Research activities in Propulsion have been pursued at the Department since its inception in 1967. The Department is also the only one to offer a post graduate specialization in Propulsion amongst all similar departments in India.
Aerodynamic Heating in Aerospace Vehicles
As part of ongoing work, a computer code is being developed to predict the time -- temperature history of an entire hypersonic vehicle. Analysis of critical regions like sweptback leading edges has revealed significant differences in the behavior of aerodynamic heating. Part of the work focuses on the optimization of the insulating thermal protection system for a hypersonic vehicle.
Basic investigations of behavior of fluid flow & heat transfer at micro scale revealed significant qualitative differences as compared to the macro scale. The effects that surface at the micro scale are being numerically identified. Some of these effects have fundamental repercussions in the understanding of the macro scale behavior as well. At present optimization of micro scale heat sink is in progress in the Department.
Ongoing work at the Department focuses on analysis leading to design of a propulsion unit for a hypersonic aircraft. The work involves analysis of various components and performance optimization over the given trajectory.
As part of work funded by Pratt and Whitney, losses incurred in the rotors and stators of a multi-stage compressor were mathematically modeled. Separate modeling was required for two- and three-dimensional flows. The work resulted in a computer code for computing overall compressor performance based on these loss models.
Work done at the department has resulted in the conceptualization of an unconventional Infrared Signature Suppression System (IRSS) for helicopter engines. The new IRSS yields a maximum contrast of only 25 deg C with the local background from almost all the view angles of concern. In other words, the IRSS ensures that a helicopter engine operating at the most most critical point of the mission would appear hotter than the surroundings by not more than 25 deg C, making it extremely difficult for a heat-seeking missile to lock on to the helicopter. Without a signature suppressor, the temperature contrast between the engine and the surroundings would exceed 400 deg C. The temperature contrast achieved by the new IRSS is far superior to almost all the IRSS devices reported in open literature, which claim a minimum temperature contrast of 80 deg C. In addition, the reported IRSS devices have relatively significant back-pressure and weight penalties that effectively increase the IR Signature level of the helicopter since the engine has to operate at a higher combustion temperature to overcome the penalties without compromising the mission. In contrast, the IRSS conceptualized in the department has no back-pressure penalty, and an insignificant weight and drag penalty.Part of the work involved making a thermal model that simulates the multi-mode heat transfer including radiation interchange using analytical view factors for discretized geometry.
In an axial flow compressor, the secondary losses constitute a major segment of the total losses incurred. Recent research in the use of three-dimensional blade designs incorporating end bends have highlighted the advantage of swept blades in improved stage loading, efficiency and stable operating range. As the aerodynamic design of compressor and turbine swept blades are pushed more and more towards the saturation point, use of swept blades (3D stacking) in compressor and turbine proved to be one more step towards it. The use of forward sweep has been found to reduce the overall losses considerably and stretches out the stable operating range. Project was aimed to improve the understanding of the effects of forward sweep on the losses by studying Pressure Characteristics the 300 parabolically swept forward blades in an axial flow compressor and compare its results with straight blades.The Swept-Swept combination was found to be more efficient in most part of the operating range at design and off-design ratings. The swept blades had a larger stable operating range, better efficiency and lower noise levels. The swept blades have some disadvantages but in overall perspective the advantages accrued far more outweighs the disadvantages. It is highly suitable for compressors of irregular mass flow or when noise levels are to be minimized.
The goal of modern compressor is to obtain high pressure ratio with reduced no of stages, increased blade loading and high stage efficiency over a wide spectrum of operation. Tandem airfoil used for higher camber angle and higher blade loading. The use of tandem blade rows in place of single blade rows increase the useful operating range. Tandem airfoil allows for variable blade cambers that can accommodate large variations in pressure ratio in rotor applications or large variations in volume flow and flow deflection in guide vanes and stators.
The gap-nozzle energizes the wake from the front tandem and promotes sustained flow attachment on the suction surface of the back tandem.
Generally, a tandem blade can achieve larger variations in operating conditions with greater efficiency than a single blade. Figure below shows the tandem CDA tandem cascade blade under visualization study using threads spread over the blade surface.