OCR Text |
Show • the general difference in the flow fields produced by expanding rotational or potential vortices or combinations of the two; • the effect of a central bluff body on the flow field; • which flows are subcritical and likely to be altered by downstream conditions; • the influence of quarl and furnace geometry on the flow if it is known whether the swirling jet is acting in a highly confined or free jet manner. The model can be readily extended to a Rankine vortex swirl profile which consists of a swirl profile having a rotational core surrounded by an irrotational outer flow [3]. Although the calculations become more complex for a Rankine swirl profile than for solid body rotation, analytic solutions which can quantify the above parameters can still be obtained. EXPERIMENTAL APPARATUS AND MEASURING TECHNIQUES The majority of the experimental work was conducted with a special solid body rotation generator. The swirl generator and settling chamber used to generate the solid body rotation with a uniform axial velocity profile is shown schematically in Figure 6. Air from a blower passes through the settling chamber and then accelerated through the convergence in such a way that the wall boundary layer is suppressed and, eventually, a uniform axial velocity is achiev~d at the exit. IIft'£II CADSS $teTION No " ... a" .. ' .,...clOt lOWE_ CIiIOSS SfCTlCIof Wlth,,--r.' .,.,.ct., IU w4 "~1·M- ~--~~~'~.'9~~~U-----~--n-,~~I-"~~~--~------.I~~--I·~·_----;1 ""enl" .... ,. " '1S.S1~ .". ,."V. I'] .)S.,"". -.,.- "1 : "t. '" u~ .. . ]O ... .,h.' ... H2.H)."4 : 111 ",uU "5 V16", "tI Fig. 6 - Swirling flow wind tunnel The low turbulence, uniform axial velocity flow obtained in the settling chamber is introduced into the swirl generator which imparts a solid body rotation to the flow. This swirl generator is basically a rotating pipe with honeycombs inside and is driven by a variable speed D.C. motor. In order to investigate the influence of the initial swirl profile on the near field flow, two other common industrial swirl generators were also used. A radial vane and two axial vane swirlers were also used to obtain different inlet swirl profiles. In Figure 7, an example of the different velocity profiles given by the swirl generators is shown. Quarls of various shapes (cylindrical, conical, concave), diameter expansion ratios B/A (1, 1.5, 2) and half angles (0°, 20°, 35°) have been 93 o ::J I ~ 4.5 -=-'°_ -_0 .- -0_0 ~o_o_o....o ~-o_---.-. 0-0-0 ~'---.-. ~~=9=-9~' -w_._._. ~~ 35 a so 9S 6r-------------~----------~ 4~------------_+-------,~--~ (a) supercri tical flows 5 .OJ9 5 .QlS 5 .0.64 S .0.52 50 95 radial position r mm (a) solid body generator o i ' t-""""'*-tr----t-...n.::~~-..-~ 5 • 0.7 0+-----~~-----_r-----_1 o 50 ,. 100 (b) radial vane o ::J 3 04-~----~~----~ __ ~ '0 60 80 95 rlmml (c) axial vane Fig. 7 - Inlet velocity profiles produced from the swirl generators tested. Furnaces of various diameters were available so that the step to a larger diameter after the quarl exit could be varied from near-zero to very large. Furnace/throat diameters ranging from Of/A, from 1.0 to 5.1, were used during the execution of these experiments. All quarls and furnaces were constructed from plexiglas to facilitate both flow visualization and Laser Doppler Anemometer (LDA) measurements. |