Some aspects of numerical simulation of control valves for steam turbines

Abstract

The contribution deals with the numerical simulation of air and steam flow through the model of control valve for steam turbines. Numerical simulations were compared with experimental measurements for the award of the same boundary conditions. Valve characteristics have been computed for individual travel heights and pressure ratios of two variants of seat inflow angle (90° and 60°). Some other aspects are discussed in the article-comparison of the axysymmetric and 3D modelling, influence of the computational domain size, comparison of characteristics for two flow media, experimental model of the valve etc. The mentioned results are important for engineering simulations and also for design of the control valves for steam turbines of the large output. The control valve in a steam turbine is a main component included in the turbine set. This system comprises control fittings (i.e. valves, screens or control partitions) that control the flow of steam into the turbine. The system includes valve control (i.e. servos or HP hydraulic system) which sets the valves and screens to the required flow rate and pressure of the steam. It also contains an electronic system with control software which enables setting the valves, i.e. changing the steam flow into the turbine and thus changing the turbo-set output, from the control centre. The control valve should reliably regulate the amount of steam flow and thus the turbine set output. The actual regulation is achieved by a change of the flow area between the plug and the valve seat. The control valve design is outlined in Figure 1. These valves are produced in many versions with various arrangements and plugs.

Numerical Simulation of Flow and Determination of Aerodynamic Forces in the Balanced Control Valve

“…If the force equals the force corresponding with the product of the annular area and the difference of pressures before and after the valve, the valve is unbalanced; if the force is lower, it is a balanced valve. The paper [2] describes results of calculations and measurements of flow-through characteristics of unbalanced valves with varying seat inflow angle and concepts corresponding to the further stated valves. In the following stage, research focused on phenomena in the balancing system and in particular the force characteristics of the plug of this balanced single-seat diffuser control valve.…”

Some aspects of numerical simulation of control valves for steam turbines

“…The pressure ratio is a ratio between the static pressure on the outlet from the control valve and the total pressure on the valve inlet. It is determined by the formula (5). 5The proportional travel height is a real travel of the valve plug related to the critical diameter of the nozzle.…”

“…The geometry was further adapted and simplified with this program. The main software tool for performing the numerical simulation of the flow was the ANSYS/FLUENT 13.0 program, the details of simulations are described in the thesis [5]. All the mathematical models were conceived without a balancing system.…”

Data Assimilation of Steam Flow Through a Control Valve Using Ensemble Kalman Filter

“…al. [9] studied a balanced steam turbine control valve with experiment and RNG k-e based simulation. The result showed that both geometry models determined similar flow characteristic curves in trend compared to the experimental results.…”