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A method is proposed for the evaluation of the added-volume coefficients of bluff bodies, by modelling the pressure gradient of the ambient stream by a remote point source. For complex body configurations, such as the automobile shapes, the new formula offers a practical alternative to the kinetic energy approach. It is shown that the longitudinal pressure gradient in a wind tunnel may affect not only the measured drag force but also the side and lift forces.

Lagally’s theorem is used to evaluate the increments to aerodynamic forces on automotive models, tested in solid-wall wind tunnels. The strengths of the model-representing singularities, pre-requisite for the application of the theory, are obtained from experimental wall pressure data, using an influence matrix method. The technique is demonstrated on the drag force acting on full-size and half-size truck models, measured in the same test section.