Airflow distortion at instrument sites on the RRS James Clark Ross during the WAGES project

Wind speed measurements obtained from anemometers mounted on ships are prone to systematic errors caused by the distortion of the airflow around the ship's hull and superstructure. This report describes the results of simulations of the airflow around the RRS James Clark Ross made using the computational fluid dynamics (CFD) software VECTIS. The airflow distortion at anemometer sites used during the WAGES project has been quantified at a wind speed of 10 m/s for relative wind directions of 0 (bow-on), 10, 20, 30, 50, 70, 90 and 110 degrees off the bow. The anemometers used in this study were located in the bows of the ship. Temperature sensors were located on the port side of the monkey island. For bow-on flows the anemometers in the bows of the ship experienced relatively small flow distortion. At these sites the flow was decelerated by about 1% of the free stream wind speed. Over the full range of relative wind directions the flow to the R3 sonic is generally accelerated with the largest wind speed biases at flows directly over the beam. The vertical displacement of the airflow increases from around 1 to 2 m for flows directly over the bow, to around 5m for flows over the ships beam as the blockage of the airflow by the ship becomes greater.The airflow distortion at the temperature sensor locations above the monkey island was typically greater than the well-exposed foremast locations. These locations experienced wind speed biases from 6% increase for an airflow directly over the bow, to large decelerations of 55 % when the instruments were in the large recirculation region for flows directly over the starboard side

Quantifying the effects of airflow distortion on anemometer wind speed measurements from merchant ships

Anemometers on Voluntary Observing Ships (VOS) are usually located above the bridge in a region where the effects of air flow distortion, created by the presence of the ship, may be large. Until now it was not known whether measurements from such anemometers would be biased high or low, and the possible magnitude of any such bias was not known. Investigations into the airflow above merchant ships have been carried out experimentally using a low-speed wind tunnel and numerically using a commercial Computational Fluid Dynamics (CFD) code VECTIS. The investigations examined the airflow over simple block models of VOS shapes. The results of the investigations were compared to wind speed measurements made from the RRS Charles Darwin. Experimental and CFD techniques have been used to devise scaling rules that predict the effects of the flow distortion. Both techniques have shown that the pattern of the flow distortion above the bridge scales with the ‘step height’, H, of the model. In the case of a tanker, H is the ‘bridge to deck’ height, i.e. the height of the accommodation block above the deck, for bow-on flows. Close to the top of the bridge the flow is severely decelerated and may even reverse in direction. Using the upwind edge of the bridge as the origin of the scaled co-ordinate system, there is a definite line above the decelerated region along which the speed of the flow is equal to the undistorted wind speed. Above this ‘line of equality’ the wind speed increases to a maximum and then decreases with increased height to a free stream wind speed. Simple equations have been devised to predict the positions of the ‘line of equality’, the maximum wind speed and the minimum wind speed within the decelerated region. Comparisons of the results with wind speed data obtained from field measurements made using a number of anemometers located on the RRS Charles Darwin agreed well and have predicted a maximum wind speed increase of approximately 15 ±5 %. Comparisons with the field data have confirmed that CFD models can be used to predict the effects of airflow distortion above merchant ships. The investigation has demonstrated the ability of the wind tunnel and CFD approaches employed to provide a better understanding of the airflow over merchant ships. Both methods have contributed to improve the understanding of how the wind speed at anemometer sites on merchant ships is affected by the ships hull and superstructure. <br/

Improving Wind Velocity Measurements on Ships: Industrial Training year at the James Rennell Centre for Ocean Circulation, 12 Aug 1993 - 9 Sept 1994

Accurate wind speed measurements are required from Research vessels for satellite validation and climate research, but the results have been shown to differ significantly from ship to ship. This report discusses an attempt to find the cause of the discrepancies and, if possible, to correct for them. A study on wind speed errors was undertaken to study the airflow distortions around a ship using numerical modelling. Simple potential models were used to study the airflow distortions around an idealised cylindrical mast to fmd the effect of the ship's mast on anemometers positioned close to it. The wake potential model was applied to wind speed data from RRS. Charles Darwin cruise 43 and partially corrected the wind speed measurements from anemometers at 5 to 6 mast diameters. The airflow distortions over the ship's hull and superstructure were then investigated to try to account for these remaining wind speed errors. Wind speed errors were calculated using a Computational Fluid Dynamics (C.FD.) package and computer generated ship models. The study is in a preliminary stage and the C.F.D. package has been validated against a wind turmel study for the C.S.S. Dawson and wind speed corrections agree to within 2 %

Metadata for the WAGES instrumentation deployed on the RRS James Clark Ross between May 2010 and September 2013

