Aerodynamic Comparison between Increasing Cascade Pitch and Turning Angle in the Highly-Loaded Design

Theoretical and numerical study was carried out based on a linear turbine cascade(the Basic cascade)to compare the influences of the increased cascade pitch and turning angle in this paper.On one hand,the two highly-loaded designs both reduced the stability of flow field through enhancing adverse pressure gradient and span-wise pressure gradient of the fluid near suction surface.Therefore,the two highly-loaded designs would both result in thicker boundary layer and stronger secondary flow,so the secondary loss would be increased and more difficult to suppress in the highly-loaded cascades.On the other hand,the two highly-loaded designs showed different influences on the pitch-wise migration of the fluid near the endwall(cross flow)because of the different load enhancing mechanisms.In other words,the increased cascade pitch(TCx highly-loaded design)would delay the pitch-wise migration of the horseshoe vortex because of the increased channel width,while the increased turning angle(Turn highly-loaded design)would do the opposite because of the increased pitch-wise pressure gradient.As a result,the enhancement of the interaction between the fluid near the suction surface and the cross flow would be much stronger in the Turn highly-loaded design than the TCx highly-loaded design,and the span-wise developing tendencies of vortexes and fluid near the suction surface would show much stronger enhancing tendency in the former than the latter.