Influence of Diaphragms on Pressure and Heat Flux Measurements in a Shock Tunnel

Abstract An experimental study investigated the flow disturbances caused by diaphragm debris in a shock tunnel, specifically between a driven tube and a nozzle. The impact of debris-induced disturbances on pressure and heat flux measurements was examined with two types of diaphragms: a single-layer ultra-thin polyethylene film and a double-layer diaphragm, where eight direction pre-cut polyethylene film was sealed with copper tape. The study involved measuring the pitot pressure and stagnation-point heat flux, using a flat-faced model and a hemisphere model, respectively. The pitot pressure was measured using a piezoelectric-based pressure transducer, while heat flux was recorded with a fast-response surface-junction coaxial thermocouple calibrated through the water-plunging method. The experimental data for both diaphragms correlated well with theoretical predictions. The shadowgraph flow visualization technique was employed to visualize diaphragm debris. The flow quality in the shock tunnel was assessed by analyzing normalized disturbances, representing fluctuations in pitot pressure, and heat flux measurements. The experimental results indicated that the double-layer diaphragm effectively reduced diaphragm debris and improved flow quality in shock tunnel experiments.