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.

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]

Experimental investigation of pressure distribution characteristics of a flying-wing model using PSP

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040088
Author(s):  
Hongbiao Wang ◽  
Baoshan Zhu ◽  
Jian Xiong
Keyword(s):  
Pressure Distribution ◽  
Surface Pressure ◽  
Pressure Measurement ◽  
Pressure Coefficient ◽  
Leading Edge ◽  
Distribution Characteristics ◽  
Characteristic Analysis ◽  
Camera System ◽  
Wing Model ◽  
The Impact

To investigate the static pressure distribution characteristics of a flying-wing model, an advanced binary pressure sensitive paint (PSP) technique is introduced. It has low-temperature sensitivity and can compensate the errors induced by temperature. The pressure measurement test was performed in 0.6 m trisonic wind tunnel at angles of attack ranging from 0[Formula: see text] to 12[Formula: see text] in supersonic condition, adopting a low-aspect-ratio flying wing model. The binary PSP is sprayed on the upper surface of the model while pressure taps are installed on the upper surface of the right wing. Luminescent images of two probes are acquired with a color charge-coupled-device camera system and processed with calibration results. During the test, the surface pressure is measured by PSP and transducer, respectively. The results obtained show that the binary paint is of advantage to the surface pressure measurement and flow characteristic analysis. The high-resolution pressure spectra at different angle of attack clearly reveal the impact of leading edge vortex on the upper surface pressure distributions. The pressure measured by PSP also agrees well with the pressure tap results. The root mean square error of pressure coefficient is 0.01 at [Formula: see text], [Formula: see text].

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.

scholarly journals A Parametric Design Method for Hybrid Airfoils for Icing Wind Tunnel Test

2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Zhao Li ◽  
Guang-jun Yang ◽  
Xiao-yan Tong ◽  
Feng Jiang
Keyword(s):  
Flow Field ◽  
Parametric Design ◽  
Design Method ◽  
Pressure Coefficient ◽  
Wind Tunnel Test ◽  
Leading Edge ◽  
Full Scale ◽  
Navier Stokes ◽  
Ice Accretion ◽  
Multiple Control

The size of aircraft models that can be tested in icing wind tunnels is limited by the dimensions of the facilities in present; it is an effective method to replace the large model with a hybrid airfoil to carry out the experiment. A design method of multiple control points for hybrid airfoil based on the similarity of flow field in the leading edge of airfoil is proposed. Aiming at generating the full-scale flow field and ice accretion on the leading edge, multiobjective genetic optimization algorithm is used to design the hybrid airfoil under different conditions by combining the airfoil parameterization and solution of spatial constraint. Pressure tests of hybrid airfoils are carried out and compared with the leading edge pressure of the corresponding full-scale airfoils. The design and experimental results show that the pressure coefficient deviation between the hybrid airfoils designed and the corresponding full-scale airfoil in the 15% chord length range of the leading edge is within 4%. Finally, the vortex distribution and ice accretion process of the two airfoils were simulated by the unsteady Reynolds-averaged-Navier–Stokes (URANS) equations and multistep ice numerical method; it is shown that the hybrid airfoil can provide the same vortex distribution and ice accretion with the full-scale airfoil.

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.

Some Experiments With Specific Types of Cavitation on Ship Propellers

1982 ◽  
Vol 104 (1) ◽  
pp. 105-114 ◽  
Author(s):  
G. Kuiper
Keyword(s):  
Boundary Layer ◽  
Laminar Boundary Layer ◽  
Leading Edge ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Bubble Cavitation ◽  
Roughness Elements ◽  
Propeller Blades

The influence of the boundary layer and of the nuclei content of the fluid on cavitation inception is investigated. Two models of ship propellers, displaying sheet cavitation and bubble cavitation respectively, are used. Generation of additional nuclei is obtained by electrolysis. It is shown that nuclei are necessary to create sheet cavitation when the laminar boundary layer separates. When the boundary layer is laminar, however, the absence of sheet cavitation is very persistent and independent of the nuclei content. Application of roughness at the leading edge of the propeller blades generates sheet cavitation independent of the nuclei content. Bubble cavitation is strongly affected by the nuclei content of the water. Roughness at the leading edge can indirectly affect bubble cavitation when nuclei are generated by the roughness elements.

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.

Numerical Simulation of Leading Edge Cavitation

2003 ◽  
Author(s):  
Youcef Ait Bouziad ◽  
Faic¸al Guennoun ◽  
Mohamed Farhat ◽  
Franc¸ois Avellan
Keyword(s):  
Pressure Distribution ◽  
Negative Pressure ◽  
Leading Edge ◽  
Future Research ◽  
Interface Tracking ◽  
Good Prediction ◽  
Surface Boundary ◽  
Specific Flow ◽  
Flow Parameters ◽  
Bubble Cavitation

In the present paper, we compare two different computation methods for the simulation of leading edge cavitation. In the first one, known as interface tracking method, the cavity interface is taken as a free surface boundary and the calculation is performed in a single phase flow. The cavity shape is then determined apart from the flow calculation using an iterative procedure. The second method is based on the socalled interface-capturing law state model, assuming a constant enthalpy during the vaporization and condensation processes. Both methods are tested in the case of an isolated Naca 0009, 2-D hydrofoil. Both models gave good prediction of the cavity length and pressure distribution. Moreover, results obtained with the Interface-tracking one predict well the pressure distribution near the cavity detachment. Either methods do not allow a good prediction of the drag coefficient nor the drop of the lift due to cavitation. We have also performed an insight experimental investigation of the onset and detachment of a leading edge cavitation. We have demonstrated how the water may withstand negative pressure upstream to the cavity while the pressure measured in the cavity is almost equal to the vapor pressure. Furthermore, flow visualization clearly shows that a well developed leading edge cavitation turns into bubble cavitation in a continuous way when specific flow parameters are gradually changed and we suppose that the cavity aspect depends highly of the vapor generation rate at its detachment location. The negative pressure measured upstream to the cavity detachment may thus be explained by the dynamic delay of vaporization due to inertia. Owing to those results, we have summarize the actual cavitation modelisation need and made a perspective of future research.

Freestream Nuclei and Traveling-Bubble Cavitation

1992 ◽  
Vol 114 (4) ◽  
pp. 672-679 ◽  
Author(s):  
R. S. Meyer ◽  
M. L. Billet ◽  
J. W. Holl
Keyword(s):  
Bubble Diameter ◽  
Pressure Coefficient ◽  
Critical Diameter ◽  
Computer Code ◽  
The Body ◽  
Water Tunnel ◽  
Cavitation Inception ◽  
Bubble Cavitation ◽  
Definition Of ◽  
Critical Bubble

Traveling-bubble cavitation inception tests were conducted in a 30.48 cm water tunnel with a Schiebe headform. A computer code was developed to statistically model cavitation inception on a Schiebe headform, consisting of a numerical solution to the Rayleigh-Plesset equation coupled to a set of trajectory equations. Using this code, trajectories and growths were computed for bubbles of varying initial sizes. An initial off-body distance was specified and the bubble was free to follow an off-body trajectory. A Monte Carlo cavitation simulation was performed in which a variety of random processes were modeled. Three different nuclei distributions were specified including one similar to that measured in the water tunnel experiment. The results compared favorably to the experiment. Cavitation inception was shown to be sensitive to nuclei distribution. Off-body effect was also found to be a significant factor in determining whether or not a bubble would cavitate. The effect of off-body trajectories on the critical bubble diameter was examined. The traditional definition of critical diameter based on the minimum pressure coefficient of the body or the measurement of liquid tension was found to be inadequate in defining cavitation inception.

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