Stephan Kordel

scientific staff

Field of work

  • Experimental Fluid Dynamics
  • Micro Particle Image Velocimetry
  • Differential Interferometry
  • Single Bubble Cavitation
     

Research topic


Investigation of cavitating flows by means of simultaneous density and velocity field measurements.

automatische Worttrennung mit hyphens

Problem
The damage of surfaces by cavitation events originates from emitted micro jets and shock waves created during the cavitation bubble implosion. The degree of damage depends on the strength of the pressure load which is related to the pressure amplitude of the shock wave. The intensity of the emitted pressure waves can vary according to the pressure level, the undissolved gas content in the cavitation bubble and the fluid properties. Up to date only few of these effects could be integrated in present models. Therefore, till today only qualitative pressure level predictions of imploding cavitation bubbles are available.

Aim
The goal of the present study is to determine pressure levels and distributions induced by cavitation bubbles by means of a combined optical measurement technique. The focus here is on the single bubble cavitation and the influence of the pressure level and fluid properties on the shock wave strength.

Method
Far field Micro-PIV and Differential Interferometry are combined in a novel manner to enable simultaneous measurements of the density and velocity distribution, using the same laser pulse for each recording.
For verification of the combined measurement technique an experiment with temperature driven circulation is established as shown in Figure 1. The circulation is created in a cuvette with heated side wall and therefore a convective flow is induced. Simultaneous image recordings of the temperature driven flow field and the temperature gradient field are determined from Micro-PIV and Interferometry recordings of two dual frame CCD cameras. The interference signal of the Dual cavity Nd-YAG laser and the Rhodamine-B coated fluid tracers are separated by a dichroic mirror and low pass filter.


Results
The measurement technique could be verified throughout time dependent density and velocity fields in a benchmark experiment. Representative results of the velocity field and the density gradient field are shown in Figure 2 a and b, respectively.
After the verification of the set-up, single bubble implosion events in a bubble trap will be investigated. Preliminary test indicate that it is possible to measure laser induced shock wave amplitudes with the recently established measurement technique.

Teaching

  • Gasdynamics Exercises




M. Sc. Stephan Kordel


Ruhr-Universität Bochum
Raum IC 3 / 79
Universitätsstraße 150
44801 Bochum

Telephone: +49 (0)234 / 32-21707

E-Mail: Stephan.Kordel@rub.de



Figure 1: Cuvette with heated side wall with marked ROI


Figure 2a: Density Gradient Field of ROI


Figure 2b: Velocity Field of ROI