Progress in the Computation of Turbulent Heat Transfer in Massively Separated Flows

2013 ◽  
Author(s):  
B. A. Younis ◽  
B. Arnold ◽  
P. Weihing ◽  
B. Weigand
Keyword(s):  
Heat Transfer ◽  
Heat Fluxes ◽  
Separated Flows ◽  
Turbulent Heat Transfer ◽  
Periodic Flow ◽  
Turbulent Heat ◽  
Fluctuating Pressure ◽  
Massively Separated Flows ◽  
Turbulent Heat Fluxes ◽  
Heated Channel

The paper reports on work in progress aimed at improving the prediction of heat transfer in turbulent separated flows. The cases considered here are the flow over a heated backward-facing step, and the periodic flow in a heated channel with square ribs. The predictions were obtained using two models not hitherto employed in these flows: a Reynolds-stress transport closure in which the model for the fluctuating pressure-strain correlations that satisfies the requirement of model objectivity while not requiring wall-damping functions, and a model for the turbulent heat fluxes that is explicit, algebraic and correctly allows for these fluxes to depend on the gradients of mean temperature and velocity. Both models have previously given good predictions in attached shear flows and the objective of this work was to determine whether this improvement carries over to separated flows. It was found that distinct improvements in the prediction of skin friction and Nusselt number can only be obtained by extending the models so as to allow the computations to extend through the viscous sub-layer directly to the wall.

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.

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.

Near-Wall Turbulent Heat Transfer at Prandtl Numbers 1 to 54

2002 ◽  
Author(s):  
Robert Bergant ◽  
Iztok Tiselj ◽  
Gad Hetsroni
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Reynolds Number ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes ◽  
Fully Developed Turbulent Flow ◽  
Prandtl Numbers ◽  
Weak Influence

Direct Numerical Simulation (DNS) of fully developed turbulent flow in a flume was used to study the heat transfer near the wall. The Reynolds number has very weak influence on the turbulent heat transfer statistics (mean temperature, RMS-fluctuations, turbulent heat fluxes), therefore our goal was to analyze the influence of the increasing Prandtl number. Three different studies were performed at three different Prandtl numbers (Pr = 1, Pr = 5.4 and Pr = 54) at the same friction Reynolds number Reτ = 171. It should be emphasized that simulation with Pr = 54 cannot be called DNS due to the unresolved smallest thermal scales but results are in expected regions anyway. The obtained results at various Prandtl numbers also allowed us to make some predictions (RMS-fluctuations) for intermediate Prandtl numbers.

Prediction of Turbulent Heat Transfer in Rotating and Nonrotating Channels With Wall Suction and Blowing

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
B. A. Younis ◽  
B. Weigand ◽  
A. Laqua
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Algebraic Model ◽  
Heat Fluxes ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Wall Suction ◽  
Suction And Blowing

This paper reports on the prediction of heat transfer in a fully developed turbulent flow in a straight rotating channel with blowing and suction through opposite walls. The channel is rotated about its spanwise axis; a mode of rotation that amplifies the turbulent activity on one wall and suppresses it on the opposite wall leading to reverse transition at high rotation rates. The present predictions are based on the solution of the Reynolds-averaged forms of the governing equations using a second-order accurate finite-volume formulation. The effects of turbulence on momentum transport were accounted for by using a differential Reynolds-stress transport closure. A number of alternative formulations for the difficult fluctuating pressure–strain correlations term were assessed. These included a high turbulence Reynolds-number formulation that required a “wall-function” to bridge the near-wall region as well as three alternative low Reynolds-number formulations that permitted integration through the viscous sublayer, directly to the walls. The models were assessed by comparisons with experimental data for flows in channels at Reynolds-numbers spanning the range of laminar, transitional, and turbulent regimes. The turbulent heat fluxes were modeled via two very different approaches: one involved the solution of a modeled differential transport equation for each of the three heat-flux components, while in the other, the heat fluxes were obtained from an explicit algebraic model derived from tensor representation theory. The results for rotating channels with wall suction and blowing show that the algebraic model, when properly extended to incorporate the effects of rotation, yields results that are essentially identically to those obtained with the far more complex and computationally intensive heat-flux transport closure. This outcome argues in favor of incorporation of the algebraic model in industry-standard turbomachinery codes.

