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Internal Cooling of Hot Turbine Structures Z. G. Tari, L. Wang, B. Sundén Division of Heat Transfer, Department of Energy Sciences, Lund University Bengt. Sunden@energy. lth. se (B. Sundén ) Research Managers H. Abrahamsson, A. Borg, L. Ström Volvo Aero Corporation, SE-461 81, Trollhättan, Sweden

Part (1) Agenda § Introduction to turbine structures § Introduction to Liquid Crystal Thermography ( LCT ) - Result § Recent HT measurements § - HT measurement for smooth test section - HT measurements with surface-mounted ribs - Selected results - Conclusions ASME-ATI-UIT article published § Next step (s) TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 2

Part (1) Introduction to turbine structures 1. Fan section 2. Compressor section 3. Combustion section 1 §A specialization within Volvo Aero is internal turbine structures Turbine section 3 2 §Intermediate turbine structures Most engines have a structure between HP and LP turbines - Two complex structures: Hot vanes Cold load carrying structure Turbofan (GP 7000) engine LPT ”hot” liner HPT ”cold” strut Cool, limit the temperature, of the cold structure bearing shaft TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 3

Typical flows in internal cooling of turbine structures § Disturbances - Surface disturbances - Blocking obstacles § Injection effects Obstacles Ribs single/ double confined jet TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 4

Liquid Crystal Thermography (LCT) § LCT is an optical and noncontact measurement technique allowing temperature measurements of the entire or part of a surface with limited effect on the surface. § LCT is an economical technique TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 5

Part (1) Introduction to LC R 35 C 10 W Liquid crystal (LC) with an event temperature 35 °C and color bandwidth of 10 °C. § Below the event temperature, LC appears transparent. § As temperature rises through the bandwidth, LC turns R (red), G (green), and B (blue) sequentially. § As temperature exceeds the clearing point, LC reverts back to being transparent. TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences LC response to heating 6

Part (1) Result-calibration blue green red Hue – temperature calibration for R 35 C 10 W §Color –temperature relationship is effective between 35 and 44 °C. §The most sensitive region is between 36 and 42 °C corresponding to the green region. §The resolution in green region is 0. 1 °C. TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 7

Part (1) Experimental apparatus Dimension of channel : Wall thickness : 20 mm Internal cross section: 320 × 80 mm 2 Height: 80 mm Schematic of test rig TBL: thermal boundary layer TBL development 250 mm Measurement region ( fully developed TBL) 250 mm inlet 100 mm 150 mm 100 250 mm configuration of thermal test section outlet Heat foils Liquid crystals TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 8

Part (1) in TBL development Result Distribution of local center line Nusselt number for the TBL development TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 9

Part (1) in fully developed TBL Result Nusselt numbers for the smooth duct, fully developed TBL The experimental result is in good agreement with asymmetric heating correlation Experiment : TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 10

Part (1) ribs? Why separated shear layer hot spot recirculation reattachment redevelopment boundary layer rib downstream Conjectured flow pattern behind a rib The presence of ribs introduces separation, re-circulation, re-attachment and re-development zones, which reduce thermal resistance and locally contribute to enhancement of the heat transfer. The use of ribs gives rise to higher flow resistance and therefore higher pumping power. TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 11

Part Rib(1) parameters affecting heat transfer §Blockage ratio, i. e. , rib height to channel height §Rib pitch-to-height ratio ( p/e) §The shape of rib, e. g. , square , triangular, V- shaped, inclined , etc. §Rib configuration and arrangement, i. e. , staggered or in-line. §Solid ribs or perforated ribs §Number of ribbed walls and the aspect ratio of the channel. TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 12

Part (1) HT measurements with ribs Arrangements of ribs ( top side ) inlet outlet 58 mm 209. 84 86. 03 mm 1. rib in upstream inlet 100. 5 mm 2. rib in middle p/e = 10. 1 p/e =11. 2 p/e = 20. 98 outlet 58 mm 88. 6 mm 98. 25 mm 4. ribs at upstream & middle Dimension of rib: Height (e) : 11 mm Length : 320 mm Cross section : 21 × 11 mm 2 85. 86 mm 100. 5 mm 5. ribs at middle & downstream 209. 84 6. ribs at upstream & downstream Motivation: - To figure out the optimum arrangement to enhance heat transfer - To understand the flow physics associated with separation and reattachment induced by ribs TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 13

Results (1 rib) Part (1) Re = 100, 000 inlet 58 mm 209. 84 1. rib at upstream Max Nu ( reattachment point ) : 308. 57 , x = 58. 05 mm Nu: 213. 3 – 198. 9 86. 03 mm 100. 5 mm 209. 84 mm 2. rib at middle Maps of local Nusselt number distribution at Re = 100, 000 TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences Max Nu ( reattachment point ) : 311. 82 , x = 173. 5 mm 14

Results (2 ribs) Part (1) Re = 100, 000 p/e = 10. 1 Nu: 209. 76 – 227. 21 58 mm 88. 6 mm 98. 25 mm 4. ribs at upstream & middle Max Nu ( reattachment point ) : 325. 8, x = 148. 1 mm p/e = 20. 98 209. 84 mm 6. ribs at upstream & downstream Maps of local Nusselt number distribution for 2 ribs at Re = 100, 000 TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences Max Nu ( reattachment point ) : 297. 24, x = 65. 77 mm 15

Results (2 ribs) Part (1) Re = 100, 000 p/e =11. 2 Nu: 200. 86 – 189. 7 85. 86 mm 100. 5 mm 209. 84 mm 5. ribs at middle & downstream Map of local Nusselt number distribution for 2 ribs at Re = 100, 000 TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences Max Nu ( reattachment point ) : 281. 46, x = 172. 86 mm 16

Part (1) Results 2 Re = 100, 000 Nu / Nu 0 1. 8 Nu (upstream) Nu (middle) 1. 6 Nu (upstream & middle) 1. 4 Nu (upstream & downstream) Nu (middle & downstream) 1. 2 1 0 50 100 X [mm] 150 200 Distribution of local center-line Nusselt number for ribs in different arrangements The best arrangement was appeared for 2 ribs( upstream & middle ) TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 17

Part (1) Conclusions §Wide – band LCT with a bandwidth 10 °C was calibrated and applied to determine heat transfer coefficients in a smooth and ribbed rectangular duct. §The experimental results in the smooth duct gave confidence for that the wide-band LCT is a decent technique. § The recent experimental results with surface-mounted ribs indicated the importance of the rib location. §The maximum local Nusselt number occurred at the reattachment points. §The best arrangement appeared for p/e = 10. 1 §Due to the low resolution of the wide-band LCT, details in some regions could not be clearly demonstrated. §Complete uncertainty analysis of the measurement technique has been started and a correction method based on a heat balance approach will be developed. TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 18

Article to be published ASME-ATI-UIT 2010 Conference on Thermal and Environmental Issues in Energy Systems , Sorrento, Italy. Heat Transfer Measurements in a Rectangular Duct Using Hue-based Calibrated Wide-band Thermochromic Liquid Crystal TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 19

Part (1) step (s) Next ØDevelopment of measurement technique ØHeat transfer measurements Flow cases : - Ribs : Improvement in recent measurement (One concept will be to repeat the recent measurements with a narrow- band ( 5 °C bandwidth) - Obstacles , wake flows - Jets TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences 20

Part (1) THANK YOU FOR ATTENTION Your Comments are Welcomed TURBO POWER Linkoping University 2010 /Zahra G. Tari / LU / Dep. of Energy Sciences