TWO PHASE FLOW ANALYSIS AND MODEL TEST RESULTS ON AIR LEAKAGE IN CONDENSER OPERATION OF PUMP TURBINE

摘要

During spinning reserve or condenser operation of large capacity pump-turbines, the.runner rotates in the compressed air depressing the water level in the upper draft tube below the runner. The swirl flow induced by the rotating runner causes the rotating and sloshing motion of the depressed water. In these operations, numerous small air bubbles are mixed in the water and are conveyed to the lower reservoir through the bend of the elbow type draft tube by the secondary flow which is made by the rotating / sloshing motion. In order to enable the continuous condenser operations in long periods with a small compressor, the air leakages are required to be reduced. The authors apply the three dimensional turbulent flow analysis program using finite volume method to design the draft tube shape of small volume of the air leakage, taking into consideration the swirl air flow induced by the runner, the secondary flow induced by the rotating / sloshing motion of water, and the motion of the mixed air bubbles. For the confirmation of several designs of the draft tubes, model tests of air leakage were conducted under the actual submergence head. The results of the flow analysis shows a good agreement with the results of model test. The quasi two phase flow analysis is useful for improving the air leakage performance of the draft tube.