1. Re-entry capsule is often used for the sample-return project, which is the project to collect and return the sample of an extra-earth planet. It is known that the flat body capsule with large nose radius and short body lengthtendsto be dynamically unstable inthe transonic speed range, and sometimes fall into self-exited pitching oscillation[1-4]. Hiraki[4]studied the dynamic stability of capsule-shaped body based on the wind tunnel experiment using a one-dimensional free-oscillation method. He measured the unsteady surface pressure of the oscillating capsule and revealed that the oscillation was promoted by the base pressure. Teramoto et al.[3]numerically simulated the flowfield around the capsule under forced pitching oscillation at transonic speeds. He indicated the base pressure of the oscillating capsule was delayed from that at the capsule of fixed pitch angle. However, it is difficult to evaluate the influence of unsteady aerodynamic force acting on entire surface of the
2. Associateprofessor,DepartmentofAerospaceEngineering,6-6-01,Aramaki-Aza-Aoba,Aoba-ku,Member
3. Professor,DepartmentofAerospaceEngineering,6-6-01,Aramaki-Aza-Aoba,Aoba-ku,AssociateFellow
4. Associateprofessor,DepartmentofMechanicalandControlEngineering,1-1Sensuityou,Tobata-ku,Member base region because the pressures only at limited points on the surface could be obtained with the pressure sensor. In addition, it needs to reveal the flowfield under the free oscillation to find out the cause of the dynamic instability. Pressure-Sensitive Paint (PSP) is one of the most promising options for global distribution measurement[5],[6]. However, the unsteady measurement of PSP is difficult because the signal-to noise ratio (SNR) is wrong. To solve this problem, in the present study, a fast responding PSP using polymer/ceramic[7]binder and an image capturing technique called Phase Lock Method[8]were used to measure unsteady pressure distributions on a capsule model undergoing the pitching motion. Additionally, surface pressure fluctuations on the capsule model are measured from time-series of high-speed video camera images[9]. In addition, schlieren visualization using high-speed video camera was used to take a picture around the flowfield of the model, together with pitch angle measurement using a potentiometer. From these results, the relation between the dynamic instabilityand the flowfield around the capsule model are discussed.