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representative of the other configurations at zero angle of attack.

The SUBOFF experiments

The SUBOFF experiments were funded by DARPA and conducted at the David Taylor Model Basin during 1988 and 1989. A number of submarine configurations, ranging from an axisymmetric body to a fully appended submarine were constructed in order to provide flow measurements for CFD validation. Each of the models was placed in the Anechoic Flow Facility (AFF) wind tunnel. The dimensions of the wind tunnel and layout of the model are shown in figure 1. The flow was measured at a Reynolds number of 1.2×107. This paper considers the flow past configuration AFF-1-, the axisymmetric body of revolution and configuration AFF-8-, the fully appended geometry at zero angle of attack.

Figure 1 The wind tunnel

For each configuration, pressure taps on the hull surface connected to rotary pressure scanners provided measurements for surface pressure. The wall shear stress was also measured at the location of selected pressure taps. A traversing mechanism was used to position hot film probes in order to measure mean and fluctuating components of the velocity. The uncertainty of the measurements, with 95% confidence, was 2.5% of U for the mean flow components and 0.2% for the Reynolds stresses, where U is the free stream inlet velocity. The uncertainty of the absolute values of the pressure and wall shear stress was within ±0.015 and ±0.0002 of their measured values respectively. A complete description of the measurement system and their uncertainty is given in reference 1.

For the axisymmetric naked hull case, AFF-1-, measurements were taken at non-dimensionalised positions of x/L=0.875, 0.904, 0.927, 0.956 and at the propulsor plane x/L=0.978 where x is the position along the hull and L is the total length of the hull. For the fully appended case, AFF-8-, measurements were taken at positions x/L=0.978, 1.040, 1.096 and 1.200. For the AFF-8- case, the flow was measured at two degree intervals for radii between r/Rmax=0.25 and 2.00 where r is the distance of the probe from the axis of the hull and Rmax is the maximum radius of the hull. The quantities obtained at each location of these wake surveys were

and the static pressure. The non-dimensional quantities Cp and Cτ are then defined by

where u=mean axial velocity component

vr=mean radial velocity component

vθ=mean tangential velocity component

u′,v′,w′=fluctuating components

p=static pressure

p=free stream static pressure

ρ=fluid density

and τw=wall shear stress

Grid generation

In order to perform a validation exercise of this type, it is necessary to have a fast, efficient grid generation system which is capable of producing high quality grids with sufficient grid density to resolve the flow features. The system chosen was the SAUNA [5,6] system produced for the DRA by the Aircraft Research Association Ltd. The system uses the elliptic multiblock method to generate grids around fully appended geometries. This system is currently being developed to generate hybrid structured and unstructured grids with hexahedral, pyramidal, prismatic and tetrahedral cells. The SAUNA system takes separate geometry component definitions and combines them together into the required configuration, calculating intersections, as required.



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