Detection of Separation Bubbles by Infrared Images in Transonic Turbine Cascades

1988 ◽  
Vol 110 (4) ◽  
pp. 504-511 ◽  
Author(s):  
W. Bra¨unling ◽  
A. Quast ◽  
H.-J. Dietrichs
Keyword(s):  
Boundary Layer ◽  
Pressure Distribution ◽  
Infrared Image ◽  
Turbine Rotor ◽  
Test Facility ◽  
Infrared Images ◽  
Wide Range ◽  
Separation Bubbles ◽  
Oil Flow ◽  
High Pressure Stage

In a test facility for straight cascades, equipped with profiles designed for a highly loaded gas turbine rotor of a high-pressure stage, experiments were conducted to clarify some effects of shock wave–boundary layer interactions. The specific aim was to determine both the position and strength of compression shocks originating from profile wake flows and the position and extent of separation bubbles. The latter are most often detected by visualization methods like surface oil flow patterns or Schlieren photographs, as well as by typical properties in wall pressure distribution curves. In addition, the infrared image technique, which has found many applications in a wide range of technical activities in the recent years, may also be used. Compared with other methods, this technique has distinct advantages in fluid mechanics applications. The whole model can be observed without disturbing the boundary layer by tappings, measuring materials, or probes. Some typical infrared images are presented and interpreted using results of pressure distribution measurements, hot-film measurements, and surface oil flow visualizations.

scholarly journals Detailed Measurements of the Flow Field in a Transonic Turbine Cascade

1991 ◽  
Author(s):  
E. Detemple-Laake
Keyword(s):  
Pressure Distribution ◽  
Three Dimensional ◽  
Side Wall ◽  
Turbine Rotor ◽  
Experimental Investigations ◽  
Flow Angle ◽  
Flow Models ◽  
Oil Flow ◽  
High Pressure Stage ◽  
Flow Effects

Systematic experimental investigations of the transonic flow through a plane cascade consisting of profiles designed for a highly loaded gas turbine rotor of a high pressure stage were performed. The experiments comprise side wall pressure distribution measurements in a blade passage and both profile pressure distribution and wake traverse measurements in various planes from midspan to the side wall. The parameters varied are the inlet flow angle and the downstream Mach number. Schlieren photopraphs and oil flow patterns on the blades and on the side wall are included. The experimental results are interpreted with respect to the existing flow models describing shock wave boundary layer interactions and secondary flow effects. The experimental data are compared with three-dimensional viscous numerical results.

The Effect of Reynolds Number and Velocity Distribution on LP Turbine Cascade Performance

1986 ◽  
Author(s):  
D. J. Patterson ◽  
M. Hoeger
Keyword(s):  
Reynolds Number ◽  
Pressure Distribution ◽  
Guide Vane ◽  
Flow Visualisation ◽  
Suction Surface ◽  
Trailing Edge ◽  
Wide Range ◽  
Oil Flow ◽  
Low Reynolds ◽  
Lp Turbine

Because of the laminar boundary-layer’s inability to withstand moderate adverse pressure gradients without separating, profile losses in LP turbines operating at low Reynolds numbers can be high. The choice of design pressure distribution for the blading is thus of great importance. Three sub-sonic LP turbine nozzle-guide-vane cascade profiles have been tested over a wide range of incidence, Mach number and Reynolds number. The three profiles are of low, medium and high deflection and, as such, display significantly different pressure distributions. The tests include detailed boundary-layer traverses, trailing-edge base-pressure monitoring and oil-flow visualisation. It is shown that the loss variation with Reynolds number is a function of pressure distribution and that the trailing-edge loss component is dominant at low Reynolds number. The importance of achieving late flow transition — rather than separation — in the suction-surface trailing-edge region is stressed. The paper concludes by remarking on the advantages and practical implications of each loading design.

Effects of Streamwise Pressure Gradient on Turbulent Spot Development

1996 ◽  
Vol 118 (4) ◽  
pp. 737-743 ◽  
Author(s):  
J. P. Gostelow ◽  
N. Melwani ◽  
G. J. Walker
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Pressure Distribution ◽  
Boundary Layer Transition ◽  
Variable Pressure ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Turbulent Layer ◽  
Wide Range

A pressure distribution representative of a controlled diffusion compressor blade suction surface is imposed on a flat plate. Boundary layer transition in this situation is investigated by triggering a wave packet, which evolves into a turbulent spot. The development from wave packet to turbulent spot is observed and the interactions of the turbulent spot with the ongoing natural transition and the ensuing turbulent boundary layer are examined. Under this steeply diffusing pressure distribution, strong amplification of primary instabilities prevails. Breakdown to turbulence is instigated near the centerline and propagates transversely along the wave packet until the turbulent region dominates. An extensive calmed region is present behind the spot, which persists well into the surrounding turbulent layer. Celerities of spot leading and trailing edges are presented, as is the spanwise spreading half-angle. Corresponding measurements for spots under a wide range of imposed pressure gradients are compiled and the present results are compared with those of other authors. Resulting correlations for spot propagation parameters are provided for use in computational modeling of the transition region under variable pressure gradients.

