Hyoung Jin Lee

Robust HLLC Riemann solver with weighted average flux scheme for strong shock

Many researchers have reported failures of the approximate Riemann solvers in the presence of strong shock. This is believed to be due to perturbation transfer in the transverse direction of shock waves. We propose a simple and clear method to prevent such problems for the Harten-Lax-van Leer contact (HLLC) scheme. By defining a sensing function in the transverse direction of strong shock, the HLLC flux is switched to the Harten-Lax-van Leer (HLL) flux in that direction locally, and the magnitude of the additional dissipation is automatically determined using the HLL scheme. We combine the HLLC and HLL schemes in a single framework using a switching function. High-order accuracy is achieved using a weighted average flux (WAF) scheme, and a method for v-shear treatment is presented. The modified HLLC scheme is named HLLC-HLL. It is tested against a steady normal shock instability problem and Quirks test problems, and spurious solutions in the strong shock regions are successfully controlled.

Flow Characteristics of Small-Sized Supersonic Inlets

The flow characteristics were investigated for two types of small-sized supersonic inlet models: rectangular and axisymmetric inlets. The twomodels were designed by the samemethod and are of similar size, with a total length of about 160 mm. The flow phenomena that were generated at the stable and unstable operating conditions of both models are visualized and discussed in detail. The main flow feature for stable operation is the existence of a shock train induced by the shock boundary-layer interactions. The results show that the shock-train shape and position are varied along with the upstream and area ratios, which strongly impact the downstream flow and total pressure recovery. For unstable operation, various buzz phenomena are observed for different area ratios. The results indicate that the buzz phenomenon of the small-sized inlet is identical to that of a large inlet, but the small inlet can be easily affected by the presence of a separation bubble. Although the shapes of the inlets are different, the base frequencies of a big buzz for bothmodels are very similar. The role of the separation on the compression surface in the buzz process of the small-sized inlet is shown.

Aerodynamic Heating Characteristics Over a Protuberance in Hypersonic Flows Using Fast Response Thermo Gauges

Through experimental investigations utilizing hypersonic shock tunnel-coaxial thermocouples as well as blow down hypersonic wind tunnel-temperature sensitive paints, the heat flux and the temperature over a protuberance were measured and analyzed. The experimental data were subsequently compared to heat flux data that was obtained by using blow down hypersonic wind tunnel and heat flux gauges. According to the comparison, both sets of data illustrated correlation with one another. The measured heat flux was large when the height of the protuberance was large. Experimental results show that heat flux measurements taken at higher locations were greater than those taken at lower locations. For high protuberances, a severe jump in the heat flux was observed, ranging in values within 0.6-0.7 of the height of the protuberances. However, when the protuberance was sufficiently short, a rise in the heat flux was rarely observed as the protuberance was totally submerged under the separation region.

Super-/Hypersonic Aero-Optical Effects Induced by External Jet Cooling

Usually, the forepart of an optical-guided missile generally composes of the body with a cone or hood shape and the optical window to seek a target. Additionally, a cooling system is necessary to reduce the surface temperature of the optical window when a missile system is flying in hypersonic flow fields, because the aero-optical window of a missile can undergo severe aerodynamic heating problems causing high heat and cracks to optical windows which eventually lead to failure of optical windows.

Aero-Optical Measurement in Shock Wave of Hypersonic Flow Field

Hypersonic flow field around a flight vehicle has density fluctuating elements such as shock wave and boundary layer. Since refractive index of light is related to density of medium, light propagation path changes while passing through the flow field. Influence of flow field property on optical characteristics is called aero-optics. As in Fig. 1, aero-optics distorts the image obtained by an optical instrument on the flight vehicle and degrades light intensity, displaces the position of an object, blurs the image, etc. To avoid these effects, various studies were conducted to relate optical characteristics with flow characteristics and to measure aero-optical aberration.

Effect of Sidewall Configurations on Hypersonic Intake Performance

For reusable space launchers and hypersonic flight vehicles, use of an air-breathing propulsion system with supersonic combustion is the most promising option in terms of cost effectiveness. At this point, only the scramjet propulsion system provides a real alternative to expensive rocket driven systems, which currently are the only way to reach a hypersonics speeds.

Heat Flux Measurement Techniques over the protuberance at the hypersonic flow of Mach 7

An experimental investigation has been conducted on the aerodynamic heating caused by an object protruding from a flat plate at hypersonic flows of Mach 7. Three different experimental techniques are applied to measure the heat flux and temperature over the protuberance, using two types of hypersonic wind tunnels, namely, blowdown and impulse types. This paper presents the experimental tec hniques needed for use in hypersonic tunnels focusing on issues such as heat flux measurement techniques, as well as the measurement of detailed experimental data. It was confirmed that the data set agree well through the comparison of data results. A large separation region is observed in front of the protuberance with that region being very sensitive to the height of the protuberance and the length of the flat plate. These flow feat ures affect the aerodynamic heating over the protuberance. Basically, the measured heat flux is large when the height of the protuberance is large and the length of the flat plate is long. Also, the heat flux measurements at the upper positions are larger than at the lower positions. For high protuberances, a severe jump in the heat flux is observed, from about 0.6~0.7 of the height of the protuberances. However, when the protuberance is sufficiently short, a rise in the heat flux is rarely observed as the protuberance is submerged totally under the separation region upstream from the protuberance.