We have developed a five-picture Cranz-Schardin system for Schlieren flow visualization on a gun tunnel facility at the University of Southern Queensland to aid the study of unsteady shock systems in nominally steady hypersonic flows. The system produces useful images at framing rates up to about 1 MHz even though the system development was constrained by a very modest budget. The system uses multiple LED light sources driven by an in-house designed device that delivers a high current pulse to each LED with a programmable time delay between each pulse. The images are captured using four separate, black and white video devices and one digital still camera. The utility of the system is demonstrated by imaging gas injection from an annulus on a 10 degree half angle cone positioned at the exit of the contoured Mach 7 nozzle. Visualisation of the cone without gas injection demonstrates that the half angle of the conical shock is approximately 13.9 degrees (the Taylor-Maccoll conical shock angle at Mach 7 for an inviscid cone half angle of 10 degrees is 12.9 degrees). The gas injection condition used in these experiments disturbed the flow field upstream of the injection point to such an extent that the thickness of the shocked flow at the point of injection was larger than the no-injection case by a factor of approximately two. The conical shock angle in the case of injection increased to approximately 19 degrees, and a variation in this shock angle of approximately 1 degree was observed during the nominally steady, facility run time.
Mechanical hysteresis problems associated with pressure sensors based on interferometric measurements of diaphragm deflection are discussed. The source and importance of each contribution to the net hysteresis is calculated and compared with experimental results. Possible methods to decrease hysteresis effects are presented. Based on these suggested methods, new sensors have been manufactured and their hysteresis evaluated. The results demonstrate that significant reductions in hysteresis can be achieved with minimum cost. Future sensor development will focus on materials selection and manufacturing methods to fully realize these improvements.
The use of computational fluid dynamics (CFD) to model the temperature and pressure distributions which drive complex thermodynamic processes in gas turbine systems contributes to more cost efficient turbine design and development.
There is considerable demand in the field of turbomachinery research to make in-situ measurements of temperature, heat flux, and pressure in large-scale flow rigs. This is driven by the desire to increase engine efficiency and reliability by improving our understanding of the flow regimes within compressors and turbines.
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