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Title: The dynamic response of a wedge separated hypersonic flow and its effects on heat transfer
Author: Smith, Andrew John Darwin
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1993
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The dynamic response of a wedge separated hypersonic flow has been investigated experimentally, with emphasis on its heat transfer effects. Tests were performed in a Mach 6.85 freestream flow, at a unit Reynolds number of 2.45x10⁶/m. The unsteady separated flowfield was generated by rapidly deflecting a trailing edge flap control surface through an angle of 35 degrees in approximately 20 ms, with velocities approaching 3000 degs./s. The principal measurements made were of the model centre line chord heat transfer distributions. These were complemented with flow visualisation of the separated flow structures, and liquid crystal surface thermographs. The unsteady response of the separated flow was interpreted by comparing measurements at instantaneous dynamic flap angles throughout the deflection range with those obtained at corresponding fixed flap angles. It was determined through the application of established criteria that the steady separated flows in these experiments were transitional, although their length scales were more typical of the fully laminar regime. In the dynamic flap tests there were no indications from the heat transfer measurements of a significant unsteady effect on the location, or process, of transition. The unsteady separated flow was observed to maintain the typical features of steady wedge type separations during its evolution. However, the heat transfer measurements, and flow visualisation, were consistent in identifying the development of a lag in its growth at moderate to high flap angles with respect to the quasi-steady separation lengths. Simple analytic models of the unsteady separated flow response, based on distinct fundamental flow adjustment mechanisms, indicated that at high flap angles these lags in growth were significantly larger than could be attributed only to pressure communication times across the interaction lengths. This was apparent for tests made both with, and without, side plates fitted to the model. It was concluded that the lags in growth at high flap angles were substantially due to mass entrainment requirements for a growing separated flow. Locally about the unsteady separation point the free-interaction process appeared maintained. There were no significant unsteady separated flow effects on the heat transfer distributions ahead of the flap in these tests. In the reattachment region there was an increase in the peak heating measured for the dynamic flap condition at its highest deflection angle compared to the level for the steady separated flow induced at an identical fixed flap angle. There also occurred an additional local rise in heat transfer towards the flap trailing edge for the unsteady separated flow.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Aerodynamics