Leichao Yang

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.

Drag Reduction Studies by Steady Energy Deposition at Mach 5

Experiments addressing the effect of energy deposition via arc discharge on 15 ◦ half angle truncated cone-cylinder configurations and a truncated cone with flare configuration in Mach 5 flow were carried out. The arc discharge was accomplished using a setup that consisted of power supply, high voltage unit and tungsten electrodes. Discharge-on cases were always compared to Discharge-off to evaluate the net effect of energy deposition. Visual observations revealed that there is a certain size of the relaxation distance as the test gas sweeps the energy spot downstream forming a heated wake. The compression waves occur on top of the wake of the heated channel and oscillatory in nature. The deposited energy of 10W has its repeatable influence on drag force for all the models. The effectiveness was found to be increasing with increased truncation or the frontal area up to a point and from thereon it started to decrease. In case of the distance between the energy spot and the frontal face, the efficiency is maximum when the distance is shortest and from thereon it decreases to a point and stays nearly constant.

Flow Control Using Thermal Bumps in Hypersonic Flow

Experimental results of flow change caused by thermal bump in Mach 5 flow over a flat plate with sharp leading edge are presented. A circular electrical resistive heating element (16 mm in diameter) with temperature of 770K and 75W power input is embedded flush to the the flat plate at 40mm from leading edge. Quantitative results including the streamwise and spanwise surface pressure distributions and pitot pressure measurements at different locations as well as qualitative Schlieren and surface oil flow flow visualisation results are used to describe the effect of the so called ‘thermal bump’ on the flow field. A weak oblique shock wave at the upstream of the bump and thickened boundary layer at the downstream of heated area are observed in Schlieren pictures that are representative effects induced by the thermal bump reported in the literature. Oil dot and oil film results show the induced vortex structures growing from downstream of heating element to the trailing edge of flat plate. The pitot probe pressure variations are observed at 2mm and 7mm above the flat plate. The highest pitot pressure decrement of 33% appears at 2mm above the heating element. The variation also appears in surface pressure measurements but the value is quite small (less than 4%) considering the measurement uncertainties. The main frequency of 175Hz as an additional disturbance was obtained on the surface pressure signal using the FFT analysis.