Calculation of Wyngaard Turbulence Distortion Coefficients and Turbulence Ratios; and Influence of Instrument-induced Wakes on Accuracy

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  • 1 Atmospheric Science Associates, Concord, Massachusetts
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Abstract

Methods that use potential-flow calculations to correct turbulence measurements for instrument-induced flow distortions are discussed in general terms for two- and three-dimensional geometries. A simple calculation method is described for the Wyngaard distortion coefficients, from which the corrections are determined, that previously had not been fully exploited. Panel methods, which are especially well suited to the simple method and allow calculations for arbitrary instrument geometries, are also discussed. Applications of all methods are illustrated by use of examples.

Distortions caused by wakes that result from flow separation from the instruments themselves cannot be corrected for by use of potential-flow calculations. Neglect of these distortions may compromise accuracy of the corrections. Severity of this problem for atmospheric turbulence measurements is illustrated by results calculated for some simple geometries.

Abstract

Methods that use potential-flow calculations to correct turbulence measurements for instrument-induced flow distortions are discussed in general terms for two- and three-dimensional geometries. A simple calculation method is described for the Wyngaard distortion coefficients, from which the corrections are determined, that previously had not been fully exploited. Panel methods, which are especially well suited to the simple method and allow calculations for arbitrary instrument geometries, are also discussed. Applications of all methods are illustrated by use of examples.

Distortions caused by wakes that result from flow separation from the instruments themselves cannot be corrected for by use of potential-flow calculations. Neglect of these distortions may compromise accuracy of the corrections. Severity of this problem for atmospheric turbulence measurements is illustrated by results calculated for some simple geometries.

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