Abstracts - KTH Mechanics

Combined Velocity and Temperature Measurement in a Buoyancy
Induced Ring Vortex
S.M.M. Salim a , J.G.C. Kunnen a , C.C.M. Rindt a and A.A. v. Steenhoven a
A combined velocity and temperature measurement in a buoyancy induced
vortex ring was conducted. The vortex ring was produced by a droplet of
Rhodemine B solution falling into a small tank filled with a solution of equal
concentration but higher temperature. The main target was to test the accuracy of a
combined velocity and temperature measurement technique using a pulsed laser.
Additionally, a dye-visualization was conducted to understand the formation process
of the ring vortex.
The experimental setup consists of a small tank filled with a Rhodamine B
solution (1.0×10
10
1
20
-4 mol/m 3 ) seeded with hollow spherical 10µm particles. A 29 Hz
single pulsed Nd:YAG laser (532nm wavelength) was used as a lightsource. A 1.0 mm
thick light sheet was created. Two 10-bit CCD cameras were used to capture the PTV
and LIF images. A high pass filter of 532nm was put in front of the camera which
captures the LIF signal emitted by the Rhodamine B (wavelength around 575nm) in
order to block the light intensity scattered by the particles.
To obtain the temperature field an innovative correction method was developed
to correct for the spatio-temporal variations of the Nd:YAG laser intensity. The
correction is local and based on a correction line by line. The method requires
knowledge of the temperature field in part of the image.
The velocity field is measured to see if the flow field could be resolved in the
vortex cores which have a maximum outer diameter of 20mm. Figure 1(a) and (b)
show the vorticity field as derived from the measured velocity field and the vorticity
distribution along a line through the vortex cores. It can be concluded that the flow
field can be resolved with high accuracy. Figure:1(c) shows the temperature field as
measured in a different realization using the correction method. The result clearly
shows the low-temperature vortex cores (Note different scale). The present method
will be used for investigation of the 3D wake behaviour behind a heated cylinder 1 .
____________________________
a
Energy Technology Group, Mechanical Engineering Department, Technische Universiteit Eindhoven,
The Netherlands
1 Ren et al., Physics of Fluids 16 (8): 3103 – 3114 (2004)
-10
0
-30
-1
0
-15 2.5 20 -15 2.5 20 0 10 20
Figure1: (a) vorticity field (b) one line vorticity (c) temperature distribution
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