scholarly journals Transition Prediction in Attached and Separated Shear Layers Using an Integral Method

1992 ◽  
Author(s):  
G. Leoutsakos ◽  
K. D. Papailiou
Keyword(s):  
Integral Method ◽  
Adverse Pressure Gradient ◽  
Shear Layers ◽  
Separated Flows ◽  
Prediction Methods ◽  
Accurate Assessment ◽  
Transition Prediction ◽  
Turbomachinery Blades ◽  
Aerodynamic Parameters ◽  
Work Done

Calculation of the aerodynamic parameters of axial turbomachinery blades, and an accurate assessment of the flow over the blade surfaces under today’s increasingly demanding requirements for higher efficiencies and optimized blade shapes, at both design and off-design conditions, impose a need for accurate prediction methods able to compute through two sensitive but highly critical phenomena: separation and transition. The present study describes work done on the modelling and prediction of transitional regions, such as those appearing on turbomachinery blading, covering both attached and separated flows. The concept of an engineering method, cheap to run and avoiding complex CFD and turbulence model formulations was always kept in mind. Results include comparisons of integral quantities and velocity profiles in zero, favourable or adverse pressure gradient attached flows, and velocity distributions including points of separation, transition and reattachment in separated airfoil flows, obtained either from a straightforward shear layer calculation or from a viscous-inviscid interaction procedure.

scholarly journals Observations of Wake-Induced Turbulent Spots on an Axial Compressor Blade

1993 ◽  
Author(s):  
G. J. Walker ◽  
W. J. Solomon ◽  
J. P. Gostelow
Keyword(s):  
Surface Film ◽  
Axial Compressor ◽  
Adverse Pressure Gradient ◽  
Shear Layers ◽  
Compressor Blade ◽  
Ensemble Average ◽  
Transitional Flow ◽  
Instability Wave ◽  
Random Disturbance ◽  
Turbulent Spots

Measurements of transitional flow in regions of strong adverse pressure gradient on an axial compressor stator are reported. The range of observations covers separating laminar flow at transition onset, and reattachment of intermittently turbulent periodically separated shear layers. Transition was characterised by the regular appearance of turbulent spots in association with the rotor blade wake disturbances. However, the initial breakdown did not coincide with the wake passage as has usually been observed by other workers. The spots rather evolved from the growth of instability wave packets which lagged the wake passage. Data presented from the compressor blade measurements include: mean and ensemble-average velocities and associated integral parameters; distributions of total, periodic and random disturbance components; typical individual velocity fluctuation records; contours of ensemble-average random disturbance level; and boundary layer intermittency distributions. Measurements of turbulent intermittency showed a significant fall in this quantity near the wall in the reattaching flow. This has significant implications for the interpretation of transition data from surface film gage observations.

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.

scholarly journals An Improved Incidence Losses Prediction Method for Turbine Airfoils

1989 ◽  
Author(s):  
S. H. Moustapha ◽  
S. C. Kacker ◽  
B. Tremblay
Keyword(s):  
Aspect Ratio ◽  
Prediction Method ◽  
Leading Edge ◽  
Prediction Methods ◽  
Accurate Assessment ◽  
Test Results ◽  
Periodic Review ◽  
Empirical Correlations ◽  
Axial Turbines ◽  
Turbine Airfoils

The off-design performance of axial turbines is usually predicted by calculating the incidence losses using empirical correlations. Periodic review and improvement to these prediction methods, to reflect recent turbine designs and test results, are essential for the accurate assessment of losses in turbine airfoils. The purpose of the present work is to evaluate existing turbine incidence loss correlations, and present an improved prediction method for profile and secondary losses at off-design conditions which correlates better with the available experimental results. The incidence losses are shown to be a function of leading edge diameter, pitch, aspect ratio and channel convergence.

