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The Power Decay Law in High Intensity Active Grid Generated Turbulence

  • Author(s): Koster, Timothy W.
  • Advisor(s): LaRue, John C
  • et al.
Abstract

The work presented herein provides an assessment of the applicability of the power law decay of turbulent kinetic energy in the isotropic and homogeneous region in a high intensity flow generated by an active grid. Two sets of indicators and data collected at mean velocities of 4, 6 and 8 m/s are used to determine the isotropic region. Results of this study are inconsistent as some of the results are consistent with a power law behavior but some results are not. For example, the ratio of dissipation computed from the time derivative of the velocity, ϵ, to the corresponding value computed using the power law decay for turbulent kinetic energy, ϵ^*, should be one. This is indeed the value found for mean velocities of 8 and 6 m s-1 but only when using a range of downstream positions corresponding to only one of the pairs of isotropy indicators. For mean velocity of 4 m s-1, ϵ/ϵ^*≠1, nor does it equal 1 for any of the mean velocities for the isotropic range indicated by the second isotropy indicator. An alternative approach for the power decay law is proposed and is based on the determination of the range using the constraint that ϵ/ϵ^*=1.

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