Laser-Doppler-Velocimetry Measurements in a Cascade of Compressor Blades at Stall

1998 ◽  
Vol 120 (1) ◽  
pp. 170-178 ◽  
Author(s):  
G. V. Hobson ◽  
A. J. H. Williams ◽  
H. J. Ganaim Rickel
Keyword(s):  
Flow Visualization ◽  
Laser Doppler Velocimetry ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Laser Sheet ◽  
Leading Edge ◽  
Flow Region ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Doppler Velocimetry

Compressor stall was simulated in the Low-Speed Cascade Wind Tunnel at the Turbopropulsion Laboratory of the Naval Postgraduate School. The test blades were of controlled-diffusion design with a solidity of 1.67, and stalling occurred at 10 deg of incidence above the design inlet air angle. All measurements were taken at a flow Reynolds number, based on chord length, of 700,000. Laser-sheet flow visualization techniques showed that the stalling process was unsteady and occurred over the whole cascade. Detailed laser-Doppler-velocimetry measurements over the suction side of the blades showed regions of continuous and intermittent reverse flow. The measurements of the continuous reverse flow region at the leading edge were the first data of their kind in the leading edge separation bubble. The regions of intermittent reverse flow, measured with laser-Doppler velocimeter, corresponded to the flow visualization studies. Blade surface pressure measurements showed a decrease in normal force on the blade, as would be expected at stall. Data are presented in a form that characterizes the unsteady positive and negative velocities about their mean, for both the continuous reverse flow regions and the intermittent reverse flow regions.

Laser-Doppler Velocimetry Measurements in a Cascade of Compressor Blades at Stall

1996 ◽  
Author(s):  
Garth V. Hobson ◽  
Andrew J. H. Williams ◽  
Humberto J. Ganaim Rickel
Keyword(s):  
Flow Visualization ◽  
Laser Doppler Velocimetry ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Laser Sheet ◽  
Leading Edge ◽  
Flow Region ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Doppler Velocimetry

Compressor stall was simulated in the Low Speed Cascade Wind Tunnel at the Turbopropulsion Laboratory. The test blades were of controlled-diffusion design with a solidity of 1.67, and stalling occurred at 10 degrees of incidence above the design inlet air angle. All measurements were taken at a flow Reynolds number, based on chord length, of 700 000. Laser-sheet flow visualization techniques showed that the stalling process was unsteady and occurred over the whole cascade. Detailed laser-Doppler-velocimetry measurements over the suction side of the blades showed regions of continuous and intermittent reverse flow. The measurements of the continuous reverse flow region at the leading edge were the first data of their kind in the leading edge separation bubble. The regions of intermittent reverse flow, measured with laser Doppler velocimeter, corresponded to the flow visualization studies. Blade surface pressure measurements showed a decrease in normal force on the blade as would be expected at stall. Data is presented in a form which characterizes the unsteady positive and negative velocities about their mean, for both the continuous reverse flow regions and the intermittent reverse flow regions.

scholarly journals Laser-Doppler Velocimetry Measurements Inside a Backward Curved Centrifugal Fan

2001 ◽  
Vol 7 (3) ◽  
pp. 173-181
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen
Keyword(s):  
Flow Rate ◽  
Turbulence Intensity ◽  
Laser Doppler Velocimetry ◽  
Reverse Flow ◽  
Flow Region ◽  
Design Flow ◽  
Laser Doppler ◽  
Centrifugal Fan ◽  
Doppler Velocimetry ◽  
Flow Rates

Laser-Doppler velocimetry (LDV) measurements are presented of relative mean velocity and turbulence intensity components inside the impeller passage of a centrifugal fan with twelve backward curved blades at design, under-design, and over-design flow rates. Additional LDV measurements were also performed at the volute outlet to examine the uniformity of the outlet flow for the three selected flow rates. Complementary flow visualization results in the tongue region are further presented. It is found that the number of characteristic flow regions and the average turbulence level increase with decreasing air flow rate. For the case of under-design flow rate, there are a through-flow region on the suction side, a reverse flow region on the pressure side, and a shear layer region in between. The corresponding average turbulence intensity is as high as 9.1% of blade tip velocity.

scholarly journals Pengukuran Intensitas Turbulensi Pada Susunan Sebaris Dan Dua Baris Pipa Bersirip Lingkaran Menggunakan Laser Doppler Velocimeter

