Examples of Fast PSP Data

     Ground-based testing resources are essential for the development of military and commercial aerospace systems.  While these facilities can be expensive to maintain and operate, the cost to acquire data can be significantly reduced by implementing measurement systems featuring high data capture rates while requiring limited modification or instrumentation of models.  Furthermore, these instrumentation tools should are robust, user-friendly, turnkey systems capable of acquiring measurements for different test conditions, and thus, suitable for use in many ground-based facilities and flight test programs.  There has recently been a significant upturn in the use of fast responding Pressure-Sensitive Paint (PSP) technology.  Fast PSP, which offers a means of acquiring unsteady pressure data at millions of locations on a model surface, has long been viewed as a disruptive technology.  Recent advancements in fast CMOS camera and LED technology have facilitated the realization of this long promised capability.  An example of the potential offered by a fast PSP data set is shown in Figure 1. In this test, one wall of a supersonic cavity was painted with fast PSP and the paint was sampled at 10,000 Hz using a Photron SA5 camera. The full data set is composed of a series of 25,000 images with each image representing 100,000 pressure taps with a spatial scale of 0.5-mm. 

fast

Figure 1: Potential for Fast PSP Systems



     The data in Figure 1 was converted to pressure allowing the visualization of the acoustic waves as they move from the front of the cavity to the back (Figure 1, top left sequence).  Data at an individual pixel can be extracted and processed as traditional pressure tap data (Figure 1, bottom left) to identify mean, rms, and spectral content.  

Baseline pressure response of Fast PSP in the cavity floor are shown below:

pressure

     An advantage of having thousands of fast pressure transducers on a surface is the ability to create high-spatial resolution maps of the amplitude of the pressure fluctuations over selected frequency bins.  Instrumentation of a wind tunnel or flight test model with an array of taps similar to that shown in Figure 1 is simply not possible.  Deployment of a fast PSP system for production testing would allow high-bandwidth high-spatial resolution pressure data to be collected on a variety of models.  This increase in the data capture rate afforded by the fast PSP system compared to traditional pressure taps is a key feature of a fast PSP system.  The additional data may not be necessary for simple flowfields, but is essential for studying complex flowfields.  Temporally and spatially resolved surface pressure measurements would allow efficient placement of flow control devices, identifying and predicting acoustic noise sources, and validating computational models.

Below, baseline (no object upstream) amplitudes of pressure fluctuations are shown up to 5 kHz and their comparison to two Kulite fast pressure transducers are shown below.  Sound pressure levels are shown in dB.

base frq

 

  

ridges

 cylinder

               Here, ridges were placed upstream of the cavity                                                                                                    In this case, a cylinder was placed upstream of the cavity

 

  ts fs

                      Steps placed upstream of the cavity                                                                                                                                  A flat spoiler was upstream of the cavity