Separation Bubbles Under Steady and Periodic-Unsteady Main Flow Conditions

2000 ◽  
Author(s):  
Weiliang Lou ◽  
Jean Hourmouziadis
Keyword(s):  
Pressure Distribution ◽  
Velocity Profiles ◽  
Main Flow ◽  
Test Facility ◽  
Free Shear Layer ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Time Space ◽  
Separation Bubbles ◽  
The Impact

Based on an experimental investigation carried out in a low speed test facility at the Berlin University of Technology, this paper describes the formation of separation bubbles under steady and periodic-unsteady main flow conditions. The aim of the investigation was to understand the mechanism of separation, transition and reattachment and the effect of main flow unsteadiness on it. Separation bubbles for various main flow conditions were generated over a large flat plate, which experienced a similar pressure distribution to that on the suction surface of blades in turbomachines. The pressure distribution was generated by a contoured wall opposite the plate. Aimed at separating the effect of the velocity and the turbulence wake, this paper considers only the influence of the velocity wake. To this effect, a rotating flap was mounted downstream of the test section to produce periodic oscillations of the main flow. The overall flow field under steady main flow conditions was obtained by hot-wire measurements. Pressure taps were used to measure the pressure distribution over the plate. The Reynolds number effects were determined and compared to the measurement results in the literature. Results for periodic-unsteady separation bubbles are shown using different Strouhal numbers, oscillation amplitudes and Reynolds numbers. Ensemble averaged mean velocity profiles and the Ensemble averaged rms velocity profiles are used to demonstrate the development of the periodic boundary layer. Time-space diagrams are plotted to show the development of the periodic-unsteady boundary layers. The characteristic instability frequencies in the free shear layer are identified. The impact of the major parameters, Strouhal number and amplitude, on the bubble formation are discussed.

scholarly journals Effects of Streamwise Pressure Gradient on Turbulent Spot Development

1995 ◽  
Author(s):  
J. P. Gostelow ◽  
N. Melwani ◽  
G. J. Walker
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Pressure Distribution ◽  
Boundary Layer Transition ◽  
Variable Pressure ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Layer Transition ◽  
Turbulent Layer ◽  
Wide Range

A pressure distribution representative of a controlled diffusion compressor blade suction surface is imposed on a flat plate. Boundary layer transition in this situation is investigated by triggering a wave packet which evolves into a turbulent spot. The development from wave packet to turbulent spot is observed and the interactions of the turbulent spot with the ongoing natural transition aad the ensuing turbulent boundary layer are examined. Under this steeply diffusing pressure distribution strong amplification of primary instabilities prevails. Breakdown to turbulence is instigated near the center line and propagates transversely along the wave packet until the turbulent region dominates. An extensive calmed region is present behind the spot which persists well into the surrounding turbulent layer. Celerities of spot leading and trailing edges are presented, as is the spanwise spreading half-angle. Corresponding measurements for spots under a wide range of imposed pressure gradients are compiled and the present results are compared with those of other authors. Resulting correlations for spot propagation parameters are provided for use in computational modeling of the transition region under variable pressure gradients.

Instability and Transition in a Separation Bubble Under a Three-Dimensional Freestream Pressure Distribution

2011 ◽  
Vol 134 (3) ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Pressure Distribution ◽  
Pressure Field ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Test Surface ◽  
Two Dimensional ◽  
Transition Processes ◽  
Pressure Distributions ◽  
Separation Bubbles

This paper presents measurements of the instability and transition processes in separation bubbles under a three-dimensional freestream pressure distribution. The measurements are performed on a flat plate on which a pressure distribution is imposed by a contoured surface facing the flat test-surface. The three-dimensional pressure distribution that is established on the test-surface approximates the pressure distributions encountered on swept blades. This type of pressure field produces crossflows in the laminar boundary layer upstream of the separation and within the separation bubble. The effects of these crossflows on the instability of the upstream boundary layer and on the instability, transition onset, and transition rate within the separated shear-layer are examined. The measurements are performed at two flow-Reynolds numbers and relatively low level of freestream turbulence. The results of this experimental study show that the three-dimensional freestream pressure field and the corresponding redistribution of the freestream flow can cause significant spanwise variation in the separation-bubble structure. It is demonstrated that the instability and transition processes in the modified separation bubble develop on the basis of the same fundamentals as in two-dimensional separation bubbles and can be predicted with the same level of accuracy using models that have been developed for two-dimensional separation bubbles.

