An Investigation On Flow And Heat Transfer Characteristics For Typical Shape Orifices In Rotation

Various forms of orifices, including round, kidney-shaped, irregularly-shaped, annular and etc, are the important throttling components of the aero engine internal air system, extensively applied to the structures such as turbine disks, drums, shafts and etc. As the disks,drums and shafts are usually under high-speed rotating condition when aero engine is operating, it is key link of aero engine internal air system design to accurately grasp the discharge characteristics, pressure and temperature distributions of all kinds of orifices.Therefore,in order to provide necessary technical support for aero engine internal air system design,this dissertation carried out an investigation on flow and heat transfer characteristics for typical shape orifices in rotation.First, the influence of area ratio and geometric shapes(including round, kidney-shaped, rectangle and hexagon) on flow and heat transfer in rotating axial orifices was investigated by numerical method. In the scope of these certain parameters, the results of the study showed that the discharge coefficient was decreasing before the area ratio rised to a certain value, above which the discharge coefficient was constant; Changes in geometric shapes had less impact(<7%) on discharge coefficient but it exerted substantial influence(>10%) on flow resistance and heat transfer characteristics, the generally order of the Nu was kidney-shaped-2, round, kidney-shaped-2, hexagon and rectangle.Afterwards, the influence of rotation, pressure ratio, radial ratio and length-to-diameter ratio on flow and heat transfer in annular channels with rotating inner cylinder was investigated by numerical method. In the scope of these certain parameters, the results of the study showed that rotation of inner wall enhances the convection heat transfer between fluid with inner cylinder but had less impact on the outer wall and flow characteristics;the velocity of fluid in the annular channel increased rapidly with the raise of pressure ratio while the separation near the outer wall region weakened, it had little effect on discharge coefficient but heightened the flow resistance and strengthened the heat transfer between fluid with both inner and outer cylinders; wirh the radial ratio increasing,the separation near the outer wall was becoming bigger and bigger,which minified the discharge coefficient and Nu of the outer wall but greatened the flow resistance and Nu of the inner wall at first,then all the flow and heat transfer characteristics were tending stable; as the length-to-diameter ratio increased,the discharge coefficient would increase first and then decrease, which was contrary to the flow resistance,and the heat transfer between fluid with inner wall would be weakened gradually but the outer wall would be changed little.Finally, an experimental investigation on the discharge coefficient of typical shape rotating orifices was conducted. The experimental results matched well with the numerical predictions,which proved the accuracy of the numerical method.