Experimental results

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Here we show some filmed sequences from Plumb & McEwan's original experiment. The sequences were viewed through a window in the side of the apparatus. The field of view covers one complete wavelength of the forcing. The counter on the lower right shows time in seconds

Run 1:

• clip Z35a
• Forcing frequency w = 0.41 s^-1
• Forcing amplitude e = 6.4 mm
• Forcing wavenumber m = 8
• Fluid depth D = 0.41 m
• Buoyancy frequency N = 0.86 s^-1

Forcing here is too weak -> wave stable -> no mean flow. Motion is speeded up about 30 times (in film) when shown at 16 frames per sec.

Run 2:

• clip Z35b
• Forcing frequency w = 0.43 s^-1
• Forcing amplitude e = 8.0 mm
• Forcing wavenumber m = 8
• Fluid depth D = 0.44 m
• Buoyancy frequency N = 1.57 s^-1

Forcing here is stronger -> wave is unstable -> mean flow is generated and begins to oscillate. Motion is speeded up about 100 times.

Run 3:

• clip Z35c
• Forcing frequency w = 0.31 s^-1
• Forcing amplitude e = 11.0 mm
• Forcing wavenumber m = 8
• Fluid depth D = 0.41 m
• Buoyancy frequency N = 1.40 s^-1

Forcing here is stronger still -> mean flow oscillates more rapidly and vigorously. Motion is speeded up about 100 times.