{"id":160963,"date":"2021-08-03T11:42:39","date_gmt":"2021-08-03T11:42:39","guid":{"rendered":"\/forum\/forums\/topic\/having-problem-with-two-phase-flow-air-and-water\/"},"modified":"2021-08-17T12:32:23","modified_gmt":"2021-08-17T12:32:23","slug":"having-problem-with-two-phase-flow-air-and-water","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/having-problem-with-two-phase-flow-air-and-water\/","title":{"rendered":"Having problem with two phase flow (air and water)"},"content":{"rendered":"
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Currently I am working on hydrodynamic design of unconventional hydro turbine. The turbine intended to be installed in canal as such the resistance from the turbine create water level difference in the upstream and downstream of the turbine. One of the main task in the design work is to determine the upstream and downstream water level in the canals, the difference between the water level in the canals is assumed to provide gross head for the turbine. The water levels in the upstream and downstream canals have been determined using energy conservation along a streamline (Bernoulli equation) as first estimation and used to set up the single phase simulation. With single phase simulation I have got seemingly very good result for turbine eff, hydraulic power, mechanical power, net head, gross head etc<\/p>\n

Now further I want to check the water level in the upstream and downstream level as well as other parameters determined from single phase simulation using two phase simulation in ANSYS CFX (Free surface flow). More or less I have applied the techniques suggested by ANSYS CFX tutorial in free surface flow over a bump in chapter 9. The simulation runs quite OK for about 65.5 revolution of the turbine, first i have used larger time step and then decreasing to lower value, to be specific (0.25 sec to 0.1sec). At about the aforementioned revolution of the turbine mass flow is conserved when checked at control surfaces, i.e at inlet and outlet are equal, expected tor is also produced from the turbine.<\/p>\n

Problem encountered:<\/p>\n

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  1. Total pressure in stationary frame are not conserved in the flow direction. i.e, I am expecting the pressure to decrease from inlet to outlet continuously but this doesn't happened. For instance the pressure at a location where the guidevane interfaced with the rotor is higher than the one at guidevane inlet. Note that the guidevane inlet is upstream of the interface.<\/li>\n
  2. The total pressure in stationary frame at the turbine outlet is much higher than the one obtained from single phase.<\/li>\n
  3. The calculated hydraulic power, which is the product of the change in total pressure in stationary frame between guidevane inlet and rotor outlet, and volume flow rate passing through turbine is much less the mechanical power.<\/li>\n<\/ol>\n

    I am waiting for any valuable suggestion why this happened in my simulation. any help is appreciated in advance<\/p>\n","protected":false},"template":"","class_list":["post-160963","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t