Experimental Study on the Effect of Number of Bubble Occurrences on Tip Vortex Cavitation Noise Scaling Law

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Jisoo Park ◽  
Woojae Seong
Keyword(s):  
Noise Level ◽  
High Speed ◽  
Scaling Law ◽  
Broad Band ◽  
Tip Vortex ◽  
Cavitation Noise ◽  
Experimental Conditions ◽  
Tip Vortex Cavitation ◽  
Band Noise ◽  
Lifting Surface

A novel scaling law for the tip vortex cavitation (TVC) noise was determined, employing the Rankine vortex model, the Rayleigh–Plesset equation, the lifting surface theory, the boundary layer effect, and the number of bubbles generated per unit time (N0). All terms appearing in the final derived scaling law are well known three-dimensional (3D) lifting surface parameters, except for N0. In this study, the dependence of N0 with inflow velocity and hydrofoil dimension is investigated experimentally while trying to retain the same TVC patterns among different experimental conditions. Afterward, the effect of N0 on the TVC noise is analyzed. Optimal TVC observation conditions are determined from consideration of cavitation number and Reynolds number of two comparable conditions. Two geometrically scaled hydrofoils are concurrently placed in a cavitation tunnel for the hydrofoil size variation experiment. Wall effects and flow field interaction are prevented with the aid of computational fluid dynamics. Images taken with a high‐speed camera are used to count N0 by visual inspection. The noise signals at all conditions are measured and an acoustic bubble counting technique, to supplement visual counting, is devised to determine N0 acoustically from the measured noise data. The broad-band noise scaling law incorporating N0 and the International Towing Tank Conference (ITTC) cavitation noise estimation rule for hydrofoil are both applied to estimate the TVC noise level for comparison with the measured noise level. The noise level estimated by the broad-band noise scaling law accounting for the acoustically estimated N0 gives the best agreement with the measured noise level.

Experimental Study of Scale Effects on the Scaling Law for Tip Vortex Cavitation Noise

2014 ◽  
Author(s):  
Jisoo Park ◽  
Cheolsoo Park ◽  
Youngmin Choo ◽  
Woojae Seong
Keyword(s):  
High Speed ◽  
Scale Effects ◽  
Scaling Law ◽  
Size Variation ◽  
Tip Vortex ◽  
Cavitation Noise ◽  
Scaling Exponents ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Vortex Model

Novel scaling law for the tip vortex cavitation (TVC) noise is derived from the physical basis of TVC, employing the Rankine vortex model, the Rayleigh-Plesset equation, the lifting surface theory, and the number of bubbles generated per unit time (N0). All terms appearing in the scaling law have physical or mathematical grounds except for N0. Therefore, to experimentally validate the N0 term, experiments are designed to keep the same TVC patterns as velocities and dimensions vary. Optimal shooting conditions with a velocity and size variation are determined from the scaling exponents, cavitation numbers and Reynolds numbers at each condition. To avoid wall effects and flow field interaction, two hydrofoils are optimally arranged by using computational fluid dynamics (CFD) for size variation. Images taken by a high speed camera are used to count N0, considering similitude of the spectra of nuclei. Scaling exponents curve fitted from five velocities and cavitation inception numbers have an exponent value of 0.371, which is closely placed on scaling exponents curve deduced from Schlichting’s friction coefficients fitting with Reynolds number. The tendency that N0 is proportional to a velocity and inversely proportional to a size can be confirmed by this study.

Observation and Scaling of Tip Vortex Cavitation on Elliptical Hydrofoils

2011 ◽  
Author(s):  
Shigeki Nagaya ◽  
Risa Kimoto ◽  
Kenji Naganuma ◽  
Takayuki Mori
Keyword(s):  
Water Quality ◽  
Reynolds Number ◽  
High Speed ◽  
Tip Vortex ◽  
Video Observation ◽  
Tip Vortex Cavitation ◽  
Air Content ◽  
Sheet Cavitation ◽  
High Speed Video ◽  
Systems Research

Experimental study on tip vortex cavitation (TVC) was carried out for elliptical hydrofoils with various chord lengths. The purpose of the experiment was to clarify the influences of Reynolds number and water quality on tip vortex cavitation. Experiments were made in a large cavitation tunnel of the Naval Systems Research Center, TRDI/Ministry of Defense Japan. The elliptical hydrofoils tested were NACA 0012 cross section with chord lengths of 500mm, 250mm and 50mm. Reynolds number based on hydrofoil chord length was 2×105 < ReC < 7.4×106. Water quality of the tunnel was characterized by air content and nuclei distribution. Air content of the tunnel was varied between 30% and 80%. Nuclei distribution was measured by a cavitation susceptibility meter (CSM) with center-body venturi. Cavitation inception was determined from high speed video observation. A standard formula, (σL/σS) = (ReL/ReS)n, was applied for the scaling. In the present study, exponent of the scaling law n was found to be 0.2 < n < 0.4. High speed video observation showed that the process of the TVC inception strongly depends on water quality. In the experiments, unsteady behaviors of TVC were also investigated. Strong interactions between sheet cavitation and TVC were observed.

scholarly journals Numerical Investigation of Tip-Vortex Cavitation Noise of an Elliptic Wing Using Coupled Eulerian-Lagrangian Approaches

2020 ◽  
Vol 10 (17) ◽  
pp. 5897 ◽  
Author(s):  
Garam Ku ◽  
Cheolung Cheong ◽  
Hanshin Seol
Keyword(s):  
Flow Field ◽  
Numerical Method ◽  
Vortex Flow ◽  
Acoustic Pressure ◽  
Tip Vortex ◽  
Experimental Result ◽  
Cavitation Noise ◽  
Navier Stokes Equation ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception

