Experimental evaluation of 2-D entropy model for open-channel flow

The purpose of this technical note is to investigate the applicability of the Principle of Maximum Entropy in hydrodynamics, particularly in velocity distribution in open channels, by comparing the predictions of two 2-D models with measured data. Both models use a curvilinear coordinate system, but whereas the first uses logarithmic law for velocity distribution, the second is derived by the principle of maximum entropy. The computed values are then compared to 1,832 point velocity measurements by means of laser-Doppler velocimetry in five experiments with rectangular smooth-wall flumes. The results show that the entropy model performs better than the logarithmic model not only in general terms (mean absolute error 12.8% versus 19.1%), but in practically all flow regions, especially in those near the channel bed (absolute error 23.8% versus 55.3%). Because the models disregard secondary flow, velocity predictions in the upper region of near-side walls are relatively poor.