A CFD Evaluation of Multiple RANS Turbulence Models for Prediction of Boundary Layer Flows on a Turbine Vane

2013 ◽  
Author(s):  
Thomas E. Dyson ◽  
David G. Bogard ◽  
Sean D. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Prandtl Number ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Turbulence Models ◽  
Experimental Measurements ◽  
Thermal Boundary Layer Thickness ◽  
Mean Velocity ◽  
High Turbulence

There is a growing trend toward the use of conjugate CFD for use in prediction of turbine cooling performance. While many studies have evaluated the performance of RANS simulations relative to experimental measurements of the momentum boundary layer, no studies have evaluated their performance in prediction of the accompanying thermal boundary layer. This is largely due to the fact that, until recently, no appropriate experimental data existed to validate these models. This study compares several popular RANS models — including the realizable k-ε and k-ω SST models — with a four equation k-ω model (“Transition SST”) and experimental measurements at selected positions on the pressure and suction sides of a model C3X vane. Comparisons were made using mean velocity and temperature in the boundary layer without film cooling under conditions of high and low mainstream turbulence. The best performing model was evaluated using modification of the turbulent Prandtl number to attempt to better match the data for the high turbulence case. Overall, the models did not perform well for the low turbulence case; they greatly over-predicted the thermal boundary layer thickness. For the high turbulence case, their performance was better. The Transition SST model performed the best with an average thermal boundary layer thickness within 15% of the experimentally measured values. Prandtl number variation proved to be an inadequate means of improving the thermal boundary layer predictions.

Momentum and Thermal Boundary-layer Thickness in a Stagnation Flow Chemical Vapor Deposition Reactor

1997 ◽  
Vol 12 (4) ◽  
pp. 1112-1121 ◽  
Author(s):  
David S. Dandy ◽  
Jungheum Yun
Keyword(s):  
Boundary Layer ◽  
Chemical Vapor Deposition ◽  
Layer Thickness ◽  
Vapor Deposition ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Numerical Solutions ◽  
Chemical Vapor ◽  
Square Root ◽  
Thermal Boundary Layer Thickness

Explicit expressions have been derived for momentum and thermal boundary-layer thickness of the laminar, uniform stagnation flows characteristic of highly convective chemical vapor deposition pedestal reactors. Expressions for the velocity and temperature profiles within the boundary layers have also been obtained. The results indicate that, to leading order, the momentum boundary-layer thickness is inversely proportional to the square root of the Reynolds number, while the thermal boundary-layer thickness is inversely proportional to the square root of the Peclet number. Values computed using the approximate expressions are compared directly with numerical solutions of the equations of motion and thermal energy equation, for a specific set of conditions typical of diamond chemical vapor deposition. Because values of the Lewis number do not vary significantly from unity for many different chemical vapor deposition systems, the expression derived here for thermal boundary-layer thickness may be used directly as an approximate concentration boundary-layer thickness.

An integral approach to the calculation of skin friction and heat transfer in the laminar flow of a high-Prandtl-number power-law non-Newtonian fluid past a wedge

1991 ◽  
Vol 69 (2) ◽  
pp. 83-89 ◽  
Author(s):  
G. Ramamurty ◽  
K. Narasimha Rao ◽  
K. N. Seetharamu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Prandtl Number ◽  
Skin Friction ◽  
Layer Thickness ◽  
Power Law ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Integral Approach ◽  
High Prandtl Number

An integral approach to the theoretical analysis for the skin friction of a non-Newtonian, power-law-fluid flow over a wedge is presented, when the inertia terms in the boundary-layer equations are small but need consideration. The method adopted for the solution of the equations considers an integrated average value of the inertia terms in the momentum equation. The values of the velocities and the boundary-layer thickness obtained from the hydrodynamic analysis are used for the calculation of the thermal-boundary-layer thickness. A linear velocity profile is assumed for the flow field within the thermal boundary layer as the fluids chosen for the analysis are high-Prandtl-number fluids. The results of the skin friction and the rates of the heat transfer are tabulated for a number of values of the flow behaviour index, n, varying from 0.05 to 5.0. This analysis is applicable to viscous polymer solutions having high Prandtl numbers.

scholarly journals KARAKTERISASI TEBAL LAPISAN BATAS FLUIDA NANO ZrO2 DI PERMUKAAN PEMANAS PADA PROSES KONVEKSI ALAMIAH

2015 ◽  
Vol 17 (3) ◽  
pp. 167
Author(s):  
V. Indriati Sri Wardhani ◽  
Henky P. Rahardjo
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Heat Source ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Cooling System ◽  
Thermal Boundary Layer Thickness ◽  
Cooling Fluid ◽  
Nano Fluid

