Pavel Rudolf

Brno University of Technology · Faculty of Mechanical Engineering

AC discharge in a dense hydrodynamic cavitation cloud in water, called CaviPlasma, has been studied at different discharge parameters. CaviPlasma stands for cavitation and plasma, which are two coupled basic phenomena of the novel technology enabling very high throughput of plasma water processing compared to other current technologies. In this art...

The present paper investigated the potential of hydrodynamic cavitation (HC) as an effective tool for activating sodium percarbonate (SPC). The method's efficiency was demonstrated by effectively removing estrogens, which are pollutants that have adverse impacts on aquatic ecosystems. The effects of the SPC concentration, temperature of solution, a...

The knowledge of hydraulic characteristics of convergentdivergent nozzles will lead to the optimal design of a nozzle for generating a cavitation cloud. Such a nozzle is a crucial component of the CaviPlasma device, which aims to tackle the ever-growing water treatment and purification issue. To measure the characteristics, a closed hydraulic circu...

Advanced oxidation processes (AOPs) cover a whole range of methods for removal of organic materials from wastewater based on hydroxyl radicals (·OH), which is a strong oxidant. AOPs play important role in so called tertiary water treatment, i.e. elimination of pharmaceuticals, hormones or pesticides at the outflow from the wastewater treatment plan...

The production and use of manufactured chemicals have risen significantly in the last few decades. With interest in preserving and improving the state of the environment, there is also growing interested in new technologies for water purification and wastewater treatment. One frequently discussed technological group is advanced oxidation processes...

Disk friction losses can significantly influence the overall pump effciency. It is most pronounced in the case of machines with low or moderate specific speed, which has to be kept in mind during a design process of a pump. However, analyses using computational fluid dynamics (CFD) often completely neglect the sidewall gaps geometry. Correctly solv...

The swirling flow in a diffuser has been studied using the stereo PIV technique. The DANTEC hardware and software were used for the experiment. The water pipe flow in the diffuser inlet has been set spinning by introducing tangential jet flow. Both piping and diffuser were of circular cross-section, however diffuser casing had rectangular (square)...

Despite the sidewall gaps of centrifugal pumps are tiny narrow spaces, the flow inside them can have a great impact on the flow field in the whole machine. Regardless of its influence, there is no full understanding of the flow in those regions. A theory exists for the simplified cylindrical cavity with a rotating disk, whose application to real hy...

The paper revisits the theory originally published by Hall that explains the presence of adverse pressure gradient at the axis of a diffuser with swirling flow. It presents the fields of the axial pressure derivative obtained by CFD simulations of flow in a swirl generator, which support the theory. The last part brings cautionary results regarding...

The very low specific speed pump (nq = 8.9) operated in turbine mode was analyzed. The experimental and numerical studies were carried out in order to show effect of different blade layout on pump-as-turbine (PaT) performance. In total three different impellers were analyzed. One impeller consisting of four main blades and two impellers consisting...

The usage of splitter blades to enhance the performances of low specific speed pumps is common practice. Based on experimental and numerical studies, the influence of the addition of one and two splitter blades is investigated on a very low specific speed pump to assess their impact not only on the performance characteristics but also on the losses...

The hydraulic turbines are recently forced to operate far away from the optimal conditions in order to balance fluctuations in electricity generation. In case of Francis, pump and propeller turbines, using only single control component of guide vanes, it means that in regions where the high residual swirl enters the draft tube, the flow is decelera...

Low specific speed pumps find applications in a broad range of domains, but suffer from a low efficiency and a risk of head instability close to shut-off. The numerical computations on these pumps performed in the last years have shown discrepancies with experimental results. Recent studies suggest that the use of wall-functions underpredicts the l...

Computer graphics visualization techniques for application on data from Computational Fluid Dynamics (CFD) simulations of the vortex rope, a phenomenon present in hydraulic turbines operating in off-design conditions, were devised. This included not only objects for visualization (what to visualize) but also methods of the visualization itself (how...

The report examined new scientific approaches to the creation of a combined cogeneration energy complex based on small or micro-hydropower. The most effective approaches to micro-hydropower facilities were considered to create a workable structural layout. A criterion has been developed that allows to evaluate the energy efficiency of hydroturbines...

The paper critically reviews the current state of the art in flow inside sidewall gaps of hydraulic pumps and turbines. It describes the consequences of the presence of this type of flow in turbomachinery and then relates it to other physical phenomena that determine the behavior, operating characteristics, and overall performance of the machine. D...

Efficient treatment of contaminated water in industrially viable volumes is still a challenging task. The hydrodynamic cavitation plasma jet (HCPJ) is a promising plasma source for industrial-scale generation of biologically active environments at high flow rates of several m3/h. The combined effect of a hydro-mechanical phenomenon consisting of hy...

A shape optimization problem is increasingly popular in various parts of industry and academia. Several shape optimization approaches emerged in the past few years. Population-based methods (PPM) are among them, with convenient attributes and characteristics that lead to a discovery of proper solutions of investigated problems. Crucial quality of P...

