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

1999 ◽  
Vol 122 (1) ◽  
pp. 164-173 ◽  
Author(s):  
J.-A. Astolfi ◽  
P. Dorange ◽  
J.-Y. Billard ◽  
I. Cid Tomas
Keyword(s):  
Reverse Flow ◽  
Pressure Coefficient ◽  
Large Angle ◽  
Separated Flow ◽  
Leading Edge ◽  
Angle Of Incidence ◽  
Two Dimensional ◽  
Velocity Measurements ◽  
Cavitation Inception ◽  
Minimum Pressure

Cavitation inception and development on a two-dimensional foil with an Eppler E817 cross section issued from an inverse calculus have been experimentally investigated. The foil is theoretically designed to have a wide cavitation-free bucket allowing a large range of cavitation-free angle of incidence (Eppler, R., 1990, Airfoil Design and Data, Springer-Verlag, Berlin). The inception cavitation numbers, the noise level, the velocity distribution, the minimum pressure coefficient, the cavitation patterns (bubble, leading edge “band type” cavitation, attached sheet cavity), together with the sheet cavity length have been experimentally determined. Effects on the velocity field have been studied too with a slightly developed cavitation. For angles of incidence larger than 1 deg, a great difference exists between the inception cavitation number and the theoretical minimum pressure coefficient. However it is in agreement with the measured one obtained from velocity measurements (for 0 deg<α<6 deg). Discrepancy between theory and experiment on scale models is generally attributed to a flow separation at the leading edge. Although there are some indications of a separated flow at the leading edge, the velocity measurements do not show reverse flow with clearly detected negative velocities excepted for a large angle of incidence equal to 10 deg. Concerning sheet cavity development, the length cavity is found to scale as [σ/2α−αiσ]−m with m close to 2, for length cavities that do not exceed half the foil chord and for σ/2α−αiσ larger than about 30. [S0098-2202(00)00201-7]

Viscous and Nuclei Effects on Hydrodynamic Loadings and Cavitation of a NACA 66 (MOD) Foil Section

1989 ◽  
Vol 111 (3) ◽  
pp. 306-316 ◽  
Author(s):  
Y. T. Shen ◽  
P. E. Dimotakis
Keyword(s):  
Pressure Distribution ◽  
Pressure Coefficient ◽  
Leading Edge ◽  
Full Scale ◽  
Pressure Loading ◽  
Foil Surface ◽  
Negative Minimum ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Bubble Cavitation

A series of experiments has been conducted on a two-dimensional NACA 66 (MOD) foil to examine the effects of viscosity and nuclei on cavitation inception. In this paper the main discussions center on two foil angles having different types of pressure loadings to represent a propeller blade section operating at design and off-design conditions. At one degree design angle of attack the foil experiences a rooftop-type gradually varying pressure distribution. At three degrees off-design angle of attack the foil experiences a sharp suction pressure peak near the leading edge. Cebeci’s viscid/inviscid interactive code is used to compute the viscous scale effects on the development of the boundary layer, lift, drag and pressure distribution on the foil. Chahine’s multibubble interaction code is used to compute the effect of nuclei, test speeds, foil size and foil surface on traveling bubble cavitation. Both computer codes are found to agree satisfactorily with the experimental measurements reported here. Two assumptions commonly used to predict full scale surface cavitation from model tests are examined experimentally and theoretically. The first assumption states that cavitation inception occurs when the static pressure reaches the vapor pressure. On the contrary, the experiments showed that the water flowing over the foil surface sustained significant amounts of tension during inception of midchord bubble cavitation as well as leading edge sheet cavitation. The second assumption states that there is no scale effect on the values of negative minimum pressure coefficient. In the case of a rooftop-type pressure loading, the second assumption is supported by the pressure numerical calculations. However, in the case of a pressure loading with a strong suction peak near the leading edge the value of negative minimum pressure coefficient is as much as 12 to 15 percent lower on a model than at full scale.

