The practical complements the second lecture course in fluid mechanics (for the eighth semester, Vertiefungsfach) and provides experience in modern measuring techniques and application-oriented flows. The following experiments are carried out.Boundary Layer Flow:
In this expeiment the logarithmic wall function is determined experimentally. The measuring technique applied is hot-wire anemometry, as introduced in the practical I in the winter term. The flow along a flat plate is investigated, which is well known and thoroughly described since the times of Blasius.
High pressure:
High pressures are applied in several fields. Processes with high pressures up to 1000 MPa have entered, for example, food and bio process engineering. They are used in the context of innovative processes for selective conversion reactions. Within these transport processes of thermal and fluidmechanical nature play an important role. To be able to control them the behaviour of the biological media has to be known under process conditions. Measurements of characteristic values can therefore only be done in-situ. The in-situ determination of viscosity - i.e. under high pressure - which has a major impact on the flow in the process plants, is subject of this experiment.
Spray flows:
The fundamentals of liquid atomisation by means of single- and twin-fluid techniques are introduced. The characteristics of sprays produced by a pressure-swirl atomiser are measured. The measuring technique introduced and used for this purpose is phase-Doppler anemometry. The statistical basics are discussed and applied for evaluating the measured data and their statistical reliability, both for local and for global properties of the sprays. The biggest challenge of this experiment is the comparison of the particulate volume flow rate in the spray as measured with the phase-Doppler anemometer and with a flow rate meter in the supply line.
Flow around a Circular Cylinder:
The flow around a circular cylinder in a wind tunnel is investigated using hot-wire anemometry. In this experiment, the frequency of vortex shedding from the edges of the cylinder is measured for varying Reynolds number of the flow. The results are of relevance for fluid-solid interactions, as they occur in many problems in, e.g., civil engineering. The measured frequencies are represented by a Strouhal number. The measured values of this number are compared with values from the literature. The behaviour of the measured quantity with varying Reynolds number is interpreted in the light of the physics of the boundary layer.
Viscosimetry:
This experiment provides insight into the methods of measuring liquid viscosity by means of capillary and rotational viscosimeters. Basic knowledge of rheology and non-Newtonian liquid behaviour are introduced. The essential differences between Newtonian and non-Newtonian fluids are that the viscosity of the former is constant (i.e. just temperature dependent), while the viscosity of the latter may depend on the flow, e.g. on the shear or stretching rates. Non-Newtonian fluids may exhibit a memory and elasticity, which is not
possible with Newtonian fluids. The physical basics of measuring viscosity are discussed in detail.