Wing Sections for Hydrofoils—Part 3: Experimental Verifications

1985 ◽  
Vol 29 (01) ◽  
pp. 39-50
Author(s):  
Young T. Shen
Keyword(s):  
High Speed ◽  
Design Theory ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Ship Wakes ◽  
Lifting Surfaces ◽  
Propeller Blades ◽  
Force Data

Lifting surfaces such as hydrofoil wings or propeller blades will encounter periodic variations in angle of attack when operated in waves or in nonuniform ship wakes. Undesirable leading-edge sheet cavitation is a common occurrence on hydrofoils and marine propellers. To effectively avoid or delay leading-edge sheet cavitation it is necessary to develop a lifting surface able to tolerate large variations in angle of attack without cavitation. Based on a profile design theory, a series of hydrofoil sections having large cavitation-free bucket widths was developed and presented in previous papers, Part 1 and Part 2. The present paper provides the experimental verification. Profile YS-920 was selected as representative of the series and was tested in a high-speed water tunnel. The measured cavitation inception characteristics and force data of YS-920 were compared with the theoretical predictions. Additionally, they were compared with the measured cavitation and force data of the widely used NACA 66 (MOD) and NACA 16–309 wing sections to show the advantages of using a newly developed hydrofoil section to delay or avoid cavitation.

An Exploratory Investigation of Cavitation Inception on the Pressure Side of Propellers

2008 ◽  
Author(s):  
Wim M. van Rees ◽  
Martijn X. van Rijsbergen ◽  
Gert Kuiper ◽  
Tom J. C. van Terwisga
Keyword(s):  
Free Stream ◽  
Leading Edge ◽  
Pressure Side ◽  
Cavitation Inception ◽  
Free Stream Turbulence ◽  
Sheet Cavitation ◽  
Edge Roughness ◽  
Exploratory Investigation ◽  
Cavitation Tunnel ◽  
Propeller Blades

Delayed sheet cavitation inception has occasionally been observed in the MARIN Depressurized Towing Tank (DTT). The problems are specifically related to the pressure side of model ship propellers, and occur despite the application of leading-edge roughness. As a consequence, no cavitation at all or cavitation on parts of the propeller blades is observed, in cases where cavitation in the cavitation tunnel or at full scale is present. In an exploratory investigation, the effect of several parameters that may influence cavitation inception is studied in the DTT. In particular, the influences of Reynolds number, free-stream turbulence and additional gas nuclei are investigated. It is concluded that the presence of sufficient gas nuclei is crucial for sheet cavitation inception, even if leading-edge roughness is applied. With additional nuclei in the propeller inflow, sheet cavitation inception in the DTT is no longer delayed with respect to the cavitation tunnel.

scholarly journals Experimental Study on the Relationship Between Cavitation and Lift Fluctuations of S-Shaped Hydrofoil

2021 ◽  
Vol 9 ◽  
Author(s):  
Haiyu Liu ◽  
Pengcheng Lin ◽  
Fangping Tang ◽  
Ye Chen ◽  
Wenpeng Zhang ◽  
...  
Keyword(s):  
High Speed ◽  
Developmental Process ◽  
Angle Of Attack ◽  
Cavitation Number ◽  
High Speed Photography ◽  
Cloud Cavitation ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Hydraulic Machinery ◽  
Stall Angle

In order to study the energy loss of bi-directional hydraulic machinery under cavitation conditions, this paper uses high-speed photography combined with six-axis force and torque sensors to collect cavitating flow images and lift signals of S-shaped hydrofoils simultaneously in a cavitation tunnel. The experimental results show that the stall angle of attack of the S-shaped hydrofoil is at ±12° and that the lift characteristics are almost symmetrical about +1°. Choosing α = +6° and α = −4° with almost equal average lift for comparison, it was found that both cavitation inception and cloud cavitation inception were earlier at α = −4° than at α = +6°, and that the cavitation length at α = −4° grew significantly faster than at α = +6°. When α = +6°, the cavity around the S-shaped hydrofoil undergoes a typical cavitation stage as the cavitation number decreases: from incipient cavitation to sheet cavitation to cloud cavitation. However, when α = −4°, as the cavitation number decreases, the cavitation phase goes through a developmental process from incipient cavitation to sheet cavitation to cloud cavitation to sheet cavitation to cloud cavitation, mainly because the shape of the S-shaped hydrofoil at the negative angle of attack affects the flow of the cavity tails, which is not sufficient to form re-entrant jets that cuts off the sheet cavitation. The formation mechanism of cloud cavitation at the two different angles of attack (α = +6°、−4°) is the same, both being due to the movement of the re-entrant jet leading to the unstable shedding of sheet cavity. The fast Fourier analysis reveals that the fluctuations of the lift signals under cloud cavitation are significantly higher than those under non-cavitation, and the main frequencies of the lift signals under cloud cavitation were all twice the frequency of the cloud cavitation shedding.

