Faculty Publications
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Item Quality and complexity comparison of H.264 intra mode with JPEG2000 and JPEG(2004) Aravind, A.L.; Rao, B.P.; Kudva, S.S.; Babu, S.; Sumam David, S.; Rao, A.V.The recently proposed H.264 video coding standard offers significant coding gains over previously defined standards. An enhanced intra-frame prediction algorithm has been proposed in H.264 for efficient compression of I-frames. This paper investigates the scope of the intraframe coder of H.264 for image coding. We compare the quality of this coder and the complexity of its decoder with the commonly used image codecs (JPEG and JPEG2000). Our results demonstrate that H.264 has a strong potential as an alternative to JPEG and JPEG2000. ©2004 IEEE.Item Numerical Investigation on Effects of Profiled Endwall Over Purge Flow in Linear Turbine Cascade(Springer Science and Business Media Deutschland GmbH, 2020) Babu, S.; Kiran, K.N.; Tom, J.K.; Anish, S.This paper describes the combined effects of purge flow and non-axisymmetric endwall profiling on the aerothermal performance of a linear turbine cascade. Purge slot with 45° ejection angle and three different endwall profiles, with varying hump to dip height, are analyzed. Performance of profiled endwall is compared with the non-profiled case. Reynolds-averaged Navier–Stokes (RANS) equation with SST turbulence model is used for numerical simulation. The analyzed results explore the demerits of current endwall profiles and how the transverse movement of weaker boundary layer fluid from the hub-pressure side corner enhanced. Compared to base case, endwall profiling enhanced the overturning and secondary flow kinetic energy at cascade exit. Apart from this, the profiled cases are providing very effective endwall protection compared to non-profiled purge case. © 2020, Springer Nature Singapore Pte Ltd.Item Accident Prediction Modelling and Crash Scene Investigation(Springer Science and Business Media Deutschland GmbH, 2023) Sumayya Naznin, P.H.; Panackel, L.S.; Zaviar, S.; Babu, S.In recent years, traffic incidents have been a major cause of deaths, injuries, and property damage in India. By definition, an accident is “an unforeseen and unplanned incident that causes harm or injury†; nevertheless, in most circumstances, accidents can be avoided by taking specific precautions. Understanding the primary and contributing factors may combat road traffic accident severity. This research uncovered new information as well as the most important target-specific contributing elements to the severity of road accidents. The goal of this study was to analyse accident data from Koratty and Angamaly towns in Kerala's Ernakulam district, and to identify and classify black spots into first, second, third, fourth, and fifth orders based on the ASI value and the crash scenes were investigated in order to analyze the causes. An attempt was made to design collision and condition diagrams, as well as develop an accident prediction model for these dangerous areas, using the information acquired thus far. The collision diagrams for various places also revealed the pattern of road accidents that occurred over a two-year period, while the condition diagrams revealed the precise site of the accident. Using this knowledge, certain short-term corrective measures/solutions for the crash studied sites were offered. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Influence of Purge Ejection Angles and Upstream Wakes/Disturbances on Low Aspect Ratio Turbine Blade Passage Aerodynamics(Springer Science and Business Media Deutschland GmbH, 2023) Babu, S.; Anish, S.The blade passage aerodynamics of turbine engine can be affected significantly by the purge flow—mainstream interaction. In this paper, aerodynamic behaviour of a turbine blade profile with aspect ratio 1.2 is investigated numerically, in the presence of purge flow and upstream wakes/disturbances. An effort is made to explore the effects of purge ejection angles and upstream wakes over turbine blade passage aerodynamics. Results indicates that purge flow has enhanced the cross passage pressure gradient. Presence of upstream wakes has altered the incidence angle non-uniformly throughout the span. However, strong flow acceleration of purge flow at lower ejection angles has caused significant reduction in the boundary layer cross flow and secondary flow losses. On the contrary higher ejection angles induced tangential and spanwise shifting of the loss core regions at the passage exit. The interaction of purge coolant and upstream wakes with the freestream has enhanced the secondary vortex formations within the blade passage. Additional secondary vortices are originated at the leading edge by the introduction of upstream wakes. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item A Numerical Analysis on Effects of Boundary Layer Fence on Blade Passage Aerodynamics and Loss Reduction(American Institute of Physics, 2024) Babu, S.; Anish, S.Mitigation of total pressure loss and improvement in aerodynamic performance are obtained on a low aspect ratio turbine blade. The turbine blade hub region is constructed with a boundary layer fence to reduce secondary losses. The major objective of implementing boundary layer fence is to restrict the pressure side leg of horseshoe vortex from reaching suction surface of adjacent blade. This decreases the loss associated with the passage vortex by delaying its development. Present analysis reveals the aerodynamic performance of boundary layer fence in three ways. Firstly a rectangular strip is kept close to the suction surface in order to break the suction side leg of horseshoe vortex. Secondly, to restrict the pressure side leg of horseshoe vortex from traversing from pressure surface to suction surface a fence of curved trailing edge is kept at the middle of the blade passage. In the third configuration the combined effects of both rectangular strip and fence have been analyzed. In this work the shape of the rectangular strip and fence do not follow the blade profile. Ansys-cfx, commercial software is used for numerical analysis. The results indicate that the presence of strip has resulted in the breakdown of suction side leg of horseshoe vortex and the location of fence has directed the pressure side leg of horseshoe vortex more axially rather than traversing across the blade passage. The combination of both geometries has achieved further reduction of total pressure loss coefficient. © 2024 American Institute of Physics Inc.. All rights reserved.