REAKTOR ◽  
2017 ◽  
Vol 9 (2) ◽  
pp. 34
Author(s):  
N. Sinaga
Keyword(s):  
Laser Doppler Velocimetry ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Doppler Velocimetry

Artikel ini memaparkan hasil pengukuran kecepatan dan intensitas turbulensi di daerah hilir susunan sebaris dan dua baris pipa bersirip, yang dilator belakangi oleh anggapan bahwa, laju perpindahan kalor dan kerugian tekanan sangat dipengaruhi oleh intensitas turbulensi yang terjadi. Pengukuran dilakukan di dalam seksi uji sebuah kanal hidrolik  berukuran 600 mm x 150 mm x 150 mm, dengan menggunakan teknik Laser Doppler Velocimetry. Pipa dan sirip disusun dalam konfigurasi sebaris dan berseling, dengan dia,eter luar silinder dan sirip masing-masing 16 mm dan 33,6 mm. kecepatan aliran masuk seksi uji dijaga konstan sebesar 1,4 m/detik atau setara dengan Re= 26000, berdasarkan kecepatan arus bebas dan diameter pipa. Disimpulkan bahwa harga intensitas turbulensi dipengaruhi oleh cara  penyusunan pipa dan sirip, dimana susunan pipa berseling cenderung membangkitkan turbulensi yang lebih besar dibandingkan dengan susunan pipa segaris. Akan tetapi, didapatkan pula, intensitas turbulensi susunan pipa segaris dapat ditingkatkan dengan menyusun sirip secara berseling.Kata Kunci : intensitas turbulensi, pipa bersirip, susunan segaris, susunan berseling

Investigation of the separation bubble formed behind the sharp leading edge of a flat plate at incidence

2000 ◽  
Vol 214 (3) ◽  
pp. 157-176 ◽  
Author(s):  
M J Crompton ◽  
R V Barrett
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Laser Doppler Anemometry ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Flow Direction ◽  
Leading Edge ◽  
Laser Doppler ◽  
Static Pressure Distribution ◽  
Sharp Leading Edge

Detailed measurements of the separation bubble formed behind the sharp leading edge of a flat plate at low speeds and incidence are reported. The Reynolds number based on chord length ranged from 0.1 × 105 to 5.5 × 105. Extensive use of laser Doppler anemometry allowed detailed velocity measurements throughout the bubble. The particular advantages of laser Doppler anemometry in this application were its ability to define flow direction without ambiguity and its non-intrusiveness. It allowed the mean reattachment point to be accurately determined. The static pressure distribution along the plate was also measured. The length of the separation bubble was primarily determined by the plate incidence, although small variations occurred with Reynolds number because of its influence on the rate of entrainment and growth of the shear layer. Above about 105, the Reynolds number effect was no longer evident. The reverse flow boundary layer in the bubble exhibited signs of periodic stabilization before separating close to the leading edge, forming a small secondary bubble rotating in the opposite sense to the main bubble.

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.

scholarly journals Numerical investigation of the effect of airfoil thickness on onset of dynamic stall

2019 ◽  
Vol 870 ◽  
pp. 870-900 ◽  
Author(s):  
Anupam Sharma ◽  
Miguel Visbal
Keyword(s):  
Reverse Flow ◽  
Separation Bubble ◽  
Time Integration ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Flow Region ◽  
Dynamic Stall ◽  
Implicit Time ◽  
Gradual Change ◽  
Dynamic Simulations