This work presents a detailed analysis of the three-dimensional flows in a Pump-as-Turbine (PaT). The flow field is studied through URANS simulations and a velocity vector analysis. Moreover, a prediction model is used to forecast the performance of the PaT. The results of these methodologies were validated using experimental results. Flow rate and...

The paper presents the results of a POD analysis of the flow in a swirl generator. The generator has two separate inlets – one straight axial inlet and one tangential inlet ended by a spiral case. This allows to set different operating points, which are in turn connected with different shapes of the vortex rope present in the flow field. In this ca...

The unsteady shape variation of a cavitating spiral vortex is experimentally studied pointing out the repetitive creation of vortex ring (or vortex loop). To generate the spiral vortex structure, a newly designed vortex generator is employed. This generator is used to study the decelerated swirling flow leading to the spiral vortex formation as a c...

Cyanobacterial water blooms represent toxicological, ecological and technological problems around the globe. When present in raw water used for drinking water production, one of the best strategies is to remove the cyanobacterial biomass gently before treatment, avoiding cell destruction and cyanotoxins release. This paper presents a new method for...

The issues of developing small-scale and microhydropower generation under present-day conditions as one of the renewable energy sources that do not aggravate environmental problems are considered. Some of the most effective approaches to designing microhydropower plants and small-scale and microhydroturbines that meet the environmental friendliness...

Due to specific physical properties, hydrodynamic cavitation (HC) is assigned to the powerful technologies for treating the biotic contamination in water including cyanobacteria. Contaminated water stream (CWS) can be cavitated directly by passing through some HC device, or indirectly when high-pressure jet stream (HPJS) is directed against its flo...

The necessity of high pressures within the combustion chamber leads to the requirement of pressure systems in order to provide the correct operability of the thruster unit. Pressure-fed or turbopump-fed propulsion systems are commonly employed. The former type is simple and reliable but is limited by the maximum pressure available in the tank and h...

This paper analyses an energy recovery solution based on the Pump-as-Turbine (PaT) technology applied in an oil refinery. Since under-ground water might be contaminated by the chemical processes, an intervention named “Pump & Treat” was adopted in the studied oil refinery to reclaim the installation site and to safeguard the zones nearby. After the...

The added effects from the fluid on a structure submerged in water significantly affect its dynamic response. Since the hydraulic turbine runner is geometrically complex and involves complicated flow phenomena, the research on simple hydrofoil offers a unique opportunity to investigate added effects and mutual interaction of the elastic structure a...

Here, we present an improved and verified rotating hydrodynamic cavitation device (RHCD) inspired by so-called cavitation heaters. The cavitation efficiency of the device is adjustable by rotation speed and flow rate and can be modified for selective removal of cyanobacteria from water with only temporal effect on algal growth or metabolic activity...

Modelling of the flow in the cavities between rotor and stator in turbomachines (e.g. pumps or turbines) is a task of great interest. Correctly evaluated pressure and velocity fields enable calculation of the disk losses and therefore assessment of efficiency. It is also crucial for determination of axial thrust and thus design of the bearings. The...

Vortex rope in Francis turbine draft tubes poses serious problems. Emphasis on operation of the turbines in wide operating range, quite far from the design point, is a challenge for both the turbine designers and power plant owners. While flow control becomes popular in aircraft and automotive industry, it is still feared in turbomachinery. Present...

Design of a pump turbine (ns = 135) is carried out using a very fast quasi-potential flow approach for the preliminary design. Theory behind this novel method is presented and its advantages discussed. Further finetuning is performed by coupling of CFD (ANSYS CFX) and particle swarm optimization method. The final design features suppression of the...

An experimental test circuit was built with submerged nozzle with diameter 1.2 mm and inlet pressure 200 bar. Several specimens of different cavitation resistant materials used for hydraulic turbines (e.g. 13Cr4Ni) and coatings (e.g. tungsten and chromium carbides) were tested. Cavitating jet tests proved to be very efficient, sufficient cavitation...

This paper analyses an energy recovery solution for the application in an oil refinery, which has undergone significant changes in the last decades due to the construction of different plants, services, storage and logistics systems. Nowadays, with the aim to reduce the water contamination close to the refinery, the local regulations imposed to int...

The added effects such as added mass and damping acting from the fluid on a structure, strongly affect the dynamic response of the structure submerged in water. The main goal of this paper is to present preliminary numerical investigations of added mass and damping effects acting on a hydrofoil placed in the cavitation tunnel test section which has...

In connection with the depletion of the world reserves of fuel resources and growing environmental safety requirements for power-generating facilities, the article presents a review analysis of the present state of conventional power supply systems in Russia and in the European Union countries (for the latter, the Czech Republic is taken as an exam...

