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Fundamental Issues and Canonical Flows

Vortical Structures and Instability Analysis for Athena Wetted Transom Flow with Full-Scale Validation

[+] Author and Article Information
Shanti Bhushan

Center for Advanced Vehicular Systems, 200 Research Blvd.,  Mississippi State University, Starkville, MS, 39759shanti@cavs.msstate.edu

Tao Xing

Department of Mechanical Engineering, Engineering Physics, Room 324F, PO Box 440902,  University of Idaho, Moscow, ID, 83844-0902xing@uidaho.edu

Frederick Stern

IIHR-Hydroscience & Engineering, C. Maxwell Stanley Hydraulics Laboratory,  The University of Iowa, Iowa City, IA, 52242-1585frederick-stern@uiowa.edu

J. Fluids Eng 134(3), 031201 (Mar 19, 2012) (18 pages) doi:10.1115/1.4006173 History: Received May 28, 2011; Revised February 17, 2012; Published March 16, 2012; Online March 19, 2012

Vortical structures and associated instabilities of appended Athena wetted transom flow in full-scale conditions are studied using DES to explain the source of dominant transom flow frequency, including verification and validation using full-scale experimental data. The results are also compared with model-scale bare and appended hull predictions and experiments. The grid used for the validation is sufficiently fine as it resolves 70% and 91% of the experimental inertial subrange and turbulent kinetic energy values, respectively. The model-scale bare and appended hull resistance predictions compare within 2.5%D and 5.4%D of the experimental data D, respectively. The full-scale appended hull resistance predictions compare within 4.2%D of the extrapolated data using the ITTC line. The averaged comparison error of the full-scale transom wave elevation mean, RMS and dominant frequency predictions and the experimental data is 8.1%D, and the predictions are validated at an averaged 11.2%D interval. The transom wave elevation unsteadiness is attributed to the Karman-like transom vortex shedding as both show the same dominant frequency. The Karman-like instability shows St = 0.148 for the bare hull and St = 0.103 ± 4.4% for model- and full-scale appended hull. The appended hull simulations also predict: horseshoe vortices at the juncture of rudder-hull with St = 0.146 ± 3.9% and strut-hull with St = 0.053 ± 2%; shear layer instability at the strut-hull intersection with St = 0.0067 ± 3%; and unsteady sinkage and trim induced by transom vortex shedding with St = 2.19. The instabilities do not show significant variation on scale, propeller or motions. The bare hull simulation also predicts flapping-like instability in the wake with St = 0.144.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Domain, grids, boundary conditions for model- and full-scale appended Athena. The LES regions are shown for (b) G4 and (c) G1.

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Figure 2

Time history and running mean of (a) the transom wave elevation at X = 1.0447, Y = 0 for G1 and (b) CT for G1, G2, G4 and G2-URANS full-scale cases

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Figure 3

Propeller RPS obtained from G5-SP is compared with the extrapolated experimental data [15]

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Figure 4

(a) Experimental and numerical spectra for the transom wave elevation unsteadiness at X = 1.115 are compared. Isosurfaces of Q = 300 obtained for (b) G3, (c) G3-FD, (d) G2, (e) G1, (f) G2- URANS and (g) G2-M. (h) The flow separation at Y = 0.01 plane is shown for G4.

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Figure 5

(a) Modeled, (b) resolved and (c) total TKE distribution at X = 1.0447 for G1

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Figure 6

The mean transom wave elevation (a) contours from the experiment [3], (b) contours from G1-SP, and (c) profiles from the experiment and G1-SP are compared. The transom corner is at X = 1.0. The profile locations A-H are shown in sub-figure (a ).

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Figure 7

The transom wave elevation RMS (a) contours from the experiment [3], (b) contours from G1-SP, and (c) profile from the experiment and G1-SP. The transom corner is at X = 1.0. The profile locations are marked in Fig. 6.

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Figure 8

The transom wave elevation unsteadiness spectra in the experiment [3] and G1-SP are compared at X = 1.0447–1.245, Y = 0. The FFT locations are marked in Fig. 6 with black dots.

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Figure 9

Contours of ωy and free-surface wave elevation at X = 1.0667 at ΔT = 0.012L/U obtained using G2-URANS (left panel) and G1-SP (right panel) are compared with experimental data [3] (dotted line). G3-FD wave elevation profiles are shown in black line on the right panel. The vorticty contour levels are from −100 to 100 at an interval of 10. The inset figure shows the isosurface of normalized helicity Q = 300.

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Figure 10

Isosurfaces of Q = 300 for instantaneous solution from G2. Inset figures are obtained using averaged solution. Three different types (A, B and C) of juncture vortices are marked and associated dominant frequency modes are shown. Contours are of the absolute pressure with levels from −0.5 to 0.1 at an interval of 0.02.

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Figure 11

(a) Time history and running mean of the pressure resistance coefficient for G1 and G0-BH-M. The spectra of the pressure resistance coefficients predicted for (b) G0-BH-M and (c) G2. (d) The piezometric pressure fluctuation at transom corner X = 0.998, Y = 0.01 for G1.

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Figure 12

Phases of Karman-like transom vortex shedding is shown for G2 at Y = 0.01 cross-section. Contours are of the absolute pressure with levels from −0.2 to 0.1 at an interval of 0.006.

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Figure 13

Fourier amplitudes of piezometric pressure fluctuations at the transom corner near the symmetry plane at X = 0.998, Y = 0.01 for model- and full-scale appended Athena simulations

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Figure 14

Fourier amplitude of piezometric pressure fluctuations at (a) rudder-hull juncture (X = 0.964, Y = 0.037) and (b) starboard strut-hull juncture (X = 0.92, Y = 0.034) for model- and full-scale appended Athena simulations

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Figure 15

Phases of hull-strut juncture vortex shedding due to shear-layer instability is shown for G2 at cross-section Y = 0.0524. The cross-section is shown in the subfigure (a) inset. Contours are of the streamwise velocity with levels from −0.25 to 0.1 at an interval of 0.01.

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Figure 16

Fourier amplitudes of piezometric pressure fluctuations on starboard strut X = 0.927, Y = 0.0524 close to the hull-strut juncture for model- and full-scale appended Athena simulations

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Figure 17

(a) Time history of predicted sinkage and trim and (b) their Fourier amplitudes for G1-SP

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Figure 18

Phases of the flappinglike instability (τP  = 0.16) for G0-BH-M. The vortical structures are shown by the isosurfaces of Q = 300 and colored by piezometric pressure with levels from −0.5 to 0.1 at an interval.

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