Effect of Leading-Edge Geometry on Separation Bubble on a Compressor Blade

2003 ◽  
Author(s):  
Huoxing Liu ◽  
Baojie Liu ◽  
Ling Li ◽  
Haokang Jiang
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Research Work ◽  
Wedge Angle ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Test Model ◽  
Edge Geometry ◽  
Separation Bubbles

Accurate prediction of flow field is the most important factor during the design of high performance compressors. In some cases the agreement of pressure ratio and efficiency between predicted and measured is excellent, but it is common for the efficiency to be in error by perhaps one or two percent. This error is enough to render the calculation unable to replace expensive experiment testing. One of the important matters in need of more study is the mechanism of boundary layer transition from laminar to turbulent flow. The objective of this fundamental research work is to acquire the detailed structure of separation bubbles on the suction side of the blade by using the PIV and pressure taps. This paper presents an experimental study of the influence of 2d leading-edge geometry on behavior of separation bubbles. The measurements on a nose of enlarged blade were conducted on a special large-scale experimental facility, the pressure distribution and flowfield of flow were measured. The test model used in this study consists of circular leading edge and elliptic leading edge. Results are presented for a range of incidence. The measurement result indicated that the leading edge shape has a large influence on flow details separation and transition as well as the boundary layer properties after reattached point. The wedge angle appears to be an important role in leading edge geometry parameters.

Effect of Leading Edge Geometry on Boundary Layer Transition-An Experimental Approach

2014 ◽  
Vol 590 ◽  
pp. 53-57 ◽  
Author(s):  
Dinesh Bhatia ◽  
Guang Jun Yang ◽  
Jing Sun ◽  
Jian Wang
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Boundary Layer Thickness ◽  
Experimental Approach ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Edge Geometry ◽  
Displacement Thickness

Boundary layers are affected by a number of different factors. Transition of the boundary layer is very sensitive to changes in geometry, velocity and turbulence levels. An understanding of the flow characteristics over a flat plate subjected to changes in geometry, velocity and turbulence is essential to try and understand boundary layer transition. Experiments were conducted in Low Turbulence wind tunnel (LTWT) at Northwestern Polytechnical University (NWPU), China to understand the effects due to changes in geometric profiles on boundary layer transition. The leading edge of the flat plate was changed and several different configurations ranging from Aspect Ratio (AR) 1 to 12 were used. Turbulence level was kept constant at 0.02% and the velocity was kept at default value of 30 m/s. The results indicated that as the AR increases, boundary layer thickness reduces at the same location along the plate. The displacement thickness shows that the fluctuations increase with an increase with AR which denotes the effect of leading edge on turbulence spot’s production. For AR≥4, an increase in AR led to an elongation of the transition zone and a delay in transition onset. Nomenclature

scholarly journals Studies on a Blade Leading Edge Separation Bubble Affected by Periodic Wakes: Its Transitional Behavior and Boundary Layer Loss Reduction

2002 ◽  
Author(s):  
K. Funazaki ◽  
Y. Kato
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Leading Edge ◽  
Circular Cylinders ◽  
Test Model ◽  
Hot Wire ◽  
Flat Plates ◽  
Wake Effect ◽  
Time Resolved ◽  
Aerodynamic Loss

This study deals with extensive hot-wire probe measurements of wake-affected separation bubble on the leading edge of a test model. The purpose of the study is to investigate time-resolved response of the separation bubble to incoming wake passing. Another focus is placed on the wake effect on aerodynamic loss generated in the separated boundary layer, seeking any relationship between the suppression of the separation bubble on a cascade airfoil and aerodynamic gain due to the clocking in turbomachines. The test model has a semicircular leading edge and two flat-plates. Incoming wakes are generated by circular cylinders which are horizontally fixed in the wake generator. Several types of wake generating cylinders are used in order to change wake properties. The hot-wire measurements have revealed the time-resolved responses of the separated boundary layer to the wake passage. Effects of calmed regions just behind the moving wakes are also identified.

