Phase-Averaged PIV for the Nominal Wake of a Surface Ship in Regular Head Waves

Abstract

Phase-averaged organized oscillation velocities (U,V,W) and random fluctuation Reynolds stresses (uu¯,vv¯,ww¯,uv¯,uw¯) are presented for the nominal wake of a surface ship advancing in regular head (incident) waves, but restrained from body motions, i.e., the forward-speed diffraction problem. A 3.048×3.048×100m towing tank, plunger wave maker, and towed, 2D particle-image velocimetry (PIV) and servo mechanism wave-probe measurement systems are used. The geometry is DTMB model 5415 (L=3.048m, 1∕46.6 scale), which is an international benchmark for ship hydrodynamics. The conditions are Froude number Fr=0.28, wave steepness Ak=0.025, wavelength λ∕L=1.5, wave frequency f=0.584Hz, and encounter frequency fe=0.922Hz. Innovative data acquisition, reduction, and uncertainty analysis procedures are developed for the phase-averaged PIV. The unsteady nominal wake is explained by interactions between the hull boundary layer and axial vortices and incident wave. There are three primary wave-induced effects: pressure gradients 4%Uc, orbital velocity transport 15%Uc, and unsteady sonar dome lifting wake. In the outer region, the uniform flow, incident wave velocities are recovered within the experimental uncertainties. In the inner, viscous-flow region, the boundary layer undergoes significant time-varying upward contraction and downward expansion in phase with the incident wave crests and troughs, respectively. The zeroth harmonic exceeds the steady-flow amplitudes by 5–20% and 70% for the velocities and Reynolds stresses, respectively. The first-harmonic amplitudes are large and in phase with the incident wave in the bulge region (axial velocity), damped by the hull and boundary layer and mostly in phase with the incident wave (vertical velocity), and small except near the free surface-hull shoulder (transverse velocity). Reynolds stress amplitudes are an order-of-magnitude smaller than for the velocity components showing large values in the thin boundary layer and bulge regions and mostly in phase with the incident wave.

An unsteady single‐phase level set method for viscous free surface flows

“…The test case chosen has been experimentally studied extensively for a DTMB 5512 model and unsteady free surface elevation, resistance, heave force and pitch moments [39,40] and velocities [41] In order to simulate the boundary layer turbulence using the model, a fine near wall discretization is necessary, with spacing around . This makes the design of the computational grid difficult, since an orthogonal grid is convenient in the far field to avoid deformation of the incoming wave.…”

“…In our case we chose to use an 8 block boundary layer body-fitted grid, a 16 block close-field orthogonal grid and a 8 block far-field orthogonal grid, for a total of 32 blocks and approximately 2,000,000 grid points. The interpolation coefficients for the overset grids were generated using Pegasus [41]. The overall grid, shown in Fig.…”

Uncertainty Assessment of a Towed Underwater Stereoscopic PIV System

“…(Gui, et al, 2001), 파랑 중에 놓인 동일 모형의 위상별 선미 유동장 계 측 (Longo, et al, 2007), 수면 관통 물체 주위의 유동장 계측 (Seol, et al, 2013)이 수행되었다. 그리고 두 대의 카메라를 이용해 2차원 평면의 3차원 속도 성 분을 얻어낼 수 있는 스테레오스코픽 입자영상유속계(sereo prticle iage vlocimetry, SPIV)가 예인수조에 도입되어 활용되었 다.…”

Towed underwater PIV measurement for free-surface effects on turbulent wake of a surface-piercing body

“…Uncertainty assessments for towing tank PIV system and other measurement instruments were also executed by Longo and Stern (2005). In addition, Longo et al (2007) measured nominal wake of a surface combatant model in head seas with 2D PIV in a towing tank and Yoon (2009) measured the flow field around a surface combatant in planar motion mechanism maneuvers with a stereo PIV system and compared with the results of CFD studies. Besides the nominal wake, the flow fields in propeller open water test were measured by Anschau and Mach (2007) with underwater stereo PIV.…”