Investigation of the double ramp in hypersonic flow using luminescent measurement systems

Compression ramp flows in supersonic and hypersonic environments present unique flow patterns for shock wave-boundary layer interaction studies. They also represent the generic geometry of two-dimensional inlets and deflected control surfaces for re-entry vehicles. Therefore, a detailed knowledge of the flow behaviour created by such geometries is critical for optimum design. The flow is made more complicated due to the presence of separation regions and streamwise Görtler vortices. The objective of the current research is to study the behaviour and characteristics of the flow over the double ramp model placed in hypersonic flow at freestream Mach number of 5. Three different incidence angles of 0°, −2°, and −4° are studied using colour Schlieren and luminescent paints consisting of anodized aluminium pressure-sensitive paint (AA-PSP) and the temperature-sensitive paint (TSP) technique. The colour Schlieren provides description of the external flow while the global surface pressure and temperature distribution is obtained through the AA-PSP and TSP methods. The TSP technique also proves that it is very effective in identifying the location and properties of the Görtler vortices; revealing the effect of incidence on the magnitude and pattern of Görtler vortices formed

Experimental investigation of surface flow pattern on truncated cones in Mach 5 flow: influence of truncation ratio

The flow characteristics on a truncated cone with a cylinder were experimentally investigated in a Mach 5 flow with a Reynolds number 3.8 × 105, based on the cylindrical diameter. Two different truncation ratios of 0.5 and 0.7 were used. The incidence angle varied from −12 to 0° with 3° intervals to investigate the influence of the truncation ratio on the surface flow pattern. The measurement techniques: unsteady pressure-sensitive paint (anodized aluminium method), color Schlieren photography, and surface oil flow were used. It was found that the distance of the external shock wave from the conical surface depends on the truncation ratio, and the surface pressure on the conical portion increases when the external shock wave moves closer to the model surface. The “external” shock wave denotes a detached shock wave and the “internal” one is the shock wave formed between the detached bow shock wave and the model surface. In the higher truncation ratio at the higher incidence angle, the internal shock wave induced by the flow separation on the conical surface impinges on the external shock wave, which results in its reflection. This reflection leads to the pressure increase on the model surface. On the other hand, this reflection does not appear in the lower truncation ratio. In spite of the different truncation ratios, the angle of the internal shock wave is identical at the same incidence angle. From the oil flow results, the wall shear stress on the leeward conical surface is lager in the higher truncation ratio model

Transverse jet-cavity interactions with the influence of an impinging shock

For high-speed air breathing engines, fuel injection and subsequent mixing with air is paramount for combustion. The high freestream velocity poses a great challenge to efficient mixing both in macroscale and microscale. Utilising cavities downstream of fuel injection locations, as a means to hold the flow and stabilise the combustion, is one mechanism which has attracted much attention, requiring further research to study the unsteady flow features and interactions occurring within the cavity. In this study we combine the transverse jet injection upstream of a cavity with an impinging shock to see how this interaction influences the cavity flow, since impinging shocks have been shown to enhance mixing of transverse jets. Utilising qualitative and quantitative methods: schlieren, oilflow, PIV, and PSP the induced flowfield is analysed. The impinging shock lifts the shear layer over the cavity and combined with the instabilities generated by the transverse jet creates a highly complicated flowfield with numerous vertical structures. The interaction between the oblique shock and the jet leads to a relatively uniform velocity distribution within the cavity

Pressure Sensitive Paints:The Basics & Applications

Surface pressure measurement is one of the fundamental measurements in fluid dynamics experiments. Pressure sensitive paint (PSP) is a relatively new tool that has the unique capability of providing a field measurement over the entire surface of a model. This method is based on the attenuation by oxygen of the luminescence emitted by certain excited molecules in the visible or ultraviolet spectrums. The higher the pressure, the higher the partial pressure of the oxygen and the more the intensity emitted by the coating is attenuated. Then all that is needed is to measure the intensity of the emission to find the pressure. Because of its many advantages over the traditional techniques, it has been extensively used in almost all the fluid dynamics flow regimes. The following document describes the basics of PSP and its applications

Toward Simultaneous Velocity and Density Measurements Using FLEET and Laser Rayleigh Scattering

Femtosecond laser electronic excitation tagging (FLEET) velocimetry and laser Rayleigh scattering are conducted concurrently and are evaluated for their suitability to measure velocity and density simultaneously in NASA Langleys 0.3-m Transonic Cryogenic Tunnel. FLEET velocimetry measurements are shown to be accurate to within 1.5 percent of the measured velocity throughout the facility testing envelope and exhibit a zero-velocity precision of 0.4 m/s. Rayleigh scattering density measurements indicate a characteristically linear dependence on flow density while having an accuracy within 5.4 percent of the measured density and a precision less than or equal to 6 percent. The preliminary assessment indicates that the joint technique would be advantageous for deployment in high-pressure, cryogenic test facilities

Visualization of boundary-layer development on turbomachine blades with liquid crystals

This report documents a study of the use of liquid crystals to visualize boundary layer development on a turbomachine blade. A turbine blade model in a linear cascade of blades was used for the tests involved. Details of the boundary layer development on the suction surface of the turbine blade model were known from previous research. Temperature sensitive and shear sensitive liquid crystals were tried as visual agents. The temperature sensitive crystals were very effective in their ability to display the location of boundary layer flow separation and reattachment. Visualization of natural transition from laminar to turbulent boundary layer flow with the temperature sensitive crystals was possible but subtle. The visualization of separated flow reattachment with the shear sensitive crystals was easily accomplished when the crystals were allowed to make a transition from the focal-conic to a Grandjean texture. Visualization of flow reattachment based on the selective reflection properties of shear sensitive crystals was achieved only marginally because of the larger surface shear stress and shear stress gradient levels required for more dramatic color differences

Applied aerodynamics: Challenges and expectations

Aerospace is the leading positive contributor to this country's balance of trade, derived largely from the sale of U.S. commercial aircraft around the world. This powerfully favorable economic situation is being threatened in two ways: (1) the U.S. portion of the commercial transport market is decreasing, even though the worldwide market is projected to increase substantially; and (2) expenditures are decreasing for military aircraft, which often serve as proving grounds for advanced aircraft technology. To retain a major share of the world market for commercial aircraft and continue to provide military aircraft with unsurpassed performance, the U.S. aerospace industry faces many technological challenges. The field of applied aerodynamics is necessarily a major contributor to efforts aimed at meeting these technological challenges. A number of emerging research results that will provide new opportunities for applied aerodynamicists are discussed. Some of these have great potential for maintaining the high value of contributions from applied aerodynamics in the relatively near future. Over time, however, the value of these contributions will diminish greatly unless substantial investments continue to be made in basic and applied research efforts. The focus: to increase understanding of fluid dynamic phenomena, identify new aerodynamic concepts, and provide validated advanced technology for future aircraft