On calculating forces from the flow field with application to experimental volume data

The use of flow field information to compute the fluid dynamic force on a body is investigated with specific application to experimental volumetric measurements. The calculation method used avoids the explicit evaluation of the pressure on the boundaries. It is shown that errors in the data introduce an artificial dependence of the calculations on the position origin, and also that these errors are amplified by the position vector. A statistical description of the calculation variation associated with origin dependence is presented. A method is developed that objectively determines an origin which reduces the effect of the amplified error. The method utilises mathematical identities which relate the measurements to the main sources of error in a physically meaningful way, and is also found to be effective for changes of the external and internal boundaries of the fluid.