Gunt Germany - Fluid Mechanics Lab

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HM 140 uses sand as an example to demonstrate important phenomena of bed-load transport in the area near the bottom. Open-channel flow without sediment transport is also possible. Discharge can be subcritical or supercritical. The core element of the HM 140 experimental flume with closed water circuit is the inclining experimental section. The side walls of the experimental section are made of tempered glass, which allows excellent observation of the experiments. All components that come into contact with water are made of corrosion-resistant materials (stainless steel, glass reinforced plastic). The inlet element is designed so that the flow enters the experimental section with very little turbulence and no sediment can flow back. The tank after the water outlet contains a sediment trap for coarse sand.

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Transient drainage processes are taken into consideration when deciding on the dimensions of storage reservoirs. The processes occur for example, in rainwater retention basins and storage lakes. The main purpose of the rainwater retention basin is to delay the drainage process by temporary intermediate storage. Storage lakes are used in applications such as water supply, energy conversion, or in flood protection. The water rises before it is fed over an overflow. The drainage processes from reservoirs is realised by pipelines, tunnels or other means. A surge chamber prevents water hammer in pipes and fittings in the event of rapid changes in flow rate.

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Sharp-crested weirs are a type of control structure that dam up an open channel in a defined manner. They are often used to determine the discharge of an open channel. HM 150.03 contains two different plate weirs as sharp-crested weirs. The two weirs are typical measuring weirs with defined weir openings: in the Thomson weir the opening is triangular; in the Rehbock weir it is rectangular. The weirs are installed and screwed in place into the HM 150 base module. The weir can be installed and replaced quickly and easily.

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In hydrostatics, the metacentre is an important point to be considered when assessing the stability of floating bodies. Stability refers to the ability of a ship to right itself from a heeled position. The metacentre is the intersection of the buoyancy vector and the vessel’s axis of symmetry at a certain heel. The HM 150.06 unit can be used to study the stability of a floating body and to determine the metacentre graphically. In addition, the buoyancy of the floating body can also be determined. The experiment is easy to set up and is particularly suitable for practical work in small groups.

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Measuring the flow rate is an important aspect in measurement technology. There are several ways to measure the flow of fluids in pipes. With HM 150.13 students can familiarise themselves with various methods for measuring flow in the pipe system and apply them in practice. The experimental unit contains different measuring instruments to determine the flow rate. These instruments are designed with transparent cases in order to visualise how they operate and function. The methods include, for example, rotameters, a Venturi nozzle or orifice plate flow meter and measuring nozzle.

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In fluid dynamics, a vortex is a circular flow of a fluid caused by sufficiently large velocity gradients. In practice, this can be observed when water flows out of a basin into a pipe or when two fluids with different speeds meet each other. The HM 150.14 experimental unit allows you to produce and study free and forced vortices. The experimental unit has a transparent tank with nozzles, various inserts on the water drain, an impeller and a point gauge for detecting the vortex profiles.

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The HM 150.39 accessory includes two transparent floating bodies with different frame shapes (hard chine and round bilge). The floating bodies are used together with HM 150.06 and extend this device’s range of experiments. The design of the floating bodies and the possible experiments are similar to those of HM 150.06.

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A wind tunnel is the classic experiment system for aerodynamic flow experiments. The model being studied remains at rest while the flow medium is set in motion, and thus the desired flow around the model is generated. HM 170 is an “Eiffel” type open wind tunnel used to demonstrate and measure the aerodynamic properties of various models. For this purpose, air is drawn in from the environment and accelerated. The air flows around a model, such as an aerofoil, in a measuring section. The air is then decelerated in a diffuser and pumped back into the open by a fan.

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Aerodynamics describes the behaviour of bodies during flow around or through bodies with a compressible fluid. The knowledge of experiments in aerodynamics has a significant influence on the development of means of transport (vehicles, ships, aircraft) and in architecture (skyscrapers, towers and bridges).

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Streamlines can be visualised in steady flow in the wind tunnel by using fog, smoke or tufts. In this way, a clear impression of an instantaneous flow field can be presented and problematic flow areas, such as stall, can be shown. The experimental unit HM 226 is an open wind tunnel, in which streamlines, flow separation and turbulence can be made visible by using fog. The evaporated fog fluid is non-toxic, water soluble and the precipitate does not affect common materials. Precipitates can be easily wiped off with a cloth. The air flow is generated by a fan. To achieve a low-turbulence flow, the air flows through a stabilisation chamber with a flow straightener. Fog is added to the flowing air through several nozzles. Then the air flows around or through a model in a experimental section and the flow field becomes visible. The experimental section has a black background and a sight window; additional lighting makes the streamlines clearly visible. Four interchangeable models (cylinder, orifice plate, aerofoil and guide vane profile) are included. The aerofoil’s angle of attack is adjustable.

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In impulse turbines, the working medium has the same static pressure in front of and behind the rotor. The conversion of pressure energy into kinetic energy takes place in the fixed nozzles of the distributor, not at the turbine rotor. This compressed-air driven experimental unit can be used to understand turbines powered by steam or water.

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In reaction turbines, the static pressure of the working medium in front of the rotor is higher than that behind it. In pure reaction turbines with a degree of reaction of one, the entire pressure energy in the rotor is converted to kinetic energy. This compressed-air driven experimental unit can be used to understand turbines powered by steam or water. HM 272 is a single-stage, pure reaction turbine with a horizontal shaft. The rotor of the turbine has four outlet nozzles and is installed in a transparent housing. The air flows radially through the rotor and expands and accelerates as it exits through the outlet nozzles. The exiting air flow drives the turbine rotor according to the reaction principle. A band brake is used to apply a load to the turbine.

