Base pressure prediction in bluff-body potential-flow models

Abstract

In a recent study by Yeung & Parkinson (1997), a wake width was proposed which allowed the bluff-body potential-flow model by Parkinson & Jandali (1970) to be extended to include the flow around an oblique flat plate. By incorporating this wake width in the momentum equation originally derived by Eppler (1954) for separated flow, the drag of the plate is related to its inclination and base pressure through a simple analytical condition. It allows the base pressure, which is usually treated as an empirical input, to be determined theoretically and thus the model becomes self-contained. Predictions of the base pressure, drag and width of wake are found to be in reasonable agreement with the experimental data. When applied to the symmetrical flow around a wedge of arbitrary vertex angle, similar agreement with experimental measurements is obtained as well. It is also demonstrated that this condition is compatible with the free-streamline models by Wu (1962) and Wu & Wang (1964) such that the corresponding predictions are in good agreement with experiment.

Drag on flat plates of arbitrary porosity

“…This poses a constraint on the problem which can be used to calculate the base pressure term. It should be noted that a similar approach was used by Yeung & Parkinson (2000) for solid plates and wedges.…”

On pressure invariance, wake width and drag prediction of a bluff body in confined flow

“…The axisymmetric flow past a cone of base diameter D and planar flow past a wedge of base thickness D, each having a half-apex angle δ, as defined in figure 1, are considered next. As demonstrated in Yeung & Parkinson (2000), the measured vortex-shedding frequency f from Simmons (1977) for wedges in unconfined flow with 10 • 6 δ 6 90 • becomes independent of δ when non-dimensionalized using 9(a), where…”

“…The bluff-body potential-flow model for a normal flat plate in an unconfined stream by Parkinson & Jandali (1970) was recently advanced by Yeung & Parkinson (2000) such that c pb = −1.385 is no longer an empirical input but predicted theoretically. The value is substantiated by the experimental measurements such as those by Fage & Johansen (1927), Simmons (1977) and Gaster & Ponsford (1984).…”

“…where F (δ) is a function of δ for cones (see figure 10a) by using the potential-flow model for wedges of arbitrary δ developed by Yeung & Parkinson (2000). Solutions of (−c pb , c d ) obtained by solving (3.3) and (3.4) are compared with data from Calvert (1976a) and Hoerner (1965) for a range of δ in figure 10(b).…”

“…where 2y = D sin θ and cos δ = 1/ 1 − c pb . For unconfined flow, Yeung & Parkinson (2000) found that c pb = −1.385. On the wetted surface, π/2 < θ < π, so…”