Analysis of Flow Fields in a Steam Turbine Control Valve With One Chamber

A flow field inside steam turbine control valves can be very variable from subsonic to transonic and with or without a flow detachment. It depends on changeable operating conditions and a valve geometry. Understanding phenomena that appear in valves helps predict and reduce pressure losses, enhancing the valve design. It also ensures safe operation and a reasonable price. The primary motivation of this paper is to provide a detailed view of different flow fields at various operating conditions. For this reason, a control valve with one chamber is analyzed using numerical simulations. It is a part of the most often used valve assembly for different steam turbines with outputs from about 10 to 1000 MW. The numerical simulations were carried out using a package of ANSYS software tools. The settings and models are based on the previous comprehensive studies, where a validation using measurements on the model was performed. Eight different valve cone lifts were computed, ranging from fully closed to fully opened valves. For each valve cone lift, about twelve different pressure ratios were defined. As a result, a complete flow characteristic of the valve was created. Based on this, the most typical cases with different flow fields are shown. At first, the position of the sonic line is analyzed. It was found that it has a direct connection with the flow contraction coefficient, which is introduced and described in detail. It is also connected with the strong field non-uniformity under the valve cone. Second, the length of the backflow region under the valve cone and in the diffuser is described and analyzed. All in all, this paper complements the previous papers about valves for steam turbines, which have already been presented at ASME Turbo Expo, created by the research and development team from the Doosan Skoda Power Company and the Institute of Thermomechanics of the Czech Academy of Sciences.