Flow and Turbulence Generated by Trips, and Design of an Internal PIV System for Characterizing Three-Dimensional Separated Boundary Layer
Abstract
This proposal describes the first phase in a project aimed at characterizing the flow andturbulence in three dimensional separated flows around inclined bodies of revolution, whichdominate their hydrodynamic performance. These flows have remained a challenge to predictunder practical conditions owing to the sensitivity of the location of separation and dimens pressure gradients, Reynolds number, boundary layer structure, surfaceroughness, and turbulence level. The overall objective of this joint effort with the University ofMichigan, Navy researchers, and several numerical groups, is to characterize of the flow aroundan inclined 3m long, 0.5 m diameter, 6:1 prolate spheroid at a body length-based Reynolds numberof 1.5x106 to 5x107, incidence an Channel (LCC). Trippingis used often in moderate Reynolds number tests in order to force early transition toturbulence, hence preventing premature laminar separation in regions of adverse pressuregradient. However, the proper method and placement of trips as well as its impact on thelocation and nature of flow separation around inclined models have not been established.Hence, a parallel study will characterize the flow and turbulence generated by trips and theirimpact on relevant adverse pressure gradient boundary layers. The FY 20 effort involves twotasks: (i) Design of the PIV system that will be utilized in the LCC measurements, and (ii) Dereo particle image velocimetry (PIV) systems. Ahigh-resolution setup will be installed inside the partially-transparent model for measuringthe mean flow and Reynolds stresses in the boundary layer upstream, at, and downstream of theseparation line at a series of locations. The resolution of the mean flow profiles will be sufficientfor measuring the distributions of wall shear stresses from the near-wall velocity gradients.Statistical analysis will examine scaling trends, mechanisms affecting transition from close to openseparation, and tripping effects. Designs of this system, which involves internal cameras,microscopic imaging through curved boundaries, fiber-guided illumination, local seeding, andfiber-guided data transmission will resume during FY 20. It would facilitate purchase of equipmentearly in FY 21, leaving sufficient time for testing and calibrations well before the measurementcampaign in FY 22. A second stereo PIV system will be submerged behind the model to measurethe evolution of mean flow and Reynolds stresses in a series of planes intersecting with theseparated region on its lee side. Data analysis will evaluate the effects of Reynolds number,tripping, and incidence angle on the wake structure and turbulence. Design of camera housing,mounting system, and the submerged illumination probe will resume in FY 20 in preparation forcalibration tests in FY 21.The second task involves a laboratory study to characterize the effect of tripping on thelocation and nature of flow separation in an adverse pressure gradient boundary layer underrelevant conditions. The experiments will be performed in the JHU refractive index matchedwater tunnel in a setup that enables 3D time-resolved velocity, pressure and wall stressmeasurements, from the trip to the point of separation. The completely characterized flowfield will be instrumental for interpreting trends of the flow around the 6:1 prolate spheroid,and for guiding the selection and placement of the trips. The configurations of test model andtrips will be designed in FY 20, in consultation with other team members. Results ofpreliminary PIV measurements will be shared with the team as guidance for selectingtripping strategy for the 6:1 prolate spheroid tests.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 17, 2020
- Source ID
- N000142012582
Entities
People
- Joseph Katz
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy