N. Gongora-Orozco

Experimental investigations of compressible vortex loops

The present study involves the shock wave and consequent vortex loop generated when a shock tube with various nozzle geometries is employed. It aims to provide quantitative and qualitative insight into the physics of these compressible phenomena. The geometries included two elliptic nozzles with minor to major axis ratios of 0.4 and 0.6, a 15 mm circular nozzle and a 30×30 mm2 square nozzle. The experiments were performed for driver gas (air) pressures of 4, 8 and 12 bars. Schlieren, shadowgraphy, and particle image velocimetry techniques were employed to visualize and quantify the induced flow field.

Effects of filters on the performance and characteristics of pressure-sensitive paints

The current study investigates the effect of four different filter combinations on the pressure sensitivity, signal level and temperature sensitivity of pressure-sensitive paint (PSP) samples in an a priori calibration. Two different PSP formulations developed at the Aero-Physics Laboratory are studied, one using hydrochloric acid (PSP1-HCl) and the other acetone (PSP2-Ace). Both are incorporated in a sol–gel solution. The results show that the effect of choosing different bandwidths, central wavelengths and transmissions of the filters for the emitted and excitation wavelengths can have a significant impact on the behaviour of PSP, luminescent signal level, pressure and temperature sensitivity, and also eliminate the undesired wavelengths which can affect the final results.The current study investigates the effect of four different filter combinations on the pressure sensitivity, signal level and temperature sensitivity of pressure-sensitive paint (PSP) samples in an a priori calibration. Two different PSP formulations developed at the Aero-Physics Laboratory are studied, one using hydrochloric acid (PSP1-HCl) and the other acetone (PSP2-Ace). Both are incorporated in a sol–gel solution. The results show that the effect of choosing different bandwidths, central wavelengths and transmissions of the filters for the emitted and excitation wavelengths can have a significant impact on the behaviour of PSP, luminescent signal level, pressure and temperature sensitivity, and also eliminate the undesired wavelengths which can affect the final results.

Global Visualization and Quantification of Compressible Vortex Loops

The physics of compressible vortex loops generated due to the rolling up of the shear layer upon the diffraction of a shock wave from a shock tube is far from being understood, especially when shock-vortex interactions are involved. This is mainly due to the lack of global quantitative data available which characterizes the flow. The present study involves the usage of the PIV technique to characterize the velocity and vorticity of compressible vortex loops formed at incident shock Mach numbers ofM=1.54 and1.66. Another perk of the PIV technique over purely qualitative methods, which has been demonstrated in the current study, is that at the same time the results also provide a clear image of the various flow features. Techniques such as schlieren and shadowgraph rely on density gradients present in the flow and fail to capture regions of the flow influenced by the primary flow structure which would have relatively lower pressure and density. Various vortex loops, namely, square, elliptic and circular, were generated using different shape adaptors fitted to the end of the shock tube. The formation of a coaxial vortex loop with opposite circulation along with the generation of a third stronger vortex loop ahead of the primary with same circulation direction are of the interesting findings of the current study.

PSP Visualization Studies on a Convergent Nozzle with an Ejector System

An in-house Pressure Sensitive Paint (PSP) formulation has been developed at the Aero-Physics Laboratory at the University of Manchester. The PSP uses Bathophenanthroline Ruthenium as the luminophore molecule and is incorporated in a sol-gel matrix. Excitation occurs at400–500 nm and emission at550–650 nm. The Stern-Volmer plot of the PSP reveals small temperature dependence, which has always been an intrinsic drawback of PSPs. As a baseline experiment the PSP has been applied to examine the side-wall pressure field of the flow through a convergent nozzle with an ejector, at fully expanded Mach numbers in the rangeMj =0.52–1.36. Simultaneous static pressure measurements were also conducted to ascertain the accuracy of the PSP results. The paint has demonstrated satisfactory capabilities in not only measuring static pressures but also in visualizing key physical elements of the flow, such as the location of the expansion and oblique shock waves present in such flows.

Experimental Studies on Shock Wave Propagating Through Junction with Grooves

Using a shock tube to generate shock waves, the wave patterns through several bifurcated junctions were studied. The effect of roughness was simulated by introducing grooves on the lower wall of the junctions, while the upper wall had a smooth surface. Five different bifurcation angles were used in the present study: 0, 30, 45, 60, and 90 degrees. The shock tube driver pressure was P4 = 12 bar, and the pressure within the shock tube driven section, P1, was atmospheric. Air was used as the driver and driven gas. High-speed schlieren photography, using the Shimadzu Hyper-Vision camera, was used to visualise the flow-field generated by the propagating incident shock wave. The interval between each frame was of 4 µs. Pressure measurements were taken to quantify the attenuation of the incident shock wave at the exit of the different junctions.