IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

The paper reports computational and experimental investigations carried out to control of laminar flow separation in LP turbine cascade blades at low Reynolds numbers. T106 LP turbine blade profile with a chord of 60 mm and blade spacing of 48 mm was used. The blade Zweifel loading factor was 1.03. Passive separation control device of Gurney flaps (GFs) of different shapes and sizes were used. Computations were carried out in Ansys-CFX. A two-equation eddy-viscosity turbulence model, shear stress transport (SST) was considered for all the computations along with gamma-theta (γ−θ) transition model. Computations were carried out for five different Reynolds numbers. Lift coefficient, total pressure loss coefficient, overall integrated loss coefficient and ratio of lift coefficient to overall integrated loss coefficient were used as a measure of aerodynamic performance for the cascade. From the computations, Flat and Quarter Round GFs of heights of 1.33% of chord were identified as the best configurations. Experiments in a seven bladed cascade were carried out for these configurations along with the basic configuration without GF at five Reynolds numbers. Experimental results agreed well with the computational results for these three cases at the five Reynolds numbers. © 2020. The American Society of Hematology. All Rights Reserved.

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Department of Mechanical Engineering

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Journal of Applied Fluid Mechanics

Computational and Experimental Investigations of Separation Control of LP Turbine Cascade Blades using Gurney Flaps

Rotor wakes shed from a compressor rotor impinge on downstream blades and is a major source of rotor-stator interaction noise and much research has been dedicated on wake attenuation. Serrated trailing edges is one such wake attenuation technique where the vortices produced at the serrated trailing edges enhance mixing and create a more uniform flow at stator inlet. The present paper investigates the effect of serrations on the trailing edge of a forced vortex axial fan blade. Experimental investigations were carried out at rotor outlet using pneumatic probes and fast response pressure sensors. It is found that total and static pressures reduce in serrated blades due to reduced turning and hence reduced work input. The absolute tangential velocity wake deficit decreases in serration valleys and improvement in axial velocity wake deficit is also found. Improvements as large as 19% and 18% decrease in absolute tangential velocity and axial velocity wake deficit are found at certain radii. The spanwise shape of the wake is altered by the serrations and a wake pattern undulating in the spanwise direction is observed. These are expected to bring down the circumferential variation of the velocity and its phase before entering the next row of blades and bring down the tonal noise. Copyright © 2016 by ASME.

GENERAL

ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE)

Experimental study of the effect of serrations on axial flow fan blade trailing edge

Performance enhancement in terms of stall margin increment, increased pressure rise coefficient and increased efficiency is of great need for low speed axial fans. Stacking line modifications in terms of sweep, skew, dihedral or combination of these, as well as blade tip geometry modifications are assumed to be one of the ways to achieve finite performance improvement. Non radial stacking of blade profiles modifies secondary flows, tip vortex effects, hub passage vortex and thus affects aerodynamic performance parameters such as stall margin, efficiency, pressure rise, blade loading. In literature many studies have confined to comparison of few cases which led to conflicting results as modification of stacking line may have different effects in different cases. In the present work, comparison of performance of axial fan rotor with three different blade configurations BSL (baseline), SWP (swept blade) and EXTN (swept blade with extended tip) are considered. The BSL configuration is designed on basis of non-free vortex design. The SWP configuration is obtained by shifting radial stacking line of the BSL in axial flow direction by 10° (Forward sweep). The EXTN configuration is obtained by extending tip profile on pressure surface as well as suction surface by 3% locally. Experiments have been conducted on these three configurations to study effects of these modifications on aerodynamic performance. The flow field has been surveyed using Kiel probe, Three hole pressure probe at many flow rates starting from fully open to fully closed. Unsteady flow analysis at exit of rotors of all configurations is carried out using fast response pressure probe. Experimental results show slight performance improvement in terms of increased stall margin, efficiency, as well as total pressure rise for SWP rotor as well as EXTN rotor compared to BSL rotor at low flow coefficients. Copyright © 2016 by ASME.

