DTIC ADA1023784: The Challenge of Unsteady Separating pdf

DTIC ADA1023784: The Challenge of Unsteady Separating

More Book Details

Description of the Book:

Unsteady separation occurs in a wide range of fluid flows of practical importance. In many applications, the ideal flow environment of a mechanical device is nominally steady, but the onset of separation is very often accompanied by some degree of undesirable and irregular unsteadiness. Adverse unsteady effects can also arise either due to self-induced motions of a body in a moving stream, or due to fluctuations or nonuniformities in the surrounding fluid. On the other hand, some devices may be required to execute time-dependent motion in order to perform their basic functions. In general, the combination of unsteadiness and flow separation produces fluctuating forces, vibrations, aeroelastic instabilities, or combinations of these, that are both undesirable and extremely difficult to predict. The fluctuating fluid dynamic forces associated with unsteady separation can be almost completely stochastic in some cases, such as buffet on an aircraft wing, or highly organized in others, such as the well-known periodic vortex shedding from a wire or cable.

Often, however, significant amounts of both random and periodic fluctuations are present, especially in flows at high Reynolds numbers. These flows represent considerable challenges to the research scientist and to the design engineer alike. The general fluid dynamic problem of unsteady separation at most practical Reynolds numbers remains an unsolved one, and no completely reliable prediction techniques exist at the present time. Instead, the modern design engineer must draw from a combination of approximate theories, empirical correlations of data, and finite difference programs based on uncertain physical modeling of turbulence. This paper attempts to describe the basic features of several representative classes of problems for which unsteady effects produce strong or unusual changes in the separation characteristics of the flow. Most of the analysis concerns external flow, and the emphasis here is on the physical

• Creator/s: Defense Technical Information Center
• Date: 6/1/1981
• Year: 1981
• Book Topics/Themes: DTIC Archive, McCroskey, William J, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MOFFETT FIELD CA AMES RESEARCH CENTER, *FLOW SEPARATION, *NONUNIFORM FLOW, AIRFOILS, BOUNDARY LAYER FLOW, DIFFUSERS, INVISCID FLOW, REPRINTS, WAKE

An excerpt captured from the PDF book