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

摘要

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 70percent and 91percent of the experimental inertial subrange and turbulent kinetic energy values, respectively. The model-scale bare and appended hull resistance predictions compare within 2.5percentD and 5.4(percent)D of the experimental data D, respectively. The full-scale appended hull resistance predictions compare within 4.2(percent)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(percent)D, and the predictions are validated at an averaged 11.2(percent)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 velence 0.148 for the bare hull and St velence 0.103 +- 4.4percent for model- and full-scale appended hull. The appended hull simulations also predict: horseshoe vortices at the juncture of rudder-hull with St velence 0.146 +- 3.9percent and strut-hull with St velence 0.053 +- 2percent; shear layer instability at the strut-hull intersection with St velence 0.0067 +- 3percent; and unsteady sinkage and trim induced by transom vortex shedding with St velence 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 velence 0.144.