On the Transition +-o Turbulent Convection 



STEADY FLOW 



CROSS 

 INSTABILITY 



Pr = 6.7 



WAVE 



i INSTABILITY 

 UNSTEADY 

 , ^ FLOW •• 



2* /steady q \ • • • , 



■°*o ^ • • 



/f I L .III M il ._ 



_u-L 



lO-^ 



10^ 



Pr- 10' 



STEADY TWO- 

 DIMENSIONAL 

 FLOW 



lO" TAYLOR NUMBER 



UNSTEADY 

 FLOW 



WAVE INSTABILITY 



J ' ■ ■ ■ ■ 



_i I I I i I I 



-»-»*► 



3 4 5 6 78910 



\0^ 

 TAYLOR NUMBER 



Tc '0' 



Fig. 12. The regime diagram for rotating B^nard convection 



IV. SUMMARY AND CONCLUSIONS 



Series of externally steady, fixed heat flux experiments were 

 performed to measure Rayleigh number, heat flux and changes in 

 flow of horizontal , non- rotating convection for 2. 5 X 10' ^ Pr ^ 

 0.85 X 10"* and 10^ < Ra < 10^. The regime diagram summarizing 

 these experiments is shown in Fig. 10. Each of the curves I, II, 

 III and IV marks a transition with a change of slope in the heat flux 

 curve. The first is the transition from the conduction state to one of 

 steady two-dimensional convection in the form of rolls. 



There is a second transition characterized by the following 

 properties: 



(i) There is a discrete change of slope of the heat flux curve 

 at Rayleigh number Rjj. near 12 R^, showing no definite 

 Prandtl number dependence in the range 10 < Pr < 10 . 



307 



