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Unsteady Subsonic Turbulent Jets

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Recent Developments in Theoretical and Experimental Fluid Mechanics

Abstract

Basic properties Such as length and velocity scales, decay of the mean velocity, rate of spread and entrainment of some unsteady, subsonic, turbulent jets are examined. Effects of cyclic excitation are dependent on the frequency and level of excitation. Oscillated jets produce extremely large spreading rates but the highest entrainment reported so far is obtained with fully pulsed jets of low duty ratio at a frequency of pulsation well below the natural frequency of the jet. Decay of centre-line velocity is slightly greater than that of steady jets for low levels of pulsation near the natural frequency of the jet. At much lower frequencies and high levels of pulsation, this decay is significantly less rapid with downstream distance than for steady jets and is thought to be due to interaction between the velocity and pressure fields downstream of the jet exit. Measurements also indicate the existance of larger length scales in fully pulsed flows than in the steady counterpart.

This paper is dedicated to Professor J.Zierep whom I met while on study leave at Karlsruhe University in the Institut für Strömungslehre und Strömungsmaschinen, Professor Zierep1 s extensive contributions to fluid mechanics teaching and research captured my imagination and the present contribution is aimed to outline just a very small part of the range of topics within his sphere of interest.

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Abbreviations

a, a1 :

Effective origins for U0;r1/2,U

Ci :

Instantaneous hot-wire anemometer cooling velocity

d:

Outlet orifice diameter

M:

Integral in Eq. (4)

n:

Polytropic expansion index

P, P∞ :

Static pressure in, and at edge of jet respectively relative to far field ambient pressure

Q, QE :

Volume flow at any x and at exit respectively evaluated at far field conditions. Radial co-ordinate

R1/2,U :

Half-value radius of U

R:

Radius of control volume

St:

Strouhal number, based on mean exit velocity and exit diameter

tP :

Period of a pulsation cycle

t1 :

Time for which a non-zero velocity exists during cycle

T:

Variable

U:

Aggregate axial velocity fluctuation

uP :

Pseudo turbulence velocity fluctuation

u1 :

Intrinsic velocity fluctuation

U:

Mean axial velocity

Ū:

Mean flow velocity at jet exit evaluated from mass flow and ambient far field temperature and pressure

UP :

Total pseudo turbulence velocity at a given instant from beginning of pulsation cycle

ÛP :

Pulse averaged pseudo turbulence velocity

U0 :

Mean axial velocity on jet axis

V,v:

Mean and fluctuating radial velocity

w:

Azimuthal velocity fluctuation

x:

Streamwise directional co-ordinate with origin at exit plane of jet orifice

x0 :

Effective origin

α:

Constant in Eq. (7)

α0 :

Level of excitation

γP :

Duty ratio

ρ:

Density

τ:

Time delay

τP :

Time from valve opening; same meaning if used as subscript

—:

Overbar denotes time averaging over many pulsating cycles

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Authors
  1. K. Bremhorst
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Editors and Affiliations

  1. Institut für Reaktorbauelemente, Kernforschungszentrum Karlsruhe, D-7514, Eggenstein-Leopoldshafen, Germany

    U. Müller (Professor) (Professor)

  2. Institut für Strömungslehre und Strömungsmaschinen, Universität Karlsruhe (TH), Kaiserstraße 12, D-7500, Karlsruhe 1, Germany

    K. G. Roesner (Professor) & B. Schmidt (Professor) (Professor) &  (Professor)

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© 1979 Springer-Verlag Berlin Heidelberg

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Bremhorst, K. (1979). Unsteady Subsonic Turbulent Jets. In: Müller, U., Roesner, K.G., Schmidt, B. (eds) Recent Developments in Theoretical and Experimental Fluid Mechanics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-67220-0_49

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  • DOI: https://doi.org/10.1007/978-3-642-67220-0_49

  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-642-67222-4

  • Online ISBN: 978-3-642-67220-0

  • eBook Packages: Springer Book Archive

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