Effects of residual riblets of impeller's hub surface on aerodynamic performance of centrifugal compressors

Abstract

In this article, the effects of residual riblets of impeller's hub surface on the aerodynamic performance of a compressor are studied in detail. Several accurate geometrical models of impellers after their hub surface are machined, with various tool passes are built. The number of tool passes for the hub surface finish of a single passage of the impeller is denoted by N. Meanwhile, a dimensionless parameter B max is introduced to characterize the size of the ribs of the arbitrary impeller, which is the percentage ratio rate of the maximum cusp height of the hub surface to the exit blade width. The geometrical models are numerically studied by solving the Reynolds averaged Navier-Stokes equations using the SST turbulent model. The predictions show that a group of secondary cross-stream vortices are generated by the interaction of streamwise vortices above the hub surface with riblets' tips. For the impeller researched in this article, with the decline of B max , the average viscous shear stress on the hub surface decreases gradually at first and then starts increasing and leveling off; accordingly, the polytropic efficiency of the compressor, on the contrary, increases gradually and then starts leveling off later. When B max comes to 0.58, the average viscous shear stress of the fluids on the hub surface reaches its minimum, and it is found that the polytropic efficiency of the compressor reaches a peak and stable value. The simulation results are validated against experimental data at the design Mu, and the maximum discrepancies are less than 3.8%.

Drag reduction within radial turbine rotor passages using riblets

“…Wall shear using riblets is reduced until reaching the rib height (h + = 19.3) where the wall shear is minimum, while increasing riblets height further leads to increase the wall shear. A similar trend for riblets performance within internal flows was spotted by Lei et al[1]…”

“…The improved understanding could lead to the introduction of intentional riblets that are increasingly becoming feasible with the fast development of three dimensional printing technology of components. Different studies have proved that smooth surfaces do not necessarily have less drag than rough surfaces [1,2,3,4]. Riblets are surface structures arranged in the streamwise direction to help in reducing wall shear stresses.…”

“…Riblets concept has been also applied to radial turbomachines. Where Lei et al [1] tested a centrifugal compressor with different machining residual riblets heights on the impeller hub. They found that using riblets decreases wall shear stress which reaches its minimum value for riblets of height 0.58 relative to impeller exit blade width.…”

“…The riblets concept has also been applied to radial flow turbomachinery by Lei and Cao 10 who studied numerically the flow within a centrifugal compressor with different riblets height and number attached to the impeller hub. They found that using riblets aligned in the stream-wise direction decreases wall shear stress by restricting the low-energy fluid motion from pressure side to suction side along the passage.…”

Computational fluid dynamic analysis of an unmanned amphibious aerial vehicle for drag reduction

“…Various riblets are incorporated on top of the canopy, as shown in Figure 8 to study the influence of wall shear stress due to skin friction (Pimenta et al, 1975;Petterson, 2006;Viswanath, 2002;Garc ıa-Mayoral and Jim enez, 2011;Lei and Lixin, 2015). The sizes of riblets are varied from 7 mm to 35 mm (Fu et al, 2017).…”