Generalization of νt-92 Turbulence Model for Shear-Free and Stagnation Point Flows

2000 ◽  
Vol 123 (1) ◽  
pp. 11-15 ◽  
Author(s):  
A. N. Secundov ◽  
M. Kh. Strelets ◽  
A. K. Travin
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Transport Model ◽  
Turbulence Models ◽  
Length Scale ◽  
Stagnation Line ◽  
Flow And Heat Transfer ◽  
Turbulence Length ◽  
The One ◽  
Turbulence Length Scale

The one-equation, eddy-viscosity transport model of Gulyaev, Kozlov, and Secundov, νt-92, is modified and supplemented by an equation for the turbulence length scale. The advantages of the model developed here are demonstrated by computing a shear-free “boundary layer” on a flat plate, and the flow and heat transfer near the forward stagnation line of a circular cylinder. Both cases are known to be challenging for conventional turbulence models.

The Effects of Freestream Turbulence, Turbulence Length Scale, and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
J. S. Carullo ◽  
S. Nasir ◽  
R. D. Cress ◽  
W. F. Ng ◽  
K. A. Thole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Surface Heat Transfer ◽  
Mach Numbers ◽  
Turbulence Length ◽  
Turbulence Length Scale

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitches of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at the exit Mach numbers of 0.55, 0.78, and 1.03, which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6×105, 8×105, and 11×105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared with the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

Darryl E. Metzger Memorial Session Paper: An Account of Free-Stream-Turbulence Length Scale on Laminar Heat Transfer

1995 ◽  
Vol 117 (3) ◽  
pp. 401-406 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Dominant Frequency ◽  
Length Scale ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Session Paper ◽  
Turbulence Length ◽  
Effective Intensity ◽  
Turbulence Length Scale

The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed that accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter that accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.

The Effects of Freestream Turbulence, Turbulence Length Scale and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

2007 ◽  
Author(s):  
J. S. Carullo ◽  
S. Nasir ◽  
R. D. Cress ◽  
W. F. Ng ◽  
K. A. Thole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Surface Heat Transfer ◽  
Mach Numbers ◽  
Turbulence Length ◽  
Turbulence Length Scale

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 × 105, 8 × 105, and 11 × 105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

A Computational Study of Convection Heat Transfer to CO2 at Supercritical Pressures in a Vertical Mini Tube

2004 ◽  
Author(s):  
S. He ◽  
P. X. Jiang ◽  
Yi-Jun Xu ◽  
Run-Fu Shi ◽  
W. S. Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Eddy Viscosity ◽  
Computational Study ◽  
Convection Heat Transfer ◽  
Turbulence Models ◽  
Vertical Tube ◽  
Convection Heat ◽  
Flow Acceleration ◽  
Turbulence Production ◽  
The One

Computational simulations of experiments on turbulent convection heat transfer of carbon dioxide at supercritical pressures in a vertical tube of diameter 0.948 mm have been carried out using low-Reynolds number eddy viscosity turbulence models. The simulations were able to reproduce the general features exhibited in the experiments. The modelling study has provided valuable information on the detailed flow and turbulence fields. It has been shown that for mini tubes such as the one used in the current study, the buoyancy effect is generally insignificant. Heat transfer can be significantly impaired when the heating is strong. This is due to the reduced turbulence production, induced by the flow acceleration which is in turn caused by strong heating.

scholarly journals Turbulence Intensity, Length Scale, and Heat Transfer Around Stagnation Line of Cylinder and Model Blade

1999 ◽  
Author(s):  
V. P. Maslov ◽  
B. I. Mineev ◽  
K. N. Pichkov ◽  
A. N. Secundov ◽  
A. N. Vorobiev ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbulence Models ◽  
Leading Edge ◽  
Circular Cylinders ◽  
Length Scale ◽  
Stagnation Line ◽  
Free Stream Turbulence ◽  
Wide Range

A hot-wire technique was used to measure turbulence characteristics in the vicinity of the stagnation line of circular cylinders and a turbine blade model (a chord length of 1 metre). Heat transfer intensity at the stagnation line of the cylinders was also measured by on-surface probes. The experiments were carried out in a wide range of the Reynolds number based on the blade leading edge/cylinder diameter, D (Re = 2.103–2.106) and integral length scale of free-stream turbulence, Le (Le = 0.1–10D) at two values of free stream turbulence intensity, Tu (Tu = 0.02 and 0.10). Along with the experimental data results of the 2D RANS computations are presented of the flow and heat transfer at the circular cylinder with the use of two turbulence models: a two-equation, k-ω SST, model of Menter, and a new two-equation, ν1-L, model developed in the course of the present study.

scholarly journals An Account of Free-Stream-Turbulence Length Scale on Laminar Heat Transfer

1994 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Dominant Frequency ◽  
Length Scale ◽  
Turbulence Parameter ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Turbulence Length ◽  
Effective Intensity ◽  
Turbulence Length Scale

The effect of length scale in free-stream turbulence is considered for heat transfer in laminar boundary layers. A model is proposed which accounts for an “effective” intensity of turbulence based on a dominant frequency for a laminar boundary layer. Assuming a standard turbulence spectral distribution, a new turbulence parameter which accounts for both turbulence level and length scale is obtained and used to correlate heat transfer data for laminar stagnation flows. The result indicates that the heat transfer for these flows is linearly dependent on the “effective” free-stream turbulence intensity.

