Mark Kenneth Quinn

Pressure-Sensitive Paint: Effect of Substrate

There are numerous ways in which pressure-sensitive paint can be applied to a surface. The choice of substrate and application method can greatly affect the results obtained. The current study examines the different methods of applying pressure-sensitive paint to a surface. One polymer-based and two porous substrates (anodized aluminum and thin-layer chromatography plates) are investigated and compared for luminescent output, pressure sensitivity, temperature sensitivity and photodegradation. Two luminophores [tris-Bathophenanthroline Ruthenium(II) Perchlorate and Platinum-tetrakis (pentafluorophenyl) Porphyrin] will also be compared in all three of the substrates. The results show the applicability of the different substrates and luminophores to different testing environments.

Pressure-sensitive paint measurements of transient shock phenomena

Measurements of the global pressure field created by shock wave diffraction have been captured optically using a porous pressure-sensitive paint. The pressure field created by a diffracting shock wave shows large increases and decreases in pressure and can be reasonably accurately captured using CFD. The substrate, a thin-layer chromatography (TLC) plate, has been dipped in a luminophore solution. TLC plates are readily available and easy to prepare. Illumination comes from two high-intensity broadband Xenon arc light sources with short-pass filters. The sample is imaged at 100 kHz using a Vision Research Phantom V710 in conjunction with a pair of long and short pass filters, creating a band. The PSP results are compared with numerical simulations of the flow using the commercial CFD package Fluent as part of ANSYS 13 for two Mach numbers.

Evaluation of Dynamic Pressure-Sensitive Paint for Improved Analysis of Cavity Flows and CFD Validation

This study has investigated the use of Dynamic Pressure-Sensitive Paint (DPSP) to analyse the complex multi-dimensional flow-field within a generic small-scale rectangular planform cavity. The analysis and understanding of cavity flows have received renewed interest due to the low-observability requirements for modern military aircraft and Unmanned Combat Aerial Vehicles (UCAVs). This study has demonstrated the use of DPSP to provide unsteady pressure data, from the full model surface coverage of a model-scale cavity ceiling in a transonic Mach number range of 0.70 ≤ M ≤ 0.95. These results were compared against traditional point transducer measurements and also compared with numerical simulations of the cavity flow-field. These comparisons demonstrate that DPSP represents a very useful tool for the validation of numerical data as well as for flow-diagnostic investigations, where point measurements from transducers would provide spatially limited data. Further analysis of the transducer and DPSP data has also demonstrated temporal intermittency of the widely known Rossiter modes within the cavity acoustic signature. This instability has been previously linked to mode switching and a breakdown in the modal generation feedback process within the cavity flowfield.

A note on the generation of a compressible vortex rings using helium as driver gas

An experimental study has been conducted on the generation and propagation of compressible vortex rings using helium as a driver gas, with the aim of evaluating the effects of multi-gas operations for real-life applications. The advantage of such system, when compared to a constant gas system based on ambient air, is to effectively increase the Mach number while keeping the pressure ratio constant. Three pressure ratios of ∼4, 8 and 12 were set, corresponding to experimental Mach numbers of approximately 1.50, 1.81 and 2.05. The increase in incident Mach number resulted in the variation of the vortex ring and trailing jet structure, and an increase in both the velocity magnitude and vorticity field. Results showed a transition from the regular-reflection shock-cell system at the experimental Mach number approximately 1.50 to the presence of a Mach reflection with a central Mach disc, which grew in size with further increase in incident Mach number. The presence of the Mach disc resulted in the formation of a subsonic jet, internal to the main trailing jet. Its velocity was measured to be in the order of magnitude of 550 m/s, with the speed of sound of helium at 1005 m/s. Results also demonstrated that shear layers formed between the subsonic and main trailing jet have opposing vorticity, with that of the subsonic jet being approximately half in magnitude. Secondary counter-rotating vortex rings were generated ahead of the main vortex and orbited around it. The analysis of the vorticity field has shown that these secondary vortices have a magnitude approximately half of that of the vorticity of the main vortex, and has confirmed that they have an opposite direction of rotation.

Miniaturisation of Pressure-Sensitive Paint Measurement Systems Using Low-Cost, Miniaturised Machine Vision Cameras

Measurements of pressure-sensitive paint (PSP) have been performed using new or non-scientific imaging technology based on machine vision tools. Machine vision camera systems are typically used for automated inspection or process monitoring. Such devices offer the benefits of lower cost and reduced size compared with typically scientific-grade cameras; however, their optical qualities and suitability have yet to be determined. This research intends to show relevant imaging characteristics and also show the applicability of such imaging technology for PSP. Details of camera performance are benchmarked and compared to standard scientific imaging equipment and subsequent PSP tests are conducted using a static calibration chamber. The findings demonstrate that machine vision technology can be used for PSP measurements, opening up the possibility of performing measurements on-board small-scale model such as those used for wind tunnel testing or measurements in confined spaces with limited optical access.