Near Wake Characteristics of a Marine Propeller in the Presence of Free Stream Turbulence
Abstract
This project's goal was to determine experimentally the effects of free stream turbulence on the near wake dynamics of a marine propeller. Theexperiments were conducted in the USNA Hydromechanics Laboratory recirculating water channel. A turbulence generating grid was placed at the opening of the channel, upstream from the propeller plane and perpendicular to the flow direction, to induce flow turbulence with 7% intensity and integral lengthscale of 0.2D (here, D is propeller diameter). Two and three-dimensional Particle Image Velocimetry (PIV) measurement techniques were used to analyze the flow domain for both unconditioned velocity measurements and phase locked measurements at a single phase of the propeller. Both sets of experiments were completed with and without the turbulence grid. The instantaneous velocity vector fields from the processed PIV data were used for analysis of multiple flow characteristics in both the unconditioned and phase-locked cases. Spatial distributions of mean velocity profiles in the near wake (x/D<9) resemble an axisymmetric wake. Horizontal velocity of jet-type velocity profile exhibits a distinct dip at the propeller centerline due to the strong and persistent presence of the hub vortex. This vortex is clearly apparent on scaled velocity profiles when properly scaled with classical wake scaling. Tip vortices at the wake boundaries persist further downstream for the case with no turbulence generation in the free stream. Conditional sampling of velocity fluctuations showed the mechanisms of how mean flow energy is transported out of the wake core and into the less energetic free stream flow. The net transport of mean flow kinetic energy by means of random fluctuations was found to be 20% greater in the case with imposed free stream turbulence. The net transport by means of coherent fluctuations was greater in the quiescent case, however this net transport is smaller in magnitude by a factor of three.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 20, 2019
- Accession Number
- AD1080807
Entities
People
- Bennitt L. Hermsen
Organizations
- United States Naval Academy