Specific features of the aerodynamic moment and the pitch damping of a re-entry vehicle model exercising free oscillatio
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DOI: 10.1134/S0869864320030026
Specific features of the aerodynamic moment and the pitch damping of a re-entry vehicle model exercising free oscillations at supersonic speeds * E.A. Chasovnikov Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia E-mail: [email protected] (Received October 10, 2019; revised November 10, 2019; accepted for publication February 10, 2020) A method for treating experimental data obtained on a setup with free oscillations over the pitching angle of the model and for determining the unsteady aerodynamic characteristics of the pitching moment coefficient is described. It is found that the pitching moment coefficient of a re-entry vehicle model at Mach numbers M = 2 and 2.25 and fixed angles of attack α depends non-linearly on the rate of change of the angle α. This circumstance makes the concept of aerodynamic derivatives inappropriate for mathematical description of the pitching moment coefficient. Keywords: re-entry vehicle model, free oscillations, pitching moment coefficient, aerodynamic characteristics, aerodynamic damping
Introduction Numerous experimental studies show that the descent of re-entry vehicles (RVs) in planetary atmosphere at moderate supersonic, trans- and subsonic speeds is often accompanied by the loss of aerodynamic damping and by the generation of non-damped oscillations over the angle of attack (self-oscillations). The self-oscillations can worsen the landing accuracy of RVs, and at the worst outcome, they can lead to an accident. Therefore, a large number of experimental and theoretical works were devoted to the study of this phenomenon [1]. Despite this, the problem still remains poorly understood. In particular, the physical nature and the production mechanisms of the self-oscillations are unclear; the influence of geometric parameters on the tendency of RVs to self-oscillations is poorly studied; there is no adequate mathematical model to describe the pitch moment during an arbitrary unsteady motion of RV, etc. In the present paper, we investigate the specific features of the formation of the pitch moment of an RV model with free oscillations over the angle of attack (pitch) and the aerodynamic damping. The initial data are the experimental data previously reported in [2, 3]. * This work was performed as part of the Program of Fundamental Scientific Research of the State Academies of Sciences for the years 2013–2020 (Project 22.6.4. Computational and experimental studies of unsteady phenomena in inhomogeneous supersonic flows); the experiments were carried out on the basis of the CUC “Mechanics”.
E.A. Chasovnikov, 2020
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E.A. Chasovnikov
It should be noted that, in the overwhelming majority of experimental works, model tests were carried out at small oscillation amplitudes, and this fact determines such an integral characteristic of the pitch moment as the equivalent aerodynamic damping [4], which is called in a number of foreign works “an effective damping” [1, 5]. The experimental data on the pitch moment during
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