The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 2—Suction Surface Boundary Layers

1988 ◽  
Vol 110 (1) ◽  
pp. 138-145 ◽  
Author(s):  
S. Deutsch ◽  
W. C. Zierke
Keyword(s):  
Boundary Layers ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Outer Region ◽  
Leading Edge ◽  
Compressor Blade ◽  
Surface Boundary ◽  
Suction Surface ◽  
Circular Arc ◽  
Edge Separation

Using the facility described in Part 1 [29], eleven detailed velocity and turbulence intensity profiles are obtained on the suction surface of a double circular arc blade in cascade. At the measured incidence angle of 5 deg, transition through a leading edge separation bubble occurs before 2.6 percent chord. A continuing recovery from this leading edge separation is apparent in the measured boundary layer profiles at 2.6 and 7.6 percent chord. Recovery appears to be complete by 12.7 percent chord. The data then illustrate the evolution of the nonequilibrium turbulent boundary layers as they approach a second region of separation. Following the criteria established by Simpson et al. [1], we find that intermittent separation occurs near 60 percent chord while detachment occurs at 84.2 percent chord. Comparison between the measured profiles and the sublimation visualization studies indicates that the flow visualization is signaling the location of incipient detachment (1 percent instantaneous backflow). Measured profiles are also considered in light of similarity techniques for boundary layers approaching separation. Outer region similarity is shown to vanish for profiles downstream of detachment.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 4 — Flow Fields for Incidence Angles of −1.5 and −8.5 Degrees

1989 ◽  
Author(s):  
W. C. Zierke ◽  
S. Deutsch
Keyword(s):  
Boundary Layers ◽  
Separation Bubble ◽  
Measurement Techniques ◽  
Leading Edge ◽  
Compressor Blade ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Suction Surface ◽  
Laminar Separation ◽  
Pressure Surface

Measurements, made with laser Doppler velocimetry, about a double-circular-arc compressor blade in cascade are presented for −1.5 and −8.5 degree incidence angles and a chord Reynolds number near 500,000. Comparisons between the results of the current study and those of our earlier work at a 5.0 degree incidence are made. It is found that in spite of the relative sophistication of the measurement techniques, transition on the pressure surface at the −1.5 degree incidence is dominated by a separation “bubble” too small to be detected by the laser Doppler velocimeter. The development of the boundary layers at −1.5 and 5.0 degrees are found to be similar. In contrast to the flow at these two incidence angles, the leading edge separation “bubble” is on the pressure surface for the −8.5 degree incidence. Here, all of the measured boundary layers on the pressure surface are turbulent — but extremely thin — while on the suction surface, a laminar separation/turbulent reattachment “bubble” lies between roughly 35% and 60% chord. This “bubble” is quite thin, and some problems in interpreting backflow data.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 4—Flow Fields for Incidence Angles of −1.5 and −8.5 Degrees

1990 ◽  
Vol 112 (2) ◽  
pp. 241-255 ◽  
Author(s):  
W. C. Zierke ◽  
S. Deutsch
Keyword(s):  
Boundary Layers ◽  
Separation Bubble ◽  
Measurement Techniques ◽  
Leading Edge ◽  
Compressor Blade ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Suction Surface ◽  
Laminar Separation ◽  
Pressure Surface

Measurements, made with laser Doppler velocimetry, about a double-circular-arc compressor blade in cascade are presented for −1.5 and −8.5 deg incidence angles and a chord Reynolds number near 500,000. Comparisons between the results of the current study and those of our earlier work at a 5.0 deg incidence are made. It is found that in spite of the relative sophistication of the measurement techniques, transition on the pressure surface at the −1.5 deg incidence is dominated by a separation “bubble” too small to be detected by the laser Doppler velocimeter. The development of the boundary layers at −1.5 and 5.0 deg is found to be similar. In contrast to the flow at these two incidence angles, the leading edge separation bubble is on the pressure surface for the −8.5 deg incidence. Here, all of the measured boundary layers on the pressure surface are turbulent—but extremely thin—while on the suction surface, a laminar separation/turbulent reattachment bubble lies between roughly 35 percent and 60 percent chord. This bubble is quite thin, and some problems in interpreting the backflow data are discussed.

scholarly journals The Effect of Nonequilibrium Boundary Layers on Compressor Performance

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Anthony M. J. Dickens ◽  
Robert J. Miller
Keyword(s):  
Boundary Layers ◽  
Compressor Blade ◽  
Surface Boundary ◽  
Order Model ◽  
Suction Surface ◽  
Surface Boundary Layer ◽  
Reduced Order ◽  
Compressor Performance ◽  
Profile Loss ◽  
Made In

