Experimental studies of subsonic flow around a tandem of permeable and solid disks

Some results of experimental studies on subsonic flow around a pair of coaxial disks are discussed with consideration of changes in the permeability of the front disk and in the attack angle of the tandem. Various schemes of flow are visualized. The aerodynamic drag is determined. The results are compared with the well-known data obtained by Bohn and Morel (1980). It is found that the front disk permeability has a stabilizing effect in the case when the mixing layer is unstable at the separation region boundary between the disks.     

Effect of gas compressibility on the stability of a boundary layer above a permeable surface at subsonic velocities

In the present study we investigate the stability of a boundary layer for the condition that the velocity perturbations at the permeable surface are nonzero. The stability for the boundary layer of an incompressible liquid in such a formulation was considered in [1]. For the case of subsonic velocities the effect of compressibility on the flow inside the boundary layer is weak, and in the present article this effect was neglected. The unsteady flow in narrow pores of a permeable covering depends strongly on the compressibility of the gas. Therefore, in the derivation of the relation connecting the pressure oscillations at the permeable surface with the oscillations of the flow through it, the effect of the compressibility was taken into consideration. It is shown that the boundary conditions, and therefore also the stability of the boundary layer at the permeable surface, depend considerably on the Mach number, even for a subsonic exterior flow.     

Aerodynamic interference of airfoils in a subsonic unsteady flow

Integral equations [1] are used to study the case of unsteady gas flow about a system consisting of a finite number of airfoils. As an example, the aerodynamic forces acting on the airfoils of a biplane in an unsteady subsonic gas flow are calculated. In this very simple case, a special study is made of the acoustic resonance effect reported previously in [1, 2].     

Investigation of the influence of the transverse sweepback of delta wings on their vortex structures and aerodynamic characteristics in the case of flow separation at low subsonic velocities

The results are given of theoretical and experimental investigations into the influence of transverse sweepback of delta wings of small aspect ratio on their lifting properties and the stability of the vortex structure in the case of flow separation. Theoretical investigations have been made using the method of discrete vortices. The physical experiment included weight tests and also investigations on the breakup of vortex filaments by means of aerometric and schlieren methods. The results of the investigations are given and the calculated and experimental data are compared.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 173–175, September–October, 1982.     

Electric characteristics of a probe in a subsonic plasma flow

Lam [1] and Su [2] have formulated and given some results of the solution to the problem of the concentration distributions of the charged particles and electric field in a weakly ionized plasma that flows past a conducting body (an electric probe) under the condition that the Reynolds number of the oncoming flow is high. In the present paper, this problem is solved by the method of exterior and interior asymptotic expansions with respect to a small parameter [3]. The form of the current-voltage characteristics of the probe is found as a function of the determining parameters of the problem. Data of an experimental verification of the obtained results for the case of a cold probe in a flowing air plasma containing added potassium are given.     

Phase-resolved flow characteristics between two shrouded co-rotating disks

Flow characteristics in the interdisk midplane between two shrouded co-rotating disks were experimentally studied. A laser-assisted particle-laden flow-visualization method was used to identify the qualitative flow behaviors. Particle image velocimetry was employed to measure the instantaneous flow velocities. The flow visualization revealed rotating polygonal flow structures (hexagon, pentagon, quadrangle, triangle, and oval) existing in the core region of the interdisk spacing. There existed a difference between the rotating frequencies of the polygon and the disks. The rotating frequency ratio between the polygonal flow structure and the disks depended on the mode shapes of the polygonal core flow structures—0.8 for pentagon, 0.75 for quadrangle, 0.69 for triangle, and 0.6 for oval. The phase-resolved flow velocities relative to the bulk rotation speed of the polygonal core flow structure were calculated, and the streamline patterns were delineated. It was found that outside the polygonal core flow structure, there existed a cluster of vortex rings—each side of the polygon was associated with a vortex ring. The radial distributions of the time-averaged and phase-resolved ensemble-averaged circumferential and radial velocities were presented. Five characteristic regions (solid-body rotation region, hub-influenced region, buffer region, vortex region, and shroud-influenced region) were identified according to the prominent physical features of the flow velocity distributions in the interdisk midplane. In the solid-body rotation region, the fluid rotated at the angular velocity of the disks and hub. In the hub-influenced region, the circumferential flow velocity departed slightly from the disks’ angular velocity. The circumferential velocities in the hub-influenced and vortex regions varied linearly with variation of radial coordinates. The phase-resolved ensemble-averaged relative radial velocity profiles in the interdisk midplane at various phase angles exhibited grouping behaviors in three ranges of polygon phase angles (θ = 0 and α/2, 0 < θ < α/2, and α/2 < θ < α) because three-dimensional flow induced similar flow patterns to appear in the same range of polygon phase angles.     

