Shock stand-off distance visualization in hypersonic shock tunnel using electrical discharge technique

Visualization of the detached shock wave that forms ahead of a blunt body flying at hypersonic Mach number using electrical discharge technique is a simple and convenient technique to measure the stand-off distance experimentally in an hypersonic shock tunnel. In this technique a thin sheet of electrical discharge generated between a point electrode attached to the wall of the test section and a line electrode embedded on the model surface reveals the position of the shock wave around the body in hypersonic flow. In this paper we present the details of this technique and sample results obtained for typical body shapes tested in HST2 shock tunnel at a freestream Mach number of 5.75. The detached shock waves in front of the test models are clearly visualized using this technique. The shock stand-off distance estimated based on the numerical results for a large angle blunt cone obtained using a commercial CFD code match well with the experimentally measured value. These results clearly demonstrate the suitability of the electrical discharge technique for visualizing the flowfields in hypersonic testing facilities having very short test time

Typhoid Fever and Its Association with Environmental Factors in the Dhaka Metropolitan Area of Bangladesh: A Spatial and Time-Series Approach

Typhoid fever is a major cause of death worldwide with a major part of the disease burden in developing regions such as the Indian sub-continent. Bangladesh is part of this highly endemic region, yet little is known about the spatial and temporal distribution of the disease at a regional scale. This research used a Geographic Information System to explore, spatially and temporally, the prevalence of typhoid in Dhaka Metropolitan Area (DMA) of Bangladesh over the period 2005-9. This paper provides the first study of the spatio-temporal epidemiology of typhoid for this region. The aims of the study were: (i) to analyse the epidemiology of cases from 2005 to 2009; (ii) to identify spatial patterns of infection based on two spatial hypotheses; and (iii) to determine the hydro-climatological factors associated with typhoid prevalence. Case occurrences data were collected from 11 major hospitals in DMA, geocoded to census tract level, and used in a spatio-temporal analysis with a range of demographic, environmental and meteorological variables. Analyses revealed distinct seasonality as well as age and gender differences, with males and very young children being disproportionately infected. The male-female ratio of typhoid cases was found to be 1.36, and the median age of the cases was 14 years. Typhoid incidence was higher in male population than female (χ2 = 5.88, p0.05). A statistically significant inverse association was found between typhoid incidence and distance to major waterbodies. Spatial pattern analysis showed that there was a significant clustering of typhoid distribution in the study area. Moran\u27s I was highest (0.879; p<0.01) in 2008 and lowest (0.075; p<0.05) in 2009. Incidence rates were found to form three large, multi-centred, spatial clusters with no significant difference between urban and rural rates. Temporally, typhoid incidence was seen to increase with temperature, rainfall and river level at time lags ranging from three to five weeks. For example, for a 0.1 metre rise in river levels, the number of typhoid cases increased by 4.6% (95% CI: 2.4-2.8) above the threshold of 4.0 metres (95% CI: 2.4-4.3). On the other hand, with a 1°C rise in temperature, the number of typhoid cases could increase by 14.2% (95% CI: 4.4-25.0)

Investigations of separated flow over backward facing steps in IISc hypersonic shock tunnel

Two backward facing step (2 mm and 3 mm step height) models are selected for surface heat transfer measurements. The platinum thin film gauges are deposited on the Macor inserts using both hand paint and vacuum sputtering technique. Using the Eckert reference temperature method the heating rates has been theoretically calculated along the flat plate portion of the model and the theoretical estimates are compared with experimentally determined surface heat transfer rate. Theoretical analysis of heat flux distribution down stream of the backward facing step model has been carried out using Gai’s non-dimensional analysis. Based on the measured surface heating rates on the backward facing step, the reattachment distance is estimated for 2 and 3 mm step height at nominal Mach number of 7.6. It has been found from the present study that for 2 and 3 mm step height, it approximately takes about 10 and 8 step heights downstream of the model respectively for the flow to re-attach

Review of hypersonic research investigations in IISc shock tunnel (HST1)

