1. Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL Instructor: Lichuan Gui lichuan-gui@uiowa.edu http://lcgui.net

2. 2 Lecture 11. Wind tunnel, water tunnel and towing tank

3. 3 Wind tunnels Suction wind tunnel - straight-line, open-circuit arrangement - fluid mover (fan) located downstream - honeycomb & screens before contraction Controlled fluid flow systems - diffuser to reduce kinetic-energy loss Blowing wind tunnel - straight-line, open-circuit arrangement - fluid mover (fan) positioned upstream - honeycomb & screens before contraction - diffuser to reduce kinetic-energy loss - settling chamber to reduce turbulence Close-circuit wind tunnel - higher power efficiency - reduced noise level - better flow management - most large wind tunnels

4. 4 Open-test-section wind tunnels b. open test section c. open working section with Eiffel chamber Specialized wind tunnels (4) stream of gas flowing from the nozzle (5) Eiffel chamber a. closed test section (1) model (2) Nozzle (contraction) (3) diffuser (6) working section - to avoid wall effects

5. 5 High-speed wind tunnels Specialized wind tunnels e.g. Two compressed-air wind tunnels (1) high-pressure compressor (2) air drier (3) high-pressure gas tank (4) throttle valves (5) nozzle receiver (6) nozzle (7) model (8) diffuser (9) ejectors (10) throttle valves (11) diffuser (12) fast-acting valve (13) vacuum gasholder (14) vacuum pump (15) air preheater (16) radiator - compressible air flow tests - transonic, supersonic, and hypersonic tunnels

6. 6 Specialized wind tunnels (1) high-pressure section (2) low-pressure section (3) membrane (4) shock wave (5) contact surface (6) nozzle (7) working section (8) tank (9) model Shock tubes Pressurized wind tunnels - to increase air density for high Reynolds number tests Cryogenic wind tunnels - reduced air viscosity at low temperature for high Re Meteorological wind tunnels - for wind engineering studies Low-temperature wind tunnels - for the study of low-temperature flow phenomena Combustion wind tunnels - for high-temperature flows

7. 7 Water tunnels Controlled fluid flow systems - close-circuit flow systems - entirely enclosed facilities - include components: Pump settling chamber contraction test section diffuser Water channels or flumes - with free surface - lower power consumption - lower free-stream disturbance - no boundary-layer effects Towing tanks - free surface with waves - relative flow w. carriage motion

8. 8 Surface waves Controlled fluid flow systems Plunger Plunger wave makers Regular head waves red dot: phase velocity, green dots: group velocity Plunger wave maker - wave frequency (f w ) & wave height (H) determined by plunger motion - encounter frequency w. model speed U c - phase speed of the waves - wave length ( ) h – depth of the channel - group speed of the waves  – angular frequency k – wave number

9. 9 Homework - Prepare for midterm test on 09/19 1. look through text notes 2. read related text 3. review homework asignments - Read textbook 6.4-6.7 on page 154-165