Fundamentals

Equipment

A vortex nozzle, developed by Dr. A. Keller, is being used in order to measure the water tensile strength. The vortex creates a minimum pressure within the fluid in the contraction of a venturi nozzle. In this way we are guaranteed that the first rupture, or cavitation event, is occuring in the bulk of the liquid.

The reason for quantifying the tensile strength is obvious when it comes to cavitation inception experiments. However it is reason to believe that the water quality or tensile strength also will affect some of the global characteristics of the observed cavitation. Additionally such a measurement will give you an indirect information of the water condition. Measurement are also taken of the dissolved oxygen content, and hopefully a correlation between those two can be established. It must be emphasized that a recirculating water tunnel is believed to have a relative constant particle population.

The LDV system supplied by TSI gives insight into the general flow field. As an extension to the system, a PDA system can be used. One of the objectives is to be able to measure the velocity and size of isolated bubbles passing through the measurement volume. The former is found by regular doppler shifts in frequency, while the latter is calculated due to phase difference in the forward scattered signal onto two receivers.

Finally a set of pressure transducers, hydrophones and lift/drag measurements are being used to provide the necessary information concerning cavitation dynamics.

Figure 1. Vortex Nozzle

Figure 2. LDV Laser

Figure 3. SCANTRON Alternating Pressure Tap