N. Sitaram

Bio: N. Sitaram is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Static pressure & Axial compressor. The author has an hindex of 5, co-authored 9 publications receiving 75 citations.

Computational study of the effect of sweep on the performance and flow field in an axial flow compressor rotor

Abstract: In the recent past, experimental studies have shown some advantages of blade lean and sweep in axial compressors. As most of the experimental results are combined with other features, it is difficult to determine the effect of individual parameters on the performance of the compressor. The present numerical studies are aimed at understanding the performance and three-dimensional flow pattern within and at the exit of swept and unswept rotors. Three rotors, namely, unswept, 20° forward swept, and 20° backward swept rotors, are analysed with a specific intention of understanding the three-dimensional flow pattern within the rotors and also the pattern of the blade boundary layer flow. The analysis was done using a fully three-dimensional viscous CFD code CFX-5. Results indicated a reduction in pressure rise with sweep. Backward sweep adversely affects the stall margin. Forward sweep changes the streamline pattern in such a way that the suction surface streamlines are deflected towards the hub and th...

A method of calibration of a seven-hole pressure probe for measuring highly three-dimensional flows

Abstract: In this paper, a non-nulling calibration method using a seven-hole pressure probe in the range of at intervals both in yaw and in pitch planes is developed and reported. Calibration is carried out in two stages, low angles (for the maximum centre hole pressure) and high angles (other cases). On the basis of the maximum probe pressure reading, the calibration region is divided into seven zones; one central zone and six side zones. The calibration coefficients are derived for each zone. For interpolation, a localized two-variable polynomial is used at each point with the calibration data surrounding it. Zone extension is another useful feature developed here, in which each boundary point of every zone is extended to the nearest calibration point of the adjacent zone. By doing so, for a measuring point falling in between the boundaries of two adjacent zones, one employs the extended zone boundary data for fitting a polynomial. In addition to calibration data, additional data are acquired in the calibration tunnel. These data are used as measured data and calibration curves of suitable zones are used to derive flow parameters. In general, the interpolation errors in flow angles are found to be within and the errors in total and static pressures are within 0.5% and 1% of the dynamic pressure respectively.

Effect of diffuser vane height and position on the performance of a centrifugal compressor

Abstract: The present paper reports experimental investigations on the effect of diffuser vane height and position on the performance of a low-speed centrifugal compressor. The diffuser vane height is systematically varied from 0.2 to 0.9 times the diffuser width. In addition, the effect of vane position is examined by fixing the partial vanes to the hub, shroud, or hub and shroud. The compressor performance is determined with these vanes in the vane and low solidity vane diffuser configurations. It is found that there is an optimum height for the diffuser vane height. In the present investigation, it is found to be 0.3 times the diffuser width. The effect of position of the partial vanes on the hub or shroud on the compressor performance is found to be negligible. However, when partial vanes are fixed on the hub and shroud staggered at half spacing, the compressor performance is improved substantially.

Performance and wall static pressure measurements on centrifugal compressor diffusers

Abstract: The results of experimental studies on performance and wall static pressure distribution in the diffuser passage of a low specie c speed centrifugal compressor are given. The performance tests were carried out with vaneless, vane and low-solidity vane diffusers at speeds of 2500, 3000 and 3500r/min. Diffuser wall static pressures measured at 3000r/min for four e ow coefe cients on the shroud and hub walls are reported. The peak energy coefe cient is maximum for the vane diffuser. The operating range of the low-solidity vane diffuser is wider than that of the vane diffuser. At high e ow coefe cients, the static pressure rise is substantially lower for the vane diffuser, as the incidence on the vane leading edge is very high. The low- solidity vane diffuser did not suffer a large drop in static pressure near the leading edge. The most probable reason may be the large area available in the low-solidity vane diffuser for e ow adjustment and weaker e ow separation zones on account of the lower number of vanes.

Investigations on low speed axial compressor with forward and backward sweep

Abstract: In the recent past, experimental studies have shown some advantages of blade lean and sweep in axial compressors. As most of the experimental results are combined with other features, it is difficult to determine the effect of individual parameters on the performance of the compressor. The present numerical studies are aimed at understanding the performance and three-dimensional flow pattern at the exit of swept and unswept rotors. Three rotors, namely; unswept, 200 forward swept and 200 backward swept rotors are analysed with a specific intention of understanding the pattern of the blade boundary layer flow. The analysis was done using a fully three-dimensional viscous CFD code CFX-5. Results indicated reduction in pressure rise with sweep. Backward sweep is detrimental as far as the performance near endwalls is considered. On the other hand total pressure loss in the wake in mid span region is less with backward sweep, which favours its application here. However, backward sweep adversely affects the stall margin. The ability of the forward sweep to deflect the streamlines towards hub gets diminished at low flow rates. Forward sweep changes the streamline pattern in such a way that the suction surface streamlines are deflected towards the hub and the pressure surface streamlines are deflected towards the casing. An opposite behaviour is observed in backward swept rotors.

Aerodynamic effects of blade sweep and skew in low-speed axial flow rotors at the design flow rate: An overview

Abstract: A detailed literature survey is presented herein in order to overview the aerodynamic impact of non-radial blade stacking techniques applied to axial flow fan and compressor rotors. The literature suggests a consensus that forward blade sweep and skew provides a means for the following advantages in the part load operational range of low-speed axial flow turbofan and compressor rotors: improvement of efficiency and performance, and extension of stall-free operating range. However, the published research results are rather diversified regarding the judgment of performance and loss modifying effects of sweep and skew at the design point. The current paper summarizes the major aerodynamic phenomena related to such blade stacking techniques, in order to contribute to a general reasoning of performance and efficiency modification at the design flow rate. Furthermore, it provides guidelines how to consider these phenomena in tailoring the blade geometry for potential efficiency gain and for achievement ...