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The weight of fluids at rest causes a pressure that is known as hydrostatic pressure or gravitational pressure. This pressure acts on any area that is in communication with the fluid, exerting a force that is proportional to the size of the area. The effect of hydrostatic pressure is highly important in many fields of engineering: in shipbuilding, in hydraulic engineering when designing locks and weirs, in sanitation and building services.

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During deceleration, acceleration and deflection of a flowing fluid, there is a change of velocity and thus a change in momentum. Changes in momentum result in forces. In practice, the motive forces are used to convert kinetic energy into work done, for example in a Pelton turbine. In HM 150.08 jet forces are generated and studied with the aid of a water jet that acts on and is diverted by an interchangeable deflector.

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The laminar, two-dimensional flow in HM 150.10 is a good approximation of the flow of ideal fluids. HM 150.10 can be used to visualise streamline fields for flows around drag bodies and flow through changes in cross-section. The streamlines are displayed in colour by injecting a contrast medium (ink). Sources and sinks are generated via four water connections in the bottom plate. The streamlines can be clearly observed through the glass plate during flow around and flow through.

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Pressure losses occur during the flow of real fluids due to friction and turbulence (vortices). Pressure losses in pipes, piping elements, fittings and measuring instruments (e.g. flow meter, velocity meter) cause pressure losses and must therefore be taken into account when designing piping systems. HM 150.11 allows to study the pressure losses in pipes, piping elements and shut-off devices. In addition, the differential pressure method is presented for measuring the flow rate.

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Pressure losses in the flow from tanks are essentially the result of two processes: the jet deflection upon entry into the opening and the wall friction in the opening. As a result of the pressure losses the real discharge is smaller than the theoretical flow rate. HM 150.12 determines these losses at different flow rates. Different diameters as well as inlet and outlet contours of the openings can be studied. Additionally, the contraction coefficient can be determined as a characteristic for different contours.

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Abruptly interrupting the water flow can cause water hammer in the pipeline. This generally undesired effect is used specifically in special equipment (hydraulic ram) to raise water to a higher level. Unlike conventional pumps, no additional mechanical drive is required here. HM 150.15 can be used to demonstrate the formation and effect of water hammer and to study how a hydraulic ram works. The water is fed to the ram via a long pipe at a gradient.

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The Osborne Reynolds experiment is used to display laminar and turbulent flows. During the experiment it is possible to observe the transition from laminar to turbulent flow after a limiting velocity. The Reynolds number is used to assess whether a flow is laminar or turbulent. With HM 150.18 the streamlines during laminar or turbulent flow are displayed in colour with the aid of an injected contrast medium (ink). The experimental results can be used to determine the critical Reynolds number. The experimental unit consists of a transparent pipe section through which water flows, with flow-optimised inlet. A valve can be used to adjust the flow rate in the pipe section. Ink is injected into the flowing water. A layer of glass beads in the water tank ensures an even and low-turbulence flow. The experimental unit is positioned easily and securely on the work surface of the HM 150 base module. The water is supplied and the flow rate measured by HM 150. Alternatively, the experimental unit can be operated by the laboratory supply.

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In structures such as hydroelectric power plants, or in systems for supplying water, changes in flow rate result in pressure fluctuations. For example during startup and shutdown of hydraulic machines or by opening and closing shut-off elements. There is a distinction to be made between rapid pressure changes that propagate with high velocity (water hammer) and slow pressure changes caused by mass oscillations. Pipeline systems use air vessels or surge chambers to dampen water hammer and mass oscillations.

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During flow through pipes, pressure losses occur due to internal friction and friction between the fluid and the wall. When calculating pressure losses, we need to know the friction factor, a dimensionless number. The friction factor is determined with the aid of the Reynolds number, which describes the ratio of inertia forces to friction forces. HM 150.01 enables the study of the relationship between pressure loss due to fluid friction and velocity in the pipe flow. Additionally, the pipe friction factor is determined.

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Bernoulli’s principle describes the relationship between the flow velocity of a fluid and its pressure. An increase in velocity leads to a reduction in pressure in a flowing fluid, and vice versa. The total pressure of the fluid remains constant. Bernoulli’s equation is also known as the principle of conservation of energy of the flow. The HM 150.07 experimental unit is used to demonstrate Bernoulli’s principle by determining the pressures in a Venturi nozzle.

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Hydrodynamics considers the relationship between the trajectory, the outlet contour and the outlet velocity during flow from tanks. These considerations have practical applications in hydraulic engineering or in the design of bottom outlets in dams, for example. HM 150.09 allows a user to study and visualise the profile of a water jet. Additionally, the contraction coefficient can be determined as a characteristic for different contours.

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The total pressure in a steady flow is constant. The sum of the static and dynamic pressures gives the total pressure. A change in the cross-section of the flow channel causes the flow velocity to vary inversely proportional to the cross-sectional area. These physical laws are fundamentals of fluid mechanics education. The HM 225.03 experimental unit – used in the aerodynamics trainer HM 225 – allows the measurement of the total pressure and the static pressure.

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Measuring pressure is important in the engineering industry, e.g. in plant, turbomachine and aircraft construction and in process engineering. Other fundamental factors such as flow rate or flow velocity can also be determined based on a pressure measurement. The WL 203 experimental unit enables the user to measure the pressure with two different measuring methods: directly by measuring the length of a liquid column (U-tube manometer, inclined tube manometer) and indirectly by measuring the change of shape of a Bourdon tube (Bourdon tube pressure gauge).