OCR Text |
Show %.M!.. Mo soo 100 1.00 EE 80 300 ~ ."' ~ 1 60 200 1.0 100 o-a~::_=== = 20 0 0 300 50C 700 300 500 x (nmJ x (nm) Fig. 11 - Effect of furnace diameter and swirl level on the expanding swirling flow B/ A=I. 5, a=20° 700 ity with highly confined flows which inviscidly expand to the furnace wall can be seen. IRZ STRENGTH - With the inviscid model presented earlier, it can be shown that the IRZ strength should be governed by the initial swirl level and the area expansion ratio of the flow [2, 3], i.e., ~/Mo a:S(b/a)2. Figure 12 shows a comparison between the predicted and experimental relationship between the IRZ strength and S(b/a)2. For small values of S(bLa)2, the agreement is quite good, but as S(b/a)2 increases, the experimental and theoretical curves diverge. It is believed that the failure of the inviscid theory for larger values of S(b/a)2 is due to the failure of the expanding flow to remain inviscid. The expanding flow loses energy either at the quarl wall or to an external recirculation zone which effectively decreases the strength of the IRZ. Despite the failure of inviscid theory to predict the IRZ strength directly, the similarity parameter derived from the model S(b/a)2 still correlates the experimental results and can be used to provide a semi-empirical prediction of the IRZ strength. SWIRL PROFILE - Inviscid theory can be used to show that only the rotational fraction of a swirling flow (Wr increases with radius) is effective in creating the special properties of swirling flows. For the three swirl generators studied in these experiments (the solid body rotation generator, the axial vane swirler having a constant tangential velocity, and the radial vane swirler which gives a Rankine vortex), it can be concluded that strongly rotational vortices act in a similar manner. Strongly rotational profiles include the solid body and constant tangential velocity swirlers and probably can be generalized to include all swirl generators which give swirl profiles where the circulation Wr increases at least linearly with radius. If the swirl profile includes a large irrotational portion (Wr = constant) then the IRZ and mixing strength is reduced relative to a completely rotational swirl profile with the same swirl number. A comparison of the flow pattern and IRZ strength obtained with the solid body rotation generator, which gives a completely rotational vortex, and the radial vane swirler, which gives 95 200 ". Mr M. 160 L.""OSCOd calculatoon /' r I I / .. ,,-'" , ... ''''- I I 70/10 ' 120 f----.-----4L • Jl V 0- 8 /A lOt/A 50mpl~ S8R IFRF vQrlOuS 0 SRV· IFRF vQrlOuS I 2.3 . .., . ARV' IFRF 20' 2 I 2.3 >- L ~ I· AS8R IFRF 35 ¥onous wi' • S8R PAJ IFRF 35 variOUS 'f I' · An "" 20 2 I 2.3 -1 ,.1 DOs~d on / rotatoonal cor~ only 80 LO o o 8 16 2L 32 Fig. 12 - Theoretical and experimental correlation between the IRZ strength and S(b/a)2 (a) I RZ boundary r-11-1-"'----......-. -----------------~ R.V... ........ --S_BR_ _____ _ (b) Mr/Mo w.) 25 o .... , / \ I I ,SBR I . (/''\" \ \ \ , \ , Axial Distance Fig. 13 - Comparison between SRV and SSBR flows, B/A=2(OF20 a ), Df /A=2.3, Uo=4 .8 mis, S=0.7 a rotational core containing about the total mass flow, is shown in expected, the IRZ strength is reduced relative to the solid body file. 40 percent of Figure 13. As considerably rotation pro- ENERGY FLUX - The inviscid model proposed in THEORETICAL BACKGROUND assumes the total energy flux defined as the total kinetic energy plus the potential pressure energy is constant during expansion and again after the IRZ begins to close. In Figures 14 and 15, a comparison between model prediction and experiment is shown. For a |