Vinayak Kulkarni

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.

Effectiveness of Aerospike for Drag Reduction on a Blunt Cone in Hypersonic Flow

IMPOSED bluntness at the nose of a hypersonic vehicle is necessary to alleviate the oncoming heat load. However, increased wave drag is the immediate consequence of the forced bluntness. Hence, research in the field of hypersonics is always centered on the reduction of wave drag encountered by the space vehicles during their ascent phase. Most of the drag-reduction techniques are directed towards modifying the flowfield ahead of the stagnation point. Among the drag-reduction techniques, retractable spike is the simplest and is an easy-to-implement technique; hence, the forward-facing aerospike technique has attracted many researchers to consider various issues. Various configurations of aerospikes were assessed by Menezes et al. [1] to arrive at the best configuration for drag reduction on a 120 deg apex angle blunt cone, and a flat-disc-tipped aerospike of unity L=D (spike length-to-cone base-diameter ratio) with a disc diameter of 1 4 D was observed to be the most efficient drag-reducing agent. Therefore, a similar flat-disctipped aerospike configuration is considered in the present study to evaluate its effect on drag of a 120 deg apex-angle blunt cone under various total-enthalpy conditions. An accelerometer-based force balance was used to measure drag on the model in a conventional hypersonic shock tunnel, IITB-ST (Indian Institute of Technology Bombay—Shock Tunnel), at low-enthalpy conditions (1:1 0:02 and 1:5 0:03 MJ=kg), and high-enthalpy tests (5 0:44 MJ=kg) were conducted on the same model in a free-piston-driven hypersonic shock tunnel, HST3. Flowfield modifications brought about by the disc-tipped spike were expected to depend on the total enthalpy of the flow, as such a dependence was observed in the case of drag-reduction studies using a fluidic spike [2]. Details of the experimental methodology and the results are presented in the following sections. II. Test Facilities, Model, and Force Balance

Performance comparison of flux schemes for numerical simulation of high-speed inviscid flows

Numerical investigations to assess the performance of different flux schemes for the spatial discretisation of the Euler equations have been performed. The schemes employed in the study include flux vector and flux difference splitting schemes as well as hybrid schemes. The schemes are cast in an unstructured high-order finite volume framework and are studied on typical engineering problems in the supersonic and hypersonic regimes. While all the flux schemes perform well in the supersonic and low hypersonic range, their performance show a marked change in the high Mach number regimes. Numerical experiments suggest that the AUSM family of schemes is the most accurate while the Rusanov scheme is the most robust for the range of Mach numbers considered in the study. These studies indicate that a robust and accurate numerical solver for high-speed compressible flows necessitate the use of blended schemes that provide a right balance between accuracy and numerical dissipation.

Delusive Influence of Nondimensional Numbers in Canonical Hypersonic Nonequilibrium Flows

AbstractA finite volume–based unstructured inviscid flow solver has been developed for the study of nonequilibrium effects in high enthalpy flows. Four different inviscid flux computation schemes are tested for literature reported test cases like unsteady wave motion in a shock tube and high enthalpy flow over cylinder/sphere. During the present assessment, encouraging agreement has been noticed in capturing all the essential flow features in the reacting media. Here, the Rusanov scheme is noticed to be computationally cheaper among all the schemes with noticeable diffusion around strong gradients. Shock tube test case revealed the existence of various shock Mach numbers for a given driving pressure ratio in the presence of reactions. Similarly, freestream Mach number is found to have limitations in representing the shock standoff distance in case of high enthalpy flow over cylinder and sphere. In line with this, real gas effects are prominently observed for the case of the cylinder in comparison with the...

Experimental Assessment of Noncontact Type Laser-Based Force Measurement Technique for Impulsive Loading

Force measurement is an essential element in the design of mechanical or nonmechanical systems. The choice of a particular technique, among the numerous measurement techniques available, depends on various parameters within which the nature of force is an important one. The measurement of impulse force is considered in this study using two techniques. In view of this, an experimental setup has been developed to understand the applicability and assessment of a laser-based extrusive technique, along with the established intrusive accelerometer-based technique for impulsive force measurement. The accelerometer-based measurements can be used to precisely predict the magnitude and temporal nature of the force. However, the velocity-based impulse prediction shows some limitation on complete representation of the system. In addition, the indirect measurement of acceleration from the velocity measured seems to have better prediction of the force.

