Turb4 Tip Cooling Effects of Guide Ribs on Heat Transfer Enhancement of an Internal Blade Tip Gongan Xie and Bengt Sundén Division of Heat Transfer, Department of Energy Sciences, Lund University, Lund Lieke Wang and Esa Utriainen Siemens Industrial Turbomachinery AB, Finspong

Fig. 2 A typical serpentine passage Introduction to Blade Tip Cooling Fig. 2 A typical serpentine passage Fig.1 Typical cooling techniques for a blade

Fig. 3 Sketch of flow pattern inside a serpentine channel Need to Be Improvement Separated flow regions associated with low heat transfer always occur at the corners in the turn region and downstream the turn along the inner wall. Fig. 3 Sketch of flow pattern inside a serpentine channel

Recent work; pin fins

Recent work; conjugated heat transfer

Recent work; dimples, protrusions .

Design Concept Smooth wall Guide rib Smooth wall with guide rib 7

Case I Smooth wall Tip-cap Rib Rib Smooth wall Coolant Guide Rib 1- partial coverage 8

Case II Smooth wall Tip-cap Rib Coolant Smooth wall Guide Rib 2-partial coverage 9

Main geometrical parameters Channel Aspect ratio = 1:2 (2.75 x 5.5) = 4 x 2.75/3 = 3.667 Tip clearance = 3.5 Inlet/outlet length = 32 Tip-cap = 5.5 x 6.5 Unit: inch Dh Rib Height = 0.5 (not full) (blockage rato = 2 x 0.5/2.75=36.4%) Thickness = 0.2 ReDh = 100,000~600,000

Flow Field Smooth wall Cross-section in the turn center Ribs “compress” the vortices and force them towards the tip-wall 11

Ribs “enlarge” low temperature region Tip Temperature Smooth wall Smooth channel Case I Case II In the first-pass tip Ribs “enlarge” low temperature region 12

Heat Transfer and Pressure Drop Smooth wall Case I: Heat Transfer increases: 20%~38% Pressure drop increases: around 15% Case II: Good Heat Transfer increases: 21%~53% Pressure drop decreases up to 12% 13

Heat Transfer and Pressure Drop Smooth wall Comparison of augmentation Properly designed guide vanes are suitable for improving heat transfer associated with less pressure drop, but is not the most effective way compared to the augmentation by surface modifications imposed on the tip directly. 14

Concluding Remarks Smooth wall 1) Guide ribs force vortices towards the to tip-wall. 2) Adding guide ribs in the turn region provides 20~50% higher tip heat transfer. 3) Guide ribs may reduce the pressure if designed and placed properly. 4) The augmentation by guide ribs is much smaller than that by a pin-fin tip. 5) Guide ribs increase blade weight slightly, while pin fins make the tip much heavier. 15

Next plan

Similar schemes but with full-height guide ribs Next plan Similar schemes but with full-height guide ribs The same height as channel height ( ribs connecting the leading wall and trailing wall) CFD simulations

Comments ?? Thanks for your attention！ Acknowledgement The research has been funded by the Swedish Energy Agency, Siemens Industrial Turbomachinery AB and Volvo Aero Corporation through the Swedish research program TURBO POWER, the support of which is gratefully acknowledged .