Faculty Publications
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Publications by NITK Faculty
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Item An aerothermal investigation of purge flow behaviour in a linear turbine cascade with upstream wakes(Bentham Science Publishers, 2018) Babu, S.; Anish, S.Background: Over all efficiency of a turbofan engine can be improved by increasing turbine inlet temperature. To withstand the high turbine inlet temperatures advanced cooling techniques and robust materials are required. Air supplied from compressor can be used to purge turbine components and disk cavities from the incoming hot gas. Objective: In the present study, an attempt is made to understand the aerodynamic and thermal effects caused by the purge flow in the presence of stationary upstream wakes. Methods: Reynolds Averaged Navier Stokes Equation coupled with SST turbulence model is used for computational study. Base case experimental data conducted on a 5 blade linear cascade is used for numerical validation. The coolant to mainstream blowing ratio is varied from 0.2 to 1.2 with a step size of 0.2. Results: It is observed that with an increase in the blowing ratio, the mass averaged total pressure losses also increase. Purge flow shifts the passage vortex away from the endwall and causes significant overturning up to a span of 30-40mm, before they exhibit underturning up to midspan. In an effort to reduce the losses, purge ejection angle is reduced to 45° from 90°. Significant loss reduction and improved endwall protection are observed at 45° ejection angle. This ejection angle provides enough acceleration and momentum to the fluid inside the endwall boundary layer. But the upstream secondary wakes and secondary flows enhanced the mixing losses within the blade passage. Conclusion: The turbulent mixing generated by upstream wakes reduced the film cooling effectiveness over the endwall. The numerical results show that film cooling effectiveness can be improved by reducing the purge ejection angle. Various patents have been discussed in this article. © 2018 Bentham Science Publishers.Item Computational predictions of velocity ratio and ejection angle on purge flow in a linear turbine cascade with upstream disturbance(Isfahan University of Technology secretary@jafmonline.net, 2020) Babu, S.; Anish, S.Secondary air bled from the compressor which bypasses the combustion chamber is used to seal the turbine components from incoming hot gas. Interaction of this secondary air or purge flow with the mainstream can alter the flow characteristics of turbine blade passage. An in depth analysis of secondary loss generation by purge flow in the presence of upstream disturbances has huge relevance. The objective of present study is to understand the aerodynamic and thermal effects caused by the purge coolant flow in the presence of an upstream wake. A linear turbine cascade is selected for the computational study and a stationary cylindrical rod which resembles the trailing edge of nozzle guide vane is kept 20 mm before the leading edge to generate the upstream wake (or disturbance). Purge flow disturbances includes strong formation of Kelvin-Helmholtz vortices at trailing edge and additional roll-up vortices at leading edge. Detailed analysis is carried out by varying the velocity ratios as well as the ejection flow angle. Higher velocity ratio and perpendicular coolant ejection reduces the mainstream axial momentum which enhances the passage cross flow. Even though the mass averaged total pressure loss is linearly dependent on the velocity ratio, a reduction in the ejection angle brings down the loss coefficient at the blade exit. A lower ejection angle will improve the film cooling effectiveness also. The presence of purge flow causes an increase in the overturning and underturning. © Isfahan University of Technology.