An Improved Incidence Losses Prediction Method for Turbine Airfoils

1990 ◽  
Vol 112 (2) ◽  
pp. 267-276 ◽  
Author(s):  
S. H. Moustapha ◽  
S. C. Kacker ◽  
B. Tremblay
Keyword(s):  
Aspect Ratio ◽  
Prediction Method ◽  
Leading Edge ◽  
Prediction Methods ◽  
Accurate Assessment ◽  
Test Results ◽  
Periodic Review ◽  
Empirical Correlations ◽  
Axial Turbines ◽  
Turbine Airfoils

The off-design performance of axial turbines is usually predicted by calculating the incidence losses using empirical correlations. Periodic review and improvement to these prediction methods, to reflect recent turbine designs and test results, are essential for the accurate assessment of losses in turbine airfoils. The purpose of the present work is to evaluate existing turbine incidence loss correlations, and present an improved prediction method for profile and secondary losses at off-design conditions which correlates better with the available experimental results. The incidence losses are shown to be a function of leading edge diameter, pitch, aspect ratio and channel convergence.

An Assessment of Attached and Mildly Separated Flows in Adverse Pressure Gradient Regions

2014 ◽  
Author(s):  
Antonio B. de Jesus ◽  
Luiz Augusto C. Schiavo ◽  
Joao Luiz F. Azevedo ◽  
Jean-Philippe Laval
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Separated Flows

scholarly journals Comparison of ω-Based Turbulence Models for Simulating Separated Flows in Transonic Compressor Cascades

1998 ◽  
Author(s):  
Tom C. Currie
Keyword(s):  
Turbulence Models ◽  
Separated Flow ◽  
Adverse Pressure Gradient ◽  
Reynolds Stress Model ◽  
Separated Flows ◽  
Navier Stokes ◽  
Test Case ◽  
Turbulent Dissipation ◽  
Transonic Compressor ◽  
Scale Variable

Separated flows in the DLR transonic compressor cascades TSG-91-8K and TSG-89-5 are simulated with a quasi-3D Navier-Stokes code using the zonal k-ω/k-ϵ “Shear Stress Transport” two-equation turbulence model of Menter and the multiscale Reynolds stress model of Wilcox. Both of these models use the specific turbulent dissipation rate ω as the length scale variable. The models are also used to simulate the low speed, separated flow, adverse pressure gradient test case of Driver. While both models predict results which are in good agreement with experiment for the latter test case, they yield relatively poor results, particularly for losses, for the cascade test cases, especially TSG-89-5 where separation occurs from both the suction and pressure surfaces. It is known from the cascade test results that the separations are laminar, so some improvement in agreement is achieved by suppressing transition to the separation points in the simulations. The poor accuracy of the models is believed to be related to severe non-equilibrium of turbulence production and dissipation predicted after the shock-induced separations.

scholarly journals On the Calculation of Recirculating Scheme of Quarry Ventilation

2015 ◽  
Vol 4 (3) ◽  
pp. 22-27
Author(s):  
Старостин ◽  
I. Starostin
Keyword(s):  
Boundary Layer ◽  
Atmospheric Pollution ◽  
Calculation Method ◽  
Integral Method ◽  
Natural State ◽  
Mining Operations ◽  
Air Volume ◽  
Aerodynamic Parameters ◽  
Ventilation Scheme ◽  
Geometry Function

A recirculating scheme of quarry ventilation has been examined. A calculation of the recirculating scheme of a quarry gas interchange employing Karman´s integral method, allowing to account for the parameters of the developed cavity (the angles of leeward and windward sides, their configuration, the size of the bottom, etc.), using the geometry function of the quarry, has been referred. Analytical dependencies for calculation of aerodynamic parameters of the recirculating ventilation scheme (air currents velocity, limits of the boundary layer, circulating air volume, etc.) have been determined. The proposed calculation method allows evaluating the natural state of gas interchange in quarries at various stages of mining operations, which is the basis for the estimation of atmospheric pollution and the development of necessary ventilation techniques.

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