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Department of Fluid Dynamics and Thermodynamics

Research Activities

The Department of Fluid Mechanics and Thermodynamics participates in a number of research projects supported both by public resources (particularly grant funds within the national programmes and European programmes) and by non-public funds in within the cooperation with industrial sphere.

Power Engineering and Combined Heat and Power Production (HPP)

The staff of the department is also engaged in the field of power engineering and combined heat and power production. Within the scope of these engagements in the period 2006-2012 the Department was the principal contractor of Research Centre 1M (funded by the Czech Ministry of Education, Youth and Sports) called “Advanced Technologies and Systems for Power Engineering“ and in 2012 also of the Centre of Competence “Advanced Technologies for the Production of Heat and Electricity“ (TPHE). Both above projects connect 4 leading Czech Technical Universities. The Centre of Competition in addition to these research and development institutions includes also 9 representatives from the application sphere.

One of the main fields of research which the Centre TPHE and the Department of Fluid Mechanics and Thermodynamics of the Faculty of Mechanical Engineering of the CTU in Prague are engaged in for a long period of time is the field of cooling namely for power engineering industry and combined heat and power production industry. The share of residual low-potential heat due to the demand for a constantly growing amount of energy, related with the unceasing industrial development of mankind, is still growing. Effective and environmentally friendly heat removal is therefore one of the priorities of contemporary science and technology. In spite of the fact that cooling towers, as we know them now, are used since the 19th century, their efficiency can still be increased on the basis of thorough knowledge of all processes which occur in such units. The department is due to its historically given orientation exceptionally equipped both materially and theoretically and is therefore able to investigate even most complex issues from the field of cooling using its own sources. Due to previously investigated projects and extensive economic activities the department staff can use experimental stands, measuring and computer technologies necessary for the investigation of a large number of technical issues in the field of classical, so-called wet cooling, dry cooling, hybrid cooling and at present the most dynamically developing field called “Water Recovery Systems“ (WRS – systems which can reduce the consumption of complementary water in classical cooling towers with forced draft and simultaneously eliminate the steam plume which is considered by the lay public to be one of the worst effects associated with the production of electric energy).

The field of cooling is at present focused on e.g. the issue of the rain zone in cooling towers (zone below the cooling fill sheets) which constitute in terms of performance about 20% of that of the whole cooling tower. From the results of research performed at the department it appears that thanks to numerical and experimental simulations carried out at the department, this performance can be nearly doubled without complicated adaptations of the cooling tower construction. At present the department also has a unique experimental stand which enables measurement of parameters of cooling fill sheets in a 1:1 geometrical scale with a thermal balance consistency accuracy of up to 3%. Parameters of classical film and splash fill sheets can be measured on this stand. The latter ones are at present used predominantly on the rapidly developing Asian markets. At present among proceeding investigations are: optical measurement of drift eliminator efficiency in cooling towers, measurement of spray nozzle characteristics or experimental assessment of heat transmission in tube nests of exchangers of dry cooling towers.

A model cooling tower fan was built in the laboratory for purposes of experimental research of components of the cooling tower. This track is designed as exhausted with measuring area of approx 1.7 x 1 x 3 m. The device allows to model the cooling process using all the elements as they are applied in real-world environments. At the same time, the track is designed so that apart from the conventional measuring techniques (thermocouples, speed sensor, hygrometer) could be used modern optical measuring methods. For measurements of velocity of fields can be used, for example, PIV (Particle Image Velocimetry) which provides detailed information on the 2D velocity fields or method IPI (Interferometric Particle Imaging) for measuring the size of the water droplets. All measuring systems are used to determine the efficiency of the cooling process and the pressure losses of individual elements but also other characteristics of the multiphase flow. In experimental way is determined, e.g. the pressure loss of the interior building in - cooling fills and eliminators, spray characteristics of water jets or efficiency of drift eliminators. The research focuses on the treatment and improvement of measurement methods. The research team has registered the methodology for measuring the size and speed of the water droplets in an environment of cooling towers by IPI as a utility model. Aerodynamic characteristics of the cooling towers are also subject to numerical modelling. Through mathematical model of cooling towers with natural draft can be captured dominant processes that take place in cooling towers and to assess the impact of these processes on the air flow in the cooling tower.

Hemodynamics

The Department has been engaged in the research of blood flow - hemodynamics. This topic is connected with fluid mechanics under special conditions different from most technical applications. Hemodynamics is a specialized field, not only because of complex properties of blood, but also for the characteristics of cardiovascular system and special pumping mechanisms that provide permanent and continuously adjustable supply of the entire body.

Research in the field of hemodynamics is carried out in collaboration with cardiologists and cardiac surgeons who have great knowledge and experience in how the vascular system work and also in pathological changes which experiences almost every patient and are caused by various factors. Diseases of the cardiovascular system are today among the most frequent causes of death and their treatment has been a priority of health care in all developed countries.

