Design against wind-induced vibration of multi-flue chimney stacks

Experimental study based on flow visualization, model oscillation testing and power spectral measurement has revealed the complexity of flow passing a multi-flue arrangement. The occurence of instability due to various aerodynamic excitation is possible. In the case of the sectional configuration having flues and structural members in a pentagonal arrangement, the oscillation induced by wind was found to be due to galloping at reduced wind velocity greater than $\text{V}{}_{\mathrm{<mtext>r</mtext>}}\text{= 16}$ with the amplitude of oscillation increasing with increase in wind velocity. With the application of slat devices to the chimneys, galloping oscillation was suppressed completely. As it is not yet possible to predict the response of a multi-flue chimney stack in wind with any certainty, it is useful to consider means of reducing any oscillatory tendency by original design. The design of the new chimney stack for the Royal United Hospital in Bath against the possibility of wind-induced vibration is discussed as an example.