Modeling of Unsteady Transitional Boundary Layers

1992 ◽  
Vol 114 (3) ◽  
pp. 580-589 ◽  
Author(s):  
J. S. Addison ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Reynolds Numbers ◽  
Considerable Proportion ◽  
Blade Surface ◽  
Hot Wire ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Hot Film ◽  
Profile Loss

In turbomachinery, a considerable proportion of the blade surface area can be covered by transitional boundary layers. This means that accurate prediction of the profile loss and boundary layer behavior in general depends on the accurate modeling of the transitional boundary layers, especially at low Reynolds numbers. This paper presents a model for determining the intermittency resulting from the unsteady transition caused by the passage of wakes over a blade surface. The model is founded on work by Emmons (1951) who showed that the intermittency could be calculated from a knowledge of the behavior of randomly formed turbulent spots. The model Is used to calculate the development of the boundary layer on the rotor of a low Reynolds number single-stage turbine. The predictions are compared with experimental results obtained using surface-mounted hot-film anemometers and hot-wire traverses of the rotor midspan boundary layer at two different rotor-stator gaps. The validity and limitations of the model are discussed.

scholarly journals Modelling of Unsteady Transitional Boundary Layers

1991 ◽  
Author(s):  
J. S. Addison ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Reynolds Numbers ◽  
Considerable Proportion ◽  
Blade Surface ◽  
Hot Wire ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Hot Film ◽  
Profile Loss

In turbomachinery, a considerable proportion of the blade surface area can be covered by transitional boundary layers. This means that accurate prediction of the profile loss and boundary layer behaviour in general depends on the accurate modelling of the transitional boundary layers, especially at low Reynolds numbers. This paper presents a model for determining the intermittency resulting from the unsteady transition caused by the passage of wakes over a blade surface. The model is founded on work by Emmons (1951) who showed that the intermittency could be calculated from a knowledge of the behaviour of randomly formed turbulent spots. The model is used to calculate the development of the boundary layer on the rotor of a low Reynolds number single-stage turbine. The predictions are compared with experimental results obtained using surface-mounted hot-film anemometers and hot-wire traverses of the rotor mid-span boundary layer at two different rotor-stator gaps. The validity and limitations of the model are discussed.

Essential Ingredients for the Computation of Steady and Unsteady Blade Boundary Layers

1991 ◽  
Vol 113 (4) ◽  
pp. 608-616 ◽  
Author(s):  
H. M. Jang ◽  
J. A. Ekaterinaris ◽  
M. F. Platzer ◽  
T. Cebeci
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Stokes Equations ◽  
Inviscid Flow ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Transitional Region ◽  
Low Reynolds Numbers ◽  
Flow Equations ◽  
Low Reynolds

Two methods are described for calculating pressure distributions and boundary layers on blades subjected to low Reynolds numbers and ramp-type motion. The first is based on an interactive scheme in which the inviscid flow is computed by a panel method and the boundary layer flow by an inverse method that makes use of the Hilbert integral to couple the solutions of the inviscid and viscous flow equations. The second method is based on the solution of the compressible Navier–Stokes equations with an embedded grid technique that permits accurate calculation of boundary layer flows. Studies for the Eppler-387 and NACA-0012 airfoils indicate that both methods can be used to calculate the behavior of unsteady blade boundary layers at low Reynolds numbers provided that the location of transition is computed with the en method and the transitional region is modeled properly.

scholarly journals Essential Ingredients for the Computation of Steady and Unsteady Blade Boundary Layers

1990 ◽  
Author(s):  
H. M. Jang ◽  
M. F. Platzer ◽  
J. A. Ekaterinaris ◽  
T. Cebeci
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Stokes Equations ◽  
Inviscid Flow ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Transitional Region ◽  
Low Reynolds Numbers ◽  
Flow Equations ◽  
Low Reynolds

Two methods are described for calculating pressure distributions and boundary layers on blades subjected to low Reynolds numbers and ramp–type motion. The first is based on an interactive scheme in which the inviscid flow is computed by a panel method and the boundary layer flow by an inverse method that makes use of the Hilbert integral to couple the solutions of the inviscid and viscous flow equations. The second method is based on the solution of the compressible Navier–Stokes equations with an embedded grid technique that permits accurate calculation of boundary layer flows. Studies for the Eppler and NACA–0012 airfoils indicate that both methods can be used to calculate the behavior of unsteady blade boundary layers at low Reynolds numbers provided that the location of transition is computed with the en–method and the transitional region is modelled properly.

