G. Jagadeesh

Counterflow drag reduction by supersonic jet for a blunt body in hypersonic flow

Counterflow drag reduction by supersonic jet for a large angle blunt cone at hypersonic Mach number is investigated in a shock tunnel. The flowfields around the test model in the hypersonic flow with an opposing supersonic jet emanating from the stagnation point of the model are visualized by high speed schlieren technique. The aerodynamic drag force is measured using the accelerometer based force balance system. The experimental measurements show about 30%–45% reduction in drag coefficient for different jet pressures.

Effect of concentrated energy deposition on the aerodynamic drag of a blunt body in hypersonic flow

Experimental results on the effect of energy deposition using an electric arc discharge, upstream of a 60° half angle blunt cone configuration in a hypersonic flow stream is reported. Investigations involving drag measurements and high speed Schlieren flow visualization have been carried out in a hypersonic shock tunnel using air and argon as the test gases; and an unsteady drag reduction of about 50% (maximum reduction) has been observed in the energy deposition experiments done in argon environment. These studies also show that the effect of discharge on the flow field is more pronounced in argon environment as compared to air, which confirms that thermal effects are mainly responsible for flow alteration with discharge. It has also been observed that the interaction of the hypersonic flow with the discharge filament results in the development of an unsteady flow field.

Film cooling effectiveness on a large angle blunt cone flying at hypersonic speed

Effectiveness of film cooling technique to reduce convective heating rates for a large angle blunt cone flying at hypersonic Mach number and its effect on the aerodynamic characteristics is investigated experimentally by measuring surface heat-transfer rates and aerodynamic drag coefficient simultaneously. The test model is a 60° apex-angle blunt cone with an internally mounted accelerometer balance system for measuring aerodynamic drag and an array of surface mounted platinum thin film gauges for measuring heat-transfer rates. The coolant gas (air, carbon dioxide, and/or helium) is injected into the hypersonic flow at the nose of the test model. The experiments are performed at a flow free stream Mach number of 5.75 and 0° angle of attack for stagnation enthalpies of 1.16 MJ/kg and 1.6 MJ/kg with and without gas injection. About 30%–45% overall reduction in heat-transfer rates is observed with helium as coolant gas except at stagnation regions. With all other coolants, the reduction in surface heat-transfer rate is between 10%–25%. The aerodynamic drag coefficient is found to increase by 12% with helium injection whereas with other gases this increase is about 27%.

Needleless Vaccine Delivery Using Micro-Shock Waves

ABSTRACT Shock waves are one of the most efficient mechanisms of energy dissipation observed in nature. In this study, utilizing the instantaneous mechanical impulse generated behind a micro-shock wave during a controlled explosion, a novel nonintrusive needleless vaccine delivery system has been developed. It is well-known that antigens in the epidermis are efficiently presented by resident Langerhans cells, eliciting the requisite immune response, making them a good target for vaccine delivery. Unfortunately, needle-free devices for epidermal delivery have inherent problems from the perspective of the safety and comfort of the patient. The penetration depth of less than 100 μm in the skin can elicit higher immune response without any pain. Here we show the efficient utilization of our needleless device (that uses micro-shock waves) for vaccination. The production of liquid jet was confirmed by high-speed microscopy, and the penetration in acrylamide gel and mouse skin was observed by confocal microscopy. Salmonella enterica serovar Typhimurium vaccine strain pmrG-HM-D (DV-STM-07) was delivered using our device in the murine salmonellosis model, and the effectiveness of the delivery system for vaccination was compared with other routes of vaccination. Vaccination using our device elicits better protection and an IgG response even at a lower vaccine dose (10-fold less) compared to other routes of vaccination. We anticipate that our novel method can be utilized for effective, cheap, and safe vaccination in the near future.

Bacterial transformation using micro-shock waves.

Shock waves are one of the most competent mechanisms of energy dissipation observed in nature. We have developed a novel device to generate controlled micro-shock waves using an explosive-coated polymer tube. In this study, we harnessed these controlled micro-shock waves to develop a unique bacterial transformation method. The conditions were optimized for the maximum transformation efficiency in Escherichia coli. The maximum transformation efficiency was obtained when we used a 30 cm length polymer tube, 100 μm thick metal foil, 200 mM CaCl(2), 1 ng/μl plasmid DNA concentration, and 1×10(9) cell density. The highest transformation efficiency achieved (1×10(-5) transformants/cell) was at least 10 times greater than the previously reported ultrasound-mediated transformation (1×10(-6) transformants/cell). This method was also successfully employed for the efficient and reproducible transformation of Pseudomonas aeruginosa and Salmonella typhimurium. This novel method of transformation was shown to be as efficient as electroporation with the added advantage of better recovery of cells, reduced cost (40 times cheaper than a commercial electroporator), and growth phase independent transformation.

Aerodynamic drag reduction by heat addition into the shock layer for a large angle blunt cone in hypersonic flow

Reduction in aerodynamic drag for a large angle blunt cone flying at hypersonic Mach number by heat addition into the shock layer is demonstrated in HST2 hypersonic shock tunnel. The heat addition is achieved by the exothermic reaction of chromium atoms ablated from the stagnation region of the chromium coated blunt cone with the atomic oxygen behind the shock wave. The measurements show about 47% reduction in the drag coefficient for a 60° apex angle blunt cone in a Mach 8 flow of 3.4 MJ/kg specific enthalpy. The reduction in drag is measured using the accelerometer based force balance system and the heat addition into the shock layer is identified by the surface mounted thin film heat flux gauges and the corresponding movement of the shock wave is visualized by schlieren pictures.

Observations on the non-mixed length and unsteady shock motion in a two dimensional supersonic ejector

Key features that drive the operation of a supersonic ejector are the complex gasdynamic interactions of the primary and secondary flows within a variable area duct and the phenomenon of compressible turbulent mixing between them, which have to be understood at a fundamental level. An experimental study has been carried out on the mixing characteristics of a two dimensional supersonic ejector with a supersonic primary flow (air) of Mach number 2.48 and the secondary flow (subsonic) which is induced from the ambient. The non-mixed length, which is the length within the ejector for which the primary and secondary flow remain visually distinct is used to characterize the mixing in the ejector. The operating pressures, flow rates and wall static pressures along the ejector have been measured. Two flow visualization tools have been implemented—time resolved schlieren and laser scattering flow visualization. An important contribution has been the development of in-house image processing algorithms on the MATLAB...

Simultaneous measurement of aerodynamic and heat transfer data for large angle blunt cones in hypersonic shock tunnel

Aerodynamic forces and fore-body convective surface heat transfer rates over a 60° apex-angle blunt cone have been simultaneously measured at a nominal Mach number of 5.75 in the hypersonic shock tunnel HST2. An aluminum model incorporating a three-component accelerometer-based balance system for measuring the aerodynamic forces and an array of platinum thin-film gauges deposited on thermally insulating backing material flush mounted on the model surface is used for convective surface heat transfer measurement in the investigations. The measured value of the drag coefficient varies by about ± 6% from the theoretically estimated value based on the modified Newtonian theory, while the axi-symmetric Navier-Stokes computations overpredict the drag coefficient by about 9%. The normalized values of measured heat transfer rates at 0‡ angle of attack are about 11% higher than the theoretically estimated values. The aerodynamic and the heat transfer data presented here are very valuable for the validation of CFD codes used for the numerical computation of flow fields around hypersonic vehicles.

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

Real gas effects dominate the hypersonic flow fields encountered by modern 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.

Density field visualization of a Micro-explosion using background-oriented schlieren

Graphical abstract