Effects of Leading Edge Sweep on Unsteady Cavitation in Inducers : 1st Report, Improvements of Cavity length Due to Forward and Backward Sweep

Experimental results are given concerning the behavior of the flow around three-dimensional base-vented hydrofoils with wetted upper side. The influence of planform is given particular consideration so that the sections of the foils are simple wedges with rounded noses. Results concern cavity configuration, the relation between the air flow rate and cavity pressure, leading-edge cavitation, cavity length, pulsation frequency, and force coefficients.

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Steady Performance of a Flexible Hydrofoil Near a Free Surface

Journal of Ship Research ◽

10.5957/jsr.1990.34.4.302 ◽

1990 ◽

Vol 34 (04) ◽

pp. 302-310

Author(s):

Salwa M. Rashad ◽

Theodore Green

Keyword(s):

Mathematical Model ◽

Free Surface ◽

Cavity Length ◽

Leading Edge ◽

Cavity Flow ◽

Cavitation Number ◽

Deformation Characteristics ◽

Flow Depth ◽

Lift And Drag ◽

The Galerkin Method

A linearized cavity-flow theory is used to develop a mathematical model to study the steady characteristics of a flexible hydrofoil near a free surface. The Galerkin method is employed to account for the mutual interaction between the fluid and structure forces. Cheng and Rott's method [1]2 is used to derive general expressions for the deformation characteristics in steady flow of an arbitrarily shaped hydrofoil, with a clamped trailing edge and free leading edge. From the analysis it is possible to determine the lift and drag coefficients, cavity length, and the foil steady deformation for any given specific foil shape, cavitation number, angle of attack, flow depth/chord ratio and rigidity. Sample numerical results are given, and the effects of flexibility and the proximity of the free surface are discussed. Chordwise flexibility tends to increase drag and decrease lift coefficients. This effect is more serious near the free surface. A slight increase of the thickness near the leading edge diminishes the flexibility effects.

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Effects of Leading Edge Sweep on the Cavitating Characteristics of Inducer Pumps

International Journal of Rotating Machinery ◽

10.1155/s1023621x01000343 ◽

2001 ◽

Vol 7 (6) ◽

pp. 397-404 ◽

Cited By ~ 13

Author(s):

Allan J. Acosta ◽

Yoshinobu Tsujimoto ◽

Yoshiki Yoshida ◽

Seiji Azuma ◽

Paul Cooper

Keyword(s):

Velocity Component ◽

Cavity Length ◽

Leading Edge ◽

Favorable Effect ◽

Geometrical Effects

It is well known that leading edge sweep has a favorable effect on the cavitation of turbomachines. However, the mechanisms of the improvement have not been made clear. It has been shown that the lift and the drag on a cavitating swept single hydrofoil can be correlated fairly well based on the velocity component normal to the leading edge. In the present paper, such correlations for swept cascades are derived and the results are examined, neglecting the full geometrical effects of the inducer rotor. It is shown that the correlations can simulate the developments of various types of cavitation, including alternate blade cavitation, rotating cavitation, and cavitation surge. This result is based on the observation that the steady cavity length, as well as the developments ofvarious types ofcavitation, is fairly well predicted by the correlation.

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Thermodynamic Effect on a Cavitating Inducer—Part I: Geometrical Similarity of Leading Edge Cavities and Cavitation Instabilities

Journal of Fluids Engineering ◽

10.1115/1.4001006 ◽

2010 ◽

Vol 132 (2) ◽

Cited By ~ 6

Author(s):

Jean-Pierre Franc ◽

Guillaume Boitel ◽

Michel Riondet ◽

Éric Janson ◽

Pierre Ramina ◽

...

Keyword(s):

Transit Time ◽

Cavity Length ◽

Cold Water ◽

Rotation Speed ◽

Leading Edge ◽

Cavitation Number ◽

Thermodynamic Effect ◽

Cavity Closure ◽

Cavity Development ◽

Onset Of Cavitation

The thermodynamic effect on a cavitating inducer is investigated from joint experiments in cold water and Refrigerant 114. The analysis is focused on leading edge cavitation and cavitation instabilities, especially on alternate blade cavitation and supersynchronous rotating cavitation. The cavity length along cylindrical cuts at different radii between the hub and casing is analyzed with respect to the local cavitation number and angle of attack. The similarity in shape of the cavity closure line between water and R114 is examined and deviation caused by thermodynamic effect is clarified. The influence of rotation speed on cavity length is investigated in both fluids and analyzed on the basis of a comparison of characteristic times, namely, the transit time and a thermal time. Thermodynamic delay in the development of leading edge cavities is determined and temperature depressions within the cavities are estimated. Thresholds for the onset of cavitation instabilities are determined for both fluids. The occurrence of cavitation instabilities is discussed with respect to the extent of leading edge cavitation. The thermodynamic delay affecting the occurrence of cavitation instabilities is estimated and compared with the delay on cavity development.

