Numerical studies of the effect of flue exit geometry on the initial jet formation in flue organ pipes

Paper in proceeding, 2007

The paper presents results from numerical simulations (CFD) of the initial jet formation in the mouth of wind instruments. A special focus is on the effects of asymmetries in the flue exit geometry. A finite element code based on a 2D flow assumption was used to solve this problem. The simulated time frame spans from the onset of air motion in the mouth to a few milliseconds after the tip of the free jet has reached the upper lip. An incompressible, viscous fluid behaviour was assumed to clearly work out the influence of the geometrical details on flow separation and possibility and type of interaction between the free jet and solid surfaces. Very good agreement between own simulation results and experimental data from the literature shows that various viscous effects play an important part in the initial jet motion and may also be of significant influence during steady state. Especially the recirculation between free jet and the front surface of the languid of metal flue organ pipes can lead to an additional force in the jet dynamics, the Coanda effect. It becomes important when the free jet is sufficiently close to the surface and the languid thick enough.