Stability And Efficiency Improvement Of Turbocharger Centrifugal Compressor By Blade Bowing

The interna l co mbustion e ngine energy sa ving is one o f the hot spots oftoday’s society, and turbocharger has become an important technica l measure forit. W ith the improvement of co mpressor pressure ratio as well as the wideningof the engine operating range, the compressor needs to have a broader range ofstable work and higher effic ie ncy. Expans ion o f stability and improveme nt ofeffic iency of the compressor has become the emphas is of turbocharger research.Drawing on research ideas of bowing b lade in the axia l compressor, thispaper has studied on centrifugal co mpressor bowing blades and their synergisticmechanis m coupled with cas ing treatment. Experiment a nd simulatio n wereapplied in paralle l. Experimental was used to get bowing compressor’sperforma nce curves, and then s imulation was used to analyze the mechanis m.The following conclus io ns have been drawn.Leading edge’s bowing has great influe nce on the MAP of compressor inhigh rotation speed. Negative bowing can increase compressor’s choke massflow a nd surge mass flow, while pos itive bowing has the opponent effect. Indesign rotation speed, negative bowing by2mm can improve choke mass flow by4.1%,and increase surge mass flow by3.9%. The flow margin remains unchanged. Bowingaffects the size of the compressor’s throat area, thereby affecting the choke massflow. Whe n near s urge, k inetic e nergy o f secondary flow migrating to the tip ofblade is s ma ll. Negative bowing b lade forms a saddle point at the top of theblade leading edge. The separation line at saddle point exacerbates low energyfluid’s accumulatio n near tip. In additio n, negative bowing greatly enhances theseparation bubble at pressure surface’s tip, and increases low energy fluid’saccumulation. All above deteriorate the flow fie ld in negative bowing blade.Positive bowing weakens this separatio n bubble, improving the flow fie ld, sothat the surge flow decreases.Negative bowing has increased the effic ienc y of the maximum e ffic ienc ypoint a nd positive bowing decreases it. Negative bowing by2mm can impro vethe maximum e ffic iency by3.8%, and positive bowing by4mm will decrease itby2.0%. Tip leakage vortex constitutes most of the compressor’s flow loss. And low-energy fluid migrating fro m suction and pressure surface to the tip is thema in source of the tip leakage vortex. Whe n at maximum e ffic ienc y point, thekinetic e nergy of secondary flow immigrating to the top is high. Negativebowing forms a saddle point in the midd le of suction s urface, so that the suctionsurface’s low-energy fluid in the boundary la yer separates in the separation line,preventing migration o f the low-energy fluid to the tip, weakening the leakagevortex, thereby red ucing the loss of the compressor. Positive bowing s lightlyenha nces the migratio n of low-energy fluid to the tip o f the suctio n surface, andenhance the leakage vortex, thereby increasing the loss of compressor effic ie ncyslightly lower. Bowing has no s ignificant effect on secondary flow near thepressure side.The mechanis m of cas ing treatme nt and bowing’s impact on choke massflow is relative ly independent. In the addition of cas ing treatment, bowing’simpact on the c hoke mass flow is essentia lly the same. Casing treatmentweakens the bowing’s impact on co mpressor’s surge mass flow. Negativebowing by2mm can increase choke mass flow b y3.95%, and increase surgemass flow by1.97%(much s mall compare to that without casing treatment).Joining casing treatme nt, negative bowing’s deterioratio n of flow fie ld isweakened relative to radia l b lade. Coupled with cas ing treatme nt, ne gativebowing has fro m a saddle point in the midd le of b lade surface near surge, justlike in the designed point when without cas ing treatment. This saddle preventsthe blade root to restore low energy fluid migrating to tip to reduce the source ofthe vortex. Casing treatment a lso reduces the separation bubble in ne gativebowing blade’s pressure surface. But in the same mass flow, casing treatmenthas less improve ment of the positive bowing’s flow fie ld than radial blade. Inadditio n with casing treatme nt, negative bowing by2mm can improve the stab leflow margin by3.34%in design rotatio n speed. And the maximum power can beimproved by3.7%.