Control of Separation Bubble on a Blade Leading Edge by a Stationary Bar Wake

2000 ◽  
Author(s):  
K. Funazaki ◽  
Y. Harada ◽  
E. Takahashi
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Leading Edge ◽  
Test Model ◽  
Flat Plates ◽  
Flow Measurements ◽  
Inlet Flow ◽  
Aerodynamic Loss ◽  
Edge Separation ◽  
Blade Leading Edge

This paper describes an attempt to suppress a blade leading edge separation bubble by utilizing a stationary bar wake. This study aims at exploration of a possibility for reducing the aerodynamic loss due to blade boundary layer that is accompanied with the separation bubble. The test model used in this study consists of semi-circular leading edge and two parallel flat plates. It can be tilted against the inlet flow so as to change the characteristics of the separation bubble. Detailed flow measurements over the test model are conducted using a single hot-wire probe. Emphasis in this study is placed on the effect of bar shifting or bar clocking across the inlet flow in order to see how the bar-wake position with respect to the test model affects the separation bubble as well as aerodynamic loss generated within the boundary layer. The present study reveals a loss reduction through the separation bubble control using a properly clocked bar wake.

scholarly journals An Inviscid-Viscous Method to Model Leading Edge Separation Bubbles

1994 ◽  
Author(s):  
W. John Calvert
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Leading Edge ◽  
Initial Boundary ◽  
Axial Compressors ◽  
Recent Experimental Study ◽  
Separation Bubbles ◽  
Blade Section ◽  
Set Up ◽  
Edge Separation

Separation bubbles are likely to occur near the leading edges of sharp-edged blade sections in axial compressors and turbines, particularly when the sections are operated at positive incidence. Typically the flow reattaches a short distance from the leading edge as a turbulent boundary layer, the thickness of which depends on the details of the separation bubble. The overall performance of the blade section can be significantly affected by the thickness of this initial boundary layer — in some cases blade stall is mainly associated with the change in thickness of the layer as blade incidence is increased. A recent experimental study at the Whittle Laboratory, Cambridge demonstrated the importance of the blade leading edge shape on the separation bubble. In the present work, an inviscid-viscous method has been set up to model the experimental data and to provide a way of predicting the performance of this critical region for different leading edge shapes.

Large Eddy Simulation of Periodic Wake Impact on Boundary Layer Transition Mechanisms on a Highly Loaded Low-Pressure Turbine Blade

2020 ◽  
Author(s):  
Benjamin Winhart ◽  
Martin Sinkwitz ◽  
Andreas Schramm ◽  
Pascal Post ◽  
Francesca di Mare
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Array Measurements ◽  
Numerical Predictions ◽  
Large Eddy ◽  
Highly Loaded

Abstract In the proposed paper the transient interaction between periodic incoming wakes and the laminar separation bubble located on the rear suction surface of a typical, highly loaded LPT blade is investigated by means of highly resolved large-eddy simulations. An annular, large scale, 1.5-stage LPT test-rig, equipped with a modified T106 turbine blading and an upstream rotating vortex generator is considered and the numerical predictions are compared against hot film array measurements. In order to accurately assess both baseline transition and wake impact, simulations were conducted with unperturbed and periodically perturbed inflow conditions. Main mechanisms of transition and wake-boundary layer interaction are investigated utilizing a frequency-time domain analysis. Finally visualizations of the main flow structures and shear layer instabilities are provided utilizing the q-criterion as well as the finite-time Lyapunov exponent.

CFD Prediction of Boundary Layer Transition and Separation on an Airfoil at Varying Angle of Attack

2007 ◽  
Author(s):  
Nicole M. Wolgemuth ◽  
D. Keith Walters
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Boundary Layer Transition ◽  
Suction Surface ◽  
Layer Transition ◽  
Turbulent Airflow ◽  
Naca 0012

This study analyzes the predicted flow over a NACA 0012 airfoil at varying angles of attack and three different Reynolds numbers. The ability of three different turbulence models to predict boundary layer separation and transition behavior is investigated. Particular interest is paid to prediction of the separation bubble that develops near the leading edge of the airfoil suction surface prior to stall. The FLUENT CFD solver was used to simulate turbulent airflow over the airfoil. The three turbulence models include the standard and realizable forms of the k-ε model, available in FLUENT, as well as a recently developed transition-sensitive k-ω model that was implemented into the solver using user-defined functions. By employing the new, transition-sensitive model, computed properties of the flow field were found to be closer to experimental data than results produced by utilizing built-in turbulence models. Most importantly, the new, transition-sensitive model predicts the occurrence of the separation bubble, which the other models are unable to predict. The new model also clearly reproduces the laminar, transitional, and turbulent flow that occurs over the airfoil.

The Effect of Leading-Edge Geometry on Wake Interactions in Compressors

2007 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Alessandro Sofia ◽  
Robert J. Miller
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Surface Profile ◽  
Leading Edge ◽  
Suction Surface ◽  
Pressure Surface ◽  
Edge Geometry ◽  
Boundary Layer Interaction ◽  
Wake Interactions ◽  
Stator Blade

The effect of leading-edge geometry on wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and circular leading-edge were tested on a Controlled Diffusion (CDA) stator-blade. Experiments were undertaken on the stator suction-surface, these included hotwire boundary-layer traverses, surface hotfilm measurements and high resolution leading-edge pressure measurements. Steady CFD predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For the blade with the elliptic leading-edge (Blade A), the leading-edge boundary-layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary-layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary-layer indicated that the wake/leading interaction for Blade A raised the suction-surface loss by 20%. For the blade with the circular leading-edge (Blade B) the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forwards whilst inducing a turbulent reattachment upstream of the time-average reattachment position. This produced a region of very high momentum thickness at the leading-edge. The suction-surface profile loss was found to be 38% higher for Blade B compared to Blade A. The total loss (suction-surface and pressure-surface) for Blade B was measured to be 32% higher than that of Blade A.

