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.

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.

Water Quality Effects on Cavitation Inception in a Trailing Vortex

1992 ◽  
Vol 114 (3) ◽  
pp. 430-438 ◽  
Author(s):  
Roger E. A. Arndt ◽  
Andreas P. Keller
Keyword(s):  
Water Quality ◽  
Tensile Strength ◽  
Lift Coefficient ◽  
Tangential Velocity ◽  
Cavitation Number ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Tangential Velocity Component ◽  
Cavitation Inception ◽  
Test Water

Tip vortex cavitation studies were made with a hydrofoil that was elliptical in planform, with an aspect ratio of 3, and having a modified NACA 662-415 profile. LDV measurements of the tangential velocity component in the vortex were used to determine that the minimum pressure in the vortex varies with lift coefficient squared, i.e., that the incipient cavitation number σi should follow a Cl2 relation (σi ≈ Cl2). This is in contradiction to previous observations (Arndt et al. 1991) that the tip vortex cavitation index varied approximately with lift coefficient to the power 1.4. By carefully monitoring the tensile strength of the water, i.e., its susceptibility to cavitation, the discrepancy was traced to the capability of the test water to sustain a tensile stress. Cavitation in “weak” water (no tensile strength) does follow the Cl2 relationship, whereas observations in “strong” water (rupture considerably below vapor pressure) more closely followed the previously observed variation, i.e., σi ≈ Cl1.4. Since the structure of the vortex cannot be affected by changes in the water quality, the discrepancy can be explained only by the amount of tension that can be sustained by the test water before inception occurs. Apparently a relatively larger value of tension can be sustained in the vortex is the strength of the vortex is increased (i.e., increasing Cl). This would explain the observed deviation from the expected Cl2 law for water with measurable tensile strength.

scholarly journals Dynamics of isolated vortex cavitation

2015 ◽  
Vol 778 ◽  
pp. 288-313 ◽  
Author(s):  
P. C. Pennings ◽  
J. Bosschers ◽  
J. Westerweel ◽  
T. J. C. van Terwisga
Keyword(s):  
Dispersion Relation ◽  
High Speed ◽  
Dynamic Behaviour ◽  
Tip Vortex ◽  
Cavity Volume ◽  
Analytical Formulation ◽  
Marine Propellers ◽  
High Speed Video ◽  
Zero Group ◽  
Good Agreement

The dynamic behaviour of vortex cavitation on marine propellers may cause inboard noise and vibration, but is not well understood. The main goal of the present study is to experimentally analyse the dynamics of an isolated tip vortex cavity generated at the tip of a wing of elliptical planform. Detailed high-speed video shadowgraphy was used to determine the cavity deformations in combination with force and sound measurements. The cavity deformations can be divided in different modes, each of which show a distinct dispersion relation between frequency and wavenumber. The dispersion relations show good agreement with an analytical formulation. Finally, experimental support is given to the hypothesis that the resonance frequency of the cavity volume variation is related to a zero group velocity.

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.

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.

Effect of Tripping Laminar-to-Turbulent Boundary Layer Transition on Tip Vortex Cavitation

1997 ◽  
Vol 41 (01) ◽  
pp. 1-9
Author(s):  
T. Pichon ◽  
A. Pauchet ◽  
A. Astolfi ◽  
D. H. Fruman ◽  
J-Y. Billard
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Cross Section ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Tip Vortex ◽  
Layer Transition ◽  
Tip Vortex Cavitation

It is by now well established that, for Reynolds numbers larger than those corresponding to the conditions of laminar-to-turbulent boundary layer transition over a flat plate (≈0.5 × 106) and for a variety of wing shapes and cross sections, desinent cavitation numbers divided by the Reynolds number to the power 0.4 correlate with the square of the lift coefficient. In the case of foils having an NACA 16020 cross section and for Reynolds numbers below or close to those leading to transition over a flat plate, the results are very much different from those obtained for well-developed turbulent boundary layer conditions. Thus, a research program has been conducted in order to investigate the effect of boundary layer manipulation on cavitation occurrence. It consisted in determining the critical cavitation numbers, the lift coefficients, and the velocities in the tip vortex of foils having either a smooth surface or tripping roughness (promoters) near the leading edge. Tests were performed using elliptical foils of NACA 16020 cross section having the promoters extending over 60, 80 and 90 percent of the semi-span. The region near the tip was kept smooth in order to distinguish laminar-to-turbulent transition effects from tip vortex cavitation inhibition effects associated with artificial roughness at the wing tip. Results obtained at very low Reynolds numbers, ≥ 0.24 × 106, with the foil tripped on both the pressure and suction sides collapse rather well with those previously obtained at much larger Reynolds numbers with the smooth foil, and correlate with the square of the lift coefficient. The differences between the tripped and smooth foil results are due to the modification of the lift characteristics through the modification of the wing boundary layer, as shown by flow visualization studies, and as a result of the local tip vortex intensity.