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.Item Aerodynamic performance of profiled endwalls with upstream slot purge flow in a linear turbine cascade having pressure side separation(American Institute of Physics Inc., 2021) Babu, S.; Anish, S.In aeroengines, purge flow directly fed from the compressor (which bypasses the combustor) is introduced through the disk space between blade rows to prevent the hot ingress. Higher quantity of purge gas fed through the wheel space can provide additional thermal protection to the passage endwall and blade surfaces. However, the interaction of purge flow with the mainstream flow leads to higher secondary losses. Secondary losses inside a turbine blade passage can be reduced effectively by endwall contouring. This paper presents computational investigation on the influence of non-axisymmetric endwall contouring over endwall secondary flow modification in the presence of purge flow with the pressure side bubble (PSB). The experimental analysis was conducted for the base case without purge and base case with purge (BCP) configurations having flat endwalls. The total pressure loss coefficient and exit yaw angle deviation were measured with the help of a five-hole pressure probe. Static pressure distribution over the blade midspan was obtained by 16 channel Scanivalve. Aerodynamic performances of three different profiled endwalls are numerically analyzed and are compared against the BCP configuration. The effects of different contoured endwall geometries on endwall static pressure distribution and secondary kinetic energy were also discussed. Analysis shows that in the first contoured endwall configuration (EC1), the formation of stagnation zones at a contour valley close to the suction surface causes the exit total pressure loss coefficient to increase. The shifting of the contour valley near to the pressure surface (EC2 configuration) has resulted in local acceleration of the diverted pressure side leg of the horseshoe vortex over the hump toward the end of the passage. In the third configuration (EC3 configuration), reduced valley depth and optimum hump height have effectively redistributed the endwall pitchwise pressure gradient. The increased static pressure coefficient at the endwall near to the pressure surface has eliminated the PSB formation. In addition, computational results of unsteady Reynolds averaged Navier-Stokes simulations are obtained for analyzing transient behavior of PSB, with more emphasis on its migration on the pressure surface and transport across the blade passage. The additional work done by the mainstream fluid to transport the low momentum PSB fluid has caused higher aerodynamic penalty at the blade exit region. In this viewpoint, the implementation of contoured endwalls has shown beneficial effects by eliminating the PSB and related secondary vortices. At 27% of axial chord downstream of the blade trailing edge, a 4.1% reduction in the total pressure loss coefficient was achieved with endwall contouring. © 2021 Author(s).Item Mitigation of secondary flows and pressure side bubble in turbine blade passage using asymmetric endwall contouring: a steady-state analysis(Institute of Physics, 2025) Babu, S.; Jannet, S.; Raja, R.; Lionel, P.; Oommen, L.P.; Surendran, A.In turbine passages, secondary vortices and pressure-side bubbles significantly contribute to aerodynamic losses and reduced blade efficiency issues that are critical in industrial gas turbine performance. Hence, it is very important to mitigate such losses to enhance overall turbine efficiency. Several research attempts have already been made to address this challenge; however, most studies have not focused explicitly on pressure-side bubble mitigation strategies. In the present investigation, an effort has been made to investigate the impact of endwall contouring in minimizing losses caused by secondary vortices, particularly focusing on pressure-side bubble formation. Experimental and numerical investigations are conducted on a low-speed blowing-type turbine cascade wind tunnel. The experimental study involves in-cascade testing, while numerical simulations are performed using ANSYS Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) turbulence model. Three contouring configurations (EC 1, EC 2, and EC 3) are compared against a non-profiled base case (BC). The results confirm that endwall curvature significantly alters secondary flow behavior and static pressure distribution. While EC 1 and EC 2 generated stagnant zones in the valleys, causing additional losses while the EC 3 profile with optimized hump height and valley depth, redistributed pressure effectively. This effectively suppressed lateral flow migration and pressure-side bubble formation, which in turn enhanced overall turbine performance. In comparison to the base case, the EC 3 design quantitatively reduced total pressure loss by 3.43%, proving its efficacy in improving aerodynamic performance. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.