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UDC 534.13:533.6.011.5 V. I. Zapryagaev and I. N. KavunThe flow with a free-stream Mach number M ∞ = 6 around a cylindrical body with a sharp spike is studied. The existence of a supersonic reverse flow for one of the phases of the pulsating flow regime is experimentally validated. A range of spike lengths is determined, which ensures a region of a supersonic reverse flow near the side surface of the spike. The time of existence of the supersonic reverse flow region is shown to be 0.15 of the period of pulsations if the spike length equals the model diameter. Introduction.A supersonic gas flow around a spiked blunt body is accompanied by the emergence of a flow with a forward separation region. At certain geometric and gas-dynamic parameters, there arises a periodic self-oscillatory flow. Two types of such a flow are distinguished, depending on the spike length. In the oscillatory flow regime, the conical shock wave bounding the separation region performs small periodic transverse oscillations. The shape of the wave remains essentially unchanged. Figures 1a and 1b show the flow structures for two typical phases of oscillations.As the spike length is reduced, the amplitude of oscillations increases, and a certain value of the amplitude gives rise to the pulsating flow regime. At this moment, the shape of the separation region becomes essentially different. Typical structures of the flow for two phases are shown in Figs. 1c and 1d. As the pulsating process evolves, the volume of the separation region increases, the conical wave transforms to a hemispherical one, and then the separation region disappears because the flow rate of the gas escaping from the separation region is significantly greater than the flow rate of the incoming gas. After this phase of pulsations is completed, a new separation zone bounded by a conical shock wave appears, and the entire process is periodically repeated. Such a flow regime, which was first discovered by Mair (see [1]), is considered in the present paper.This problem has been studied in many experimental and theoretical investigations (see, e.g., [2][3][4][5][6]). The physical pattern of such a flow, however, has not been adequately addressed, which necessitates further research.According to [4,6], the main reason for origination of a pulsating flow regime is the formation of an annular supersonic jet J (Fig. 1c) at the point T of intersection of the conical shock wave W c and the bow shock wave W 1 . The mechanism responsible for the emergence of a pulsating flow is as follows. A high-velocity gas flow behind a weak shock wave W c moves in the form of an annular jet J in the region between this wave and the separation-region boundary toward the body on which this flow is impinging. Because of jet curving toward the model centerline, the gas predominantly enters the separation region. The size of this region increases, which converts the conical shock wave W c into the detached curved shock wave W 1 . At a certain stage of development of the pulsating process, the increase in the r...

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In the present paper, we give a brief overview of the studies of supersonic jet flows which were performed recently with the aim of gaining experimental data on the formation of the shock-wave structure and jet mixing layer in such flows. Considerable attention is paid to a detailed description of discharge conditions for supersonic jets, to enable the use of measured data for making a comparison with numerical calculations. Data on the 3D flow structure in the mixing layer of the initial length of a supersonic jet are reported. Scientific interest in this phenomenon is due to its practical significance in studying the possibility of intensifying the mixing process as well as in studying the sound-generation process.

A three-dimensional (3D) structure of a separated §ow in a compression corner at a free-stream Mach number í = 6 is studied. The model is a §at plate with an almost sharp leading edge on which a 30 • ramp is mounted. The spanwise size of the model is equal to the length of the plate from the leading edge to the ramp. The angle of attack is varied from 0 • to 15 • . The shock wave structure of the §ow near the model is shown. The existence of a thin high total pressure layer (dynamic layer) is found. The dynamic layer is located above the boundary layer on the ramp, downstream from the reattachment line. The existence streamwise vortices near the reattachment line is shown. The measured spectra of the wall pressure §uctuations in the reattachment region are presented.