Unsteady pressure measurement around circular cylinder in hypersonic flows using fast response PSP

The fast response Pressure Sensitive Paint (PSP)was studied to develop the capa-bility of making global pressure measurements under unsteady and short duration flow condi-tions.Fast response PSP is necessary for measuring unsteady flow fields in hypersonic wind tun-nels and short-duration wind tunnels.By the use of the fast response PSP,unsteady flow field can be accurately measured.Various PSP formulations are under continuous development in col-laboration between CAAA and Institute of Chemistry China Academy of Science.These pressure sensitive paints use PtTFPP as luminophore,which is relatively photo-stable:the decay of lumi-nescent intensity with continuous illumination is 1 .5 percent/h.This paint can be sprayable on all kinds of model surfaces.It is durable enough to withstand the aerodynamic forces.With the development of porous PSP,there has been a need for accurate characterization of the response time of PSP.Dynamic calibration methods have been developed to meet this need.Response time of PSP was measured from a step change of pressure created by solenoid valve and pulsating jet. Two dynamic calibration devices were developed to test the response time of PSP.For unsteady calibration the paint was sprayed onto 20 mm × 20 mm aluminum plates.Photo multiplier tube (PMT)was used as the light detector,which is the most critical component in the dynamic cali-bration device.Several fast response PSP was developed and tested.The typical response time of PSP is 0.2ms.The static calibration system was used to get the relation between the pressure and luminescence intensity.PSP samples were installed in a pressure chamber in which both the pres-sure and temperature can be set.The sample was excited by UV light and its photoluminescence was detected by a CCD digital camera.The experiment was conducted at different pressures and temperatures.After data processing,the relationship between the luminescence intensity and pressure can be obtained.To demonstrate the capability of PSP for pressure measurements in hy-personic wind tunnel,a cylinder mounted on a flat plate was tested in a Mach 5 hypersonic wind tunnel.The experiment was conducted in the blow down hypersonic wind tunnel FD-03 of China Academy of Aerospace Aerodynamics (CAAA).The diameter of circular cylinder is 25mm.The pressure on the plate surface was measured by several pressure taps simultaneously.The temper-ature of the model was detected by a Pt100 temperature sensor in real time.A 200-mm-diameter observation window on the ceiling was used as the optical access.Two 450W xenon lamps with bandpass filter (365±10 nm)were used for excitation light.The emission from the PSP was de-tected by photron high-speed camera SA5 with 12-bit intensity resolution.A bandpass filter (650 ±10 nm)was placed in front of the camera lens.The surface pressure distributions were ac-quired.Unsteady pressure behavior around the cylinder measured by the unsteady PSP was shown clearly.The pressure distribution results were obtained at Ma= 5 ,and the unsteady PSP measurement frame rate was 250 frames/s.A detailed pressure distribution pattern of complex flow phenomena including shock wave/shock wave interactions could be clearly measured with PSP.It was confirmed that fast response PSP could be used for quantitative unsteady pressure distribution measurements in hypersonic wind tunnel.