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, 20 0 forward swept and 20 0 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.

Stall characteristics and tip clearance effects in forward swept axial compressor rotors

“…4 compares the spanwise variation of total pressure rise coefficient (ψ o ) from present CFD study with the data measured from the experiments done by Govardhan et al [5] . Both the experimental data and CFD plot correspond to a tip gap of τ/ch = 0.007 and 0.54 flow coefficient.…”

“…Govardhan et al [5] studied flow behind unswept, 20 o forward swept rotor, 20° backward swept axial compressor rotors with specific intention of understanding the pattern of blade boundary layer flow. They found flow deflection towards hub regions with forward swept rotors.…”

“…The present investigation is aimed at understanding the nature of the three-dimensional flow in a low speed axial flow compressor, when the blades are swept in different schemes and for various tip clearance levels, so that the combined effect of sweep and tip clearance can τ/ch = 0.7% 0.5 mm Practical case; Govardhan et al [5] used this clearance in their experiments.…”