The paper investigates the effect of nonequilibrium behavior of boundary layers on the profile loss of a compressor. The investigation is undertaken using both high fidelity simulations of a midheight section of a compressor blade and a reduced order model, MISES. The solutions are validated using experimental measurements made in the embedded stage of a multistage low speed compressor. The paper shows that up to 35% of the suction surface boundary layer of the compressor blade exhibits nonequilibrium behavior. The size of this region reduces as the Reynolds number is increased. The nonequilibrium behavior was found to reduce profile loss in cases of attached transition and raise loss where transition occurs through separation.

scholarly journals The Effect of Non-Equilibrium Boundary Layers on Compressor Performance

2017 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Anthony M. J. Dickens ◽  
Robert J. Miller
Keyword(s):  
Boundary Layers ◽  
Compressor Blade ◽  
Surface Boundary ◽  
Suction Surface ◽  
Surface Boundary Layer ◽  
Reduced Order ◽  
Compressor Performance ◽  
Profile Loss ◽  
Made In ◽  
Non Equilibrium

The paper investigates the effect of non-equilibrium behaviour of boundary layers on the profile loss of a compressor. The investigation is undertaken using both direct numerical simulation (DNS) of a mid-height section of a compressor blade and a reduced order model, MISES. The solutions are validated using experimental measurements made in the embedded stage of a multistage low speed compressor. The paper shows that up to 35% of the suction surface boundary layer of the compressor blade exhibits non-equilibrium behaviour. The size of this region reduces as the Reynolds number is increased. The non-equilibrium behaviour was found to reduce profile loss in most cases, however, in a range of cases where transition occurs through a small separation the presence of non-equilibrium behaviour was found to increase profile loss.

scholarly journals Oscillating Cascade Aerodynamics at Large Mean Incidence

1998 ◽  
Vol 120 (1) ◽  
pp. 122-130 ◽  
Author(s):  
D. H. Buffum ◽  
V. R. Capece ◽  
A. J. King ◽  
Y. M. EL-Aini
Keyword(s):  
Separation Bubble ◽  
Incidence Angle ◽  
Separated Flow ◽  
Leading Edge ◽  
Pressure Measurements ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Attached Flow ◽  
Blade Tip ◽  
Fan Blade

The aerodynamics of a cascade of airfoils oscillating in torsion about the midchord is investigated experimentally at a large mean incidence angle and, for reference, at a low mean incidence angle. The airfoil section is representative of a modern, low-aspect-ratio, fan blade tip section. Time-dependent airfoil surface pressure measurements were made for reduced frequencies of up to 1.2 for out-of-phase oscillations at a Mach number of 0.5 and chordal incidence angles of 0 and 10 deg; the Reynolds number was 0.9 × 106. For the 10 deg chordal incidence angle, a separation bubble formed at the leading edge of the suction surface. The separated flow field was found to have a dramatic effect on the chordwise distribution of the unsteady pressure. In this region, substantial deviations from the attached flow data were found, with the deviations becoming less apparent in the aft region of the airfoil for all reduced frequencies. In particular, near the leading edge the separated flow had a strong destabilizing influence while the attached flow had a strong stabilizing influence.

scholarly journals Oscillating Cascade Aerodynamics at Large Mean Incidence

1996 ◽  
Author(s):  
Daniel H. Buffum ◽  
Vincent R. Capece ◽  
Aaron J. King ◽  
Yehia M. El-Aini
Keyword(s):  
Separation Bubble ◽  
Incidence Angle ◽  
Separated Flow ◽  
Leading Edge ◽  
Pressure Measurements ◽  
Suction Surface ◽  
Airfoil Surface ◽  
Attached Flow ◽  
Blade Tip ◽  
Fan Blade

The aerodynamics of a cascade of airfoils oscillating in torsion about the midchord is investigated experimentally at a large mean incidence angle and, for reference, at a low mean incidence angle. The airfoil section is representative of a modern, low aspect ratio, fan blade tip section. Time-dependent airfoil surface pressure measurements were made for reduced frequencies of up to 1.2 for out-of-phase oscillations at a Mach number of 0.5 and chordal incidence angles of 0° and 10°; the Reynolds number was 0.9×106. For the 10° chordal incidence angle, a separation bubble formed at the leading edge of the suction surface. The separated flow field was found to have a dramatic effect on the chordwise distribution of the unsteady pressure. In this region, substantial deviations from the attached flow data were found with the deviations becoming less apparent in the aft region of the airfoil for all reduced frequencies. In particular, near the leading edge the separated flow had a strong destabilizing influence while the attached flow had a strong stabilizing influence.

scholarly journals Effect of Incidence Angle on Entropy Generation in the Boundary Layers on the Blade Suction Surface in a Compressor Cascade

Entropy ◽  
2019 ◽  
Vol 21 (11) ◽  
pp. 1049 ◽  
Author(s):  
Shi ◽  
Ma
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Entropy Generation ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Leading Edge ◽  
Generation Process ◽  
Mean Flow ◽  
Compressor Cascade ◽  
The Mean

