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Abstract. This work aims to determine the impact of orifice plate deformation on the differential pressure at the high-pressure natural gas pipelines. The article focuses on the differences of the pressure values, velocity values and flow directions between deformed and undeformed orifice plate. The article contains deformation analysis of the orifice plate and CFD simulations of flowing natural gas through the orifice plates. CFD simulations contain basic models of the turbulence for both types of orifice plate. Whole research is based on the elimination of the negative influence of the deformation on the precise flow measuring of natural gas at the high-pressure pipelines.

The paper presents an approach to calculate the static pressure rise upstream of a valve in a pressure penstock of a hydropower plant (HPP), i.e. a valve upstream of a turbine, during an emergency closure of the flow. The calculated value of the pressure rise is applied for the design of the appropriate time of the valve emergency closure in the HPP penstock and for the sizing of the various parts of the HPP (structural and mechanical). The basic theoretical background of the problem, calculation relations, the range of validity of the used calculation relations are explained and then the procedure applied to the solution of a specific task from practice is explained.

When designing a hydropower plant with a long pressure penstock, special attention must be paid to the pressure conditions in the penstock, especially during emergency flow shutdown. In this paper, the main principles of the calculation of static pressure rise in the pressure pipeline during rapid flow shutdown are presented. The results obtained by analytical methods (calculation of direct and indirect water hammer) and numerical methods (mathematical modelling in Matlab software environment) are compared on specific examples. The influence of some input parameters of the numerical model on the results of the numerical calculation is analysed separately.

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