Boundary-Layer Transition in Separation Bubbles Over Rough Surfaces

2004 ◽  
Author(s):  
S. K. Roberts ◽  
M. I. Yaras
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Suction Side ◽  
Boundary Layer Transition ◽  
Test Surface ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Separation Bubbles

This paper documents the effects of surface roughness on boundary layer transition in separation-bubbles under low free-stream turbulence conditions (<1%). The experiments were performed on a flat surface, upon which a pressure distribution similar to those prevailing on the suction side of low-pressure turbine blades was imposed. The test matrix consists of four variations in the roughness conditions, including a reference test case with a smooth surface. The remaining roughness levels are typical of in-service turbine blades in gas turbine engines. The measurements were performed at flow Reynolds numbers of 350,000 and 470,000, based on the length of the test surface. The separation, transition inception, transition completion, and re-attachment locations, and the streamwise intermittency distributions in the transition region are documented for each of the test cases. Increasing surface roughness is shown to result in earlier transition inception, and consequently, a reduced size of the separation-bubble. However, the presence of surface roughness does not appear to have a significant effect on the rate of transition within the separation-bubble.

The Effect of Leading-Edge Geometry on Wake Interactions in Compressors

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Alessandro Sofia ◽  
Robert J. Miller
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Leading Edge ◽  
Suction Surface ◽  
Surface Loss ◽  
Edge Geometry ◽  
Boundary Layer Interaction ◽  
Wake Interactions ◽  
Stator Blade ◽  
Profile Loss

The effect of leading-edge geometry on the wake/boundary-layer interaction was studied in a low-speed single-stage HP compressor. Both a 3:1 elliptic and a circular leading edge were tested on a controlled diffusion aerofoil stator blade. Experiments were undertaken on the stator suction surface; these included hotwire boundary-layer traverses, surface hotfilm measurements, and high resolution leading-edge pressure measurements. Steady computational fluid dynamics (CFD) predictions were also performed to aid the interpretation of the results. The two leading-edge shapes gave rise to significantly different flows. For a blade with an elliptic leading edge (Blade A), the leading-edge boundary layer remained attached and laminar in the absence of wakes. The wake presence led to the formation of a thickened laminar boundary layer in which turbulent disturbances were observed to form. Measurements of the trailing-edge boundary layer indicated that the wake/leading-edge interaction for Blade A raised the suction-surface loss by 20%. For a blade with a circular leading edge (Blade B), the leading-edge boundary-layer exhibited a separation bubble, which was observed to reattach laminar in the absence of wakes. The presence of the wake moved the separation position forward while inducing a turbulent reattachment upstream of the leading-edge time-average reattachment position. This produced a region of very high momentum thickness at the leading edge. The suction-surface loss was found to be 38% higher for Blade B than for Blade A. Wake traverses downstream of the blades were used to determine the total profile loss of each blade. The profile loss of Blade B was measured to be 32% higher than that of Blade A.

scholarly journals Transitional separation bubbles and unsteady aspects of aerofoil stall

2008 ◽  
Vol 112 (1133) ◽  
pp. 395-404 ◽  
Author(s):  
N. D. Sandham
Keyword(s):  
Boundary Layer ◽  
Potential Flow ◽  
Large Scale ◽  
Transition Process ◽  
High Amplitude ◽  
Accurate Solution ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Integral Boundary ◽  
Separation Bubbles

AbstractA time-accurate solution method for the coupled potential flow and integral boundary-layer equations is used to study aerofoils near stall, where laboratory experiments have shown high-amplitude low-frequency oscillations. The laminar-turbulent transition model incorporates an absolute instability formulation, which allows the transition process in separation bubbles to be sustained in the absence of upstream disturbances, in agreement with recent direct numerical simulations. The method is demonstrated to capture large scale flow oscillations with Strouhal numbers and amplitudes comparable to experiments. The success of this particular physical model suggests that bubble bursting is primarily due to a potential-flow/boundary-layer interaction effect, in which relatively simple models of boundary layer transition and turbulence suffice to describe the key phenomena.

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