A Note on the Causes of Thin Aerofoil Stall

1959 ◽  
Vol 63 (588) ◽  
pp. 724-730 ◽  
Author(s):  
T. W. F. Moore
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Reverse Flow ◽  
Leading Edge ◽  
Two Dimensional ◽  
Separation Theory ◽  
Turbulent Separation

Recent Researches have led to some possible explanations for thin aerofoil stalling behaviour. Apart from the Owen Klanfer criterion these are the reverse flow breakdown hypothesis of McGregor and Wallis's turbulent separation theory.This note describes simple theoretical boundary layer calculations which indicate the feasibility of Wallis's hypothesis. In addition the results of some experiments on a thin two-dimensional aerofoil with various leading edge configurations with Reynolds number, based on model chord, of 1.8 million and 1 million support either of these hypotheses, depending on the leading edge configuration. It is concluded that thin aerofoil stall can occur broadly, through either of the suggested mechanisms, depending on conditions in the nose region.

scholarly journals Optimization for Cavitation Inception Performance of Pump-Turbine in Pump Mode Based on Genetic Algorithm

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Ran Tao ◽  
Ruofu Xiao ◽  
Wei Yang ◽  
Fujun Wang ◽  
Weichao Liu
Keyword(s):  
Genetic Algorithm ◽  
Pressure Drop ◽  
Cfd Simulation ◽  
Pressure Coefficient ◽  
Leading Edge ◽  
Algorithm Optimization ◽  
Pump Mode ◽  
Local Flow ◽  
Cavitation Inception ◽  
Blade Thickness

Cavitation is a negative factor of hydraulic machinery because of its undesirable effects on the operation stability and safety. For reversible pump-turbines, the improvement of cavitation inception performance in pump mode is very important due to the strict requirements. The geometry of blade leading edge is crucial for the local flow separation which affects the scale and position of pressure drop. Hence, the optimization of leading edge shape is helpful for the improvement of cavitation inception performance. Based on the genetic algorithm, optimization under multiple flow rate conditions was conducted by modifying the leading edge ellipse ratio and blade thickness on the front 20% meanline. By using CFD simulation, optimization was completed with obvious improvements on the cavitation inception performance. CFD results show that the pressure drop location had moved downstream with the increasement of the minimum pressure coefficient. Experimental verifications also got an obvious enhancement of cavitation inception performance. The stability and safety was improved by moving the cavitation inception curve out of the operating range. This optimization is proved applicable and effective for the engineering applications of reversible pump-turbines.

Transition Over C4 Leading Edge and Measurement of Intermittency Factor Using PDF of Hot-Wire Signal

1995 ◽  
Author(s):  
Birinchi K. Hazarika ◽  
Charles Hirsch
Keyword(s):  
Separated Flow ◽  
Leading Edge ◽  
Threshold Value ◽  
Angle Of Incidence ◽  
Bypass Transition ◽  
Hot Wire ◽  
Suction Surface ◽  
Intermittency Factor ◽  
Conditional Averaging

The variation of intermittency factors in the transition region of a C4 leading edge flat plate is measured at three incidence angles in a low turbulence free-stream. During the determination of intermittency factor the threshold value of the detector function and the validity of conditional averaging are verified by a method based on the direct application of PDF of the hot-wire output. As the angle of incidence is increased, the transition progressively moves through all the three modes on the suction surface : at zero incidence the bypass transition, at 2° incidence the natural transition and at 4° incidence the separated-flow transition occur respectively. All the three modes of transition exhibited the chord-wise intermittency factor variation in accordance with Narasimha’s universal intermittency distribution, thus the method based on spot production rate is applicable to all the three modes of transition. In the transition zone of the attached boundary layers, the conditionally averaged inter-turbulent profiles are fuller than the Blasius profile while the conditionally averaged turbulent profiles follow a logarithmic profile with a variable additive parameter.