Hydrodynamic cavitation represents complex physical phenomenon undesirably affecting operation as well as lifespan of many hydraulic machines from small valves to the large hydro power plants. On the other hand, the same phenomenon and its concomitants such as pressure pulsations can be exploited in many positive ways. One of them which seems to be...

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga's idea were proposed. All modifications are drive...

The present study was experimentally examines the primary atomization processes in a newly developed atomizer, similar to effervescent atomizer concept, at low pressures and low gas-to-liquid ratios (GLR). Several experimental and post-processing techniques are applied to investigate the spray spatial evolution. The near-nozzle area is captured by...

The aim of this paper is to present a new cavitation tunnel, which has been designed and later will be built at Viktor Kaplan Department of Fluid Engineering at Brno University of Technology. The tunnel will be used to investigate the effect of hydrofoil trailing edge shape on wake dynamics and its interaction with the mechanical structure. Prelimi...

Vortex rope, which induces substantial pressure pulsations, arises in the draft tube (diffuser) of Francis turbine for off-design operating conditions. Present paper focuses on mitigation of those pulsations using active water jet injection control. Several modifications of the original Susan-Resiga’s idea were proposed. All modifications are drive...

Several modifications were developed when designing the nozzle valve. This study offers an assessment of the properties of new modifications of the nozzle valve design. The main operating characteristics, such as loss and flow coefficients, were determined using a CFD methods. Besides mentioned coefficients, the forces acting on the valve disc are...

It is obvious that the main function of the nozzle valve is to shut off the stream of fluid in the piping system. The response rate of the valve to the decreasing or reversing flow in the system will then depend on the valve properties and equally on the properties of the piping system. The interaction of these two elements is also important for th...

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 cavi...

The swirling flow exiting the runner of a hydraulic turbine is further decelerated in the discharge cone of the draft tube to convert the excess of dynamic pressure into static pressure. When the turbine is operated far from the best efficiency regime, particularly at part load, the decelerated swirling flow develops a self-induced instability with...

Cavitation is usually considered as undesirable phenomena. On the other hand, it can be utilized in many applications. One of the technical applications is using cavitation in water treatment, where hydrodynamic cavitation seems to be effective way how to reduce cyanobacteria within large bulks of water. The main scope of this paper is investigatio...

Hydrodynamic cavitation in single and multihole orifices was experimentally investigated to assess their hydraulic characteristics: loss coefficients, inception cavitation number, cavitation number for transition to supercavitation. Significant difference for singlehole and multihole orifices was observed in terms of the measured loss coefficient....

A study of shape optimization has become increasingly popular in academia and industry. A typical problem is to find an optimal shape, which minimizes (or maximizes) a certain cost function and satisfies given constraints. Particle Swarm Optimization (PSO) has received a lot of attention in past years and is inspired by social behaviour of some ani...

The following study is focused on the flow analysis within the concentric in-line check valve. In-line check valve is part of the pipe and shut off the stream of fluid. In case that backflow occurs on the downstream side, the valve is fully or partially lifted and then abruptly closes. This effect brings undesirable pressure shocks in the entire sy...

Cavitation is a complex physical phenomenon, which occurrence is usually considered as an undesirable condition. The efficiency, lifespan and operation range of the hydraulic machines and equipment such as pumps, turbines or valves can be significantly reduced by the cavitation and its concomitants: pressure pulsations, vibrations, acoustic emissio...

Contribution is focused on discussion of different design modifications of the volute, impeller and rotor-stator cavity in case of very low specific speed pump with recirculation channels. Amount of the liquid flowing through the recirculation channels has significant effect on delivery height, stability of the head curve and hydraulic efficiency....

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 domai...

Hydraulic turbine diffuser recovers pressure energy from residual kinetic energy on turbine runner outlet. Efficiency of this process is especially important for high specific speed turbines, where almost 50% of available head is utilized within diffuser. Magnitude of the coefficient of pressure recovery can be significantly influenced by designing...

The decelerated swirling flow often breaks down into helical structure which is unstable and causes unsteady velocity and pressure fields. The numerical and experimental investigation of this flow pattern is carried out on the experimental apparatus consisting of the swirl generator (source of strong swirling flow) and the conical diffuser (equippe...

Cavitating flow in converging-diverging nozzle (axisymmetric Venturi tube) is investigated. Characterization of the cavitating flow was done with high speed camera and the basic flow patterns were determined: incipient cavitation, partial cavitation, fully developed cavitation and supercavitation. Pressure transducers of tenzometric and piezoelectr...

Contribution is focused on modification of low-specific speed pump impellers with respect to stability of their Y-Q curves (i.e. head curves). The design modifications are driven by analysis of the dissipated power. First, dissipated power is evaluated by CFD software in individual working parts of the pump and then its dependence on flow rate is i...

Pump pre-swirl or uneven flow distribution in front of the pump can induce pump-intake vortices. These phenomena result in blockage of the impeller suction space, deterioration of efficiency, drop of head curve and earlier onset of cavitation. Real problematic case, where head curve drop was documented, is simulated using commercial CFD software. C...