Nature of C_{loss} coefficient for porous plateNature of C_{loss} coefficient for porous platehttps://oss.deltares.nl/c/message_boards/find_thread?p_l_id=1806765&threadId=5652662020-11-27T18:11:36Z2020-11-27T18:11:36ZNature of C_{loss} coefficient for porous plateSimon Waldmanhttps://oss.deltares.nl/c/message_boards/find_message?p_l_id=1806765&messageId=5652652015-01-19T10:01:51Z2015-01-19T10:01:41ZDear forum,<br /><br />Like a number of other forum users before me, I'm looking at representing tidal turbines in Delft3D-FLOW using porous plates.<br />Based on the information given in the manual, my understanding is that the c_{loss} parameter can be stated as,<br /><br />c_{loss} = (- C_t A_t) / 2 dydz<br /><br />where C_t is the thrust coefficient of the turbine(s), A_t is the total cross-sectional area of turbine rotor in the cell when viewed in the appropriate direction (total, because there may be more than one turbine), and dydz is the cross-sectional area of the cell in the direction being considered.<br /><br />Intuitively, I think that this can be thought of as representing the proportion of the momentum passing through the cell that is removed, and on this basis must be between zero and one. (actually between zero and 0.5, given the division by two above)<br /><br />However, the example values given in the manual are 800 and 1000, a discrepancy of some orders of magnitude! Some initial testing suggests that using values <0.5 in a model gives plausible results, wheras using values a thousand times higher looks more like a brick wall has been placed in the flow.<br /><br />A number of people have asked the same, or substantially similar questions, before, but none has received a full answer[1]. Please can anybody clarify whether I have misunderstood somewhere, or whether the example values in the manual are implausible? Alternatively, any pointers as to how this is handled in the code might be helpful. <br /><br />Many thanks<br />Regards<br />Simon.<br /><br />[1] Previous questions on the same topic:<br />http://oss.deltares.nl/web/delft3d/delwaq/-/message_boards/view_message/119996<br />http://oss.deltares.nl/web/delft3d/delwaq/-/message_boards/view_message/264796Simon Waldman2015-01-19T10:01:41Z