scholarly journals Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations

2003 ◽  
Author(s):  
Derek Liechty ◽  
Scott Berry ◽  
Brian Hollis ◽  
Thomas Horvath
Keyword(s):  
Boundary Layer ◽  
Comparison Of Methods ◽  
Edge Conditions ◽  
Boundary Layer Edge

Boundary-layer equations in the linear theory of thin elastic shells

1962 ◽  
Vol 269 (1339) ◽  
pp. 481-491 ◽  
Keyword(s):  
Boundary Layer ◽  
Elastic Shell ◽  
Three Dimensional ◽  
Boundary Layer Equations ◽  
Smooth Edge ◽  
Elasticity Equations ◽  
Edge Conditions ◽  
Isotropic Elasticity ◽  
Stress Boundary Conditions ◽  
Stress Boundary

Starting with the three-dimensional equations of classical isotropic elasticity, equations are obtained for boundary-layer effects near any smooth edge of an elastic shell. Solutions of these equations are combined with solutions of the equations of the 'interior’ problem so that any specified edge conditions in terms of stresses can be satisfied. The usual Kirchhoff stress boundary conditions for the major terms of the interior stresses are deduced from the analysis.

An Entropic Minimization Technique for Turbine Blade Profiles

2002 ◽  
Author(s):  
Ed Walsh ◽  
Mark Davies ◽  
Roy Myose
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Boundary Layers ◽  
Turbine Blade ◽  
Entropy Generation ◽  
Incompressible Flows ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimization Technique ◽  
Boundary Layer Edge

The optimization of the boundary layer edge velocity distribution may hold the key to the minimization of entropy generation in the boundary layers of turbomachinery blades. A preliminary optimization analysis in the laminar region of a non film cooled turbine blade is presented, which demonstrates the concept of how the entropy generation rate may be reduced by varying the boundary layer edge velocity distribution along the suction surface, whilst holding the work done by the blade constant. In the laminar region the analytical technique developed by Pohlhausen and others to predict the boundary layer momentum thickness in the presence of pressure gradients has been adopted to predict the entropy generated as described in other papers by the same authors. The result gives an expression for the entropy generation rate in terms of the boundary layer edge velocity distribution for incompressible flows. The boundary layer edge velocity distribution may then be represented as a polynomial with undefined variables. This allows a minimization technique to be used to minimize the entropy generation rate on these variables. Constraints are included to keep the work output constant and the diffusion low to avoid separation. In this analysis it is only the laminar region that is considered for minimization, thus it is necessary to ensure that the modified boundary layer edge velocity distribution does not undergo transition earlier than the baseline boundary layer edge velocity distribution. This is accomplished by considering transition and separation criteria available in the literature. The result of this analysis indicates that the entropy generation rate may be reduced in the laminar boundary layers by using this technique.

Development of a boundary layer parameters identification method for transition prediction with complex grids

2016 ◽  
Vol 231 (11) ◽  
pp. 2068-2084 ◽  
Author(s):  
Zihui Hao ◽  
Chao Yan ◽  
Ling Zhou ◽  
Yupei Qin
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Thermal Protection ◽  
Cross Flow ◽  
Parallel Execution ◽  
Boundary Layer Transition ◽  
Prediction Methods ◽  
Transition Prediction ◽  
Cross Flow Velocity ◽  
Boundary Layer Edge