Effect of Free-Stream Turbulence on Heat Transfer and Fluid Flow in a Transonic Turbine Stage

2006 ◽  
Author(s):  
F. Mumic ◽  
B. Sunden
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Turbulence Intensity ◽  
Rotational Speed ◽  
Free Stream ◽  
Length Scale ◽  
Turbine Stage ◽  
Free Stream Turbulence ◽  
Turbulence Length ◽  
Turbulence Length Scale

In the present work, a numerical study has been performed to simulate the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow for a transonic high-pressure turbine stage with tip clearance. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The focus is on turbine aerodynamics and heat transfer behavior at the mid-span location, and at the rotor tip and casing region. The results of the fully 3D CFD simulations are compared with experimental results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, the local Nusselt number increases, at the same turbulence length scale, as the turbulence intensity increases, and the location of the suction side boundary layer transition moves upstream towards the blade leading edge. Comparison of the different length scales at the same turbulence intensity shows that the stagnation heat transfer was significantly increased as the length scale increased. However, the length scale evidenced no significant effects on blade tip or rotor casing heat transfer. Also, the results presented in this paper show that the rotational speed in addition to the turbulence intensity and length scale has an important contribution to the turbine blade aerodynamics and heat transfer.

Numerical Investigation of Flow and Heat Transfer Characteristics in Wire-Wrap Tight Lattice 19-Rod Bundle

2013 ◽  
Author(s):  
Minggang Li ◽  
Jun Wang ◽  
Changhua Nie ◽  
Xiao Yan ◽  
Yanping Huang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Heat Transfer Characteristics ◽  
Transfer Velocity ◽  
Transfer Characteristics ◽  
Rod Bundle ◽  
Flow And Heat Transfer ◽  
Tight Lattice

Flow and heat transfer characteristics in wire-wrap tight lattice rod bundle have been investigated through CFD code ANSYS CFX 13.0. The bundle consists of 19 fuel rods with triangular tight lattice configuration. The rod ratio of rod pitch to rod diameter is 1.167. Four wires with a diameter of 0.5 mm are helically wrapped on the surface of each fuel rod. The ratio of wire-wrap helical pitch to the rod diameter is varied from 27.5 to 52.5. Through simulating wire-wrap 3-rod bundle with tetrahedron and hexahedron grid systems, the grid system which applies to simulating the wire-wrap tight lattice rod bundle has been obtained. The predicted results of eddy viscosity based turbulence models (k–ε, SST) and Reynolds stress turbulence models (BSL, SSG) are compared with each other and several experimental correlations for friction factor and Nusselt number. The predicted results of all the turbulence models are almost the same in some respects, but the friction factor predicted by the eddy viscosity models is higher than that predicted by the RSM. The effect of wire-wrap on pressure drop, friction factor, secondary flow, heat transfer, velocity distribution and temperature distribution in different subchannels (interior, edge and corner) has been analyzed by comparing with those of the bare rod bundle. The effect of wire-wrap pitch on the flow and heat transfer characteristics has also been studied.

Effects of Freestream Turbulence Intensity, Turbulence Length Scale, and Exit Reynolds Number on Vane Endwall Secondary Flow and Heat Transfer in a Transonic Turbine Cascade

2020 ◽  
Author(s):  
Zhigang Li ◽  
Bo Bai ◽  
Luxuan Liu ◽  
Jun Li ◽  
Shuo Mao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Secondary Flow ◽  
Turbulence Intensity ◽  
Thermal Load ◽  
Secondary Flows ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Turbulence Length ◽  
Turbulence Length Scale

Abstract In gas turbine engines, the first-stage vanes usually suffer harsh incoming flow conditions from the combustor with high pressure, high temperature and high turbulence. The combustor-generated high freestream turbulence and strong secondary flows in a gas turbine vane passage have been reported to augment the endwall thermal load significantly. This paper presents a detailed numerical study on the effects of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the endwall secondary flow pattern and heat transfer distribution of a transonic linear turbine vane passage at realistic engine Mach numbers, with a flat endwall no cooling. Numerical simulations were conducted at a range of different operation conditions: six freestream turbulence intensities (Tu = 1%, 5%, 10%, 13%, 16% and 20%), six turbulence length scales (normalized by the vane pitch of Λ/P = 0.01, 0.04, 0.07, 0.12, 0.24, 0.36), and three exit isentropic Mach number (Maex = 0.6, 0.85 and 1.02 corresponding exit Reynolds number Reex = 1.1 × 106, 1.7 × 106 and 2.2 × 106, respectively, based on the vane chord). Detailed comparisons were presented for endwall heat transfer coefficient distribution, endwall secondary flow field at different operation conditions, while paying special attention to the link between endwall thermal load patterns and the secondary flow structures. Results show that the freestream turbulence intensity and length scale have a significant influence on the endwall secondary flow field, but the influence of the exit Reynolds number is very weak. The Nusselt number patterns for the higher turbulence intensities (Tu = 16%, 20%) appear to be less affected by the endwall secondary flows than the lower turbulence cases. The thermal load distribution in the arc region around the vane leading edge and the banded region along the vane pressure side are influenced most strongly by the freestream turbulence intensity. In general, the higher freestream turbulence intensities make the vane endwall thermal load more uniform. The Nusselt number distribution is only weakly affected by the turbulence length scale when Λ/P is larger than 0.04. The heat transfer level appears to have a significant uniform augmentation over the whole endwall region with the increasing Maex. The endwall thermal load distribution is classified into four typical regions, and the effects of freestream turbulence, exit Reynolds number in each region were discussed in detail.

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