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.

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.

Prediction of compressible turbulent boundary layer via a symmetry-based length model

2018 ◽  
Vol 857 ◽  
pp. 449-468 ◽  
Author(s):  
Zhen-Su She ◽  
Hong-Yue Zou ◽  
Meng-Juan Xiao ◽  
Xi Chen ◽  
Fazle Hussain
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Layer Structure ◽  
Analytic Form ◽  
Algebraic Model ◽  
Length Function ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Reynolds Analogy ◽  
The Mean

A recently developed symmetry-based theory is extended to derive an algebraic model for compressible turbulent boundary layers (CTBL) – predicting mean profiles of velocity, temperature and density – valid from incompressible to hypersonic flow regimes, thus achieving a Mach number ($Ma$) invariant description. The theory leads to a multi-layer analytic form of a stress length function which yields a closure of the mean momentum equation. A generalized Reynolds analogy is then employed to predict the turbulent heat transfer. The mean profiles and the friction coefficient are compared with direct numerical simulations of CTBL for a range of$Ma$from 0 (e.g. incompressible) to 6.0 (e.g. hypersonic), with an accuracy notably superior to popular current models such as Baldwin–Lomax and Spalart–Allmaras models. Further analysis shows that the modification is due to an improved eddy viscosity function compared to competing models. The results confirm the validity of our$Ma$-invariant stress length function and suggest the path for developing turbulent boundary layer models which incorporate the multi-layer structure.

The Importance of Relative Wind Speed in Estimating Air–Sea Turbulent Heat Fluxes in Bulk Formulas: Examples in the Bohai Sea

2020 ◽  
Vol 37 (4) ◽  
pp. 589-603 ◽  
Author(s):  
Xiangzhou Song
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Speed ◽  
Bohai Sea ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Surface Currents ◽  
The Bohai Sea ◽  
Turbulent Heat Fluxes ◽  
Relative Wind

AbstractSea surface currents are commonly neglected when estimating the air–sea turbulent heat fluxes in bulk formulas. Using buoy observations in the Bohai Sea, this paper investigated the effects of near-coast multiscale currents on the quantification of turbulent heat fluxes, namely, latent heat flux (LH) and sensible heat flux (SH). The maximum current reached 1 m s−1 in magnitude, and a steady northeastward current of 0.16 m s−1 appeared in the southern Bohai Strait. The predominant tidal signal was the semidiurnal current, followed by diurnal components. The mean absolute surface wind was from the northeast with a speed of approximately 3 m s−1. The surface winds at a height of 11 m were dominated by the East Asian monsoon. As a result of upwind flow, the monthly mean differences in LH and SH between the estimates with and without surface currents ranged from 1 to 2 W m−2 in July (stable boundary layer) and November (unstable boundary layer). The hourly differences were on average 10 W m−2 and ranged from 0 to 24 W m−2 due to changes in the relative wind speed by high-frequency rotating surface tidal currents. The diurnal variability in LH/SH was demonstrated under stable and unstable boundary conditions. Observations provided an accurate benchmark for flux comparisons. The newly updated atmospheric reanalysis products MERRA-2 and ERA5 were superior to the 1° OAFlux data at this buoy location. However, future efforts in heat flux computation are still needed to, for example, consider surface currents and resolve diurnal variations.

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.

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.

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.

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.

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.

Heat Transfer Scaling Close to the Wall for Turbulent Channel Flows

2013 ◽  
Vol 65 (3) ◽  
Author(s):  
Chiranth Srinivasan ◽  
Dimitrios V. Papavassiliou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbulent Flow ◽  
Turbulent Heat Flux ◽  
Turbulent Heat Transfer ◽  
Wall Region ◽  
Turbulent Heat ◽  
Mean Temperature ◽  
Scaling Parameters ◽  
The Mean

This work serves a two-fold purpose of briefly reviewing the currently existing literature on the scaling of thermal turbulent fields and, in addition, proposing a new scaling framework and testing its applicability. An extensive set of turbulent scalar transport data for turbulent flow in infinitely long channels is obtained using a Lagrangian scalar tracking approach combined with direct numerical simulation of turbulent flow. Two cases of Poiseuille channel flow, with friction Reynolds numbers 150 and 300, and different types of fluids with Prandtl number ranging from 0.7 to 50,000 are studied. Based on analysis of this database, it is argued that the value and the location of the maximum normal turbulent heat flux are important scaling parameters in turbulent heat transfer. Implementing such scaling on the mean temperature profile for different fluids and Reynolds number cases shows a collapse of the mean temperature profiles onto a single universal profile in the near wall region of the channel. In addition, the profiles of normal turbulent heat flux and the root mean square of the temperature fluctuations appear to collapse on one profile, respectively. The maximum normal turbulent heat flux is thus established as a turbulence thermal scaling parameter for both mean and fluctuating temperature statistics.

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