Coherent Structures in Trailing-Edge Cooling and the Challenge for Turbulent Heat Transfer Modelling

2012 ◽  
Author(s):  
Hayder Schneider ◽  
Hans-Jörg Bauer ◽  
Dominic von Terzi ◽  
Wolfgang Rodi
Keyword(s):  
Heat Transfer ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Blowing Ratio ◽  
Gradient Diffusion

In the present paper, we test the capability of a standard Reynolds-Averaged Navier-Stokes (RANS) turbulence model to predict the turbulent heat transfer in a generic trailing-edge situation with a cutback on the pressure side of the blade. The model investigated uses a gradient-diffusion assumption with a scalar turbulent-diffusivity and constant turbulent Prandtl number. High-fidelity Large-Eddy Simulations (LES) were performed for three blowing ratios to provide reliable reference data. Reasonably good agreement between the LES and recent experiments was achieved for mean flow and turbulence statistics. For increasing blowing ratio, the LES replicated an also experimentally observed counter-intuitive decrease of the cooling effectiveness. In contrast, the model failed in predicting this behavior and yielded significant overpredictions. It is shown that the model cannot predict the strong upstream and wall-directed turbulent heat fluxes, which were found to cause the counter-intuitive decrease of the cooling effectiveness.

DNS of Heat Transfer Reduction in Viscoelastic Turbulent Channel Flows

2015 ◽  
Author(s):  
Kyoungyoun Kim ◽  
Radhakrishna Sureshkumar
Keyword(s):  
Heat Transfer ◽  
Channel Flow ◽  
Reduction Rate ◽  
Turbulent Channel Flow ◽  
Passive Scalar ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Uniform Heat Flux ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes

A direct numerical simulation (DNS) of viscoelastic turbulent channel flow with the FENE-P model was carried out to investigate turbulent heat transfer mechanism of polymer drag-reduced flows. The configuration was a fully-developed turbulent channel flow with uniform heat flux imposed on both walls. The temperature was considered as a passive scalar. The Reynolds number based on the friction velocity (uτ) and channel half height (δ) is 125 and Prandtl number is 5. Consistently with the previous experimental observations, the present DNS results show that the heat-transfer coefficient was reduced at a rate faster than the accompanying drag reduction rate. Statistical quantities such as root-mean-square temperature fluctuations and turbulent heat fluxes were obtained and compared with those of a Newtonian fluid flow. Budget terms of the turbulent heat fluxes were also presented.

Investigation of MHD RANS Modeling Base on DNS Database Under the Advanced Blanket Design Conditions Utilized Molten Salt

2014 ◽  
Author(s):  
Naoki Osawa ◽  
Yoshinobu Yamamoto ◽  
Tomoaki Kunugi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulence Model ◽  
Turbulent Channel Flow ◽  
Turbulent Heat Transfer ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Mhd Turbulence ◽  
Rans Modeling ◽  
Heat Transfer Degradation

In this study, validations of Reynolds Averaged Navier-Stokes Simulation (RANS) based on Kenjeres & Hanjalic MHD turbulence model (Int. J. Heat & Fluid Flow, 21, 2000) coupled with the low-Reynolds number k-epsilon model have been conducted with the usage of Direct Numerical Simulation (DNS) database. DNS database of turbulent channel flow imposed wall-normal magnetic field on, are established in condition of bulk Reynolds number 40000, Hartmann number 24, and Prandtl number 5. As the results, the Nagano & Shimada model (Trans. JSME series B. 59, 1993) coupled with Kenjeres & Hanjalic MHD turbulence model has the better availability compared with Myong & Kasagi model (Int. Fluid Eng, 109, 1990) in estimation of the heat transfer degradation in MHD turbulent heat transfer.

Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pipe Flow ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Pitch Ratio ◽  
The Mean

In the current investigation, we performed large eddy simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow in order to study the effects of periodically mounted square ribs on heat transfer characteristics. The ribs were implemented on a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models were used to model Reynolds stresses and turbulent heat flux terms. A constant and uniform wall heat flux was imposed on all the solid boundaries. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number is fixed at Pr = 0.71. The blockage ratio (BR) based on the pipe diameter and rib height is fixed with 0.0625, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology, we focus on its effects on the characteristics of turbulent heat transfer. Mean flow and temperature fields are presented in the form of streamlines and contours. How the surface roughness, manifested by the wall-mounted ribs, affects the mean streamwise-velocity profile was investigated by comparing the roughness function. Local heat transfer distributions between two neighboring ribs were obtained for the pitch ratios under consideration. The flow structures related to heat transfer enhancement were identified. Friction factors and mean heat transfer enhancement factors were calculated from the mean flow and temperature fields, respectively. Furthermore, the friction and heat-transfer correlations currently available in the literature for turbulent pipe flow with surface roughness were revisited and evaluated with the LES data. A simple Nusselt number correlation is also proposed for turbulent heat transfer in ribbed pipe flow.

