František Pochylý

Identification and Experimental Verification of the Adhesive Coefficient of Hydrophobic Materials

This work presents a methodology for the determination of adhesive coe cient of a liquid ow over a hydrophobic surface. The starting point for this work was a study, which describes the general boundary condition for shear stress on a general curvilinear surface depending on the adhesive coe cients. The adhesive coe cient is determined on the basis of an experiment that utilizes the motion of a droplet on an inclined plane.

Study of the Adhesive Coefficient Effect on the Hydraulic Losses and Cavitation

The article is focused in three areas. In the first part there are analyzed the adhesion forces at the liquid and solid surface interface. There are shown the measured values of surface energy for different types of surfaces. The value of surface energy is decisive for determining the extent of the surface wettability by the liquid.The second part points to the possible negative effects of partly wettable surfaces, showing susceptibility to cavitation. The third section describes the practical aspects of surface wettability by the liquid. Under the new boundary conditions bases, expressing the effect of adhesion forces, there are determined the centrifugal pump characteristics.

Assessment of cavitation creation depending on the surface wettability

The flow of fluids near the slide surface is analyzed in the work introduction. Surface is considered as partly hydrophobic, depending on the surface energy for different types of material surfaces. There is point out the relationship of the adhesion force to liquid/surface interaction. This creates a new boundary condition, different from the adhesion conditions. On the adhesion force basis is assessing the conditions of cavitation creation, depending on the surface energy change.

Bearing with magnetic fluid and hydrophobic surface of the lining

This work focuses on the setting of the stiffness and damping matrix of the long cylindrical bearing. Additional effects of the electrically conductive fluids are determined on the magnetic induction dependence. The new boundary conditions are used, which express the effect of the adhesion forces between the liquid and the solid surface. The boundary condition allows the definition of the transition from a hydrophobic surface to the hydrophilic one.

Tensors of added damping, stiffness and mass in a thin gap of hydrodynamic machine

The methodology of determining the additional effects of a liquid acting on hydrodynamic machine rotor is presented in the paper. Special attention is paid to the force effects of the liquid inside the hydrodynamic sealing gap. A new mathematical model is derived from which is evident an influence of different parameters of the liquid bond on the additional stiffness, mass and damping.

The swirl turbine

In the article is introduced the new type of the turbine - swirl turbine. This turbine is based on opposite principle than Kaplan turbine. Euler equation is satisfied in the form gHηh = −u2vu2. From this equation is seen, that inflow of liquid into the runner is without rotation and on the outflow is a rotation of liquid opposite of rotation of runner. This turbine is suitable for small head and large discharge. Some constructional variants of this turbine are introduced in the article and theoretical aspects regarding losses in the draft tube. The theory is followed by computational simulations in Fluent and experiments using laser Doppler anemometry.

Dynamics of the cavitating flow downstream of the orifice plate

Orifices with varying number of holes, but with the same flow cross-sections were tested in a cavitation circuit. Static characteristics, in term of loss coefficients, were measured in a range of non-cavitating and cavitating regimes. Since cavitating flow has very rich dynamics attention was also paid to spectral properties, especially in the cavitating regime. Data evaluated from several pressure transducers placed downstream of the orifice and for different orifice types are presented and discussed. Marked differences in both static and dynamic characteristics are observed between single-hole and multi-hole orifices.Orifices with varying number of holes, but with the same flow cross-sections were tested in a cavitation circuit. Static characteristics, in term of loss coefficients, were measured in a range of non-cavitating and cavitating regimes. Since cavitating flow has very rich dynamics attention was also paid to spectral properties, especially in the cavitating regime. Data evaluated from several pressure transducers placed downstream of the orifice and for different orifice types are presented and discussed. Marked differences in both static and dynamic characteristics are observed between single-hole and multi-hole orifices.

Analysis of novel low specific speed pump designs

Centrifugal pumps with very low specific speed present significant design challenges. Narrow blade channels, large surface area of hub and shroud discs relative to the blade area, and the presence of significant of blade channel vortices are typical features linked with the difficulty to achieve head and efficiency requirements for such designs. This paper presents an investigation of two novel designs of very low specific speed impellers: impeller having blades with very thick trailing edges and impeller with thick trailing edges and recirculating channels, which are bored along the impeller circumference. Numerical simulations and experimental measurements were used to study the flow dynamics of those new designs. It was shown that thick trailing edges suppress local eddies in the blade channels and decrease energy dissipation due to excessive swirling. Furthermore the recirculating channels will increase the circumferential velocity component on impeller outlet thus increasing the specific energy, albeit adversely affecting the hydraulic efficiency. Analysis of the energy dissipation in the volute showed that the number of the recirculating channels, their geometry and location, all have significant impact on the magnitude of dissipated energy and its distribution which in turn influences the shape of the head curve and the stability of the pump operation. Energy dissipation within whole pump interior (blade channels, volute, rotor- stator gaps) was also studied.

The Cavitation Effect on the Electromagnetic Field

It is generally known, that liquids, including water, are electrically conducting. The electric conductivity magnitude among others depends on the minerals concentration. Using the additives it is possible to increase the electric conductivity.

Numerical modelling of the Stokes flow with Coulomb slip boundary conditions

This paper deals with the formulation, discretization and implementation of the Stokes system involving Coulomb’s type slip boundary conditions. The computational strategy is based on a fixed-point formulation of the problem and the method of successive approximations. Numerical experiments confirm the usability of this approach.