138 channel simultanesous-sample hot-wire anemometer system.

This system was designed to measure the streamwise velocity field in the axisymmetric jet mixing layer at x/D=3. The goal is to determine the large scale structures in the layer and study their dynamics using the proper orthogonal decomposition (POD). The system operated with the following properties:

  1. All 138 single-wire, hot-wire probes sampled simultaneously
  2. Each channel had its own anti-alias Bessel filters and sample-and-hold
  3. A 2048 Hz sampling rate was achieved for each channel
The measurements of the probe array provided "snapshots" of the entire streamwise velocity field in the mixing layer at 0.5 msec intervals for 300 blocks of 0.5 seconds total measurement time.

Here are some pictures of the experimental setup:

Click on the pictures to view better quality images

The cart on the left in the first picture houses the 138 anemometers, The jet on the left on the upper table was used to create the axisymmetric mixing layer and the probe array with the 138 hot-wire probes is situated directly in front of this jet. The probe array is facing away from the picture but the picture on the right gives a better view of it. Each of the brass tubes is a holder for a single-wire hot-wire anemometer probe. The coaxial cable which connects the probe is fed through the tube. The flow blockage of the entire probe array was less than 4%.

Flow visualization was performed over the probe array to insure there was no flow blockage. The picture below shows the streamlines entering the probe array are straight and no signs of flow blocking are apparent.

The flow from the jet exit is left to right and the bundle of probes on the right is the 138 hot wire probe array. The flow is made visible with a smoke wire which burns vegetable oil when current is passed through it. The bundle of tubes is suspended using an old bicycle rim and dacron fishing line. A mpeg movie of the smoke visualization is available by clicking here.