Predicting boundary layer transition accurately is important to thermal protection and drag reduction of flight vehicles. Up to now, there has been many transition prediction methods. However, most of those methods need boundary layer parameters, which are difficult to obtain in massively parallel execution since some parameters are nonlocal variables, thus greatly limiting the application of those methods. A grid-reorder method is developed to obtain the boundary layer parameters, which is suitable for parallel computing in this paper. With the grid-reorder method the wall normal grid cells can be easily found, and two criteria are used to determine the boundary layer edge in the wall normal direction, then the boundary layer parameters such as boundary layer thickness, boundary layer momentum thickness, boundary layer edge velocity, cross-flow velocity, and so on, can be obtained accurately and efficiently. The method has been coupled to three transition prediction methods, the γ-Reθ model, the k-ω-γ model, and the transition correlations, to validate its effectiveness. For the γ-Reθ model, the cross-flow velocity is obtained with the grid-reorder method, then a cross-flow intermittency factor is developed and introduced into the model, and the inclined prolate spheroid case is used to test the performance of the model. For the k-ω-γ model, the grid-reorder method is applied to obtain the boundary layer edge velocity and the inflection point velocity which are of vital importance to form the second-mode timescale for hypersonic transition prediction. For the transition correlations, Reθ/ Me is obtained effectively with the grid-reorder method. The X-51 forebody is selected to test the effectiveness of Reθ/Me for complex geometries and the results show a good correspondence with the experiment results. The successful application in three transition prediction methods demonstrates that the grid-reorder method has an excellent performance in obtaining the boundary layer parameters and can broaden the application of the existing transition prediction method in engineering.

The Effect of a Turbulent Wake on the Stagnation Point: Part I — Skin Friction Results

1990 ◽  
Author(s):  
Dennis E. Wilson ◽  
Anthony J. Hanford
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Stagnation Point ◽  
Turbulent Wake ◽  
Incoming Flow ◽  
Two Dimensional ◽  
Unsteady Boundary Layer ◽  
Characteristic Parameters ◽  
Stagnation Region ◽  
Boundary Layer Edge

The response of a boundary layer in the stagnation region of a two-dimensional body to fluctuations in the freestream is examined. The analysis is restricted to laminar incompressible flow. The assumed form of the velocity distribution at the edge of the boundary layer represents both a pulsation of the incoming flow, and an oscillation of the stagnation point streamline. Both features are essential in accurately representing the effect which freestream spatial and temporal nonuniformities have upon the unsteady boundary layer. Finally, a simple model is proposed which relates the characteristic parameters in a turbulent wake to the unsteady boundary-layer edge velocity. Numerical results are presented for both an arbitrary two-dimensional geometry and a circular cylinder.

An Investigation Using Wavelet Analysis Into Velocity Perturbations Under the Influence of Elevated Freestream Turbulence at Transition Onset

2006 ◽  
Author(s):  
Domhnaill M. Hernon ◽  
Edmond J. Walsh ◽  
Donald M. McEligot
Keyword(s):  
Boundary Layer ◽  
Wavelet Analysis ◽  
Transitional Flow ◽  
Computational Techniques ◽  
Wall Region ◽  
Freestream Turbulence ◽  
Turbulent Spot ◽  
Perturbation Velocity ◽  
Boundary Layer Edge ◽  
Near Wall

The development of streamwise-orientated disturbances at transition onset for zero-pressure gradient boundary layer flow under the influence of 1.3% freestream turbulence intensity is presented. The analysis concentrates on the development of turbulent spots and other coherent structures with the use of wavelet analysis. The turbulent spot structure is shown to change dramatically in shape, sign of perturbation velocity and energy content from the near wall region to the boundary layer edge. An increased number of trubulent structures are observed near the boundary layer edge, all with negative perturbation velocities, compared to those of positive perturbation velocity in the near wall region. The wavelet maps demonstrate some interesting features of turbulent spot development including regions of high frequency disturbance growth prior to the spot passing the sensor. Distributions of peak negative, peak positive and averaged perturbation velocities were obtained at three streamwise positions prior to transition onset. As transition onset approached the magnitude of the negative value far exceeded the positive and their relative positions within the boundary layer changed considerably. The results presented in this report give further insight into the physics of pre-transitional flow illustrating the influence of negative perturbation velocity in the transition process. Furthermore, the importance of peak instantaneous perturbations compared to averaged values is also demonstrated, a feature of the flow that computational techniques will have to model in order to accurately predict transition phenomena.

