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A low-order BEM

A low-order BEM has been developed by Morino and Kuo [2] for solving the boundary integral equation (6) in the case of fully wetted (non-cavitating) flow. The hydrofoil surface is approximated with N flat panels on which constant strength dipoles and sources are distributed. The source strengths are proportional to tex2html_wrap_inline51 and are known via equation (3). The dipole strengths are proportional to tex2html_wrap_inline15 and are determined from applying equation (6) at the mid-points of the panels.

The Kutta condition is numerically implemented by employing Morino's condition [2].

  equation117

where tex2html_wrap_inline55 and tex2html_wrap_inline57 are the potentials at the upper and lower trailing edge panels, respectively.

The discretized version of equation (6) may be written in the following matrix form:

  equation121

where tex2html_wrap_inline59 and tex2html_wrap_inline61 are the vectors with N components the perturbation potentials and their normal derivatives on each panel, respectively.

In the case a cavity is present, the low-order BEM was extended by Kinnas and Fine [3]. In this case equation (6) still applies. Now, the source strengths are only known on the wetted part of the hydrofoil. However, by integrating equation (5) over the cavity surface, tex2html_wrap_inline15 on the cavity can be expressed in terms of the arclength and the cavitation number tex2html_wrap_inline25 . The unknown sources on the cavity surface, the unknown potentials on the wetted surface, and the cavitation number are determined from inverting equation (6). The cavity surface of course is not known, and its shape is determined iteratively. The method was shown in [3] to converge quickly with number of iterations, where the cavity shape in the first approximation was taken the same as that from linear cavity theory [4].



Baris Gucun
Tue Mar 4 18:15:49 CST 1997