Real gas effects dominate the hypersonic flow fields encountered by modem day hypersonic space vehicles. Measurement of aerodynamic data for the design applications of such aerospace vehicles calls for special kinds of wind tunnels capable of faithfully simulating real gas effects. A shock tunnel is an established facility commonly used along with special instrumentation for acquiring the data for this purpose within a short time period. The hypersonic shock tunnel (HST1), established at the Indian Institute of Science (IISc) in the early 1970s, has been extensively used to measure the aerodynamic data of various bodies of interest at hypersonic Mach numbers in the range 4 to 13. Details of some important measurements made during the period 1975-1995 along with the performance capabilities of the HST1 are presented in this review. In view of the re-emergence of interest in hypersonics across the globe in recent times, the present review highlights the Suitability of the hypersonic shock tunnel at the IISc for future space application studies in India

Gas temperature layer visualization in hypersonic shock tunnel using electric discharge

A novel technique for visualizing the gas temperature layer around bodies flying at hypersonic speeds is presented. The high temperature zone is visualized by photographing the light emitted from the electric discharge generated over a model exposed to hypersonic flow in a shock tunnel. The technique is based on electrical discharge phenomena, where the frequency of radiation emitted by the discharge path passing through the flow field varies with the temperature of the gas medium in the discharge path. The experiments are carried out in the hypersonic shock tunnel HST-1 at a nominal Mach number of 5.75 using helium as the driver gas, with free stream velocity of 1.38 km/s and free stream molecular density of $2.3396×10^{16} molecules/cm^3$. The electric discharge is generated across a line electrode embedded in the model surface and a point electrode suspended in the free stream. A high voltage discharge device (1.6 kV and 1 A) along with a micro-controller based pulse delay control module is integrated with the shock tunnel for generating and controlling electric discharge which lasts for ~2 μs. The gas temperature layer at zero angle of incidence around a flat plate and slightly blunted (5 mm bluntness radius) 20° apex angle slender cone model are visualized in this study. The visualized thickness of the high temperature layer around the flat plate is ~2 mm, which agrees well with numerical simulation, carried out using 2-D Navier-Stokes equation

Measurement of Heat Transfer Rate on Backward-Facing Steps at Hypersonic Mach Number

Two backward-facing models with step heights of 2 and 3 mm are used to measure the convective surface heat transfer rates by using platinum thin-film gauges, deposited on Macor inserts. Heat transfer rates have been theoretically calculated along the flat plate portion of a model using the Eckert reference temperature method. The experimentally determined surface heat transfer rate distributions are compared with theoretical and numerical estimations. Experimental heat flux distribution over a flat plate model showed good agreement with the reference temperature method at stagnation enthalpy range of 0.8-2 MJ/kg. Theoretical analysis has been used for downstream of a backward-facing step using Gai's nondimensional analysis. It has been found from the present study that approximately 10 and 8 step heights are required for the flow to reattach for 2 and 3 mm step height backward-facing step models, respectively, at a nominal Mach number of 7.6

Experimental investigation of heat transfer reduction using forward facing cavity for missile shaped bodies flying at hypersonic speed

Forward facing circular nose cavity of 6 mm diameter in the nose portion of a generic missile shaped bodies is proposed to reduce the stagnation zone heat transfer. About 25% reduction in stagnation zone heat transfer is measured using platinum thin film sensors at Mach 8 in the IISc hypersonic shock tunnel. The presence of nose cavity does not alter the fundamental aerodynamic coefficients of the slender body. The experimental results along with the numerically predicted results is also discussed in this paper

Forebody convective hypersonic heat transfer measurements over large-angle blunt cones

KNOWLEDGE of surface heat transfer rates for a vehicle con-. guration under hypersonic � ow is essential to quantify the heat-shieldingrequirement for the thermal protectionsystem (TPS) of space missions. Typically low-lift and high-drag bodies such as large-angle blunt cones are used as heat shields in modern aeroassisted orbital transfer vehicles1 (AOTVs). The development of these space vehicles requires a large volume of heat transfer data, which can also be used to validate computational uid dynamic codes. Although most of the AOTVs operate at very high velocities and high altitudes, the maximum convective heating will occur at conditions corresponding to continuum/near-continuum ow.2 Hence, carefullydesignedground-basedexperimentsin typicalhigh enthalpy continuum ow conditions will be very useful in designing the requisite TPS for such space missions. Previously, many authors have reported heat transfer measurements over large-angle blunt bodies