scholarly journals Viscous Effects in the Inception of Cavitation on Axisymmetric Bodies

1973 ◽  
Vol 95 (4) ◽  
pp. 519-527 ◽  
Author(s):  
V. H. Arakeri ◽  
A. J. Acosta
Keyword(s):  
Boundary Layer ◽  
Experimental Evidence ◽  
Flow Separation ◽  
Pressure Coefficient ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Visualization Method ◽  
Viscous Effects ◽  
Cavitation Inception ◽  
Axisymmetric Bodies

Cavitation inception and development on two axisymmetric bodies was studied with the aid of a Schlieren flow visualization method developed for that purpose. Both bodies were found to exhibit a laminar boundary layer separation; cavitation inception was observed to occur within this region of separated flow. The incipient cavitation index was found to be closely correlated with the magnitude of the pressure coefficient at the location of flow separation on one of the bodies. There is also experimental evidence that events at the site of turbulent reattachment of the separated flow may also greatly influence cavitation inception.

The Effects of Turbulence Stimulators on Cavitation Inception of Axisymmetric Headforms

1986 ◽  
Vol 108 (2) ◽  
pp. 261-268 ◽  
Author(s):  
T. T. Huang
Keyword(s):  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Repeated Measurements ◽  
Direct Transition ◽  
Patch Type ◽  
Mean Values ◽  
Cavitation Inception ◽  
Minimum Pressure ◽  
Small Band ◽  
Made In

Cavitation inception observations were made in the DTNSRDC 36-inch water tunnel on three axisymmetric headforms with and without various turbulence stimulators installed. Direct transition measurements, made on two of the headforms with and without distributed surface roughness, were found to correlate reasonably well with the computed spatial amplification factors, eN, at the separation locations. The computed eN factors were then used to estimate transition at other test conditions (without direct transition measurements). The predicted transition locations on all three smooth headforms occur at positions considerably aft of the minimum pressure locations. The three smooth headforms have different types of incipient cavitation—small band, transient spot, traveling bubble, and attached spot. The measured cavitation inception numbers for those cases are all significantly smaller than the computed negative values of the minimum pressure coefficient, −Cpmin. The predicted transition locations on the three headforms with densely and loosely packed 60-μm distributed roughness occur at a considerable distance upstream of the minimum pressure locations. Therefore, the flows over all three headforms with distributed roughness are turbulent at the Cpmin locations for the Reynolds numbers tested. Under this condition, the measured cavitation inception numbers are found to approximate well with the values of −Cpmin. The incipient cavitation is in the form of attached small bubble lines evenly distributed around the minimum pressure locations. The measured cavitation inception numbers for the three headforms with an isolated roughness band located upstream of the minimum pressure locations are found to approximate the computed values of −Cpmin when the roughness Reynolds number (Rk = ukK/ν) is equal to 600 and to be smaller than the values of −Cpmin when the value of Rk is less than 600. The incipient cavitation observed is attached patch type cavitation occurring in the vicinity of the minimum pressure location. The uncertainty of the measured cavitation inception numbers, in terms of the maximum deviations form the mean values of repeated measurements, is generally less than 0.02.

Effect of Hydrofoil Planform on Tip Vortex Roll-Up and Cavitation

1995 ◽  
Vol 117 (1) ◽  
pp. 162-169 ◽  
Author(s):  
D. H. Fruman ◽  
P. Cerrutti ◽  
T. Pichon ◽  
P. Dupont
Keyword(s):  
Reynolds Number ◽  
Incidence Angle ◽  
Pressure Coefficient ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Velocity Profiles ◽  
The Other ◽  
Tip Vortex ◽  
Trailing Edge ◽  
Cavitation Inception

