Vladimír Habán

Simulation of low pressure water hammer

Numerical solution of water hammer is presented in this paper. The contribution is focused on water hammer in the area of low pressure, which is completely different than high pressure case. Little volume of air and influence of the pipe are assumed in water, which cause sound speed change due to pressure alterations. Computation is compared with experimental measurement.

Spatio-temporal description of the cavitating flow behavior around NACA 2412 hydrofoil

Spatio-temporal description of the cavitating flow around hydrofoil with 8 degrees incidence using proper orthogonal decomposition (POD) is presented. POD is a suitable tool, which provides information not only about the flow dynamics, but also about relevance of different flow structures. POD also enables to track energy transport within the domain and energy transfer among the eigenmodes of the flow field. Analysis documents change of the flow structure for decreasing cavitation number, which can be most likely attributed to sheet/cloud cavitation transition.

Damping of Self-Excited Pressure Pulsations in Petrodiesel Pipeline

A pumping station in a fuel storage suffered from pressure pulsations in a petrodiesel pipeline. Check valves protecting the station against back flow made a big noise when disc hit a seat. Due to employees complaints we were asked to solve the problem, which could lead to serious mechanical problems. Pressure measurement in the pipeline showed great pulsations, which were caused by self-excited oscillation of control valves at the downstream end of pipeline. The operating measurement did not catch it because of too low sampling frequency. One dimensional numerical model of the whole hydraulic system was carried out. The model consisted of check valve, pipeline and control valve, which could oscillate, so it was possible to simulate the unsteady flow. When the model was validated, a vessel with nitrogen was added to attenuate pressure pulsations. According to the results of numerical simulation, the vessel was installed on the location. Subsequent measurement proved noticeably lower pulsations and almost no noise.

Experimental and acoustic modal analysis of the submerged steel plate in water

The immersed body has different natural frequencies compared to body in vacuum or air. This is one of added effects of fluid on submerged solid. In this work this is studied on steel plate both experimentally and in simulation. Comparison between these methods is given and ability of ANSYS Acoustic to predict frequency change with reasonable accuracy is presented. Frequency change as well as change of order of mode types correlates with experimental measurement. Difference in measurement for submerged and partially submerged body is discussed.The immersed body has different natural frequencies compared to body in vacuum or air. This is one of added effects of fluid on submerged solid. In this work this is studied on steel plate both experimentally and in simulation. Comparison between these methods is given and ability of ANSYS Acoustic to predict frequency change with reasonable accuracy is presented. Frequency change as well as change of order of mode types correlates with experimental measurement. Difference in measurement for submerged and partially submerged body is discussed.

Experimental investigation of check valve behaviour during the pump trip

The paper is focused on the description of an experimental investigation of a nozzle check valve. Attention is paid to the behaviour during transitions when the flow is decelerating. Flow reversal is often accompanied with the check valve slam, because the check valve closes with a delay after the flow changes its direction. The maximal back flow velocity determines the maximal pressure peak when the check valve closes, so this velocity was found for different flow decelerations.

Hydraulic machine with non-uniform cascade

In this article is introduced the sentence of an extension of operational zone of hydraulic machines. The problems of its extending is based on the design of non-uniform cascade. The non-uniform cascade is connected with other factors. The change of own frequency of the runner of a hydraulic machine and pressure pulsations. The suitable construction of non-uniform cascade is introduced on the results of computational simulation and experiment.