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.

scholarly journals Three-point MEMS heat flux sensor for turbulent heat transfer measurement in internal combustion engines

2018 ◽  
Vol 20 (7) ◽  
pp. 696-705 ◽  
Author(s):  
Kazuhito Dejima ◽  
Osamu Nakabeppu ◽  
Yuto Nakamura ◽  
Tomohiro Tsuchiya ◽  
Keisuke Nagasaka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Standard Deviation ◽  
Heat Fluxes ◽  
Wall Heat Flux ◽  
Turbulent Heat Transfer ◽  
Heat Flux Sensor ◽  
Turbulent Heat ◽  
Mems Sensor ◽  
Flux Sensor

A heat flux sensor was developed with micro-electro-mechanical systems (MEMS) technologies for investigating turbulent heat transfer characteristics in engines. The sensor has three thin-film resistance temperature detectors (RTDs) of a square 315 µm on a side on a 900 µm diameter circle in rotational symmetry. The performances of the MEMS systems sensor were tested in an open combustion chamber and a laboratory engine. In the open chamber tests, it was revealed that the MEMS sensor can measure the wall heat fluxes reflecting flow states of gas phase. In addition, the noise was evaluated as 3.8 kW/m2 with the standard deviation against the wall heat flux of a few hundred kW/m2. From these results, it was proved that the MEMS sensor has the potential to observe turbulent heat transfer on the order over 10 kW/m2 in the engine. In the laboratory engine test, the wall heat flux for continuous 200 cycles was measured with a good signal-to-noise ratio. The noise was evaluated as 13.4 kW/m2 with the standard deviation despite the noisy environment. Furthermore, it was proved that the MEMS sensor has the comparable scale with the turbulence in the engine because the three adjacent detectors measured similar but different phase oscillations in the local instantaneous heat fluxes. In addition, a heat flux vector reflecting the state of the local instantaneous heat transfer was visualized by the adjacent three-point measurement. It is expected that the three-point MEMS sensor will be a useful tool for the engine heat transfer research.

DNS of Turbulent Heat Transfer in Channel Flow With Heat Conduction in the Solid Wall

2001 ◽  
Vol 123 (5) ◽  
pp. 849-857 ◽  
Author(s):  
Iztok Tiselj ◽  
Robert Bergant ◽  
Borut Mavko ◽  
Ivan Bajsic´ ◽  
Gad Hetsroni
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Channel Flow ◽  
Temperature Fluctuations ◽  
Heat Fluxes ◽  
Wall Turbulence ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Fluid Temperature

The Direct Numerical Simulation (DNS) of the fully developed velocity and temperature fields in the two-dimensional turbulent channel flow coupled with the unsteady conduction in the heated walls was carried out. Simulations were performed at constant friction Reynolds number 150 and Prandtl numbers between 0.71 and 7 considering the fluid temperature as a passive scalar. The obtained statistical quantities like root-mean-square temperature fluctuations and turbulent heat fluxes were verified with existing DNS studies obtained with ideal thermal boundary conditions. Results of the present study were compared to the findings of Polyakov (1974), who made a similar study with linearization of the fluid equations in the viscous sublayer that allowed analytical approach and results of Kasagi et al. (1989), who performed similar calculation with deterministic near-wall turbulence model and numerical approach. The present DNS results pointed to the main weakness of the previous studies, which underestimated the values of the wall temperature fluctuations for the limiting cases of the ideal-isoflux boundary conditions. With the results of the present DNS it can be decided, which behavior has to be expected in a real fluid-solid system and which one of the limiting boundary conditions is valid for calculation, or whether more expensive conjugate heat transfer calculation is required.

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