A Robust Scheme for Control of Skin Friction and Heat Transfer in Turbulent Boundary Layers via New Instability Mechanism
Abstract
Using direct numerical simulations of turbulent channel flow, we present a new method for skin friction reduction by prevention of streamwise vortex formation near the wall. Based on recent evidence of streak instability-induced vortex generation, we develop a new technique for drag reduction, enabling large-scale flow forcing without requiring instantaneous flow information. As proof-of-principle, x-independent forcing, with a wavelength of 400 wall units and an amplitude of only 6% of the centerline velocity, produces a significant sustained drag reduction 20% for imposed counterrotating streamwise vortices and 50% for colliding, z-directed wall jets. The drag reduction results from weakened longitudinal vortices near the wall, due to forcing-induced suppression of the underlying streak instability. In particular, the forcing significantly weakens the wall-normal vorticity flanking lifted low-speed streaks, thereby arresting the streaks' instability responsible for vortex generation. These results suggest promising new drag reduction strategies, e.g., passive vortex generators or colliding spanwise jets from x-aligned slots, involving large-scale (hence more durable) actuation and requiring no wall sensors or control logic.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1998
- Accession Number
- ADA368325
Entities
People
- Fazle Hussain
- Wade Schoppa
Organizations
- University of Houston