Faculty Publications
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Item An investigation on the effect of pitchwise endwall design in a turbine cascade at different incidence angles(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2017) Kiran, K.N.; Anish, S.This paper describes the effects of non-axisymmetric endwall profiling on the aerodynamic performance of a linear turbine cascade at different incidence angles. The sinusoidal profiling is carried out with constant profile curvature along the mean streamline path. Three different profiles, with varying hump to dip height, are analyzed numerically and the performances are compared with the planar profile. Reynolds Averaged Navier Stokes (RANS) equations are solved in their conservative form using Finite Volume Method with SST turbulence model. The calculated results indicate that the profiled endwall minimizes the lateral movement of weaker boundary layer fluid from the hub-pressure side corner. In comparison with planar case, the flow deviations are largely contained with endwall profiling but closer to the endwall it enhances the overturning and secondary flow kinetic energy. The reduction in loss coefficient is estimated to be 1.3%, 8.7% and 38% for incidence angles of ?10°, nominal and +15° respectively. The sinusoidal profiling has brought down the pitch averaged flow deviation and secondary flow kinetic energy at nominal and positive incidence angles but the impact is insignificant at negative incidence. Profiling minimizes the rolling up of the passage vortex and makes the passage vortex to migrate closer to the endwall. This flow modification brings down the losses in the core flow but enhances the losses near the endwall. © 2017 Elsevier Masson SASItem 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 investigation on secondary flows in a linear turbine cascade with tapered dual fence(Korean Society of Mechanical Engineers, 2019) Kiran, K.N.; Babu, B.; Anish, S.The focus of the present work is to minimize the secondary flow losses inside a linear turbine cascade by means of a novel design of streamwise dual fence. The leading edge and trailing edge of the fences have been modified so as to reduce the total pressure loss coefficient in the passage. The study has been carried out computationally based on RANS simulations with SST turbulence model. Numerous simulations have been undertaken with single fence and dual fence models and compared with the base case model. The dual fence model with tapered trailing edge exhibits significant loss reduction compared to the base case. A suitable fence height ratio (FHR) has been identified for the dual fence model. The FHR = 2 configuration reduces the secondary flow kinetic energy by 78 % within the blade passage and it reduces the exit angle deviation significantly throughout the span. Detailed flow field analysis has been carried out to understand the physical mechanism behind the loss reduction with dual fence models. It is observed that fence-1 breaks the pressure side leg of the horse shoe vortex at the beginning of their formation itself. The radial penetration of the suction side leg of the horse shoe vortex is restrained by fence-2. These combined effects prevent the formation and mixing of two prominent loss core regions thereby avoiding the accumulation of low energy fluid near the suction side of blade. © 2019, KSME & Springer.Item Computational investigations on the hemodynamic performance of a new swirl generator in bifurcated arteries(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) Prashantha, B.; Anish, S.Hemodynamic behaviour of blood in the bifurcated arteries are closely related to the development of cardiovascular disease. The secondary flows generated at the bifurcation zone promotes the deposition of atherogenic particles on the outer walls. The present study aims at suppressing the development of atherosclerosis plaque by inducing helical flow structure in the arterial passage. To realize this objective a novel swirl generator (stent like structure with an internal groove) has been developed to induce helicity in the bifurcated passage. The functional requirement of the swirl generator is to minimize the relative residence time (RRT) of the fluid layer near the endothelial wall without generating any additional pressure drop. Different configurations of the swirl generator have been tested computationally using large eddy simulation (LES) model. It is observed that the induced helical flow redistributes the kinetic energy from the centre to the periphery. A single rib swirl flow generator proximal to the stent treated passage can generate sufficient helicity to bring down the RRT by 36% without generating any additional pressure drop. The swirl flow adds azimuthal instability which increase vortex formations in the passage. The induced helical flow in the domain provokes more linked vortices, which may act as self-cleaning mechanism to the arterial wall. © 2018, © 2019 Informa UK Limited, trading as Taylor & Francis Group.Item Transient analysis of upstream wake inside turbine blade passage with purge flow(Elsevier Masson SAS 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2020) Babu, B.; 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 (also known as purge flow) with the mainstream flow can alter the flow characteristics of turbine blade passage. This paper presents numerical investigation of interaction between ejected purge flow and mainstream flow in the presence of upstream disturbances/wakes. Steady as well as unsteady simulations are carried out using Reynolds Averaged Navier Stokes equations and SST turbulence model. The numerical results are validated with experimental measurements obtained at the blade exit region using an L shaped 5 hole probe and Scanivalve. Upstream wakes are generated by a circular cylinder, kept upstream of blade leading edge at different pitch-wise positions. For transient analysis cylinders are kept at stagnation line (STW) and middle of the blade passage (MW). The analysis reveals the interaction effects of two more additional vortices, viz. the cylinder vortex (Vc) and the purge vortex (Vp). Steady state analysis shows an increase in the underturning at blade exit due to the squeezing of the pressure side leg (PSL) of horse shoe vortex towards the pressure surface by the cylinder vortices (Vp). The unsteady analysis reveals the formation of filament shaped wake structures which breaks into smaller vortical structures at the blade leading edge for STW configuration. These filaments lead to the formation of additional pressure surface vortices. On the contrary, in MW configuration, the obstruction created by the purge flow causes the upper portion of cylinder vortices bend forward, creating a shearing action along the spanwise direction. In MW configuration, the horse shoe vortices generated from the upstream cylinder are broken by the purge vortex whereas in the STW configuration it slides over the purge vortex and move towards the suction surface under the influence of the pitchwise pressure gradient. © 2019 Elsevier Masson SASItem 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 Energy and exergy analysis of solar air heater with non-uniform porous medium under varying solar intensity and radiation effects: a 3-D CFD study(Taylor and Francis Ltd., 2025) Nidhul, K.; Joshi, A.; Yadav, A.K.; Anish, S.The effect of a thin porous layer on the performance of a solar air heater (SAH) is investigated for both uniform and non-uniform configurations. 3-D computational fluid dynamic (CFD) simulations of SAH are performed for turbulent flow, and the transient performance with porous medium configurations is studied. A discrete-ordinate (D-O) model is employed, and diurnal variations of solar heat flux and inlet air temperature variations are considered in this study. The porous medium above the absorber plate significantly enhances the SAH's thermo-hydraulic performance parameter (THPP). The proposed configuration reduces the irreversibility in heat transfer and the possible hot spots that could occur when ribs are employed as artificial roughness, thereby enhancing the Nusselt number (Nu). The highest increment in Nu is obtained as 7.5 times, leading to maximum enhancement in THPP by 60% for descending porous medium compared to uniform porous medium configuration. Further, from the exergy analysis, the descending porous medium reported higher collector efficiency (66-70%). Owing to higher exergy gain and lower exergy losses, the energetic efficiency of the descending porous configuration is higher than the uniform porous configuration. Both thermo-hydraulic and exergy performance increases due to conduction and radiation within the porous medium apart from convection. © 2025 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.