(b) What’s the Reynold number？ Explain the meaning of Reynold number. (10％)

2. In the region just downstream of a sluice gate, the water may develop a reverse flow region as is in Fig-1. The velocity profile is assumed to consist of two uniform regions, one with velocity Va =3 m/s and the other with Vb =0.9 m/s. Determine the net flowrate of water across the portion of the control surface at section (2) if the channel is 6 m wide. (20%)