Airflow distortion at instrument sites on the RRS James Clark Ross

Abstract

Wind speed measurements obtained from anemometers mounted on ships are prone to systematic errors caused by the distortion of the air flow around the ship's hull and superstructure. This report describes the results of simulations of the air flow around the R.R.S. James Clark Ross made using the Computational Fluid Dynamics (CFD) software VECTIS. The airflow distortion at a number of anemometer sites has been quantified for wind speeds of 5 m/s and 15 m/s blowing a) directly over the bows of the ship, and b) directly over the port beam (90° to port of the bow). The anemometers in this study were located in the bows of the ship and also on the port bridge wing.

For bow-on flows the instrument sites in the bows of the ship experienced relatively small flow distortion. At these sites the flow was accelerated by between -1% to 1% and displaced vertically by between 1.7 m and 2.2 m. In contrast, the instrument sites on the port bridge wing experienced a severely distorted flow. The wind speed error varied rapidly from -40% to 20% depending on the exact location of the instrument, and the vertical displacement varied between 5.3 m and 6.3 m.

For flows over the port beam the instrument sites in the bows of the ship experienced moderate flow distortion with wind speed errors of 9 % to 13 % and vertical displacements of between 4.8 m and 5.4 m. The instruments sites located on the port bridge wing experienced wind speed errors of -7.1 % to 2.6 %, and vertical displacements of 9.4 m to 10.4 m.

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