Some Measurements of Leading Edge Separation Bubbles on a 10 per cent Thick Symmetrical Aerofoil

1953 ◽  
Vol 57 (516) ◽  
pp. 819-823 ◽  
Author(s):  
J. Black ◽  
R. D. Hunt
Keyword(s):  
Thin Film ◽  
Boundary Layer ◽  
Liquid Film ◽  
Pressure Distribution ◽  
Constant Pressure ◽  
Leading Edge ◽  
Pressure Distributions ◽  
Separation Bubbles ◽  
Edge Separation

Pressure Distribution and liquid-film tests on a 10 per cent, thick aerofoil revealed the presence of separation “bubbles” close to the leading edge. These bubbles are formed beneath the boundary layer which separates near the leading edge and re-attaches farther aft; their existence is usually indicated by localised constant-pressure regions in the pressure distributions. It is also believed that if a thin film of liquid (such as a suspension of lamp-black in paraffin) is spread on the surface, the scrubbing action of the air rotating in the bubble will tend to draw liquid forward into the bubble, and hence the location and extent of the bubble may be indicated approximately by the accumulation of the fluid.Many boundary layer traverses of bubbles on N.A.C.A. aerofoils have been made, but it was felt that similar measurements of the bubbles on this particular aerofoil would provide useful data, since the separation characteristics of this section appeared to differ from those in the N.A.C.A. tests.

Modeling Oil Flows on Seal Runners and Engine Sump Walls

2004 ◽  
Vol 127 (4) ◽  
pp. 827-834 ◽  
Author(s):  
Masayoshi Shimo ◽  
James V. Canino ◽  
Stephen D. Heister
Keyword(s):  
Boundary Layer ◽  
Flow Behavior ◽  
Axial Direction ◽  
Outer Wall ◽  
Two Dimensional ◽  
Ambient Conditions ◽  
Boundary Layer Equations ◽  
Wide Range ◽  
Boundary Layer Method ◽  
Oil Flow

Oil flow behavior within a lubrication system utilized in a turbofan engine has been studied using a two-dimensional model for a seal runner and a sump wall. A two-dimensional, axisymmetric boundary layer method is utilized to derive a model for the film on the seal runner. An integral method analysis of boundary layer equations are utilized to derive a model for the film behavior on the outer wall of the sump neglecting variations in the axial direction. Parametric studies for oil flow at the seal runner and one the sump wall have been generated for a wide range of oil film properties and ambient conditions.

Separation Bubbles Under Steady and Periodic-Unsteady Main Flow Conditions

2000 ◽  
Vol 122 (4) ◽  
pp. 634-643 ◽  
Author(s):  
Weiliang Lou ◽  
Jean Hourmouziadis
Keyword(s):  
Pressure Distribution ◽  
Velocity Profiles ◽  
Main Flow ◽  
Test Facility ◽  
Free Shear Layer ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Time Space ◽  
Separation Bubbles ◽  
The Impact

Based on an experimental investigation carried out in a low-speed test facility at the Berlin University of Technology, this paper describes the formation of separation bubbles under steady and periodic-unsteady main flow conditions. The aim of the investigation was to understand the mechanism of separation, transition, and reattachment, and the effect of main flow unsteadiness on it. Separation bubbles for various main flow conditions were generated over a large flat plate, which experienced a similar pressure distribution to that on the suction surface of blades in turbomachines. The pressure distribution was generated by a contoured wall opposite the plate. Aimed at separating the effect of the velocity and the turbulence wake, this paper considers only the influence of the velocity wake. To this effect, a rotating flap was mounted downstream of the test section to produce periodic oscillations of the main flow. The overall flow field under steady main flow conditions was obtained by hot-wire measurements. Pressure taps were used to measure the pressure distribution over the plate. The Reynolds number effects were determined and compared to the measurement results in the literature. Results for periodic-unsteady separation bubbles are shown using different Strouhal numbers, oscillation amplitudes, and Reynolds numbers. Ensemble-averaged mean velocity profiles and the ensemble-averaged rms velocity profiles are used to demonstrate the development of the periodic boundary layer. Time–space diagrams are plotted to show the development of the periodic-unsteady boundary layers. The characteristic instability frequencies in the free shear layer are identified. The impact of the major parameters, Strouhal number and amplitude, on the bubble formation are discussed. [S0889-504X(00)01204-6]

Instability and Transition in a Separation Bubble Under a Three-Dimensional Freestream Pressure Distribution

2008 ◽  
Author(s):  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Pressure Distribution ◽  
Pressure Field ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Test Surface ◽  
Two Dimensional ◽  
Transition Processes ◽  
Pressure Distributions ◽  
Separation Bubbles

This paper presents measurements of the instability and transition processes in separation bubbles under a three-dimensional freestream pressure distribution. Measurements are performed on a flat plate upon which a pressure distribution is imposed by a contoured surface facing the flat test surface. The three-dimensional pressure distribution that is established on the test surface approximates the pressure distributions encountered on swept blades. This type of pressure field produces crossflows in the laminar boundary layer upstream of separation and within the separation bubble. The effects of these crossflows on the instability of the upstream boundary layer and on the instability, transition onset and transition rate within the separated shear layer are examined. The measurements are performed at two flow Reynolds numbers and relatively low level of freestream turbulence. The results of this experimental study show that the three-dimensional freestream pressure field and the corresponding redistribution of the freestream flow cause significant spanwise variation of the separation-bubble structure. It is demonstrated that the instability and transition processes in the modified separation bubble develop on the basis of the same fundamentals as in two-dimensional separation bubbles, and can be predicted with the same level of accuracy using models that have been developed for two-dimensional separation bubbles.

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