Numerical Simulation of Cavitation on a Horizontal Axis Tidal Turbine
Paper i proceeding, 2016
For tidal turbines mounted on floating structures the possibility of
cavitation occurring on the blades is higher than for seabed mounted
tidal turbines. In this study we present Reynolds-Averaged Navier-
Stokes (RANS) solutions of the well-studied Southampton three bladed
horizontal axis tidal turbine (HATT). The numerical simulations were
carried out using the ReFRESCO viscous flow solver using three types
of simulations: (i) steady wetted flow; (ii) unsteady wetted flow and
(iii) unsteady cavitating flow. The wetted flow simulations gave overall
good prediction of thrust and power coefficients over the entire
experimental range of tip speed ratios (TSRs), with the unsteady
solution providing the better result. Low numerical uncertainties were
obtained for medium to high TSRs and larger for low TSR values,
where the flow is transitional and highly separated. The dynamic
cavitation simulation was carried out for the case of a cavitation
number of 0.63 at a TSR of 7.5. The simulations showed a good
agreement of the extent of the sheet cavity. However, the dynamics of
the sheet cavities have not been fully captured and the power and thrust
coefficients are under predicted compared to the experiments. This is
most likely due to lack of mesh resolution outside the wetted flow
boundary layer where the cavity dynamics occur, and due to high
numerical and experimental uncertainties for such a complex flow case.
The simulations showed that existing methodology used for computing
cavitation on marine propellers could be applied to HATTs, yielding
reliable results. Importantly, simulation of cavitation on HATTs could
be used as input for noise and erosion predictions.
Unsteady RANS
Cavitation
Horizontal Axis Tidal Turbine