Optimal Application of Riblets on Compressor Blades and Their Contamination Behavior

Abstract

During the last decades, riblets have shown a potential for viscous drag reduction in turbulent boundary layers. Several investigations and measurements of skin-friction in the boundary layer over flat plates and on turbomachinery-type blades with ideal riblet geometry have been reported in the literature. The question of where riblets must be applied on the surface of a compressor blade is still not sufficiently answered. In a first step, the profile loss reduction by ideal triangular riblets with a trapezoidal groove and a constant geometry along the surface on the suction and pressure sides of a compressor blade is investigated. The results show a higher potential on the profile loss reduction by riblets on the suction side. In a second step, the effect of laser-structured ribs on the laminar separation bubble and the influence of these structures on the laminar boundary layer near the leading edge are investigated. After clarifying the best choices where riblets should be applied on the blade surface, a strategy for locally adapted riblets is presented. The suction side of a compressor blade is laser-structured with segmented riblets with a constant geometry in each segment. The measured profile loss reduction shows the increasing effect on the profile loss reduction of this locally adapted structure compared to a constant riblet-geometry along the surface. Furthermore, the particle deposition on a riblet-structured compressor blade is investigated and compared to the particle deposition on a smooth surface. Results show a primary particle deposition on the riblet tips followed by an agglomeration. The particle deposition on the smooth surface is stochastic.

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

“…Klumpp, Meinke, Schröoder, Feldhaus, andKlocke (2009), Büttner andSchulz (2010) developed the rolling technique and electrodeposition technique, respectively, to manufacture riblets on turbine blades; total drag reduction of 4.7% and 4.9% were obtained, respectively. Furthermore, Lietmeyer, Oehlert, and Seume (2013) had clarified the best choices where riblets should be applied on the blade surface. The results showed a higher potential of the profile loss reduction by riblets on the suction side.…”

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

“…The experimental results of Lietmeyer et al [117] suggested the use of riblet tip that is as sharp as possible. A riblet angle of 30 • or even 45 • is technologically feasible according to Bechert et al [102].…”

“…According to Bechert et al [102], a trapezoidal riblet shape has a better drag reduction than a v-type riblet shape. Recently, trapezoidal riblets have been used on axial compressor blades because they represent the best compromise between drag reduction and structural strength [117]. A recent review of the drag reduction performance of riblets, which was written by Dean and Bhushan [118], concluded that the blade-shaped riblets provide the optimum drag reduction; however, due to their fragile nature, trapezoidal or scalloped riblets are recommended.…”

“…Lietmeyer et al [117] suggested that the riblet geometry should be adapted locally to the flow conditions because high riblets near the blade leading edge increase friction due to earlier transition resulting from a roughness effect. Drag reduction potential outside the separation region was pointed out by Lietmeyer et al [117], but was not investigated.…”

“…Values of the dimensionless riblet spacing s + in the range of 15-17 have been suggested [99,117]. The riblet spacing must be small enough (s + < 30), or otherwise one streamwise vortex would fit into one groove between the riblets resulting in increased drag [102].…”