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ME 322: Instrumentation Lecture 34

ME 322: Instrumentation Lecture 34. April 16, 2014 Professor Miles Greiner. Announcements/Reminders. This week: Lab 10 Vibrating Beam Sign up for 1.5-hour Lab 11 periods with your partner in lab Extra-Credit LabVIEW Workshop Friday , April 18, 2014, 2-4 PM, Jot Travis Room 125D

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ME 322: Instrumentation Lecture 34

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  1. ME 322: InstrumentationLecture 34 April 16, 2014 Professor Miles Greiner

  2. Announcements/Reminders • This week: Lab 10 Vibrating Beam • Sign up for 1.5-hour Lab 11 periods with your partner in lab • Extra-Credit LabVIEW Workshop • Friday, April 18, 2014, 2-4 PM, Jot Travis Room 125D • Sign-up on WebCampus • The second session (Noon-2) was canceled • Help wanted (see me greiner@unr.edu) • Summer: Help construct a convection heat transfer augmentation experiment • Spring 2015: ME 322r Lab Assistant

  3. Lab 11 Unsteady Speed in a Karman Vortex Street • Nomenclature • U = air speed (instead of V) • VCTA = Constant temperature anemometer voltage • Two steps • Statically calibrate hot film CTA using a Pitot probe • Find frequency, fP with largest URMS downstream from a cylinder of diameter D for a range of air speeds U • Compare to expectations (StD= DfP/U = 0.2-0.21)

  4. Calibration Calculations • Based on physical analysis we expect • ;

  5. Process Sample Data • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2011%20Karmon%20Vortex/Lab%20Index.htm

  6. Hot Film System Calibration • The fit equation VCTA2 = aU0.5+b appears to be appropriate for these data.

  7. Unsteady Karman Vortex Flow

  8. Fig. 4 Spectral Content in Wake for Highest and Lowest Wind Speed (a) Lowest Speed URMS [m/s] fp = 751 Hz URMS [m/s] (b) Highest Speed fp = 2600 Hz • The sampling frequency and period are fS = 48,000 Hz and TT = 1 sec. • The minimum and maximum detectable finite frequencies are 1 and 24,000 Hz. • It is straightforward to distinguish fP from this data. Its uncertainty is Wfp = 0.5 Hz.

  9. Dimensionless Frequency and Uncertainty • UA from LabVIEW VI • fP from LabVIEW VI plot • ½(1/tT) or eyeball uncertainty • Re = UADr/m (power product) • StD = DfP/UA(power product)

  10. Fig. 5 Strouhal versus Reynolds • The reference value is from A.J. Wheeler and A.R. Ganji, Introduction to Engineering Experimentation, 2nd Edition, Pearson Prentice Hall, 2004, p. 337. • Four of the six Strouhal numbers are within the expected range.

  11. How to Construct VI (Block Diagram)

  12. Front Panel

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