VISUALIZATION OF UNDEREXPANDED JET FLOWS OVER A PLATE BY PRESSURE - SENSITIVE PAINT TECHNIQUE

A pressure measurement technique which employs the tools of molecular spectroscopy has recently received considerable attention in the aerodynamic community. Measurements are made via oxygen sensitive molecules attached to the surface of interest as a coating, or paint. The pressure sensitive paint (PSP) measurement technique is now commonly used in stationary wind tunnel tests for both steady and unsteady tests. In the present research, low-cost PSP system is developed and experiments are performed on sonic under-expanded jet issuing from a converging nozzle and impinging on a flat plate at different oblique incidences. Pressure measurements on the plate surface are acquired by pressure transducers at discrete points and by PSP intensity based measurement method. The paint employed in the present research is Bathophen Ruthenium Chloride (Ru(ph2-phen) or Ru(dpp) ) dissolved in dichloromethane while Silicon is used as a binder. Pressure transducer readings are used to calibrate the image obtained by PSP, a process known as ”in- situ” calibration. Commercially available, inexpensive Charge-Couple Device (CCD) camera is used to capture the PSP images.
Corrections due to darkness are applied via locally-developed post processing software. The images obtained by the developed low-cost PSP system show high spatial resolution of the pressure distribution compared with normal measurement techniques. The results can be used as validation test cases for computational fluid dynamics (CFD) solvers.