Experimental analysis into the effects of air compressibility in OWC model testing

It is well documented that the effect of air compressibility will potentially influence the performance of an Oscillating Water Column (OWC) device, with a number of previous theoretical studies examining these effects [1-5]. The implications of air compressibility have the most significant effect at full scale, which can be attributed to the large air chamber volume and the increase in associated pressure and flow rate. However, the development of wave energy converter technology relies significantly on model scale testing, which is often scaled using the Froude criterion. This scaling method are not appropriate for the modelling of air compressibility and introduces uncertainties in the prediction the performance results at full-scale. To account for these effects, methods have been derived to more accurately represent the effect of air compressibility at small scale, one of which requires scaling the air chamber volume by the scale factor squared as opposed to the traditional scale factor cubed following the Froude criterion methodology [1]. This paper examines a preliminary investigation into the effect of air compressibility through hydrodynamic experimentation of a bent duct OWC device, from which the behaviour of the obtained results are compared with the expression proposed analytically by Sarmento and Falcao [1].