Flow Noise and Outer Decoupler Studies
Abstract
This program has started on the development of a rudimentary description of the nature of the low-wavenumber noise production mechanisms and features. Certain responses and mechanisms must be considered and included in even a minimal model of the turbulent boundary layer (TBL) low-wavenumber pressure fluctuation production processes and the attendant stipulation of outer decoupler design guidelines. The observed features of the noise spectra must include: (1) Cyclic, self-sustaining nonlinear interactions of packets of finite-amplitude Tollmien-Schlicting waves intrinsically subject to large phase modulations. (2) The continuous spectrum of modes of response of the TBL to Reynolds stress bursts. (3) Nonlinear interactions between the continuous spectrum modes. This report shows that the interacting fluctuations are of spacial scale 2 delta and lie at small angles (theta < or = 10 deg) to the wall. Therefore, it develops, from first principles, design criteria for outer decouplers that defeat the low wavenumber flow noise by: (1) Responding to pressure fluctuations in a scale-selective fashion, transmitting with adequate fidelity the acoustic waves of interest but rejecting the fluctuation 'carrier' components of scale 2 delta; and (2) Rejecting the noise component that arrives at the decoupler at grazing incidence angles. The resultant design constraints are manifold but achievable.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 03, 1982
- Accession Number
- ADA139911
Entities
People
- I. Dyer
- R. Collier
- R. Hoglund
- R. Vaglio-laurin