Influence of water quality on the tip vortex cavitation inception

2019 ◽  
Vol 31 (2) ◽  
pp. 023303 ◽  
Author(s):  
Linya Chen ◽  
Lingxin Zhang ◽  
Xiaoxing Peng ◽  
Xueming Shao
Keyword(s):  
Water Quality ◽  
Tip Vortex ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Influence Of Water

Tip-Vortex Induced Cavitation on a Ducted Propulsor

2003 ◽  
Author(s):  
Christopher J. Chesnakas ◽  
Stuart D. Jessup
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Three Dimensional ◽  
Tip Vortex ◽  
Number Range ◽  
Vortical Structures ◽  
Tip Vortices ◽  
Tip Vortex Cavitation ◽  
Cavitation Inception ◽  
Ducted Rotor

An extensive experimental investigation was carried out to examine tip-vortex induced cavitation on a ducted propulsor. The flowfield about a 3-bladed, ducted rotor operating in uniform inflow was measured in detail with three-dimensional LDV; cavitation inception was measured; and a correlated hydrophone/high-speed video system was used to identify and characterize the early, sub-visual cavitation events. Two geometrically-similar, ducted rotors were tested over a Reynolds number range from 1.4×106 to 9×106 in order to determine how the tip-vortex cavitation scales with Reynolds number. Analysis of the data shows that exponent for scaling tip-vortex cavitation with Reynolds number is smaller than for open rotors. It is shown that the parameters which are commonly accepted to control tip-vortex cavitation, vortex circulation and vortex core size, do not directly control cavitation inception on this ducted rotor. Rather it appears that cavitation is initiated by the stretching and deformation of secondary vortical structures resulting from the merger of the leakage and tip vortices.

scholarly journals Visualization in the Ranque-Hilsch vortex tube using high-speed video recording

2021 ◽  
Vol 2119 (1) ◽  
pp. 012104
Author(s):  
M R Gordienko ◽  
N I Yavorsky ◽  
M Kh Pravdina ◽  
S V Kakaulin ◽  
I K Kabardin
Keyword(s):  
Cross Section ◽  
High Speed ◽  
Vortex Tube ◽  
Double Helix ◽  
Video Recording ◽  
Circulation Zone ◽  
Flow Core ◽  
High Speed Video ◽  
Input Pressure ◽  
Over Time

Abstract Visualisation via video recording was carryed out in a Ranque-Hilsch vortex tube with a square cross-section. Video files were captured at recording speeds from 1000 to 10 000 frames per second. The best video files were obtained at a shooting frequency of 7600 frames per second with an input pressure of 1 bar. The video confirmed the presence of a double helix in the flow core in the second section of the tube. The video files showed the presence of a circulation zone between the flow core and the periphery, which is constantly changing over time. It can be clearly seen the angle at which the particles move in the peripheral flow.

scholarly journals Столкновения капель жидкости разной формы в газовом потоке

2019 ◽  
Vol 45 (6) ◽  
pp. 23
Author(s):  
Г.В. Кузнецов ◽  
П.А. Стрижак
Keyword(s):  
High Speed ◽  
Angle Of Attack ◽  
Video Monitoring ◽  
High Speed Video ◽  
Surface Configuration ◽  
Water Drops ◽  
Gas Medium

AbstractWe have experimentally studied the interaction between water drops of various surface configurations moving in a gas medium. Results of high-speed video monitoring provide a database on these collisions (in coagulation, expansion, and fragmentation regimes) for particles of spherical, oblate, and elongated ellipsoids. It is established that a determining role belongs to the surface configuration of drops (in addition to traditional notions about the influence of their dimensions, velocities, and angle of attack). The values of Weber numbers have been calculated for description of the conditions of interaction between drops of various shapes.

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