Effect of axial sweep and tip extension on performance of an axial fan

Stall margin improvement, though finite, has great influence on performance of a compressor and fan. Modification to the geometry of the recess and the recess vane used in the recess vane casing treatment approach would increase the operating range of an axial flow fan by removing the whirl component of circulatory flow near the blade tip. The present paper investigates the combined effect of variation of recess height and amount of blade chord exposure on flow characteristics and stall margin in low speed axial flow fan. Numerical simulations and modeling was performed using CFX 13.0 and ICEMCFD. The simulated pressure rise, work input and efficiency characteristics agreed well with the experimental data of a low sped fan obtained from the literature. The range of the flow rates which correspond to the stall free operating range of the untreated fan is compared with the same for the different modifications carried out to the geometry. The sensitivity of the operating range to the modifications is analyzed and the effect of recess vane geometry parameters on stall margin improvement is evaluated. Simulations suggest that within the ranges of parameters investigated stall margin improvement increases with both blade chord exposure and height. Copyright © 2013 by ASME.

Computational analysis of recess vane geometry modification in the casing treatment approach to enhance stall margin in axial flow fans

The experimental and numerical investigations of an axisymmetric jet issuing from a nozzle are reported here. Experiments have been carried out using hot-wire anemometer and theoretical predictions made using the finite volume technique. The k-ε models, with modified constants to take care of free shear flows, have been used for the physical modelling. The present investigations are aimed at comparing the predicted results with reported experimental measurements. The present numerical method along with k-ε model has been found to predict the flow quite well. Therefore, the k-ε model can be used with confidence for the evaluation of flow characteristics of similar turbulent flows.

Indian Journal of Engineering and Materials Sciences

Experimental and numerical investigation of an axisymmetric free jet

This paper outlines the combined effects of swirl and circumferential inlet flow distortion on the flow field of an axial flow fan rotor at design and off-design flow conditions. Distortion is simulated by a perforated screen of 120° extent and swirl is effected through inlet guide vanes. Experiments are conducted at rotor inlet and rotor exit by using miniaturised pneumatic pressure probes. Measurements are obtained in the radial direction from the hub to the tip and in the circumferential direction from 0° to 360°. Total pressures, flow angles and axial velocities are presented in the form of contours and pitch averaged values. At design flow coefficient, swirl causes deterioration in the performance of the fan in addition to that caused by distortion. The attenuation of the defect appears to be high in the presence of swirl.

Journal of the Institution of Engineers (India): Mechanical Engineering Division

Study of the Flow Field of an Axial Flow Fan Rotor Subjected to Circumferential Inlet Flow Distortion and Swirl

The combined effects of swirl and circumferential inlet flow distortion on the flow field of an axial flow fan stage are reported in this paper. The study involves measurements at the inlet of the rotor and exit of the rotor and stator at design and off design flow conditions. The study indicated that at the design flow condition, swirl had caused deterioration of the performance in addition to that caused by distortion. Pressure rise imparted in the distortion zone is higher than in the free zone. The attenuation of distortion is high in the presence of swirl.

Journal of Thermal Science

Investigations on an axial flow fan stage subjected to circumferential inlet flow distortion and swirl

This paper reports a study of the combined effects of swirl and circumferential inlet flow distortion on the flow field of an axial flow fan stage. The study, involves steady state measurements of the flow field at the rotor inlet, exit and the stator exit of the single stage axial flow fan subjected to circumferential inlet flow distortion and swirl. Flow field survey was done at two flow coefficients, namely, φ = 0.45 and φ = 0.285. The flow at the inlet to the rotor was measured using a three hole pressure probe and five hole pressure probes were used at the rotor and stator exits. The study indicated that at the design flow coefficient swirl had caused deterioration of the performance in addition to that caused by distortion. In addition, the attenuation of distortion was high in the presence of swirl. Copyright © 1996 by ASME.