No abstract

In the present work new criteria of optimal design method for turbine runner [1] are proposed. Firstly, based on the efficient method which couples direct simulation of 3D turbulent flow and engineering semi empirical formulas, the combined method is built for hydraulic energy losses estimation in the whole turbine water passage and the efficiency criterion is formulated. Secondly, the criterion of dynamic loads minimization is developed for those caused by vortex rope precession downstream of the runner. This criterion is based on the finding that the monotonic increase of meridional velocity component in the direction to runner hub, downstream of its blades, provides for decreasing the intensity of vortex rope and thereafter, minimization of pressure pulsation amplitude. The developed algorithm was applied to optimal design of 640 MW Francis turbine runner. It can ensure high efficiency at best efficiency operating point as well as diminished pressure pulsations at full load regime.

In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. Prediction of the runaway speed at the stage of runner design would allow to select a runner considering this characteristic. Given in this paper is the numerical prediction of the runaway speed for a Kaplan turbine. Two approaches for numerical simulation were discussed. In the first one, the flow in the turbine flow passage was simulated using 3-D RANS equations of incompressible fluid using k-ε turbulence model. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. CFD calculations were carried out with using CADRUN flow solver. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.

This article describes the process of dragging a pipeline through a channel. In the simulation of this process, the interactions between the pipeline, the drill rod, the soil and the bentonite mud are taken into account. Dragging of the pipeline through the well is hampered by frictional forces of the pipeline and the drill rod against the soil, as well as the drag force of the pipeline when it moves in the drilling fluid. In the construction of a mathematical model, the influence of these forces is taken into account. To determine the frictional forces, the pipeline and the drill rod were considered as a flexible non-stretch filament. An algorithm for determining the tractive effort is created and implemented. A separate stage of the work is devoted to the accounting of ballasting of the pipeline.

In this article, the process of overcoming the stony obstacle while dragging pipeline through the channel is considered. Depending on the size of the duct and the pipeline itself the permissible size of the obstacle that the pipeline can overcome without resting against the upper part of the channel, is considered. To solve this problem, the pipeline is conditionally divided into two sections: the site located up to the obstacle and resting on it, and a free area that is after the obstacle. Directly on the process of dragging through an obstacle are acting the forces and moments which have influence on the pipeline. Starting from the equations of moment equilibrium for different points of the pipeline, and also from the equations of bending beams the value of the obstacle is evaluated.