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An Experimental Investigation of Cavitation Inception and Development on a Two-Dimensional Hydrofoil

Journal of Ship Research ◽

10.5957/jsr.2000.44.4.259 ◽

2000 ◽

Vol 44 (04) ◽

pp. 259-269

Author(s):

J.-A. Astolfi ◽

J.-B. Leroux ◽

P. Dorange ◽

J.-Y. Billard ◽

F. Deniset ◽

...

Keyword(s):

Reynolds Number ◽

Velocity Distribution ◽

Cavity Length ◽

Pressure Coefficient ◽

Sudden Change ◽

Leading Edge ◽

Cavitation Number ◽

Cavity Surface ◽

Cavitation Inception ◽

Flow Visualizations

The cavitation inception (and desinent) angles at given cavitation numbers, the velocity distribution, and the resulting pressure coefficient, together with the sheet cavity lengths developing on a hydrofoil surface, have been investigated experimentally for a Reynolds number ranging between 0.4 × 106 and 1.2 × 106. It is shown that the cavitation inception (and desinent) angle decreases progressively when the Reynolds number increases and tends to be close to the theoretical (inviscid) value when the Reynolds number is larger than 0.8 × 106. The magnitude and the position of the minimum surface pressure coefficient, inferred from the velocity distribution measured at the leading edge, were shown to be dependent upon the Reynolds number as well. An investigation of the cavitating flow velocity field upstream of the cavity and on the cavity surface showed that the pressure in the cavity was very close to the vapor pressure. The detachment location of the cavity was found to occur very close to the leading edge (at about one hundredth of the foil chord for both Re = 0.4 × 10® and Re = 0.8 × 106). The length cavities measured from flow visualizations exhibited a sudden change for a Reynolds number passing from 0.7 × 106 to 0.8 × 106 with a given angle of incidence (α= 6 deg) and cavitation number (σ = 1.3). Photographs of the sheet cavity show that the cavity length can be inferred also from the extent of the region for which the pressure coefficient is close to the cavitation number. It was shown to have the values l/c 0.03 for Re = 0.4 × 106 and l/c ~ 0.06 for Re = 0.8 × 10® and σ = 1.8 with the latter value very close to the value obtained from flow visualizations. Photographs of the cavity show that the increase of the cavity length is coupled to the migration, towards the leading edge, of a transition point on the cavity surface when the Reynolds number increases.

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An Experimental Investigation of Thermal Effects in a Cavitating Inducer

Journal of Fluids Engineering ◽

10.1115/1.1792278 ◽

2004 ◽

Vol 126 (5) ◽

pp. 716-723 ◽

Cited By ~ 78

Author(s):

Jean-Pierre Franc ◽

Claude Rebattet ◽

Alain Coulon

Keyword(s):

Thermal Effects ◽

Cavity Length ◽

Cold Water ◽

Pressure Fluctuations ◽

Leading Edge ◽

Operating Conditions ◽

Fluid Temperature ◽

Two Phase ◽

Thermodynamic Effect ◽

Comparison Of Tests

The thermal effects which affect the development of leading edge cavitation in an inducer were investigated experimentally using refrigerant R114. For different operating conditions, the evolution of the cavity length with the cavitation parameter was determined from visualizations. The tests were conducted up to two-phase breeding. The comparison of tests in R114 and in cold water allowed us to estimate the amplitude of the thermodynamic effect. The results show that the B-factor depends primarily upon the degree of development of cavitation but not significantly upon other parameters such as the inducer rotation speed or the fluid temperature, at least in the present domain of investigation. These trends are qualitatively in agreement with the classical entrainment theory. In addition, pressure fluctuations spectra were determined in order to detect the onset of cavitation instabilities and particularly of alternate blade cavitation and rotating cavitation. If the onset of alternate blade cavitation appeared to be connected to a critical cavity length, the results are not so clear concerning the onset of rotating cavitation.

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The Study of Blockages Effect at Leading Edge on Rectangular Cavity in Subsonic Flow Using Particle Image Velocimetry (PIV)

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.300-301.781 ◽

2013 ◽

Vol 300-301 ◽

pp. 781-784

Author(s):

Ahsan Nur Mubarak Annuar ◽

Azmin Shakrine M. Rafie ◽

Mohamed Thariq Hameed Sultan

Keyword(s):

Particle Image Velocimetry ◽

Velocity Profile ◽

Particle Image ◽

Cavity Length ◽

Leading Edge ◽

Rectangular Cavity ◽

Mean Velocity ◽

Subsonic Wind Tunnel ◽

Image Velocimetry ◽

Image Pairs

In this present paper, laminar cavity flow is analysed at Re = 5.12 x 104 based on cavity length. The experiments were conducted in an open subsonic wind tunnel using Particle Image Velocimetry (PIV). A rectangular cavity with constant depth of 4 cm with length-to-depth ratio of 4 was used. Several types of blockage had been located at the leading edge of cavity and each experiment was performed by acquiring 700 image pairs to filter out the velocity vectors. The results are given in terms of mean velocity profile accordingly and compared thoroughly by dividing cavity into 4 sections. The result had been shown in mean velocity profile in u and v velocity component.

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