The Effects of Incident Turbulence and Moving Wakes on Laminar Heat Transfer in Gas Turbines

1994 ◽  
Vol 116 (1) ◽  
pp. 23-28 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Boundary Layers ◽  
Gas Turbines ◽  
Free Stream ◽  
Turbulence Parameter ◽  
Constant Acceleration ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Good Agreement

The effect of free-stream turbulence and moving wakes on augmenting heat transfer in accelerating laminar boundary layers is considered. First, the effect of free-stream turbulence is re-examined in terms of a Nusselt number and turbulence parameter, which correctly account for the free-stream acceleration and a correlation for both cylinders in crossflow and airfoils with regions of constant acceleration is obtained. This correlation is then used in a simple quasi-steady model to predict the effect of periodically passing wakes on airfoil laminar heat transfer. A comparison of the predictions with measurements shows good agreement.

scholarly journals The Effects of Incident Turbulence and Moving Wakes on Laminar Heat Transfer in Gas Turbines

1992 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Free Stream ◽  
Cross Flow ◽  
Turbulence Parameter ◽  
Constant Acceleration ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Good Agreement

The effect of free-stream turbulence and moving wakes on augmenting heat transfer in accelerating laminar boundary layers is considered. First, the the effect of free-stream turbulence is re-examined in terms of a Nusselt number and turbulence parameter which correctly account for the free-stream acceleration and a correlation for both cylinders in cross flow and airfoils with regions of constant acceleration is obtained. This correlation is then used in a simple quasi-steady model to predict the effect of periodically passing wakes on airfoil laminar heat transfer. A comparison of the predictions with measurements shows good agreement.

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.

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 Influence of Deterministic Surface Roughness and Free-Stream Turbulence on Transitional Boundary Layers: Heat Transfer Distributions and a New Transition Onset Correlation

2021 ◽  
Author(s):  
Christoph Gramespacher ◽  
Matthias Stripf ◽  
Hans-Jörg Bauer
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Flat Plate ◽  
Boundary Layers ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Data Set ◽  
Length Scales ◽  
Free Stream Turbulence

Abstract Heat transfer measurements in transitional flat plate boundary layers subjected to surface roughness, strong pressure gradients and free stream turbulence are presented. The surfaces considered, consist of a smooth reference and twenty six deterministic surface topographies that vary in roughness element aspect ratio, height and density. They are designed to cover the full range of roughness regimes from smooth over transitionally rough to fully rough. For each surface, two pressure distributions, characteristic for a suction and a pressure side turbine vane, are investigated. Inlet Reynolds numbers range from 3.0 · 105 to 6.0 · 105 and inlet turbulence intensity is varied between 1% to 8%. Furthermore, different turbulence Reynolds numbers, i.e. turbulence length scales, are realized while the incident turbulence intensity is kept constant. Additionally, the turbulence intensity and Reynolds stress distributions in the free-stream along the flat plate are measured using x-wire probes. Results show a strong influence of roughness and turbulence intensity on the onset of transition. The new data set is used to develop an improved correlation considering the roughness height, density and shape as well as the turbulence intensity and turbulent length scales.

Calculation of Transitional Boundary Layers With an Improved Low-Reynolds-Number Version of the k–ε Turbulence Model

1994 ◽  
Vol 116 (4) ◽  
pp. 765-773 ◽  
Author(s):  
D. Biswas ◽  
Y. Fukuyama
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbine Rotor ◽  
Limiting Behavior ◽  
Free Stream Turbulence ◽  
Low Reynolds

Several well-known low-Reynolds-number versions of the k–ε models are analyzed critically for laminar to turbulent transitional flows as well as near-wall turbulent flows from a theoretical and numerical standpoint. After examining apparent problems associated with the modeling of low-Reynolds-number wall damping functions used in these models, an improved version of the k–ε model is proposed by defining the wall damping factors as a function of some quantity (turbulence Reynolds number Ret) that is only a rather general indicator of the degree of turbulent activity at any location in the flow rather than a specific function of the location itself, and by considering the wall limiting behavior, the free-stream asymptotic behavior, and the balance between production and destruction of turbulence. This new model is applied to the prediction of (1) transitional boundary layers influenced by the free-stream turbulence, pressure gradient, and heat transfer; (2) external heat transfer distribution on the gas turbine rotor and stator blade under different inlet Reynolds number and free-stream turbulence conditions. It is demonstrated that the present model yields improved predictions.

scholarly journals The Turbulence That Matters

1997 ◽  
Author(s):  
R. E. Mayle ◽  
K. Dullenkopf ◽  
A. Schulz
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbines ◽  
Free Stream ◽  
Transitional Flow ◽  
Stream Velocity ◽  
Length Scale ◽  
Effective Frequency ◽  
Large Wave ◽  
Free Stream Turbulence

A unified expression for the spectrum of turbulence is developed by asymptotically matching known expressions for small and large wave numbers, and a formula for the one-dimensional spectral function which depends on the turbulence Reynolds number Reλ is provided. In addition, formulas relating all the length scales of turbulence are provided. These relations also depend on Reynolds number. The effects of free-stream turbulence on laminar heat transfer and pre-transitional flow in gas turbines are re-examined in light of these new expressions using our recent thoughts on an ‘effective’ frequency of turbulence and an ‘effective’ turbulence level. The results of this are that the frequency most effective for laminar heat transfer is about 1.3U/Le, where U is the free-stream velocity and Le is the length scale of the eddies containing the most turbulent energy, and the most effective frequency for producing pre-transitional boundary layer fluctuations is about 0.3U/η where η is Kolmogorov’s length scale. In addition, the role of turbulence Reynolds number on stagnation heat transfer and transition is discussed, and new expressions to account for its effect are provided.

scholarly journals Calculation of Transitional Boundary Layers With an Improved Low-Reynolds Number Version of the k-ε Turbulence Model

1993 ◽  
Author(s):  
Debsish Biswas ◽  
Yoshitaka Fukuyama
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Turbine Rotor ◽  
Limiting Behavior ◽  
Free Stream Turbulence ◽  
Low Reynolds

Several well known low-Reynolds version of the k-ε models are analyzed critically for laminar to turbulent transtional flows as well as near wall turbulent flows from theoretical and numerical standpoint. After examining apparent problems associated with the modelling of low-Reynolds number wall damping functions used in these models, an improved version of k-ε model is proposed by defining the wall damping factors as a function of some quantity (turbulence Reynolds number Rt) which is only a rather general indicator of the degree of turbulent activity at any location in the flow rather than a specific function of the location itself, and by considering the wall limiting behavior, the free-stream asyptotic behavior, and the balnce between production and destruction of turbulence. This new model is applied to the prediction of 1) transitional boundary layers influenced by the free-stream turbulence, pressure gradient and heat transfer; 2) external heat transfer distribution on the gas turbine rotor and stator blade under different inlet Reynolds number and free-stream turbulence conditions. It is demonstrated that the present model yield improved predictions.

Sign in / Sign up

Export Citation Format

Share Document