Limit angular velocities of variable thickness rotating disks

Elastic and plastic limit angular velocities are calculated for rotating disks of variable thickness in power function form. Analytical solution is obtained and used to calculate elastic limit angular velocities of variable thickness rotating annular disks and annular disks with rigid inclusion. An efficient numerical solution procedure is designed and used to obtain the elastic limit angular velocities of variable thickness rotating solid disks. Von Mises yield criterion and its flow rule is used to estimate plastic limit angular velocities. Both linear and nonlinear hardening material behaviors are treated numerically. The results are verified by comparing with those of uniform thickness rotating solid disks available in the literature. Elastic and plastic limit angular velocities are found to increase with the reduction of the disk thickness at the edge as well as the reduction in the disk mass due to the shape of the profile.     

Experimental study of laminar-turbulent transition on a swept wing with local boundary-layer suction at subsonic velocities

The effect of local suction of the boundary layer gas near the leading edge of the upper surface of a swept wing (with the sweep anglex=35°) on the extent of the laminar flow region is studied on a large half-model at subsonic velocities. Various experimental methods were used. The data are subjected to a comparative analysis. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 65–73, July–August, 1998.     

Aerodynamic characteristics of a delta wing in hypersonic flow

Novosibirsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 2, pp. 66–69, March–April, 1994.     

Calculation of the viscosity effect on the aerodynamic characteristics of slender bodies at hypersonic flow velocities

Approximating dependences of the local coefficients of friction, heat transfer, and pressure induced by a boundary layer on the generalized similarity parameters, including the inviscid flow characteristics, are obtained on the basis of the results of a numerical calculation of hypersonic flow past a number of plane and axisymmetric bodies. If the inviscid flow characteristics are known, these relations can be used to take the viscosity approximately into account under conditions of interaction between the laminar boundary layer and the hypersonic inviscid stream [1].Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 142–150, July–August, 1995.     

Measurements of fluctuations for high subsonic velocities using a hot-wire anemometer

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 3, pp. 80–84, May–June, 1988.     

Unsteady aerodynamic characteristics of a three-dimensional plate cascade in a subsonic gas flow

M. A. Lavrent'ev Institute of Hydrodynamics of the Siberian Division of the Russian Academy of Sciences, 630090 Novosibirsk. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 2, pp. 45–55, March–April, 1995.     

Flow past a thin wedge in a wind tunnel with partially perforated walls at high subsonic velocities

The problem of flow past a thin two-dimensional wedge at high subsonic velocity in a wind tunnel with partially perforated walls is considered for low suction flow rates. The solution of this model problem may be used in determining the optimal parameters of the suction system for which the aerodynamic characteristics in the tunnel are closest to those in an unbounded stream.In conclusion the author wishes to thank E. M. Kalinin for suggesting the study of this problem.     

Damping characteristics of a reentry vehicle at hypersonic velocities

The experimental equipment, model, test conditions, and methods used for determining the streamwise damping on a setup with free oscillations on rolling bearings are described. Characteristics of aerodynamic damping of the model with two positions of the rotation axis and Mach numbers M_∞ = 2, 4, and 6 are measured. Irregular oscillations of the model with a greater displacement of the rotation axis with respect to the longitudinal axis are found to arise at M_∞ = 2.     

Method of calculating the longitudinal,lateral, and crossed aerodynamic derivatives of an aircraft at subsonic velocities

It is impossible to take account of the numerous, sometimes contradictory, requirements in the design of modern aircraft without carrying out broad parametric investigations. Therefore, there is a need for effective and sufficiently exact methods of computer calculation, making it possible to carry out a large volume of investigations in a short period of time, even in the design stage of aircraft. The present article sets forth a method for calculating the longitudinal, lateral, and crossed aerodynamic derivatives and the induced resistance, taking account of the thickness of the carrying elements and suspensions of an aircraft moving at a subsonic velocity and performing harmonic vibrations with a small frequency. The method allows of a sufficiently exact calculation of the aerodynamic characteristics of an aircraft of any given complex configuration. A limitation is the development of critical phenomena (breakaway of the flow and a zone of supersonic flows).Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 76–88, March–April, 1978.The author thanks N. N. Tyunin for kindly furnishing the experimental data on m _x ^y + m _x ^* .