Heat Transfer in the Laminar - Turbulent Transition Region at Elevated Flow Turbulence

2000 ◽  
Vol 31 (1-2) ◽  
pp. 17-20
Author(s):  
Eleonora Ya. Epik ◽  
E. P. Dyban ◽  
Tatyana T. Suprun
Keyword(s):  
Heat Transfer ◽  
Transition Region ◽  
Turbulent Transition ◽  
Flow Turbulence ◽  
Laminar Turbulent Transition

Opposing Mixed Convection Heat Transfer in the Inclined Flat Channel in a Laminar-Turbulent Transition Region

2010 ◽  
Author(s):  
Povilas Poskas ◽  
Robertas Poskas ◽  
Giedrius Drumstas
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Transition Region ◽  
Convection Heat Transfer ◽  
Density Stratification ◽  
Convection Heat ◽  
Flat Channel ◽  
Turbulent Transition ◽  
Mixed Convection Heat Transfer ◽  
Laminar Turbulent Transition

In this paper we present the results on experimental and numerical investigations of the local opposing mixed convection heat transfer in an inclined flat channel (φ = 60° from horizontal position) with symmetrical heating in the laminar-turbulent transition region. The experiments were performed in airflow (p = 0.2 and 0.4 MPa) in the range of Re from 1.5 · 103 to 5.3 · 104 and Grq up to 1.5 · 1010 and at the limiting condition qw1 ≈ qw2 ≈ const. The experimental data show similar tendencies in the heat transfer as it was revealed in vertical channel. It is already some difference in the local heat transfer for upper (stable density stratification) and bottom (unstable density stratification) walls. The data of the experimental investigations have been compared with the results of numerical modelling using Ansys Fluent 12.0 code. The modelling was performed using laminar and transition models for Rein = 3.1 · 103 and Grqin = 1.9 · 109 for the same conditions as during the experiment, i.e. with the same airflow pressure (0.4 MPa), velocity, and temperature at the inlet and heat flux at the walls of the flat channel with the same geometrical characteristics.

Assessment of the Impact of Laminar-Turbulent Transition on the Accuracy of Heat Transfer Coefficient Prediction in High Pressure Turbines

2006 ◽  
Author(s):  
Mahmoud L. Mansour ◽  
Khosro Molla Hosseini ◽  
Jong S. Liu ◽  
Shraman Goswami
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
High Pressure ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Cases ◽  
Turbine Cascade ◽  
High Pressure Turbine ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

This paper presents a thorough assessment for two of the contemporary CFD programs available for modeling and predicting nonfilm-cooled surface heat transfer distributions on turbine airfoil surfaces. The CFD programs are capable of predicting laminar-turbulent transition and have been evaluated and validated against five test cases with experimental data. The suite of test cases considered for this study consists of two flat plat cases at zero and non-zero pressure gradient and three linear-turbine-cascade test cases that are representative of modern high pressure turbine designs. The flat plate test cases are the ERCOFTAC T3A and T3C2, while the linear turbine cascade cases are the MARKII, the Virginia Polytechnic Institute (VPI), and the Von Karman Institute (VKI) turbine cascades. The numerical tools assessed in this study are 3D viscous Reynolds Averaged-Navier-Stokes (RANS) equations programs that employ a variety of one-equation and two-equation models for turbulence closure. The assessment study focuses on the one-equation Spalart and Allmaras and the two-equation shear stress transport K-ω turbulence models with the ability of modeling and predicting laminar-turbulent transition. The RANS 3D viscous codes are Numeca’s Fine Turbo and ANSYS-CFX’ CFX5. Numerical results for skin friction, surface temperature distribution and heat transfer coefficient from the CFD programs are compared to measured experimental data. Sensitivity of the predictions to free stream turbulence and to inlet turbulence boundary conditions is also presented. The results of the study clearly illustrate the superiority of using the laminar-turbulent transition prediction in improving the accuracy of predicting the heat transfer coefficient on the surfaces of high pressure turbine airfoils.

Drag-Reducing Flows in Laminar-Turbulent Transition Region

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Shu-Qing Yang ◽  
Donghong Ding
Keyword(s):  
Transition Region ◽  
Reynolds Shear Stress ◽  
Flow Characteristics ◽  
Physical Nature ◽  
Weighting Factor ◽  
Intermittent Flow ◽  
Mean Velocity ◽  
Turbulent Transition ◽  
Intermittency Factor ◽  
Laminar Turbulent Transition

This study makes an attempt to investigate Newtonian/non-Newtonian pipe flows in a laminar-turbulent transition region, which is an extraordinarily complicated process and is not fully understood. The key characteristic of this region is its intermittent nature, i.e., the flow alternates in time between being laminar or turbulent in a certain range of Reynolds numbers. The physical nature of this intermittent flow can be aptly described with the aid of the intermittency factor γ, which is defined as that fraction of time during which the flow at a given position remains turbulent. Spriggs postulated that a weighting factor can be used to calculate the friction factor, applying its values in laminar and turbulent states. Based on these, a model is developed to empirically express the mean velocity and Reynolds shear stress in the transition region. It is found that the intermittency factor can be used as a weighting factor for calculating the flow structures in the transition region. Good agreements can be achieved between the calculations and experimental data available in the literature, indicating that the present model is acceptable to express the flow characteristics in the transition region.

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