ABSTRAK KARAKTERISASI Tebal Lapisan Batas Fluida Nano ZrO2 di permukaan pemanas pada Proses Konveksi Alamiah. Pendinginan sistem sangat dipengaruhi oleh proses perpindahan panas konveksi dari sumber panas ke fluida pendingin. Biasanya sebagai fluida pendingin digunakan fluida konvensional seperti air. Pendinginan suatu sistem dengan air tersebut dapat ditingkatkan dengan menggunakan fluida lain seperti fluida nano, yaitu fluida yang dibuat dari campuran air ditambah partikel dengan ukuran nano. Peneliti Batan Bandung telah membuat fluida nano ZrO2 dari bahan local. Telah dibuat pula peralatan eksperimen untuk mempelajari sifat-sifat termohidrolik fluida nano tersebut. Hal ini dilakukan untuk mendapatkan fluida nano yang tepat jika digunakan sebagai fluida pendingin sistem. Dalam penelitian ini dilakukan eksperimen untuk mempelajari sifat-sifat termohidrolik fluida nano ZrO2 yang terbuat dari campuran air dengan partikel nano ZrO2 yang berukuran 10-7-10-９nm dengan konsentrasi 1 gr/lt yang digunakan sebagai pendingin pada proses pendinginan konveksi alamiah. Proses tersebut sangat bergantung pada perubahan temperatur dari sumber panas ke fluida pendingin. Dalam pendinginan konveksi alamiah perubahan temperatur itu akan terjadi di dalam tebal lapisan batas termalnya. Oleh karena itu perlu diteliti tebal lapisan batas termal dari fluida nano ZrO2 yang selanjutnya juga dapat untuk menentukan kecepatan aliran lokalnya. Eksperimen dilakukan melalui proses perpindahan panas konveksi alamiah dengan memasukkan beberapa variasi daya pemanas, kemudian dilakukan pengukuran temperatur di beberapa titik secara horizontal untuk melihat distribusi temperaturnya. Hasil pengukuran distribusi temperatur tersebut dapat digunakan untuk menentukan tebal lapisan batas dan kecepatan alirannya. Diperoleh bahwa tebal lapisan batas termal dan kecepatan konveksi alamiah fluida nano ZrO2 tidak jauh berbeda dari fluida konvensional air. Kata kunci: Lapisan batas, fluida nano ZrO2, konveksi alamiah.  ABSTRACT CHARACTERIZATION of boundary layer thickness OF nano FLUID ZrO2 on natural convection process. Cooling system is highly influenced by the process of convection heat transfer from the heat source to the cooling fluid. The cooling fluid usually used conventional fluid such as water. Cooling system performance can be improved by using fluids other than water such as nano fluid that is made from a mixture of water and nano-sized particles. Researchers at Batan Bandung have made nano fluid ZrO2 from local materials, as well as experimental equipment for studying the thermohidraulic characteristics of nano fluid as the cooling fluid. In this study, thermohidraulic characteristics of nano fluid ZrO2 are observed through experimentation.  Nano fluid ZrO2 is made from a mixture of water with ZrO2 nano-sized particles of 10-7-10-9 nm whose concentration is 1 g/ltr. This nano fluid is used as coolant in the cooling process of natural convection. The natural convection process depends on the temperature difference between heat source and the cooling fluid, which occur in the thermal boundary layer. Therefore it is necessary to study the thermal boundary layer thickness of nano fluid ZrO2, which is also able to determine the local velocity. Experimentations are done with several variation of the heater power and then the temperature are measured at several horizontal points to see the distribution of the temperatures. The temperature distribution measurement results can be used to determine the boundary layer thickness and flow rate. It is obtained that thermal boundary layer thickness and velocity of nano fluid ZrO2 is not much different from the conventional fluid water. Keywords: Boundary layer, nanofluid ZrO2, natural convection.

Effects of temperature-dependent viscosity and thermal conductivity on mixed convection flow along a magnetized vertical surface

2016 ◽  
Vol 26 (5) ◽  
pp. 1580-1592 ◽  
Author(s):  
Ashraf Muhammad ◽  
Ali J Chamkha ◽  
S Iqbal ◽  
Masud Ahmad
Keyword(s):  
Magnetic Field ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Prandtl Number ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Content Type ◽  
Variation Parameter ◽  
Momentum Boundary Layer

Purpose – The purpose of this paper is to report a numerical solution for the problem of steady, two dimensional boundary layer buoyant flow on a vertical magnetized surface, when both the viscosity and thermal conductivity are assumed to be temperature-dependent. In this case, the motion is governed by a coupled set of three nonlinear partial differential equations, which are solved numerically by using the finite difference method (FDM) by introducing the primitive variable formulation. Calculations of the coupled equations are performed to investigate the effects of the different governing parameters on the profiles of velocity, temperature and the transverse component of magnetic field. The effects of the thermal conductivity variation parameter, viscosity variation parameter, magnetic Prandtl number Pmr, magnetic force parameter S, mixed convection parameter Ri and the Prandtl number Pr on the flow structure and heat transfer characteristics are also examined. Design/methodology/approach – FDM. Findings – It is noted that when the Prandtl number Pr is sufficiently large, i.e. Pr=100, the buoyancy force that driven the fluid motion is decreased that decrease the momentum boundary layer and there is no change in thermal boundary layer is noticed. It is also noted that due to slow motion of the fluid the magnetic current generates which increase the magnetic boundary layer thickness at the surface. It is observed that the momentum boundary layer thickness is increased, thermal and magnetic field boundary layers are decreased with the increase of thermal conductivity variation parameter =100. The maximum boundary layer thickness is increased for =100 and there is no change seen in the case of thermal boundary layer thickness but magnetic field boundary layer is deceased. The momentum boundary layer thickness shoot quickly for =40 but is very smooth for =50.There is no change is seen for the case of thermal boundary layer and very clear decay for =40 is noted. Originality/value – This work is original research work.

