Wind Tunnel Testing of a Generic Telescope Enclosure Experiment Scaling Experimental Setup Smoke Visualization

Wind Tunnel Testing of a Generic Telescope Enclosure Experiment		 Scaling Experimental Setup Smoke Visualization www.phwiki.com

Wind Tunnel Testing of a Generic Telescope Enclosure Experiment Scaling Experimental Setup Smoke Visualization

Dyer, Richard, Managing Editor has reference to this Academic Journal, PHwiki organized this Journal Wind Tunnel Testing of a Generic Telescope Enclosure Tait S. Pottebaum Douglas G. MacMynowski Cali as long as nia Institute of Technology June 2004 as long as merly D. MacMartin macmardg@cds.caltech.edu Experiment Model: Empty telescope enclosure Square opening size appropriate as long as roughly f/1.3 30° Zenith angle (fixed) Diameter = 0.83m, ~1% scale Turbulent flow at M2 location Probably not turbulent at M1 location Data: Flow visualization Digital particle image velocimetry (DPIV) data in a vertical plane containing the telescope axis near the dome opening Hot-wire anemometer data along the axis of the telescope Scaling Dimensionless parameters where L is the side length of the opening Convective frequency scaling Helmholtz frequency scaling where V is the enclosed volume in addition to c is the speed of sound

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Experimental Setup Clear Lucite dome with opening Camera in addition to mirror as long as visualization & DPIV Hotwire mounted on traverse Mirror in addition to optics as long as laser sheet Lucas adaptive wall wind tunnel 5’ by 6’ un-adapted Mounted on turn-table Large scale flow, 0° in addition to 180 ° Smoke Visualization 0° azimuth Smoke injected from outside the dome U

Velocity (hot-wire) spectrum inside enclosure 35m/s 20m/s data at 0°, r/R = 0.934 Large 2nd peak Dominant 1st peak fH fH -5/3 slope Shear layer modes: Frequency: f ~ 0.65nU/L Present as long as AZ 90° Mode n depends on speed; influenced by Helmholtz mode DPIV data Focus on area near the opening Principle of measurements Seed flow with tracer particles (water droplets) Illuminate a thin sheet with a laser (vertical plane on centerline of dome) Synchronize laser with the camera Record images in pairs with small time separation Correlate small regions of image to determine displacement Weaknesses In regions of steep gradients, velocity is typically underestimated Scales smaller than the interrogation regions cannot be resolved Only the in-plane components of velocity are measured Obtain mean in addition to statistics from large number of image pairs 2400 pairs as long as 0° 4495 pairs as long as 180° Sample data image: 1st snapshot

Sample data image: 2nd snapshot Mean in-plane velocity, 0° In-plane rms fluctuation, 0°

Mean in-plane velocity, 180° In-plane rms fluctuation, 180° Profiles on telescope axis

Conclusions Upwind viewing Shear layer across enclosure opening periodically rolls up into large vortices Frequencies are well described by convection velocity of shear layers in addition to a mode number Mode selection may be influenced by coupling of the shear layer instability with Helmholtz oscillations Large fluctuation velocities are likely to exert significant unsteady as long as ces on the secondary mirror in addition to support structure Downwind viewing Opening is inside the wake recirculation Mean velocity local maximum exists inside the dome Fluctuation levels are low, so most as long as ces are likely to be steady Further analysis Data being used as long as comparison with CFD (Konstantinos Vogiatzis, AURA NIO) Additional testing done with venting; data analysis in progress. Significant attenuation of shear layer modes

Dyer, Richard East Mesa Independent Managing Editor www.phwiki.com

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