Performance Comparison of Straight and Curved Diffusers

Abstract

Experimental studies have been carried out to compare the performance of two dimensional straight and curved diffusers of same area ratio and effective divergence angle in the Reynolds number range of7.8 X 105 to 1.29 X 105. Free stream turbulence effects have.also been studied at the increased turbulence level to 3.4per cent. The results indicate that straight diffuser pressure recovery is slightly higher as compared to the curved diffusers. However, stream turbulence, which improves the pressure recovery in both cases, has been observed to have greater effect in case of curved diffuser. Boundary layer velocity profiles on the diffuser surfaces have also been presented at various streamwise stations. It is observed that the growth of inner surface boundary layer has a major effects on losses in case of a curved diffuser. Nomenclature

Effect of turning angle on performance of 2-D turning diffuser via Asymptotic Computational Fluid Dynamics

“…Turning angle () is one of important geometrical parameters that is deemed to influence significantly the performance of turning diffuser. Sullerey et al [13] found that the Cp of 55 o turning diffuser was slighly lower than a straight diffuser. It may however improve comparable to the performance of straight diffuser by applying the turbulent intensity of minimum 3.4%.…”

Flow characteristics of 3-D turning diffuser using particle image velocimetry

“…This can be achieved by employing turning diffusers in the fluid flow systems. A turning diffuser is characterised by its expansion directions into two types, namely, two dimensional (2-D) turning diffuser and three-dimensional (3-D) turning diffuser [1,2,3]. A geometric layout of a 90 o turning diffuser is shown in Fig.…”

“…The flow through a 90 o turning diffuser is complex, apparently due to the expansion and sharp inflexion introduced along the direction of flow. The inner wall is subjected to curvature-induced effects where under a strong adverse pressure gradient, the boundary layer on the inner wall is likely to separate, and the core flow tends to deflect toward the outer wall region [2,6]. Flow separation is basically undesirable as it would decrease the core flow area, induce the presence of secondary flow vortices and ultimately affect the flow uniformity [4].…”

Passive Effusion Cooling in a Rectangular S-Bend Diffuser

“…Among the studies of flow separation in curvature passages, Sullerrey et al [2] showed that a high pressure recovery was' obtained in a curved diffuser by testing it under highly turbulent flow conditions to suppress the flow separation generated by the adverse pressure gradient at the downstream section of the convex surface'. An investigation of flow separations at the first bend convex surface in an S-bend diffuser by Whitelaw and Yu [3] revealed that increased flow separation induced larger counterrotating vortices which led to greater distortion of outlet flow-field uniformity.…”