Effect of airfoil thickness on onset of dynamic stall is investigated using large eddy simulations at chord-based Reynolds number of 200 000. Four symmetric NACA airfoils of thickness-to-chord ratios of 9 %, 12 %, 15 % and 18 % are studied. The three-dimensional Navier–Stokes solver, FDL3DI is used with a sixth-order compact finite difference scheme for spatial discretization, second-order implicit time integration and discriminating filters to remove unresolved wavenumbers. A constant-rate pitch-up manoeuver is studied with the pitching axis located at the airfoil quarter chord. Simulations are performed in two steps. In the first step, the airfoil is kept static at a prescribed angle of attack ($=4^{\circ }$). In the second step, a ramp function is used to smoothly increase the pitch rate from zero to the selected value and then the pitch rate is held constant until the angle of attack goes past the lift-stall point. The solver is verified against experiments for flow over a static NACA 0012 airfoil. Static simulation results of all airfoil geometries are also compared against XFOIL predictions with a generally favourable agreement. FDL3DI predicts two-stage transition for thin airfoils (9 % and 12 %), which is not observed in the XFOIL results. The dynamic simulations show that the onset of dynamic stall is marked by the bursting of the laminar separation bubble (LSB) in all the cases. However, for the thickest airfoil tested, the reverse flow region spreads over most of the airfoil and reaches the LSB location immediately before the LSB bursts and dynamic stall begins, suggesting that the stall could be triggered by the separated turbulent boundary layer. The results suggest that the boundary between different classifications of dynamic stall, particularly leading edge stall versus trailing edge stall, is blurred. The dynamic-stall onset mechanism changes gradually from one to the other with a gradual change in some parameters, in this case, airfoil thickness.

scholarly journals Shock Measurements Based on Pendulum Excitation and Laser Doppler Velocimetry: Primary Calibration by SI-Traceable Distance Measurements

2020 ◽  
Vol 125 ◽  
Author(s):  
Muhammad Y. Afridi ◽  
Jon Geist ◽  
Michael Gaitan
Keyword(s):  
Laser Doppler Velocimetry ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Doppler Velocimetry ◽  
Rigid Block ◽  
Random Errors ◽  
Type B ◽  
Velocity Data ◽  
Distance Measurements ◽  
Before And After

A new method is described to provide a primary calibration of shock measurements produced by a shock measurement system consisting of pendulum excitation and laser Doppler velocimetry. The method uses the laser Doppler velocimeter to determine the total distance traveled by a rigid block that slides along a Teflon (fluorocarbon) channel after being struck by a pendulum head, and the resulting distance is compared to the distance measured by an SI-traceable length measurement. The instantaneous velocity of the block is measured by the velocimeter and is used to calculate the displacement of the block by integrating the velocity data. The result is compared to the displacement measured using calibrated rulers and calipers. The method was applied to an independently calibrated commercial velocimeter for impact accelerations ranging from 2000 to 30,000 m/s2. The results of the independent mechanical-displacement measurements agreed with those from the commercial velocimeter to within ±0.3 %, with better agreement above accelerations of order 10,000 m/s2 to within ±0.1 %. A conservative, upper-bound, uncertainty analysis included the effects of noise and other random errors, as well as type B estimates for systematic errors from occasional momentary demodulation failures (dropouts), use of a different number of rulers before and after shock distance measurement, and the relative frequency response of the velocimeter.

Cutaneous circulation is correlated with Merino wool production

1994 ◽  
Vol 45 (4) ◽  
pp. 757 ◽  
Author(s):  
Edwards JE Hocking ◽  
PI Hynd
Keyword(s):  
Blood Flow ◽  
Laser Doppler Velocimetry ◽  
Vascular Tissue ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Doppler Velocimetry ◽  
Wool Production ◽  
Merino Wool ◽  
Wool Growth ◽  
Cutaneous Circulation

Laser Doppler velocimetry was used to investigate the cutaneous circulation and its relationship to wool growth in Finewool and Strongwool Merinos. Skin blood flow measured with the laser Doppler velocimeter (LDV) was highly correlated with estimates of blood flow obtained using 57Co-labelled microspheres (R2 = 0.85; P < 0.01), although the absolute values estimated by the microsphere technique were significantly higher (P < 0.001). Strongwool Merinos had a greater rate of blood flowing through the skin than Finewool Merinos, and this was associated with both wool production per unit area of skin (R2 = 0.27, P < 0.01) and with the total volume of germinative tissue in the skin (R2 = 0.54; P < 0.04). The relationship between the microvascular anatomy of the skin and blood flow was also examined in four Finewool Merinos and four Strongwool Merinos. Silicone rubber was infused into the deep circumflex iliac artery within the abdominal flank, from which an index of the area of vascular tissue per unit volume of skin was estimated. This index was not related to blood flow, wool growth or follicle density within nor between strains of Merinos. Both the usefulness and limitations of the LDV are discussed, and it was concluded that (a) blood flow has an important role in the level of wool produced both within and between strains of Merinos, and (b) laser Doppler velocimetry is a useful tool for the study of blood flow in the skin of sheep.

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