The effect of the planform of hydrofoils on tip vortex roll-up and cavitation has been investigated by testing three foils having the same NACA 16020 cross section but different shapes. One foil has an elliptical shape while the other two are shaped like quarters of ellipses; one with a straight leading edge and the other with a straight trailing edge. Experiments were conducted in the ENSTA, Ecole Navale and IMHEF cavitation tunnels with homologous foils of different sizes to investigate Reynolds number effects. Hydrodynamic forces as well as cavitation inception and desinence performance were measured as a function of Reynolds number and foil incidence angle. Laser Doppler measurements of the tangential and axial velocity profiles in the region immediately downstream of the tip were also performed. At equal incidence angle and Reynolds number, the three foils show different critical cavitation conditions and the maximum tangential velocity near the tip increases as the hydrofoil tip is moved from a forward to a rear position. However, the velocity profiles become more similar with increasing downstream distance, and at downstream distances greater than one chord aft of the tip, the differences between the foils disappear. The rate of tip vortex roll-up is much faster for the straight leading edge than for the straight trailing edge foil and, in the latter case, a significant portion of the roll-up occurs along the foil curved leading edge. The minimum of the pressure coefficient on the axis of the vortex was estimated from the velocity measurements and correlated with the desinent cavitation number for the largest free stream velocities. The correlation of data is very satisfactory. At the highest Reynolds number tested and at equal lift coefficients, the straight leading edge foil displays the most favorable cavitation desinent numbers.

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

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.

scholarly journals Flow Past a Flat Plate With a Vortex/Sink Combination

1996 ◽  
Vol 63 (2) ◽  
pp. 543-550 ◽  
Author(s):  
N. J. Mourtos ◽  
M. Brooks
Keyword(s):  
Flat Plate ◽  
Current Model ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Leading Edge ◽  
Classical Solutions ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Kutta Condition ◽  
Attached Flow

This paper presents a potential flow model for the leading edge vortex over a two-dimensional flat plate at an angle of attack. The paper is an extension of a model by Saffman and Sheffield (1977). A sink has been added in this model in an effort to satisfy the Kutta condition at both the leading edge and the trailing edge of the plate. The introduction of the sink was inspired by the fact that most steady vortices in nature appear in combination with a flow feature which can be interpreted as a sink at their cores when the flow is analyzed in a two-dimensional observation plane. As in the Saffman and Sheffield model, the presence of a vortex results in increased lift; however, in the current model a unique vortex/sink position is found at each angle of attack. A comparison has also been made between the lift and the drag of this model and the corresponding results for two classical solutions of flow over a flat plate: (a) the fully attached flow with the Kutta condition satisfied at the trailing edge only and (b) the Helmholtz solution of fully separated flow.

Transition Over C4 Leading Edge and Measurement of Intermittency Factor Using PDF of Hot-Wire Signal

1997 ◽  
Vol 119 (3) ◽  
pp. 412-425 ◽  
Author(s):  
B. K. Hazarika ◽  
C. Hirsch
Keyword(s):  
Separated Flow ◽  
Leading Edge ◽  
Threshold Value ◽  
Angle Of Incidence ◽  
Bypass Transition ◽  
Hot Wire ◽  
Suction Surface ◽  
Intermittency Factor ◽  
Conditional Averaging

The variation of intermittency factors in the transition region of a C4 leading edge flat plate is measured at three incidence angles in a low-turbulence free stream. During the determination of intermittency factor, the threshold value of the detector function and the validity of conditional averaging are verified by a method based on the direct application of PDF of the hot-wire output. As the angle of incidence is increased, the transition progressively moves through all the three modes on the suction surface: at zero incidence the bypass transition, at 2 deg incidence the natural transition, and at 4 deg incidence the separated-flow transition occur, respectively. All three modes of transition exhibited the chordwise intermittency factor variation in accordance with Narasimha’s universal intermittency distribution; thus, the method based on spot production rate is applicable to all the three modes of transition. In the transition zone of the attached boundary layers, the conditionally averaged interturbulent profiles are fuller than the Blasius profile, while the conditionally averaged turbulent profiles follow a logarithmic profile with a variable additive parameter.

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