Experimental investigation into the routes to bypass transition and the shear-sheltering phenomenon

2007 ◽  
Vol 591 ◽  
pp. 461-479 ◽  
Author(s):  
DOMHNAILL HERNON ◽  
EDMOND J. WALSH ◽  
DONALD M. McELIGOT
Keyword(s):  
Boundary Layer ◽  
Penetration Depth ◽  
Free Stream ◽  
Leading Edge ◽  
Transition Process ◽  
Bypass Transition ◽  
Fluctuation Velocity ◽  
Low Speed ◽  
Experimental Support ◽  
Boundary Layer Edge

The objective of this investigation is to give experimental support to recent direct numerical simulation (DNS) results which demonstrated that in bypass transition the flow first breaks down to turbulence on the low-speed streaks (or so-called negative jets) that are lifted up towards the boundary-layer edge region. In order to do this, wall-normal profiles of the streamwise fluctuation velocity are presented in terms of maximum positive and negative values over a range of turbulence intensities (1.3–6%) and Reynolds numbers for zero pressure gradient flow upstream of, and including, transition onset. For all turbulence intensities considered, it was found that the peak negative fluctuation velocity increased in magnitude above the peak positive fluctuations and their positions relative to the wall shifted as transition onset approached; the peak negative value moved towards the boundary-layer edge and the peak positive value moved toward the wall. An experimental measure of the penetration depth (PD) of free-stream disturbances into the boundary layer has been gained through the use of the skewness function. The penetration depth (measured from the boundary-layer edge) scales as PD ∝ (ω Rexτw)−0.3), where ω is the frequency of the largest eddies in the free stream, Rex is the Reynolds number of the flow based on the streamwise distance from the leading edge and τw is the wall shear stress. The parameter dependence demonstrated by this scaling compares favourably with recent solutions to the Orr–Sommerfeld equation on the penetration depth of disturbances into the boundary layer. The findings illustrate the importance of negative fluctuation velocities in the transition process, giving experimental support to suggestions from recent DNS predictions that the breakdown to turbulence is initiated on the low-speed regions of the flow in the upper portion of the boundary layer. The representation of pre-transitional disturbances in time-averaged form is shown to be inadequate in elucidating which disturbances grow to cause the breakdown to turbulence.

scholarly journals Effects of Leading-Edge Roughness on Fluid Flow and Heat Transfer in the Transitional Boundary Layer Over a Flat Plate

1994 ◽  
Author(s):  
Mark Pinson ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Turbine Blades ◽  
Leading Edge ◽  
Transition Process ◽  
Stanton Number ◽  
Edge Roughness ◽  
Wide Range ◽  
Edge Conditions

An experimental study was undertaken to gain insight into the physical mechanisms that affect the laminar-turbulent transition process downstream of the leading-edge roughness condition. Three sizes of sandpaper strips were chosen to simulate the randomly distributed roughness located near the leading edge of a turbine blade, and three sizes of cylinders were chosen to simulate the relatively isolated peak nature of the roughness structure. The roughness Reynolds numbers tested covered a wide range, from 2 to 2840. The roughness sizes were selected based on the measured roughness characteristics of used gas turbine blades. The results indicated that at low free-stream velocities (5 m/s), the maximum roughness height was the primary contributor to deviations from the undisturbed case. At higher free-stream velocities (5–7 m/s), three of the rough leading-edge conditions exhibited a dual-slope region between the laminar and turbulent Stanton number versus Reynolds number correlations. Analysis of the boundary layer indicated that the first segment of the dual-slope was laminar, but the wall heat transfer significantly deviates from the laminar correlation. The second segment was transitional. The dual-slope behavior and the waviness of the Stanton number distribution at higher free-stream velocities observed downstream of the rough leading-edge conditions are believed to have been caused by nonlinear amplification introduced by the finite disturbances at the leading edge.

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