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.

Investigation of Unsteady Sheet Cavitation and Cloud Cavitation Mechanisms

1999 ◽  
Vol 121 (2) ◽  
pp. 289-296 ◽  
Author(s):  
T. M. Pham ◽  
F. Larrarte ◽  
D. H. Fruman
Keyword(s):  
High Speed ◽  
Leading Edge ◽  
Pressure Measurements ◽  
Foil Surface ◽  
Mean Velocity ◽  
Cloud Cavitation ◽  
Fluctuating Pressure ◽  
Sheet Cavitation ◽  
Cavitation Instability ◽  
Unsteady Characteristics

Sheet cavitation on a foil section and, in particular, its unsteady characteristics leading to cloud cavitation, were experimentally investigated using high-speed visualizations and fluctuating pressure measurements. Two sources of sheet cavitation instability were evidenced, the re-entrant jet and small interfacial waves. The dynamics of the re-entrant jet was studied using surface electrical probes. Its mean velocity at different distances from the leading edge was determined and its role in promoting the unsteadiness of the sheet cavitation and generating large cloud shedding was demonstrated. The effect of gravity on the dynamics of the re-entrant jet and the development of interfacial perturbations were examined and interpreted. Finally, control of cloud cavitation using various means, such as positioning a tiny obstacle (barrier) on the foil surface or performing air injection through a slit situated in the vicinity of the leading edge, was investigated. It was shown that these were very effective methods for decreasing the amplitude of the instabilities and even eliminating them.

Study on Vortex Generators for Control of Attached Cavitation

2017 ◽  
Author(s):  
Bangxiang Che ◽  
Dazhuan Wu
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Main Flow ◽  
Vortex Generators ◽  
Streamwise Vortices ◽  
Fluid Machinery ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
Cavitation Phenomenon

Attached cavitation is a type of common cavitation phenomenon in fluid machinery. It is important to develop methods to control its generation. From the view of cavitation inception, the generation of attached cavitation is greatly influenced by the separated boundary layer upstream of cavitation detachment. In this research, a row of microscopic delta-shaped counter-rotating vortex generators (VGs) was applied on the leading edge of the NACA0015 hydrofoil in order to suppress the boundary layer separation and then suppress the generation of attached cavitation. The application of VGs fixed the position of cavitation inception on hydrofoil thus the sheet cavitation became more stable and the cloud cavity shed from hydrofoil with trim trailing edge more regularly. It was found that cavitation inception always appeared adjacent to VGs due to the low pressure in the corner of streamwise vortices induced by VGs. Hydrofoil with VGs showed an entirely different cavitation morphology on the leading edge. A row of separate microscopic vortex cavitation was induced by the counter-rotating vortices firstly. With the lower the height of VGs, the longer the length of these vortex cavitation due to the weaker interaction between vortices and main flow. Following the vortex cavitation, the attached cavitation was developing, but without typical “finger” structure anymore.

Scale Effects on the Cavitation Development in Fluid Machinery

2011 ◽  
Author(s):  
Weiping Yu ◽  
Xianwu Luo ◽  
Yao Zhang ◽  
Bin Ji ◽  
Hongyuan Xu
Keyword(s):  
Turbulence Model ◽  
High Speed ◽  
Scale Effects ◽  
Design Procedure ◽  
Leading Edge ◽  
Characteristic Size ◽  
Cavitation Model ◽  
Fluid Machinery ◽  
Cloud Cavitation ◽  
Sheet Cavitation

The prediction of cavitation in a design procedure is very important for fluid machinery. However, the behaviors of cavitation development in the flow passage are believed to be much different due to scale effects, when the characteristic size varies greatly for fluid machines such as pumps, turbines and propellers. In order to understand the differences in cavitation development, the evolution of cavity pattern in two hydro foils were recorded by high-speed video apparatus. Both foils have the same section profile, and their chord lengths are 70mm and 14mm respectively. For comparison, the cavitating flows around two foils were numerically simulated using a cavitation model based on Rayleigh-Plesset equation and SST k-ω turbulence model. The experiments depicted that for both hydro foils, there was attached sheet cavitation near the leading edge, which separated from the rear part of the cavity and collapsed near the foil trailing edge. There was clear cloud cavitation in the case of the mini foil. The results also indicated that the numerical simulation captured the cavitation evolution for the ordinary foil quite well compared with the experiments, but could hardly predict the cloud cavitation for the mini foil. Thus, it is believed that both the cavitation model and the turbulence model should be carefully treated for the scale effect on cavitation development in fluid machinery.

