex flow

The flow birefringence induced in solutions of rigid particles is studied experimentally in the region of the axisymmetrical Taylor vortex flow which arises once the velocity gradient G in the annular gap of a conventional Couette cell reaches a critical value G _c .The measurements are performed for several values of G > G _c and for 10 radial observation points in the annular gap. Solutions of two types of rigid particles are investigated: the first is a suspension of flattened clay particles like bentonite, while the second contains rod-like particles of tobacco mosaic virus (TMV). The variations of the birefringence intensity n and of the extinction angle measured in the domain of the axisymmetrical flow show a different behavior according to the shape of the particle in solution. This fact is confirmed theoretically with a good agreement for the measurements performed with solutions of flat particles.