GB943741A - Improvements relating to machines for inducing flow of fluid, being machines of the cross-flow type - Google Patents

Abstract

943,741. Boundary layer control. FIRTH CLEVELAND Ltd. Dec. 8,1959 [Dec. 9, 1958], No. 41656/59. Heading F2R. [Also in Division F1] In a fluid-flow machine of the transverse-flow type and in which a guide means co-operates with the rotor of the machine to set up a cylindrical vortex having a core eccentric to the rotor axis and a flow at the pressure side which includes faster and slower streams, a dividing wall at the pressure side extends, or is adapted to extend, in the direction of flow to separate faster streams from slower streams. This allows the slower streams to be removed, whereby energy losses due to breakaway of the slower streams from the walls of the subsequent flow passages are avoided. Fig. 3 shows a machine in which the bladed rotor 1 is bounded by guide walls 34 and 30, the latter converging with the rotor in the direction 2 of rotation and co-operating with the rotor to set up a vortex having a core V as described in Specification 876,611. Further guide walls 32, 35 form a diffuser passageway 33 at the discharge side of the machine. The walls 34, 35 are pivotable about pins 37, 38 respectively into the positions shown dotted to provide a gap 40 through which slower streams are returned to the ambient fluid, while faster streams pass through the passageway 33. Energy losses due to breakaway of slower streams from the diffuser walls are thereby reduced. The gap 40 may be closed at higher rotor speeds and opened at lower rotor speeds, when the tendency towards breakaway is more marked. To assist further in reducing breakaway, the boundary layer is removed through holes 45 in the wall 35 and slots 49 in the side walls of the diffuser. When the wall 35 is in the full line position, the holes 45 are closed by pegs 46 mounted in fixed positions and the slots 49 are closed by hit-and-miss shutters 47 rigid with the wall 35 and having slots 48 which are brought out of register with the slots 49. The blower shown in Fig. 8 comprises a slightly concave control flap 84 pivoted at 85 to a guide wall 80 similar in function to the guide wall 30 of Fig. 3. When the flap 84 is moved to one of the dotted positions, it interferes with the vortex formation whereby the output is reduced; the noise produced by the blower is also reduced. Slow streams adjacent a wall 82 are discharged through the gap between the wall and the diffuser 12. Fins 86 on the wall 82 and fins 87 within the inlet end of the diffuser 12 constrain the marginal flow adjacent the wall 82 and within the diffuser inlet to remain laminar whereby breakaway of flow and consequent noise are prevented. In a modification (Fig. 1, not shown), the control flap 84 and the fins 86, 87 are omitted, and the diffuser has its inlet end spaced slightly downstream of the discharge passage 11 to provide an annular gap through which the slower streams are discharged. In the embodiment shown in Fig. 10, the fastest streams enter a narrow diffuser 102 to operate on a closed circuit symbolized by a cylinder 104 containing a piston 105. The back of the piston 105 is exposed through a pipe 115 to the pressure within the vortex core V, which is well below the ambient pressure. A by-pass channel 101 receives fluid flow adjacent the outlet side of the vortex core V and returns it adjacent the inlet side of the core to intensify the vortex. Fig. 5 shows the first stage of a multi-stage machine while Fig. 6 shows the first two stages. Fluid enters the first stage at an opening 60a and the fastest streams at the outlet pass through a diffuser 58 to the second stage, the remaining streams being returned, as shown by the arrows 56a, to the suction region. The outlet end 60 of the diffuser 58 is bent round to discharge through a hole in a partition 51 into the region of the second stage. The second and subsequent stages are similar to the first stage, but with the inlet opening 60a omitted. Fig. 17 shows a multi-stage machine comprising identical units 170, 171<1>, 170<11>, 170<111> juxtaposed as shown to provide a direct connection between each stage and the next one. In each stage, the faster streams are discharged through a diffuser 155a while the slower streams enter a secondary outlet 155b and then flow through a return duct 171 for reintroduction into the rotor. In a modification (Figs. 15 and 16, not shown), the return duct 171 is replaced by return ducts formed in the end walls of the unit. Specifications 291,007 and 757,543 also are referred to.