The RRS James Clark Ross makes meteorological measurements around Antarctica during the austral summer, in the Arctic during the boreal summer and in the Atlantic during passages between the two poles. In May 2010, as part of the WAGES project the ships existing systems were complemented by the AutoFlux system (Yelland et al., 2009) to measure the transfers of momentum, heat and CO2 between the atmosphere and the ocean. Similarly, a commercial directional wave radar "WAVEX" made by the Norwegian firm MIROS was installed. This report describes the metadata for the WAGES instrumentation deployed on the RRS James Clark Ross between May 2010 and September 2013. Sensor serial numbers, dates of sensor changes and problems with sensors are contained in the associated tables

Metadata for the WAGES instrumentation deployed on the James Clark Ross between May 2010 and September 2011

The RRS James Clark Ross makes meteorological measurements around Antarctica during the austral summer, in the Arctic during the boreal summer and in the Atlantic during passages between the two poles. In May 2010, as part of the WAGES project the ships existing systems were complemented by the AutoFlux system (Yelland et al., 2009) to measure the transfers of momentum, heat and CO2 between the atmosphere and the ocean. Similarly, a commercial directional wave radar "WAVEX" made by the Norwegian firm MIROS was installed.This report describes the metadata for the WAGES instrumentation deployed on the RRS James Clark Ross between May 2010 and September 2011. Sensor serial numbers, dates of sensor changes andproblems with sensors are contained in the associated tables

Possible biases in wind speed measurements from merchant ships

Wind speed measurements obtained from ship-mounted anemometers are biased by the presence of the ship which distorts the airflow to the anemometer. Until recently this bias had only been quantified for a few well-exposed anemometer sites on individual research ships, whereas the magnitude and even the sign of the bias was unknown for anemometers on merchant ships. Three-dimensional numerical simulations of the airflow over a typical tanker/bulk carrier have been performed to quantify the pattern of the airflow above the ship’s bridge. The accuracy of the numerical simulations has been verified by comparison to wind tunnel studies. Typically, the flow is accelerated by up to 18±6 % or decelerated by 100% depending on position. In practice, an anemometer located above the bridge should be mounted as high and as far forwards as possible

Metadata for the WAGES instrumentation deployed on the James Clark Ross between May 2010 and September 2011.

The RRS James Clark Ross makes meteorological measurements around Antarctica during the austral summer, in the Arctic during the boreal summer and in the Atlantic during passages between the two poles. In May 2010, as part of the WAGES project the ships existing systems were complemented by the AutoFlux system (Yelland et al., 2009) to measure the transfers of momentum, heat and CO2 between the atmosphere and the ocean. Similarly, a commercial directional wave radar "WAVEX" made by the Norwegian firm MIROS was installed. This report describes the metadata for the WAGES instrumentation deployed on the RRS James Clark Ross between May 2010 and September 2011. Sensor serial numbers, dates of sensor changes andproblems with sensors are contained in the associated tables

Airflow distortion at instrument sites on the ODEN during the ACSE project

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 ODEN made using the computational fluid dynamics (CFD) software VECTIS. The airflow distortion at anemometer sites used during the ACSE project has been quantified at a wind speed of 7 ms-1 for a wide range of wind directions: every 10 degrees from bow on to 120 degrees off the bow, and an additional run was undertaken at 150 degrees off the bow. The anemometers used in this study were located in the bows of the ship. The vertical displacements of the airflow at the anemometer sites and at a location of an aerosol intake are included. Wind speed profiles above a motion-stabilised doppler lidar were also obtained. For bow-on flows the anemometers in the bows of the ship experienced relatively small flow distortion. At these sites the flow was decelerated by about 3% of the free stream wind speed. Over the full range of relative wind directions the flow to the METEK sonic is generally accelerated with the largest wind speed biases at flows directly over the beam. The vertical displacement of the airflow increases from around 3 m for flows directly over the bow, to around 6 m for flows over the ship's beam as the lockage of the airflow by the ship becomes greater. The vertical displacement at the aerosol intake location varied from 6m for flows directly over the bow, to around 16 m for flows over the ship's beam. The ship imposes a significant obstacle to the flow and forces a strong vertical velocity in the lowest few tens of meters above the lidar

Air Flow Distortion Over Merchant Ships

Anemometers on voluntary observing ships (VOS) are usually sited above the bridge in a region where the effects of flow distortion may be large. Until recently it was unclear whether measurements from such anemometers would be biased high or low, and the magnitude of any such bias was not known. This report describes the progress made in determining the effects of flow distortion and hence in predicting the possible bias in such anemometer measurements of the wind speed