Abstract: This paper investigates vortex shedding processes
occurring at the end of a stack of parallel plates, due to an oscillating
flow induced by an acoustic standing wave within an acoustic
resonator. Here, Particle Image Velocimetry (PIV) is used to quantify
the vortex shedding processes within an acoustic cycle
phase-by-phase, in particular during the “ejection" of the fluid out of
the stack. Standard hot-wire anemometry measurement is also applied
to detect the velocity fluctuations near the end of the stack.
Combination of these two measurement techniques allowed a detailed
analysis of the vortex shedding phenomena. The results obtained show
that, as the Reynolds number varies (by varying the plate thickness
and drive ratio), different flow patterns of vortex shedding are
observed by the PIV measurement. On the other hand, the
time-dependent hot-wire measurements allow obtaining detailed
frequency spectra of the velocity signal, used for calculating
characteristic Strouhal numbers. The impact of the plate thickness and
the Reynolds number on the vortex shedding pattern has been
discussed. Furthermore, a detailed map of the relationship between the
Strouhal number and Reynolds number has been obtained and
discussed.
Abstract: The unsteady wake of an EPPLER 361 airfoil in
pitching motion has been investigated in a subsonic wind tunnel by
hot-wire anemometry. The airfoil was given the pitching motion
about the one-quarter chord axis at reduced frequency of 0182.
Streamwise mean velocity profiles (wake profiles) were investigated
at several vertically aligned points behind the airfoil at one-quarter
chord downstream distance from trailing edge. Oscillation amplitude
and mean angle of attack were varied to determine the effects on
wake profiles. When the maximum dynamic angle of attack was
below the static stall angle of attack, weak effects on wake were
found by increasing oscillation amplitude and mean angle of attack.
But, for higher angles of attack strong unsteady effects were
appeared on the wake.
Abstract: The presented paper shows the possibility of using
holographic interferometry for measurement of temperature field in
moving fluids. There are a few methods for identification of velocity
fields in fluids, such us LDA, PIV, hot wire anemometry. It is very
difficult to measure the temperature field in moving fluids. One of the
often used methods is Constant Current Anemometry (CCA), which
is a point temperature measurement method. Data are possibly
acquired at frequencies up to 1000Hz. This frequency should be
limiting factor for using of CCA in fluid when fast change of
temperature occurs. This shortcoming of CCA measurements should
be overcome by using of optical methods such as holographic
interferometry. It is necessary to employ a special holographic setup
with double sensitivity instead of the commonly used Mach-Zehnder
type of holographic interferometer in order to attain the parameters
sufficient for the studied case. This setup is not light efficient like the
Mach-Zehnder type but has double sensitivity. The special technique
of acquiring and phase averaging of results from holographic
interferometry is also presented. The results from the holographic
interferometry experiments will be compared with the temperature
field achieved by methods CCA method.