Novel pressure-sensitive paint for cryogenic and unsteady wind-tunnel testing

A novel pressure-sensitive paint (PSP) formulation suitable for use in cryogenic and unsteady wind-tunnel testing has been developed. This new PSP uses poly [1-(trimethylsilyl)-1-propyne] [poly(TMSP)] as a binder. Poly(TMSP) is a glassy polymer having extremely high gas permeability. Unlike the conventional polymer-based paints, PSP based on poly(TMSP) maintains oxygen sensitivity even at cryogenic temperatures and exhibits fast response time. This paint is sprayable on any model surface including stainless steel and ceramics. These capabilities allow us to apply this PSP to a cryogenic wind tunnel and a short-duration shock tunnel. To demonstrate the capability of poly(TMSP)-PSP for pressure measurements in a cryogenic wind tunnel, a circular-arc bump model and a delta wing model were tested in the National Aerospace Laboratory 0.1-m Cryogenic Wind Tunnel at 100 K. It has been verified that poly(TMSP)-PSP can provide high S/N pressure distribution data at high O₂ concentration. A comparison of the measured intensity data with the pressure tap measurements has suggested that the in situ calibration can be used to obtain quantitative pressure data. It was also demonstrated that poly(TMSP)-PSP could visualize the complex flowfield on a stainless steel delta wing, including primary and secondary separation vortices and their breakdown.