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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 the pressure surface streamlines are deflected towards the casing. An opposite behaviour is observed in the backward swept rotors. High axial velocities reduce the secondary losses near the hub, resulting in a high pressure rise in forward swept rotor.

There are a number of performance indices for a turbomachine on the basis of which its strength is evaluated. In the case of axial compressors, pressure ratio, efficiency and stall margin are few such indices which are of major concern in the design phase as well as in the evaluation of performance of the machine. In the process of improving the blade design, 3D blade stacking, where the aerofoil sections constituting the blade are moved in relation to the flow. Tilting the blade sections to the flow direction (blade sweep) would increase the operating range of an axial compressor due to modifications in the pressure and velocity fields on the suction surface. On the other hand, blade tip gap, though finite, has great influence on the performance of a turbomachine. The present work investigates the combined effect of these two factors on various flow characteristics in a low speed axial flow compressor. The objective of the present paper is thereby confined to study the collective effects of sweep and tip clearance without attempting to suggest an outright new design. In the present numerical work, the performance of Tip Chordline Sweeping (TCS) and Axial Sweeping (AXS) of low speed axial compressor rotor blades are studied. For this, 15 computational domains were modeled for five rotor sweep configurations and three different clearance levels for each rotor. Through the results, 20°AXS rotor is found to be distinctive among all the rotors with highest pressure rise, higher operating range and less tip clearance loss characteristics. TCS rotors produced improved total pressure rise at the low flow coefficients when the tip gap is increased. Hence there is a chance that an “optimum” tip gap exists for the TCS rotors in terms of total pressure coefficient and operating range, while AXS rotors are at their best with the minimum possible clearance.

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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.

The present study attempts to reduce secondary flow losses by application of streamwise endwall fence. After comprehensive analysis on selection of objective function for secondary flow loss reduction, coefficient of secondary kinetic energy (CSKE) is selected as the objective function in this study. A fence whose height varies linearly from the leading edge to the trailing edge and located in the middle of the flow passage produces least CSKE and is the optimum fence. The reduction in CSKE by the optimum fence is 27% compared to the baseline case. The geometry of the fence is new and is reported for the first time. Idea of this fence comes from the fact that the size of the passage vortex (which is the prime component of secondary flow) increases as it travels downstream, hence the height of fence should vary as the objective of fence is to block the passage vortex from crossing the passage and impinging on suction surface of the blade. Optimum fence reduced overturning and underturning of flow by more than 50% compared to the baseline case. Magnitude and spanwise penetration of the passage vortex were reduced considerably compared to the baseline case.

Wells turbine is a self-rectifying air turbine capable of converting pneumatic power of the periodically reversing air stream in Oscillating Water Column (OWC) into mechanical energy. The Wells turbine has inherent disadvantages; lower efficiency, poorer starting characteristics, higher axial force and lower tangential force in comparison with conventional turbines. Guide vanes before and after the rotor suggest a means to improve the tangential force, hence its efficiency. In the present computational investigations, the performance of the Wells turbine is predicted for constant chord (CONC) rotor, variable chord (VARC) rotor and variable chord rotor using guide vanes on upstream and downstream side of rotor. The predicted values of pressure drop with flow coefficient shows almost a linear variation and are in agreement with the experimental results. Power coefficient obtained from the VARC rotor with and without guide vanes is more than the CONC rotor at all flow coefficients. Due to recovery of rotor exit kinetic energy by the downstream guide vanes, the pressure drop across the turbine has increased, resulting in higher energy transfer and consequently higher turbine efficiency in VARC rotor.

This article presents the study of Tip Chordline Sweeping (TCS) and Axial Sweeping (AXS) of low-speed axial compressor rotor blades against the performance of baseline unswept rotor (UNS) for different tip clearance levels. The first part of the paper discusses the changes in design parameters when the blades are swept, while the second part throws light on the effect of sweep on tip leakage flow-related phenomena. 15 domains are studied with 5 sweep configurations (0 • , 20• TCS, 30• TCS, 20• AXS, and 30• AXS) and for 3 tip clearances (0.0%, 0.7%, and 2.7% of the blade chord). A commercial CFD package is employed for the flow simulations and analysis. Results are well validated with experimental data. Forward sweep reduced the flow incidences. This is true all over the span with axial sweeping while little higher incidences below the mid span are observed with tip chordline sweeping. Sweeping is observed to lessen the flow turning. AXS rotors demonstrated more efficient energy transfer among the rotors. Tip chordline sweep deflected the flow towards the hub while effective positive dihedral induced with axial sweeping resulted in outward deflection of flow streamlines. These deflections are more at lower mass flow rates.