STEADY STATE HEAT TRANSFER TO FULLY DEVELOPED TURBULENT FLOW IN A CURVED CHANNEL

1957 ◽  
Vol 35 (4) ◽  
pp. 410-434
Author(s):  
A. W. Marris
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Curved Channel ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
Angular Velocities ◽  
The Mean

A vorticity transfer analogy theory of turbulent heat transfer is developed first for the case of fully developed turbulent flow under zero transverse pressure and temperature gradients such as that in the annulus between concentric cylinders rotating with different angular velocities or in a "free vortex". The mean flow is assumed to be two-dimensional. The theory, which requires that the turbulence be statistically isotropic, yields a temperature distribution in agreement with experiment except in narrow regions immediately adjacent to the boundaries. An argument is given to show that the boundary layer thickness should be of the order of the reciprocal of the square root of the mean velocity, these boundaries are introduced, and Nusselt moduli are defined and their dependence on Reynolds and Prandtl numbers is investigated.The temperature distributions for the case of non-zero transverse temperature and pressure gradients, i.e. for the case of flow in a curved channel in which the fluid does not flow back into itself, are then obtained and the applicability of the simpler equations for zero transverse gradients to this case is investigated.

Numerical Study on the Effects of V-Shaped Rib Angle on Film Cooling Performance for Turbine Blade Trailing Edge

2018 ◽  
Author(s):  
Lin Ye ◽  
Cun-liang Liu ◽  
Hai-yong Liu ◽  
Qi-jiao He ◽  
Gang Xie
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Film Cooling ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio

The trailing edge of the high-pressure turbine blade presents significant challenges to cooling structure design. To achieve better cooling performance at turbine blade trailing edge, a novel ribbed cutback structure is proposed for trailing edge cooling, which has rib structures on the cutback surface for heat transfer enhancement. In this study, numerical simulations have been performed on the effects of V-shaped rib angle on the film cooling characteristics and flow physics. Three V-shaped rib angles of 30°, 45° and 60° are studied. The distributions of adiabatic cooling effectiveness and heat transfer coefficient are obtained under blowing ratios with the value of 0.5, 1.0 and 1.5 respectively. Due to the relatively small rib height, the effect of V-shaped ribs on the film cooling effectiveness is not notable. The disadvantage of V-shaped ribs mainly exhibits at the downstream area of cutback surface. With the increase of V-shaped rib angle, the film cooling effectiveness becomes lower, but the values are still above 0.9. The V-shaped ribs obviously enhance the heat transfer on trailing edge cutback surface. The area-averaged heat transfer coefficient of the V-rib case is higher than that of the smooth case by 26.3–41.2%. The 45° V-rib case has higher heat transfer intensity than the other two V-shaped rib cases under all the three blowing ratios. However, the heat transfer coefficient distribution of the 60° V-rib case is more uniform. The heat transfer intensity of the 30° V-rib case is higher in the downstream region than the other two cases, but lower in the upstream region in which the difference becomes smaller with the increase of blowing ratio. The 45° V-rib case and the 60° V-rib case both reach the maximum value of area-averaged heat transfer intensity under blowing ratio is 1.0. Under higher blowing ratio, the 30° V-rib case and the 45° V-rib case outperform 2.1% and 6.7% higher value relative to the 60° V-rib case respectively due to the smaller velocity gradient in the 60° V-rib case in the downstream.

An Explicit Algebraic Model for Turbulent Heat Transfer in Wall-Bounded Flow With Streamline Curvature

2006 ◽  
Vol 129 (4) ◽  
pp. 425-433 ◽  
Author(s):  
B. A. Younis ◽  
B. Weigand ◽  
S. Spring
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Algebraic Model ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Streamline Curvature ◽  
Turbulent Heat Fluxes ◽  
The Mean

Fourier’s law, which forms the basis of most engineering prediction methods for the turbulent heat fluxes, is known to fail badly in capturing the effects of streamline curvature on the rate of heat transfer in turbulent shear flows. In this paper, an alternative model, which is both algebraic and explicit in the turbulent heat fluxes and which has been formulated from tensor-representation theory, is presented, and its applicability is extended by incorporating the effects of a wall on the turbulent heat transfer processes in its vicinity. The model’s equations for flows with curvature in the plane of the mean shear are derived and calculations are performed for a heated turbulent boundary layer, which develops over a flat plate before encountering a short region of high convex curvature. The results show that the new model accurately predicts the significant reduction in the wall heat transfer rates wrought by the stabilizing-curvature effects, in sharp contrast to the conventional model predictions, which are shown to seriously underestimate the same effects. Comparisons are also made with results from a complete heat-flux transport model, which involves the solution of differential transport equations for each component of the heat-flux tensor. Downstream of the bend, where the perturbed boundary layer recovers on a flat wall, the comparisons show that the algebraic model yields indistinguishable predictions from those obtained with the differential model in regions where the mean-strain field is in rapid evolution and the turbulence processes are far removed from local equilibrium.

Numerical Investigation on Air Side Performance of Fin-and-Tube Heat Exchangers With Large Diameter Tubes and Large Number of Tube Rows

2011 ◽  
Author(s):  
Feng Zhou ◽  
David Geb ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Large Diameter ◽  
Turbulent Heat Transfer ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Tube Heat Exchanger ◽  
Ansys Cfx ◽  
Sst Model ◽  
Volume Method

In the present study, air-side turbulent heat transfer and friction characteristics of fin-and-tube heat exchangers with a large number of tube rows and large diameter of tubes are investigated numerically. Finite Volume Method based CFD software, Ansys CFX, was used as the 3-D Reynolds-averaged Navier-Stokes Solver. A k-ω based Shear-Stress-Transport (SST) model was used to predict the turbulent flow and heat transfer through the fin-and-tube heat exchanger coil. The effects of parameters such as Reynolds number, the number of tube rows, tube diameter, tube pitches and fin pitch are examined. In the end, correlations for the Nusselt number and friction factor which applicable to fin-and-tube heat exchangers with large number of large-diameter tube rows are proposed.

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