Quantifying the Airflow Distortion over Merchant Ships. Part I: Validation of a

The effects of flow distortion created by the ship’s hull and superstructure bias wind speed measurements made from anemometers located on ships. Flow distortion must be taken into account if accurate air–sea flux measurements are to be achieved. Little work has been undertaken to examine the wind speed bias due to flow distortion in wind speed reports from voluntary observing ships (VOS). In this first part of a two-part paper the accuracy of the computational fluid dynamics (CFD) code VECTIS in simulating the airflow over VOS is investigated. Simulations of the airflow over a representation of the bridge of a VOS are compared to in situ wind speed measurements made from six anemometers located above the bridge of the RRS Charles Darwin. The ship’s structure was ideal for reproducing the flow over VOS when the wind is blowing onto either beam. The comparisons showed VECTIS was accurate to within 4% in predicting the wind speed over ships, except in extreme cases such as wake regions or the region close to the bridge top where the flow may be stagnant or reverse direction. The study showed that there was little change in the numerically predicted flow pattern above the bridge with change in Reynolds number between 2 10 5 and 1 10 7 . The findings showed that the CFD code VECTIS can reliably be used to determine the mean flow above typical VOS.

[1]  S. Murakami,et al.  COMPARISON OF VARIOUS TURBULENCE MODELS APPLIED TO A BLUFF BODY , 1993 .

[2]  D. Spalding.  A novel finite difference formulation for differential expressions involving both first and second derivatives , 1972 .

[3]  J. Hunt,et al.  Kinematical studies of the flows around free or surface-mounted obstacles; applying topology to flow visualization , 1978, Journal of Fluid Mechanics.

[4]  W. Rodi,et al.  A low dispersion and bounded convection scheme , 1991 .

[5]  R. Stull.  An Introduction to Boundary Layer Meteorology , 1988 .

[6]  H. Graber,et al.  Impact of flow distortion corrections on turbulent fluxes estimated by the inertial dissipation method during the FETCH experiment on R/V L'Atalante , 2003 .

[7]  Bengamin I. Moat,et al.  Quantifying the effects of airflow distortion on anemometer wind speed measurements from merchant ships , 2003 .

[8]  C. Tropea,et al.  The Flow Around Surface-Mounted, Prismatic Obstacles Placed in a Fully Developed Channel Flow (Data Bank Contribution) , 1993 .

[9]  S. Popinet,et al.  Experimental and Numerical Study of the Turbulence Characteristics of Airflow around a Research Vessel , 2004 .

[10]  Theodore Blanc,et al.  Superstructure Flow Distortion Corrections for Wind Speed and Direction Measurements Made from Tarawa Class (LHA1-LHA5) Ships. , 1986 .

[11]  Anthony F. Molland,et al.  Quantifying the Airflow Distortion over Merchant Ships. Part II: Application of the Model Results , 2006 .

[12]  S. Orszag,et al.  Development of turbulence models for shear flows by a double expansion technique , 1992 .

[13]  Bengamin I. Moat,et al.  CFD model estimates of the airflow distortion over research ships and the impact on momentum flux measurements , 2002 .

[14]  S. Planton,et al.  Toward a Better Determination of Turbulent Air–Sea Fluxes from Several Experiments , 2003 .

[15]  A. J. Minson,et al.  EXPERIMENTAL VELOCITY MEASUREMENTS FOR CFD VALIDATION , 1995 .

[16]  Bengamin I. Moat,et al.  Wind Stress Measurements from the Open Ocean Corrected for Airflow Distortion by the Ship , 1998 .