The onset of convective turbulence in large aspect ratio layers

✍ Scribed by C. Clark; J. Shaumeyer; C. Agosta

• Publisher: Elsevier Science
• Year: 1983
• Tongue: English
• Weight: 90 KB
• Volume: 118
• Category: Article
• ISSN: 0378-4371
• DOI: 10.1016/0378-4371(83)90220-0

✦ Synopsis

Thermal measurements of the onset of turbulence in normal liquid helium have been made in cylindrical containers with aspect ratios r = 6.22 and 7.87. (Here r = D/2d, where D is the diameter, and d the height of the fluid layer.) We find qualitatively different behavior for the onset of turbulence in the two containers even though the respective Prandtl numbers, 0.55, and 0.61, differ relatively little. For r = 6.22, the onset of time-dependence is first characterized by reproducible periodic flow at a reduced Rayleigh number R/R, = 1.17. Several periodic flows exist over narrow bands in R/R, with non-periodic flows observed otherwise. The final route to chaotic flow is characterized by period doubling buried in a non-periodic flow.

For r = 7.87, only one band of periodicity was observed. However, the nature of this oscillatory flow strongly resembles states observed for r = 4.72 by Ahlers and Walden. However, the intermittency observed by these authors was not observed in either of our aspect ratios.

It seems apparent that small changes in r can appreciably change the onset of turbulence when r is large enough. Whether these changes are systematic can only be determined by studying considerably more aspect ratios. However, there are indications of possible systematic behavior in our observed period doubling states and the similar periodic states for r = 7.87 and 4.72.