Hand in hand with progress in the treatment of vascular and heart diseases, and the increasing possibility of operative interventions go still more specific questions about local hemodynamic of pathological phenomena, such as stenosis (narrowing of blood vessels) and aneurysm (bulge vessels), or parts of the bloodstream such as bifurcation (splitting vessels) and anastomoses (connections of blood vessels). Hemodynamics also deals with the functions of the heart and its parts, in terms of pathological changes, for example, valvular incompetence. To study hemodynamics is important not only in terms of understanding the phenomena occurring in the human body, but also to design synthetic functional replacements which are modified for each patient.

Research of blood flow can be carried out in two different ways. "In vivo", i.e. in natural conditions when are carried out measurements and observations directly to the patient and "in vitro", i.e. in artificial conditions, when the conditions in the vascular system are modelled in the laboratory. These two approaches are also adapted to measuring methods used. Research of hemodynamics at the Department of Fluid Mechanics and Thermodynamics is focused mainly on modification of modern anemometric methods so that they can be usefully applied to the measurement of vascular models in vitro and also for comparison of the results with relevant measurement methods used by cardiologists and cardiac surgeons in vivo.

The laboratory is equipped with an experimental stand for modelling transient state flow controlled by computer according to the chosen flow curves. This track enables measurement by optical measurement (PIV, PLIF (Planar Laser Induced Fluorescence)), pressure measurement and the measurement method CTA (Constant Temperature Anemometry) in models with rigid and flexible wall.

External and internal aerodynamics

In the field of external and internal aerodynamics the staff of the department is engaged mainly in applications in aeronautical and automotive industry. However, they focus also on power engineering - namely on the field of renewable resources which deals with issues related with concepts and optimization of rotors for water and wind power plants.

Within the first of the above fields, investigation is focused both on wing profiles of classical design and profiles of flexible wings (used typically in powered parachutes – PPC). In recent years has been carried out a project of an aerodynamic flying test-bed within the field of classical wing profiles. The main aim of the project was to create a platform for a variety of aerodynamic measurements. An airplane with a span of 3.5m and 20kg of weight is equipped with a recording device which can record flight data such as the aircraft position, speed, altitude and bank. Flight can be controlled either in a stabilized mode, when the plane is controlled by the pilot from land or in a fully automatic flight mode when the plane follows a pre-planned flight path. The flying testbed is equipped with wing-end extensions and measuring equipment which measures the pressure distribution along the examined profile. Within the second of the above categories which is focused on the development of flexible wings in cooperation with a leading Czech producer of powered parachutes was carried out project of a remote controlled powered parachute which enables testing of parachute wings up to a ratio 1:2.5.
Another sphere of research in the field of aeronautical applications in which the department has been engaged for a long time is the design and optimization of airplane propellers of small up to medium sizes. The Department has developed an optimization software which can design and optimize airplane propellers for a specific application. Moreover, has been built an airplane propeller test room for the measurement of static thrust. Optimization calculations of the shape of blades of wind power plant of classical design can also be included in this category.

From the point of view of research and development in the field of automotive industry the Department is engaged in long term cooperation with Škoda Auto, a.s. with a special focus on the field of internal dynamics of the engine compartment.

Measurement Technology

In the recent years the Department has been engaged in the design, development and testing of its own measurement technologies for a variety of applications for their own research purposes but mainly for cooperation with partner from industrial sphere. This led to development of a number of absolutely unique gauges, which are often protected by national patents or utility and industrial models. In the area of aerodynamics, heat and mass transfer is the Department able to provide comprehensive experimental services from initial design through implementation of experimental stands, evaluation and analysis of the results, or even training of operators in the workplace of an industrial partner. This collaboration was then repeatedly checked by major industrial partners from all the EU, for example. Skoda Auto, a.s., the VW Group, FANS, , a.s., Brentwood Industries, Electrolux Italia S.p.A. and many others.

In general, the essential part of every experiment is a set of tools which enables to observe processes currently in progress in the given experiment. These tools are usually measuring and detecting appliances. Since microelectric development is directly incorporated within the field of fluid mechanics, it is possible to react flexibly to topical requirements of the experiments in progress. This often requires an authorial approach (patents, etc.) and development of measuring devices based on new physical principles. During the existence of the team engaged in the development of measuring technologies at the department were developed numerous unique measuring devices and measuring procedures. Deep understanding of the physical fundamentals and above all of the particular technology of individual measuring devices enabled the rest of the department staff to improve considerably the accuracy of measurements performed in individual experiments.

Numerical modelling

The experimental research in all the mentioned fields is very complex and thus it is appropriate to use, besides experimental procedures, also the results of numerical simulations. Numerical simulations of issues concerning flow, transfer of heat and mass are at present a strong and accessible tool which enables gaining further insight into the investigated issues. Numerical solutions can also serve as tools for the analysis of existing components, at present they represent an irreplaceable feature above all in testing new concepts and also in tasks dealing with geometrical optimization. The Department of Fluid Dynamics and Thermodynamics has long-term experience in the application of tools of computer fluid dynamics in research, both in projects of basic and applied research and direct cooperation with the application sphere.