Evaluation of a Model Helical Bladed Hydrokinetic Turbine Characteristics From In-Situ Experiments

Hydro power has always been a major source of electricity generation among different renewable energy technologies. However, due to the construction of dams, the conventional hydro energy extraction techniques cause disturbance to the ecology by diverting the natural flow of water and migrating population from their native land. Of late, energy extraction from the natural flow of water is considered as potential source of renewable power since it is clean and reliable. In view of this, the present study deals with the development and performance characterization of a vertical-axis helical-bladed hydrokinetic turbine. Considering the various design parameters, a NACA 0020 bladed vertical-axis turbine of solidity ratio 0.38 and aspect ratio 1.0 has been developed. In-situ experiments have been carried out at an irrigation sluice having a water velocity of 1.1 m/s. Further, its performance characteristics are evaluated at different mechanical loading conditions with the help of a mechanical dynamometer. It has been observed that the developed helical-bladed turbine demonstrates a peak power coefficient of 0.16 at a tip-speed ratio of 0.85. The present experimental investigation has clearly demonstrated the usefulness of the hydrokinetic turbine. It has also been logged that the average water velocity at the concerned site has a great importance on the turbine design.Copyright

Separation mitigation using pressure feedback technique for hypersonic shock wave boundary layer interaction

Present studies are focused on the use of pressure feedback technique as a separation control technique for ramp induced flow separation at hypersonic speed. Numerical simulations portrayed that though pressure feedback technique can reduce the flow separation, further cooling of the feedback channel enhances its potential for separation control. Marginal cooling of channel walls to 175 K has reduced separation bubble size by 18.18% while strong cooling of those walls to 50 K reduced the separation by 30%. Such low enthalpy perfect gas simulations also showed the lower effectiveness of pressure feedback technique with increased ramp angle. Further, it has been noticed from the perfect and nonequilibrium gas flow simulations that the cooling of pressure feedback channel introduces differential separation size for the same wall-to-total temperature ratio cases. Integration of cooled pressure feedback channel with blunt leading edge configuration showed reduced separation size for any bluntness radius. Effectiveness of this integration is seen in lowering the values of inversion and equivalent radii. Thus, use of cooled pressure feedback technique in conjunction with leading edge bluntness is not only seen to have reduced the intensity of shock wave boundary layer interaction but also has enhanced the controllability of blunted leading edge without altering the entropy layer–boundary layer interaction.

Alterations in Critical Radii of Bluntness of Shock Wave Boundary Layer Interaction

AbstractAny configuration consisting of flat plate attached to a ramp experiences shock wave boundary layer interaction (SWBLI) at supersonic or hypersonic Mach numbers. This interaction can lead t...

Soft Computing Based Force Recovery Technique for Hypersonic Shock Tunnel Tests

A hemispherical model equipped with a three component accelerometer force balance has been tested in a shock tunnel at Mach 8.0 freestream conditions. A novel technique has been devised using the Artificial Neuro-Fuzzy Inference System (ANFIS) for recovering the forces experienced by the model during the experiments. Implementation of this methodology in calibration of the force balance showed encouraging agreement with the impulse forces recovered from the calibration tests. The same recovery procedure is then adopted to obtain the time history of the forces for 0∘ and 15∘ angle of attack experiments. The drag recovered in steady state is found to agree well with the conventional methods with minor discrimination for the lift and pitching moment. In light of the limitation of the accelerometer force balance theory due to the unaccountability of model dynamics, the force recovery technique proposed herein is found simple to implement and can be opted as a tool for prediction of the aerodynamic coefficient...

Shock Tube as an Impulsive Application Device

Current investigations solely focus on application of an impulse facility in diverse area of high-speed aerodynamics and structural mechanics. Shock tube, the fundamental impulse facility, is specially designed and calibrated for present objectives. Force measurement experiments are performed on a hemispherical test model integrated with the stress wave force balance. Similar test model is considered for heat transfer measurements using coaxial thermocouple. Force and heat transfer experiments demonstrated that the strain gauge and thermocouple have lag time of 11.5 and 9 microseconds, respectively. Response time of these sensors in measuring the peak load is also measured successfully using shock tube facility. As an outcome, these sensors are found to be suitable for impulse testing. Lastly, the response of aluminum plates subjected to impulsive loading is analyzed by measuring the in-plane strain produced during deformation. Thus, possibility of forming tests in shock is also confirmed.