Investigation of Bypass Transition in the Presence of a Separation Bubble With Tomographic PIV

2016 ◽  
Author(s):  
Christoph Lyko ◽  
Dirk Michaelis ◽  
Dieter Peitsch ◽  
Mirko Dittmar
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Bypass Transition ◽  
Hot Wire ◽  
Integral Boundary ◽  
Low Reynolds Numbers ◽  
Tomographic Piv ◽  
Low Reynolds

Low pressure turbines of small and medium sized engines may operate at very low Reynolds numbers. In consequence transition is delayed to an extend where laminar separation, detached transition and reattachment occur. The wakes from upstream blade rows lead to overall high turbulence levels which play a key role in the transition process. Freestream eddies buffeting the laminar boundary layer induce streamwise vortices known as Klebanoff Modes. To investigate this type of flow a flat plate was exposed to a pressure distribution. It is based on the PAK-B suction side and was created by a contoured wall facing the plate. The PAK-B is a Pratt & Whitney design and a Mach number scaled version of a highly aft loaded low pressure turbine airfoil. Due to the latter it suffers from a large separation bubble at low Reynolds numbers. The flow has been intensively investigated by hot-wire anemometry with a very high spatial resolution. This allows obtaining very precise information about the location of characteristic flow areas; for instance the separation and reattachment positions. Based on this information, Tomographic PIV was employed to expose detailed features in specific areas of the flow field. This technique provides the velocity vector information inside a flow volume. It complements hot-wire results, which give a time resolved information but only planar velocity magnitudes. Combining these techniques and comparing their results is therefore an excellent way to raise the physical understanding of the flow behaviour. This has been done using velocity profiles, skin friction coefficients and integral boundary layer parameters. As the 3D-PIV information allows calculation of derived quantities, like the vector field rotation, a picture of the coherent structures can be drawn.

Actuated Transition in an LP Turbine Laminar Separation: An Experimental Approach

2011 ◽  
Author(s):  
Jenny Baumann ◽  
Ulrich Rist ◽  
Martin Rose ◽  
Tobias Ries ◽  
Stephan Staudacher
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Stream Velocity ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Lp Turbine

The reduction of blade counts in the LP turbine is one possibility to cut down weight and therewith costs. At low Reynolds numbers the suction side laminar boundary layer of high lift LP turbine blades tends to separate and hence cause losses in turbine performance. To limit these losses, the control of laminar separation bubbles has been the subject of many studies in recent years. A project is underway at the University of Stuttgart that aims to suppress laminar separation at low Reynolds numbers (60,000) by means of actuated transition. In an experiment a separating flow is influenced by disturbances, small in amplitude and of a certain frequency, which are introduced upstream of the separation point. Small existing disturbances are therewith amplified, leading to earlier transition and a more stable boundary layer. The separation bubble thus gets smaller without need of a high air mass flow as for steady blowing or pulsed vortex generating jets. Frequency and amplitude are the parameters of actuation. The non-dimensional actuation frequency is varied from 0.2 to 0.5, whereas the normalized amplitude is altered between 5, 10 and 25% of the free stream velocity. Experimental investigations are made by means of PIV and hot wire measurements. Disturbed flow fields will be compared to an undisturbed one. The effectiveness of the presented boundary layer control will be compared to those of conventional ones. Phase-logged data will give an impression of the physical processes in the actuated flow.

Boundary-layer measurements on an airfoil at low Reynolds numbers

1988 ◽  
Vol 25 (7) ◽  
pp. 612-617 ◽  
Author(s):  
M. Brendel ◽  
T. J. Mueller
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds
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