LARGE EDDY SIMULATION OF THE HEAT TRANSFER DUE TO SWIRLING AND NON-SWIRLING JET IMPINGEMENT Naseem Uddin, Sven Olaf Neumann, Bernhard Weigand

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1 ASME Summer Heat Transfer Conference LARGE EDDY SIMULATION OF THE HEAT TRANSFER DUE TO SWIRLING AND NON-SWIRLING JET IMPINGEMENT Naseem Uddin, Sven Olaf Neumann, Bernhard Weigand der Luft und Raumfahrt, Germany

2 Outline Motivation: Some Applications Basic Features of Non-Swirling & Swirling Impinging Jets Computational Setup - Inlet Condition - Solver - Grid etc. Results: - Velocity Distribution, Turb. Kinetic Energy - Heat Transfer Summary/Conclusions 2

3 Applications I Cooling of Hot Coffee: Cool Air Impingement 3

4 Applications II Electronic Component Cooling: Cooling of electronic components with surface enlargement 4

5 Applications III Cooling Concepts for Gas Turbine Blades: Lakshminarayana, 1996 RR: The jet engine 5

6 Non-Swirling Jet Impingement: Basic Features 6

7 Structure of Non-Swirling Jet Impingement Vortex ring Entrainment Secondary vortices Smoke-Visualization by Popiel & Trass (1981) 7

8 Swirling Jet Impingement Addition of Swirl leads generally to: Increased turbulence Swirl increases entrainment Increased mixing and spreading rate but, what remains at the target surface? 8

9 Nomenclature U r U ax U θ radial velocity axial velocity tangential velocity 9

10 Inlet Condition: Axial Velocity Distribution Convective Heat and Mass Transfer, 4th ed. Kays, Crawford & Weigand + superimposed fluctuations generated u ax /U b by a digital filter based procedure, Klein et al. (2003) r/r 10

11 Inlet Condition: Tangential Velocity Distribution Heat transfer and fluid flow in fields of centrifugal forces, vol-iii Khalatov, Avramenko & Shevchuk 2002 ϑ = fct( r) 11

12 Simulated Cases Case Swirl S Re Jet s Inlet T (K) I II III Re (swirling jet) = Re (non swirling jet) = 12

13 Grid Quality (Non-Swirling Jet) Non-Swirling Jet Impingement r+ = 36.3 (r θ)+= 20 Mean spacing in the Jet = 6.6η 5 Million CV 13

14 Grid Quality (Swirling Jet) Swirling Jet Impingement r+ = 27 (r θ)+= 20 Mean spacing in the Jet = 6η 6.4 Million CV 14

15 Numerical Method (LES) FASTEST (Flow Analysis Solving Transport Equations Simulating Turbulence) Space Discretisation: 2 Order (Central Difference) Time Discretisation: 2 Order (Crank-Nicolson Method) Coupling of pressure & velocity fields: SIMPLE Algorithm Computations on Intel cluster/cray Opteron Cluster/ NEC SX-8 Höchstleistungsrechenzentrum (HLRS), Structured hexahedral grids 15

16 Large Eddy Simulation (LES) Top-Hat Filtering Subgrid Model Dynamic Smagorinsky Model proposed by Germano et al. (1991) For Turbulent Flows Artificial inlet turbulence conditions proposed by Klein et al. (2003) Outlet BC Convective Subgrid Prandtl number 0.9 No Wall Model 16

17 Results: Instantaneous Velocity Distribution Re=23000 & S=0.0 (No Swirl) u 17

18 Results: Instantaneous Velocity Distribution S=0.4 (With Swirl) u 18

19 Results: Heat Transfer due to Non-Swirling Jet Nu/Re 2/ Giovaninni & Kim (2006) Fenot (2004) Baughn & Shimizu (1989) 0.20 Lee & Lee (1999) Baughn (1991) 0.15 Yan & Saniei (1998) LES (non-swirling jet) r/d 19

20 Results: Heat Transfer due to Swirling Jet (S=0.47) LES, Re=23000 S=0.47 Yan & Saniei Re=23000 S=0.47 (1998) Nu r/d 20

21 Results: Heat Transfer due to Swirling Jet Nu 220 LES, Re=23000, S=0 LES, Re=23000, S= Lee et al. (2002) Yan & Saniei (1998) 180 v2-f model (Yan & Kalvakota) (2006) r/d (S=0.2) 21

22 Velocity Distribution in Swirling Jet (S=0.2) 22

23 Turbulent Kinetic Energy (S=0.2) 23

24 Turbulent Kinetic Energy (S=0.47) 24

25 Summary/Conclusions 1. In case of the swirling jet high temperature fluid is trapped in a recirculation zone which causes the deterioration of the heat transfer. 2. The swirl gives no perceptible increase in the overall heat transfer for the H/D=2 case. 3. In case of high swirl number jet, the peak in radial distribution of Nusselt number is better correlated with the occurrence of maximum turbulent kinetic energy close to wall. However at small swirl number the peak in the Nusselt number radial distribution is correlated with the approaching velocity. Thank you very much for your attention! 25

26 Back Up

27 Phenomenological Complexities vs Grid Important : Grid resolution in shear layer Important: Grid Resolution in Wall jet region Laminar Jet Re < 300 Fully laminar 300 < R e<1000 Transition or semi-turbulent 1000 < Re <3000 Fully turbulent Re >3000 Source: R. Viskanta Impingment -Jet deflection with strong acceleration -Radial spreading and decceleration

28 Applications III Vertical take-off and landing aircrafts 28

29 Grid cross-section (non-swirling jet) 29

30 Grid cross-section (swirling jet) 30

31 Addition of Swirl to Jet Increased turbulence Swirl increases entrainment Increased mixing and spreading rate 31

32 Swirl Number 32

33 Heat Transfer due to swirling jet T j =293 K T j =300 K 33