CHARACTERISTICS OF AN UNDEREXPANDED JET AND ITS SURFACE IMPINGEMENT FOR COMBUSTION BURNTHROUGH

The flow from an underexpanded free jet and a jet impinging on a perpendicular planar surface has been characterised for a pressure ratio (N) of 40 with a nozzle to plate spacing (L/D) of 3 nozzle diameters. Surface heatflux (Q), temperature (7), pressure (P) and flow visualisation techniques have been used extensively to examine the flow within the jet and on the plate surface. From these it is shown that the flow is non-axisymmetric in nature. The experimental programme has been conducted across several facilities within the UK which has allowed the influence of Reynolds number to be determined. The results of this work show marked similarities in flow characteristics irrespective of Reynolds number variation. Heat transfer on the impingement plate is largely determined by Taylor-Gortler vortex flow and total temperature separation resulting from shearing flows. Evidence for Taylor-Gortler vortex flow within the jet has been reinforced by comparison of the free jet element of this work with other research. Infra-Red camera measurements have confirmed the presence of strong total temperature separation on the impingement surface with local surface temperature step variation of greater than 200K (360 degrees F) in the presence of a high temperature jet running at approximately 1900K (2960 degrees F). This feature is dictated by this N and L/D and is shown to occur over a wide range of jet total temperature.