scholarly journals The Effect of the Gap Ratio on the Flow and Heat Transfer over a Bluff Body in Near-Wall Conditions

2022 ◽  
Vol 18 (1) ◽  
pp. 109-130
Author(s):  
Shaohua Zhai ◽  
Guannan Xi
Keyword(s):  
Heat Transfer ◽  
Bluff Body ◽  
Flow And Heat Transfer ◽  
Gap Ratio ◽  
Near Wall

Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sunil Patil ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Large Eddy Simulations ◽  
Internal Cooling ◽  
Mean Flow ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
Near Wall

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.

Computation of Flow and Heat Transfer in Two-Pass Channels With 60 deg Ribs

2001 ◽  
Vol 123 (3) ◽  
pp. 563-575 ◽  
Author(s):  
Yong-Jun Jang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Moment Closure ◽  
Closure Model ◽  
Second Moment ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Sharp Turn ◽  
Second Moment Closure ◽  
Near Wall

Numerical predictions of three-dimensional flow and heat transfer are presented for a two-pass square channel with and without 60 deg angled parallel ribs. Square sectioned ribs were employed along one side surface. The rib height-to-hydraulic diameter ratio e/Dh is 0.125 and the rib pitch-to-height ratio (P/e) is 10. The computation results were compared with the experimental data of Ekkad and Han [1] at a Reynolds number (Re) of 30,000. A multi-block numerical method was used with a chimera domain decomposition technique. The finite analytic method solved the Reynolds-Averaged Navier Stokes equation in conjunction with a near-wall second-order Reynolds stress (second-moment) closure model, and a two-layer k-ε isotropic eddy viscosity model. Comparing the second-moment and two-layer calculations with the experimental data clearly demonstrated that the angled rib turbulators and the 180 deg sharp turn of the channel produced strong non-isotropic turbulence and heat fluxes, which significantly affected the flow fields and heat transfer coefficients. The near-wall second-moment closure model provides an improved heat transfer prediction in comparison with the k-ε model.

Flow and Heat Transfer in a Rotating Square Channel With 45° Angled Ribs by Reynolds Stress Turbulence Model

2000 ◽  
Author(s):  
Yong-Jun Jang ◽  
Hamn -Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Convective Transport ◽  
Moment Closure ◽  
Closure Model ◽  
Time Step ◽  
Second Moment ◽  
Square Channel ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Near Wall

Numerical predictions of three -dimensional flow and heat transfer are presented for a rotating square channel with 45° angled ribs as tested by Johnson et al. (1994). The rib height-to-hydraulic diameter ratio (e/Dh) is 0.1 and the rib pitch-to-height ratio (P/e) is 10. The cross-section of the ribs has rounded edges and corners. The computation results are compared with Johnson’s et al. (1994) experimental data at a Reynolds number (Re) of 25,000, inlet coolant-to-wall density ratio (Δρ/ρ) of 0.13, and three rotation numbers (Ro) of 0.0, 0.12, 0.24. A multi-block numerical method has been employed with a near-wall second-moment turbulence closure model. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method. Pressure is computed using a hybrid SIMPLER/PISO approach, which satisfies the continuity of mass and momentum simultaneously at every time step. The second-moment solutions show that the secondary flows induced by the angled ribs, rotating buoyancy, and Coriolis forces produced strong non-isotropic turbulent stresses and heat fluxes that significantly affected flow fields and surface heat transfer coefficients. The present near-wall second-moment closure model provided an improved flow and heat transfer prediction.

scholarly journals Numerical Prediction of Flow and Heat Transfer in a Two-pass Square Channel with 90°Ribs

2001 ◽  
Vol 7 (3) ◽  
pp. 195-208 ◽  
Author(s):  
Yong-Jun Jang ◽  
Hamn-Ching Chen ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Moment Closure ◽  
Closure Model ◽  
Second Moment ◽  
Square Channel ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Sharp Turn ◽  
Near Wall

Numerical predictions of three-dimensional flow and heat transfer are presented for a two-pass square channel with°parallel ribs. Square sectioned ribs were employed along the one side surface. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.125 and the rib pitch-to-height ratio(P/e)is 10. The computation results were compared with the experimental data of Ekkad and Han (1997) at a Reynolds number (Re) of 30,000.A multi-block numerical method was used with a chimera domain decomposition technique. The finite analytic method solved the Reynolds-Averaged Navier-Stokes equation in conjunction with a near-wall second-order Reynolds stress (secondmoment) closure model, and a two-layerk − εisotropic eddy viscosity model. Comparing the second-moment and two-layer calculations with the experimental data clearly demonstrated that the rib turbulators and the 180°sharp turn of the channel produced strong non-isotropic turbulence and heat fluxes, which significantly affected the flow fields and heat transfer coefficients. The near-wall second-moment closure model provides an improved heat transfer prediction in comparison with thek − εmodel.

Numerical Investigation of the Compressible Flat-Plate Turbulent Boundary Layer with Extended GAO-YONG Turbulence Model

2013 ◽  
Vol 444-445 ◽  
pp. 416-422
Author(s):  
Yang Yang Tang ◽  
Zhi Qiang Li ◽  
Yong Wang ◽  
Ya Chao Di ◽  
Huan Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Empirical Coefficients ◽  
Near Wall

The extended GAO-YONG turbulence model is used to simulate the flow and heat transfer of flat-plate turbulent boundary layer, and the results indicate that GAO-YONG turbulence model may well describe boundary layer flow and heat transfer from near-wall region to far outer area, without using any empirical coefficients and near-wall treatments, such as wall-function or modified low Reynolds number model, which are used widely in all RANS turbulence models.

Algebraic Anisotropic Eddy Viscosity Model for Separated Flows of Internal Cooling Channels

2014 ◽  
Author(s):  
Weihong Li ◽  
Li Yang ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Separated Flows ◽  
Viscosity Model ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Eddy Viscosity Model ◽  
Flow And Heat Transfer ◽  
Turbulent Characteristics ◽  
Near Wall

A new algebraic anisotropic eddy viscosity model (AEVM) is developed to account for the anisotropic characteristics of flow fields for internal cooling channels in a gas turbine. The model consist of two parts: k and ε near wall modeling are improved to obtain precise near wall turbulent characteristics and eddy viscosity; anisotropic ratios are derived to account for anisotropy and further modify the normal Reynolds stresses by combining implicit algebraic stress model and isotropic eddy viscosity model. The new algebraic anisotropic eddy viscosity model is validated in two cases: 1) flow prediction of backward facing step, better results are obtained especially turbulent quantities, 2) flow and heat transfer predictions of internal channels with ribs, numerical reattachment length after each rib is more close to the measured value after anisotropic modification, and heat transfer prediction accuracy is increased by 6–10%. Results indicate the present model can be applied to flow and heat transfer prediction of separated flows in internal cooling channels efficiently.

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