Nekkanti Sitaram

Bio: Nekkanti Sitaram is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Impeller & Centrifugal compressor. The author has an hindex of 6, co-authored 17 publications receiving 114 citations.

Computational Investigations on the Effects of Gurney Flap on Airfoil Aerodynamics

Abstract: The present study comprises steady state, two-dimensional computational investigations performed on NACA 0012 airfoil to analyze the effect of Gurney flap (GF) on airfoil aerodynamics using k-e RNG turbulence model of FLUENT. Airfoil with GF is analyzed for six different heights from 0.5% to 4% of the chord length, seven positions from 0% to 20% of the chord length from the trailing edge, and seven mounting angles from 30° to 120° with the chord. Computed values of lift and drag coefficients with angle of attack are compared with experimental values and good agreement is found at low angles of attack. In addition static pressure distribution on the airfoil surface and pathlines and turbulence intensities near the trailing edge are present. From the computational investigation, it is recommended that Gurney flaps with a height of 1.5% chord be installed perpendicular to chord and as close to the trailing edge as possible to obtain maximum lift enhancement with minimum drag penalty.

Computational investigation of impeller—diffuser interaction in a centrifugal compressor with different types of diffusers

Abstract: A computational study has been conducted to analyse the performance of a centrifugal compressor with different types of diffusers under various levels of impeller—diffuser interactions. Vaneless (VLD), vaned (VD), low solidity vaned (LSVD), and partial vaned diffusers (PVD) are used for this purpose. The study is carried out using commercial software ANSYS CFX. The interaction level is varied by varying the radial gap between the impeller and diffuser by keeping the diffuser vane at three different radial locations. Numerical simulations have been conducted for four different flow coefficients. At design flow coefficient maximum efficiency occurs when the leading edge is at R3 (ratio of radius of the diffuser leading edge to the impeller tip radius) = 1.10 for all vane-type diffuser configurations. At below design flow coefficient higher stage efficiency occurs when the diffuser vanes are kept far away (R3 = 1.15) and at above design flow coefficient R3 = 1.05 gives better efficiency. The highest ...

Effect of Reynolds Number on Aerodynamics of Airfoil with Gurney Flap

Abstract: Steady state, two-dimensional computational investigations performed on NACA 0012 airfoil to analyze the effect of variation in Reynolds number on the aerodynamics of the airfoil without and with a Gurney flap of height of 3% chord are presented in this paper. RANS based one-equation Spalart-Allmaras model is used for the computations. Both lift and drag coefficients increase with Gurney flap compared to those without Gurney flap at all Reynolds numbers at all angles of attack. The zero lift angle of attack seems to become more negative as Reynolds number increases due to effective increase of the airfoil camber. However the stall angle of attack decreased by 2° for the airfoil with Gurney flap. Lift coefficient decreases rapidly and drag coefficient increases rapidly when Reynolds number is decreased below critical range. This occurs due to change in flow pattern near Gurney flap at low Reynolds numbers.

Conjugate Heat Transfer Analysis on the Interior Surface of Nozzle Guide Vane with Combined Impingement and Film Cooling

Abstract: Abstract The effect of conjugate heat transfer is investigated on a first stage nozzle guide vane (NGV) of a high pressure gas turbine which has both impingement and film cooling holes. The study is carried out computationally by considering a linear cascade domain, having two passages formed between the vanes, with a chord length of 228 mm and spacing of 200 mm. The effect of (i) coolant and mainstream Reynolds numbers, (ii) thermal conductivity (iii) temperature difference between the mainstream and coolant at the internal surface of the nozzle guide vane are investigated under conjugate thermal condition. The results show that, with increasing coolant Reynolds number the lower conducting material shows larger percentage decrease in surface temperature as compared to the higher conducting material. However, the internal surface temperature is nearly independent of mainstream Reynolds number variation but shows significant variation for higher conducting material. Further, the temperature gradient within the solid thickness of NGV is higher for the lower conductivity material.

Techniques for aerodynamic and turbulence measurements in turbomachinery rotors

Abstract: Nonoptical techniques currently used to measure flows in turbomachine rotors are reviewed, with particular reference to the measurement of the three-dimensional mean velocity, turbulence intensity, Reynolds stresses, static and stagnation pressures, and blade surface measurements. The high level of sophistication of rotor flow measurement techniques is demonstrated. Rotating probe measurements are well suited for low- and moderate-speed turbomachinery, while stationary quick-response probes (hot-wire and pressure probes) are applicable both in low- and high-speed turbomachines. Hot-wire probes, blade pressure transducers, and telemetry systems will provide the urgently needed basic information on steady and unsteady flow through a blade passage, including blade boundary layer, shock configuration, leakage and secondary flows.