Evaluation of an Eddy Dissipation Rate Calculation Method for Boundary Layer Weak Turbulence Conditions

A current effort to determine safe and efficient aircraft separations to protect against wake vortex encounters relies on a physics-based circulation model, which in turn requires reliable climatological distributions of near-surface eddy dissipation rate (EDR). EDR can be computed from high temporal resolution wind observations such as from sonic anemometers or vertically-pointing Doppler lidar stares. Many computational techniques assume the decay of energy in the inertial subrange specified by Kolmogorov’s hypothesis, but lack an apparent metric for assessing adherence to this assumption. For example, marginally stable conditions with light winds represent the most likely conditions for the longest-lived wakes, which represent the high-risk range of the wake vortex encounter spectrum. Unfortunately, these same conditions typically present a challenge to this assumption due to the small inertial subrange.

This talk will focus on the use of a variance-based EDR calculation technique proposed by O’Connor et al (2010) and applied to base data from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) field site. The O’Connor method is easy to implement as it does not require the calculation of explicit wind energy spectra. To evaluate its performance in regimes of interest for wake modeling, the slope of energy decay associated with this technique’s guiding parameters will be explicitly calculated and compared to the -5/3 theoretical rate. Adherence will be characterized, especially with respect to the associated stability. EDR values associated with poor quality estimates will be examined with reference to the temporally-nearest high-quality calculations to determine if such estimates, while not strictly satisfying theoretical assumptions, may nonetheless be reasonable and useful.

O’Connor, E.J., A.J. Illingworth, I.M. Brooks, C.D. Westbrook, R.J. Hogan, F. Davies, and B.J. Brooks, 2010: A method for estimating the turbulent kinetic energy dissipation rate from a vertically pointing Doppler lidar, and independent evaluation from balloon-borne in situ measurements. J. Atmos. Ocean. Tech., 27, 1652-1664.

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This material is based upon work supported by the Federal Aviation Administration under Air Force Contract No. FA8702-15-D-0001. Any opinions, findings, conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Federal Aviation Administration.