scholarly journals Numerical results for influence the flow of MHD nanofluids on heat and mass transfer past a stretched surface

2021 ◽  
Vol 10 (1) ◽  
pp. 28-38
Author(s):  
Nader Y. Abd Elazem
Keyword(s):  
Boundary Layer ◽  
Temperature Field ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Lewis Number ◽  
Numerical Results ◽  
Eckert Number ◽  
Concentration Profiles ◽  
Thermal Boundary Layer Thickness

Abstract Due to its significant applications in physics, chemistry, and engineering, some interest has been given in recent years to research the boundary layer flow of magnetohydrodynamic nanofluids. The numerical results were analyzed for temperature profile, concentration profile, reduced number of Nusselt and reduced number of Sherwood. It has also been shown that the magnetic field, the Eckert number, and the thermophoresis parameter boost the temperature field and raise the thermal boundary layer thickness while the Prandtl number reduces the temperature field at high values and lowers the thermal boundary layer thickness. However, if Lewis number is higher than the unit and the Eckert number increases, the concentration profiles decrease as well. Ultimately, the concentration profiles are reduced for the variance of the Brownian motion parameter and the Eckert number, where the thickness of the boundary layer for the mass friction feature is reduced.

The structure of a highly decelerated axisymmetric turbulent boundary layer

2021 ◽  
Vol 929 ◽  
Author(s):  
N. Agastya Balantrapu ◽  
Christopher Hickling ◽  
W. Nathan Alexander ◽  
William Devenport
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Convection Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Experiments were performed over a body of revolution at a length-based Reynolds number of 1.9 million. While the lateral curvature parameters are moderate ( $\delta /r_s < 2, r_s^+>500$ , where $\delta$ is the boundary layer thickness and r s is the radius of curvature), the pressure gradient is increasingly adverse ( $\beta _{C} \in [5 \text {--} 18]$ where $\beta_{C}$ is Clauser’s pressure gradient parameter), representative of vehicle-relevant conditions. The mean flow in the outer regions of this fully attached boundary layer displays some properties of a free-shear layer, with the mean-velocity and turbulence intensity profiles attaining self-similarity with the ‘embedded shear layer’ scaling (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592–642). Spectral analysis of the streamwise turbulence revealed that, as the mean flow decelerates, the large-scale motions energize across the boundary layer, growing proportionally with the boundary layer thickness. When scaled with the shear layer parameters, the distribution of the energy in the low-frequency region is approximately self-similar, emphasizing the role of the embedded shear layer in the large-scale motions. The correlation structure of the boundary layer is discussed at length to supply information towards the development of turbulence and aeroacoustic models. One major finding is that the estimation of integral turbulence length scales from single-point measurements, via Taylor's hypothesis, requires significant corrections to the convection velocity in the inner 50 % of the boundary layer. The apparent convection velocity (estimated from the ratio of integral length scale to the time scale), is approximately 40 % greater than the local mean velocity, suggesting the turbulence is convected much faster than previously thought. Closer to the wall even higher corrections are required.

The rough-wall turbulent boundary layer from the hydraulically smooth to the fully rough regime

2007 ◽  
Vol 580 ◽  
pp. 381-405 ◽  
Author(s):  
M. P. SCHULTZ ◽  
K. A. FLACK
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Outer Layer ◽  
Boundary Layer Thickness ◽  
Strong Support ◽  
Roughness Height ◽  
Rough Wall ◽  
Root Mean Square Roughness ◽  
Mean Velocity ◽  
Number Range

Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a three-dimensional rough surface geometrically similar to the honed pipe roughness used by Shockling, Allen & Smits (J. Fluid Mech. vol. 564, 2006, p. 267). The present work covers a wide Reynolds-number range (Reθ = 2180–27 100), spanning the hydraulically smooth to the fully rough flow regimes for a single surface, while maintaining a roughness height that is a small fraction of the boundary-layer thickness. In this investigation, the root-mean-square roughness height was at least three orders of magnitude smaller than the boundary-layer thickness, and the Kármán number (δ+), typifying the ratio of the largest to the smallest turbulent scales in the flow, was as high as 10100. The mean velocity profiles for the rough and smooth walls show remarkable similarity in the outer layer using velocity-defect scaling. The Reynolds stresses and higher-order turbulence statistics also show excellent agreement in the outer layer. The results lend strong support to the concept of outer layer similarity for rough walls in which there is a large separation between the roughness length scale and the largest turbulence scales in the flow.

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