Airflow distortion at instrument sites on the RV Knorr

Abstract

This report describes an investigation of the air flow around the RV Knorr using the Computational Fluid Dynamics software package "VECTIS" to simulate a flow of air directly over the bows of the ship. Section 2 gives a brief description of the model. This work was undertaken at the request of researchers from the Bedford Institute of Oceanography (BIO), the National Oceanic and Atmospheric Administration (NOAA) and Kiel University who had used the ship to carry meteorological instrumentation on a purpose-built mast (the "lattice tower") during an experiment in the Labrador Sea in the winter of 1997. One advantage of the VECTIS software is the ability to vary the computational mesh density; this allows regions of particular interest to be modelled using a much higher resolution than that employed elsewhere in the model. In the case of the Knorr, the highest mesh density was located around the instrument sites on the lattice tower. In Section 3 the distortion of the air flow to these instrument sites is examined, and the vertical displacement of the flow and the percentage wind speed error is calculated for each site. Section 4 describes the flow at the separate IMET instrument sites on the ship’s foremast and bowmast. The mesh resolution at the IMET sites is not as great as that around the lattice tower since data for the IMET sites were requested towards the end of the study. The results are summarised and discussed in Section 5.