Computation of Two-Phase Drag Reduction by Gas Injection

Open Access
Author:
Maciejewski, Daniel
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 10, 2012
Committee Members:
  • Eric G Paterson, Thesis Advisor
  • Scott Miller, Thesis Advisor
Keywords:
  • microbubble drag reduction
  • turbulent boundary layer
  • CFD
  • multiphase
  • two-phase
  • turbulence
Abstract:
The skin friction drag on ships and other solid bodies moving through water can be reduced by introducing air through the solid surface into the attached turbulent boundary layer. This phenomenon is known as microbubble drag reduction (MBDR), or simply bubble drag reduction (BDR). Air is typically introduced through micropores in sintered plates or through thin slots. Continuing experimental efforts since the 1970s have revealed several physical mechanisms acting in the two-phase mixture to cause a localized reduction in skin friction. Motivated to reduce total vehicle drag, researchers in this field have focused on finding the functional dependence of the drag reduction. A homogeneous, two-phase, compressible computational flow solver is used to simulate these flows. The homogenized fluid's mixture properties are determined from local volume fractions of air and water. Mixing of phases after injection is modeled through use of a turbulent dispersion term. Experiments conducted by Madavan, Deutsch and Merkle (1984) in the twelve-inch water tunnel at ARL/PSU are used for validation. Good agreement between experiment and model is found for the total drag reduction with air injection. The return to no-injection skin friction values downstream of the injection region is also predicted by the model. Agreement with experiment is found for both single phase simulations and multiphase simulations with gas injection. Validation was achieved by comparison of velocity profiles and wall-shear profiles between simulation and experiment.