The entropy generation that occurs within boundary layers over a C4 blade at a Reynolds number of 24,000 and incidence angles (i) of 0°,2.5°,5°,7.5°, and 10° are investigated experimentally using a particle image velocimetry (PIV) technique. To clarify the entropy generation process, the distribution of the entropy generation rates (EGR) and the unsteady flow structures within the PIV snapshots are analyzed. The results identify that for a higher incidence angle, the separation and transition occur further upstream, and the entropy generation in the boundary layer increases. When the separation takes place at the aft portion of the blade, the integral EGR decrease near the leading edge, remain minimal values in the middle portion of the blade, and increase sharply in the vicinity of the mean transition. More than 35% of the entropy generation is generated at the region downstream of the mean transition. When the separation occurs at the fore portion of the blade, the contributions of mean-flow viscous dissipation decrease to less than 20%. The entropy generation with elevated value can be detected over the entire blade. The entire integral entropy generation in the boundary layer increases sharply when the laminar separation bubble moves upstream to the leading edge.

scholarly journals Periodicity and Repetivity of Unsteady Measurements of an Annular Turbine Cascade at Off Design Flow Conditions

1993 ◽  
Author(s):  
A. Bölcs ◽  
H. Körbächer
Keyword(s):  
Steady State ◽  
Test Data ◽  
Separation Bubble ◽  
Incidence Angle ◽  
Leading Edge ◽  
Design Flow ◽  
Turbine Cascade ◽  
Flow Conditions ◽  
Suction Surface ◽  
Shock Region

A two-dimensional section of a gas turbine cascade has been investigated experimentally in an annular non-rotating cascade facility as regards to its steady-state and time-dependent aerodynamic characteristics at off-design flow conditions. The blades vibrated in the first traveling wave bending mode. Steady-state and unsteady data were obtained for an off-design incidence angle of about 22° and for an isentropic outlet Mach number of M2s=1.19. At this flow condition, a separation bubble was present on the suction surface close to the leading edge. A shock appeared at trans- and supersonic outlet flow conditions on the suction surface. The data showed high unsteady loads close to the leading edge and in the shock region. It was found that the steady and the unsteady pressures in the shock region on the blade surface seemed to be very sensitive to small changes in the flow conditions. The periodicity and repetitivity of the steady and the unsteady pressures (σ=180°) was checked at several circumferential channel positions. This was done to figure out to which extend test data obtained in an annular ring channel can serve as a basis for the comparison with numerically obtained data. The aim of this paper is to show where problems may arise when comparing calculated results with test data.

Flow Visualization Experiments on Tethered Flying Green Lacewings Chrysopa Dasyptera

1992 ◽  
Vol 169 (1) ◽  
pp. 143-163 ◽  
Author(s):  
DMITRY L. GRODNTTSKY ◽  
PAHVEL P. MOROZOV
Keyword(s):  
Spatial Structure ◽  
Functional Morphology ◽  
Insect Flight ◽  
Separation Bubble ◽  
Leading Edge ◽  
Vortex Wake ◽  
Green Lacewings ◽  
Visualization Experiments ◽  
Edge Separation ◽  
Stroke Cycle

Experiments on dust visualization of the flow around tethered flying green lacewings showed that, contrary to expectations based on the Weis-Fogh clap-andfling mechanism, a leading edge separation bubble does not exist near either fore-or hindwings. At the beginning of the stroke cycle each wing operates as an independent generator of vorticity. The vortex bubbles of all the four wings then unite, producing a single U-shaped bubble. A hypothetical spatial structure for the vortex wake is derived from a series of registrated sections of the wake illuminated with a flat light beam. Some problems of wing functional morphology and insect flight aerodynamics are also discussed.

Large Eddy Simulation of Wake-Shear Layer Interactions Over a Multi-Element Aerofoil

2020 ◽  
Author(s):  
Souvik Naskar ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Shear Layer ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Suction Surface ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Modern commercial airliners use multi-element aerofoils to enhance take-off and landing performance. Further, multielement aerofoil configurations have been shown to improve the aerodynamic characteristics of wind turbines. In the present study, high resolution Large Eddy Simulation (LES) is used to explore the low Reynolds Number (Re = 0.832 × 104) aerodynamics of a 30P30N multi-element aerofoil at an angle of attack, α = 4°. In the present simulation, wake shed from a leading edge element or slat is found to interact with the separated shear layer developing over the suction surface of the main wing. High receptivity of shear layer via amplification of free-stream turbulence leads to rollup and breakdown, forming a large separation bubble. A transient growth of fluctuations is observed in the first half of the separation bubble, where levels of turbulence becomes maximum near the reattachment and then decay depicting saturation of turbulence. Results of the present LES are found to be in close agreement with the experiment depicting high vortical activity in the outer layer. Some features of the flow field here are similar to those occur due to interactions of passing wake and the separated boundary layer on the suction surface of high lift low pressure turbine blades.

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