In this study, a numerical methodology is developed to investigate the tip-vortex cavitation of NACA16-020 wings and their flow noise. The numerical method consists of a sequential one-way coupled application of Eulerian and Lagrangian approaches. First, the Eulerian method based on Reynolds-averaged Navier–Stokes equation is applied to predict the single-phase flow field around the wing, with particular emphasis on capturing high-resolution tip-vortex flow structures. Subsequently, the tip-vortex flow field is regenerated by applying the Scully vortex model. Secondly, the Lagrangian approach is applied to predict the tip-vortex cavitation inception and noise of the wing. The initial nuclei are distributed upstream of the wing. The subsequent time-varying size and position of each nucleus are traced by solving spherically symmetric bubble dynamics equations for the nuclei in combination with the flow field predicted from the Eulerian approach. The acoustic pressure at the observer position is computed by modelling each bubble as a point source. The numerical results of the acoustic pressure spectrum are best matched to the measured results when the nuclei number density of freshwater is used. Finally, the current numerical method is applied to the flows of various cavitation numbers. The results reveal that the cavitation inception determined by the predicted acoustic pressure spectrum well matched the experimental result.

Block-sparse compressive localization for incipient tip vortex cavitation noise

2019 ◽  
Vol 145 (3) ◽  
pp. 1936-1936
Author(s):  
MinSeuk Park ◽  
Woojae Seong ◽  
Youngmin Choo ◽  
Yongsung Park
Keyword(s):  
Tip Vortex ◽  
Cavitation Noise ◽  
Tip Vortex Cavitation

The Case of the Singing Vortex

1997 ◽  
Vol 119 (2) ◽  
pp. 271-276 ◽  
Author(s):  
B. Maines ◽  
R. E. A. Arndt
Keyword(s):  
Water Quality ◽  
Cross Section ◽  
High Speed ◽  
Angle Of Attack ◽  
High Amplitude ◽  
Cavitation Number ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
High Speed Video ◽  
Noise Data

A relatively high amplitude, discrete tone is radiated from fully developed tip vortex cavitation under certain conditions. The phenomenon of the “singing vortex” was first reported by Higuchi et al. (1989). This study more closely examines the singing phenomenon by varying the hydrofoil cross-section, scale, angle of attack, water quality, and cavitation number in two different facilities. Noise data were collected for each condition with visual documentation using both still photography and high speed video in an effort to explain the mechanism of vortex singing. The theory of Kelvin (1880) provides a framework for correlating all the data obtained.

Wingtip Devices for Tidal Turbines: Performance Improvement and Cavitation Mitigation

2016 ◽  
Author(s):  
Ivaylo Nedyalkov ◽  
Ian Gagnon ◽  
Jesse Shull ◽  
John Brindley ◽  
Martin Wosnik
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
High Speed ◽  
Lift Coefficient ◽  
Small Diameter ◽  
Tip Vortex ◽  
Power Exponent ◽  
Test Bed ◽  
Tip Vortex Cavitation ◽  
Tidal Turbines

Wingtip devices are common in aeronautical applications and are increasingly used on wind turbines. However, their use in hydrokinetic energy conversion applications such as tidal turbines to date is minimal, due to the concern for increased bio-fouling and also the fact that there is little or no data publically available describing their cavitation characteristics. In this study, three wingtip designs were considered for hydrokinetic turbine applications: a plain foil with a rounded tip (considered the reference case), a generic wingtip device (a winglet), and a novel “split-tip” device. The tips were studied numerically and experimentally at different angles of attack. The numerical simulations were performed in OpenFOAM using the k-omega SST model to predict the lift and drag characteristics of a “base” foil with each of the three wingtip devices. Additionally the pressure and vorticity were observed. Experiments were conducted in the University of New Hampshire High-Speed Cavitation Tunnel – HiCaT. A modular experimental test bed with an elliptical foil section was developed specifically for the study. The test bed extends to the centerline of the tunnel where wingtips are attached, and has four small-diameter tube openings to accommodate pressure measurements and/or mass injection studies. Water tunnel data were obtained for lift, and cavitation inception, and compared to the numerical simulations. The numerical results show decreased vorticity with presence of the wingtip devices, however, the advantage of using wingtips for decreasing drag and increasing lift forces is not conclusively exhibited. The experimental measurements suggest that there is a significant suppression of tip vortex cavitation with the use of wingtip devices at high angles of attack (around 10 degrees), but the advantage of using the wingtip devices diminishes at lower angles of attack. It was shown by Arndt [1] that tip-vortex cavitation on hydrofoils can be related to the lift coefficient and the Reynolds number, where the cavitation index at inception is proportional to the square of the section lift coefficient and the Reynolds number based on hydrofoil chord, taken to the power m. The power exponent m has been generally accepted to be approximately 0.4. This relation is made into an equation via a coefficient of proportionality K, which depends on the wingtip and foil section geometry, and has been empirically determined to have values between 0.025 and 0.056 for previously investigated wings. While the value of the coefficient K for the reference wing tip remained comparatively constant for the range of conditions investigated (angles of attack, Reynolds numbers), it varied significantly for the foil terminated by the winglet. This may be due to the non-elliptical load distribution in the span-wise direction, but also raises the question whether the standard tip-vortex cavitation correlation for hydrofoils is applicable for general wingtip devices.

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