Turbulent Incompressible Jets
Here one is concerned with a problem of free turbulent flow, because no solid wall confines the turbulent eddies.
- PDF / 5,523,686 Bytes
- 110 Pages / 480.541 x 688.368 pts Page_size
- 85 Downloads / 232 Views
ARIO ROMITI TECHNICAL
UNIVERSITY
OF
TURIN
FLUID DYNAMICS OF JET AMPLIFIERS
COURSE HELD AT THE DEPARTMENT OF HYDRO - AND GASDYNAMICS SEPTEMBER 1970
Springer-Verlag Wien GmbH 1970
This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. © 1972 by Springer-Verlag Wien Originally published by Springer-Verlag Wien-New York in 1972
ISBN 978-3-211-81152-8 DOI 10.1007/978-3-7091-2880-0
ISBN 978-3-7091-2880-0 (eBook)
PREFACE Jet amplifiers are the basic devices on which most of fluidic control systems rely. Signal amplification is obtained by controlling the deviation of a jet. In order to have an insight of the phenomenon, one must investigate the dynamic behaviour of the flow into the device. The fluid dynamics of separated flow has to be considered, taking into account the eventual reattachment of the stream. In the short course that is presented here, the fundamental laws describing free jet spreading are first given ; then, the effect of nearby walls is considered. These preliminary concepts are used for examination of jet interactions, stability, vibrations. Finally, conclusions about jet amplifier design, either of bistable or proportional type, are drawn.
Udine, September 1970
Chapter I
SUBMERGED JETS The fluid flow issuing from a nozzle into a surrounding medium is called a jet. A submerged jet spreads out in a medium made of its same fluid. The flow velocity at the nozzle output is approximately uniform. A potential core can be observed, that keeps the same velocity at any point, but decreases in size until finally it vanishes. A growing boundary layer appears, that is lim ited at its inner side by the potential core, and at its outer side it has free boundaries; it makes little difference if one considers an infinite layer with asymptotic velocity profilas or a finite thickness layer limited by a line joining the zero axial velocity boundary points.(see Fig.l.l). The boundary layer is due to mixing and entra'inment effects between the stream issued from the nozzle and the surreund ing fluid. Such effects are due in their turn to the properties
of viscous fluid, that allow a
Fig. 1.1
continuous transfer of mass and
Chap. I. Submerged jets
6
momentum between the gas issued from the nozzle and the ambient gas. As any flow, jet flow may be laminar or turbulent, depending upon the relative importance of viscous and inertia stresses. Pure viscous stresses obey to the Newton law:
'C=~g~
( 1.1)
where
p
. t , . t y coe ff.1c1en . . th e v1scos1 1s
cl u, ein
the velocity
gra-
dient normal to the streamlines , and 1:' is the tangential stress. Tangential stresses in laminar flow are given by
eq. ( l.l) . Laminar flow is characterize d by smooth, separate streamline patterns. The ratio between inertia and viscous stresses is characterize d by the Reynolds number' Re = th
Data Loading...
