Investigation and Analysis of Attack Angle and Rear Flow Condition of Contra-Rotating Small Hydro-Turbine

At present, there is strong impetus for renewable energy to replace the traditional energy sources because of the environmental pollution. Small hydropower is a promising renewable energy source; however, small hydro-turbines easily become blocked and impacted, and the efficiency of such devices is lower. Therefore, we examined contra-rotating rotors to overcome these disadvantages. We have made modifications to the blade thickness and to the front hub of the original model. In this paper, we focus on the attack angle and rear flow condition of the original model and the modified one. The axial and circumferential velocities are given as outputs, from which the attack angle is then calculated. The results show that the attack angle of new model is smaller at the hub area. The stagnation point of the rear rotor was moved slightly to the pressure surface of the rear blade, and the separation at leading edge area was suppressed. The crowed flow at the tip clearance area is also reduced. The high turbulent kinetic energy area is moved forward to the middle of the blade. The rear rotor’s torque is bigger and changes more smoothly. Therefore, the rear flow conditions of the new model are improved.