Passive and Active Patterned Roughness for Cross-Flow Transition Control at Mach 6
Abstract
The program was designed investigate passive and active (plasma) patterned roughness for transition control on a sharp right-circular cone at an angle of attack at Mach 6.0. A cone angle of attack of 6deg. was set to produce a mean cross-flow velocity component in the boundary layer over the cone by which the cross-flow instability was the dominant mechanism of turbulent transition. The approach to transition control was based on exciting less-amplified (subcritical) stationary cross-flow modes that suppress the growth of the more-amplified (critical) cross-flow modes, and thereby delay transition. The passive roughness consisted of an azimuthal array of indentations (dimples) at an axial location that is just upstream of the first linear stability neutral growth branch for cross-flow modes. Two roughness azimuthal wavenumbers were examined: one that was in the band of most amplified stationary cross-flow modes, representing the "critical" roughness condition; and the second being at a 1.5-times higher azimuthal wavenumber that represented the "subcritical" roughness condition intended to suppress transition. In subsequent experiments a plasma actuator on the cone surface, just downstream of the roughness array, was used to produce a disturbance at the most amplified traveling cross-flow mode frequency. The purpose was to investigate under controlled conditions, a nonlinear (quadratic) interaction between the stationary and traveling cross-flow modes that could affect the transition location. The experiments were performed in the Air Force Academy Mach 6.0 Ludwieg Tube Facility, that is not designed to produce "quiet" flow. Under these conditions, the subcritical wave number roughness increased the transition Reynolds number by 25%. This was less than the 40% obtained with the same model and roughness in a "quiet" Mach 3.5 tunnel.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 03, 2019
- Accession Number
- AD1085967
Entities
People
- Eric Matlis
- Thomas C. Corke
Organizations
- University of Notre Dame