Experimental investigation on spiked body in hypersonic flow

2008 ◽  
Vol 112 (1136) ◽  
pp. 593-598 ◽  
Author(s):  
R. Kalimuthu ◽  
R. C. Mehta ◽  
E. Rathakrishnan
Keyword(s):  
Drag Reduction ◽  
Hypersonic Flow ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Geometrical Parameters ◽  
Potential Candidate ◽  
Hypersonic Wind Tunnel ◽  
High Speed Vehicle

Abstract A spike attached to a hemispherical body drastically changes its flowfield and influences aerodynamic drag in a hypersonic flow. It is, therefore, a potential candidate for drag reduction of a future high-speed vehicle. The effect of the spike length, shape, spike nose configuration and angle-of-attack on the reduction of the drag is experimentally studied with use of hypersonic wind-tunnel at Mach 6. The effects of geometrical parameters of the spike and angle-of-attack on the aerodynamic coefficient are analysed using schlieren picture and measuring aerodynamic forces. These experiments show that the aerodisk is superior to the aerospike. The aerodisk of appropriate length, diameter and nose configuration may have the capability for the drag reduction. The inclusion of an aero disk at the leading edge of the spike has an advantage for the drag reduction mechanism if it is at an angle-of-attack, however consideration to be given for increased moment resulting from the spike is required.

Inception and Dynamics of Traveling-Bubble-Type Cavitation in a Venturi

2003 ◽  
Author(s):  
Keiichi Sato ◽  
Kouji Hachino ◽  
Yasuhiro Saito
Keyword(s):  
Tensile Strength ◽  
Count Rate ◽  
High Speed ◽  
Cavitation Number ◽  
Venturi Tube ◽  
Local Pressure ◽  
Cavitation Inception ◽  
Sheet Cavitation ◽  
High Speed Video ◽  
Bubble Cavitation

The inception of cavitation is basically caused by a bubble nucleus which flows into the low pressure region in the liquid flow. Therefore the phenomenon is dependent on the tensile strength or the nuclei concentration of tested water. The cavitation susceptibility of water which controls the cavitation inception point has been made clear though various methods were proposed to measure the nuclei concentration. Cavitation susceptibility meter using a small venturi tube is also one of the methods to measure the nuclei concentration. It is pointed out that this method can be directly related to active nuclei for cavitation inception and gives a useful and simple device to estimate the tensile strength of water. In the present paper, to establish a measurement method of cavitation susceptibility using a venturi tube, the following points are investigated, such as; the relation between the occurrence, count rate of cavitation bubbles and cavitation number, the measurement of positions and local pressure of bubble occurrence and the high-speed video observation of bubble aspects from inception to collapse. As the result, the main points obtained are as follows. A traveling-bubble cavitation appears dominantly in a nozzle-type venturi tube with little possibility of flow separation. Cavitation aspects and the bubble occurrence count rate change with cavitation number and water quality (dissolved gas content). Unstable sheet cavitation can be also observed near the venturi diffuser and at relatively low cavitation number. The various behaviors of traveling bubble cavitation in a venturi are observed from inception to collapse using a high-speed video camera system.

Application of a Numerical Optimization Technique to the Design of Cavitating Propellers in Nonuniform Flow

1997 ◽  
Vol 41 (02) ◽  
pp. 93-107 ◽  
Author(s):  
Shigenori Mishima ◽  
Spyros A. Kinnas
Keyword(s):  
Optimization Algorithm ◽  
High Speed ◽  
Optimization Technique ◽  
Design Parameters ◽  
Nonuniform Flow ◽  
Surface Design ◽  
Sheet Cavitation ◽  
Propeller Design ◽  
Cavity Characteristics ◽  
Propeller Blades

High-speed propulsor blades often experience moderate to substantial amounts of unsteady cavitation, and up to now have been designed via design methods for noncavitating blades combined with methods for the analysis of cavitating flows in a trial-and-error manner. In this paper, a numerical nonlinear optimization algorithm is developed for the automated, systematic design of cavitating blades. The method is first applied to the design of propeller blades in uniform flow. The blade mean camber surface is defined via a cubic B-spline polygon net in order to facilitate the handling of the geometry, and to reduce the number of the design parameters. Noncavitating blade geometries designed by the present method are directly compared with those designed via an existing lifting-line/lifting-surface design approach. Finally, the optimization algorithm is applied to the design of cavitating blades in nonuniform flow. The objective of the design is to obtain maximum propeller efficiency for given conditions by allowing controlled amounts of sheet cavitation. Several constraints on the unsteady cavity characteristics, such as the area of cavity planform and the amplitudes of the cavity volume velocity harmonics, are incorporated in the optimization technique. The effect of the constraints on the efficiency of the propeller design is demonstrated with various test cases.

Numerical simulation of high-speed civil transport inlet operability with angle of attack

AIAA Journal ◽  
1998 ◽  
Vol 36 ◽  
pp. 1223-1229
Author(s):  
Ge-Cheng Zha ◽  
Doyle Knight ◽  
Donald Smith ◽  
Martin Haas
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Angle Of Attack
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