Abstract
In typical median and small aeroengines, the air used to realize the functions such as cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, adjusting of rotating assembly axial load is normally drawn through the rear cavity of centrifugal impeller, so the thorough understanding of flow characteristics and pressure distribution and the proposal of the corresponding control methods in the cavity are the key to design the rational secondary air system. With an impeller rear cavity in a small turbofan engine as an object, the current study was dedicated to the investigation of flow control methods in the cavity. Two methods, namely, baffle and swirl-controlled orifice, were proposed to regulate the pressure loss and distribution in the cavity. Furthermore, the influence of geometry parameters of the two methods such as the length of baffle, the space between the baffle and rotating disk wall, the orientation, and radial position of swirl-controlled orifice was investigated. The CFD results show that the swirl-controlled orifice which could deswirl the flow is more effective in regulating the pressure loss and its distribution in cavity than baffle. The variation of the radial position of the swirl-controlled orifice had little influence on pressure loss but obvious influence on pressure distribution; therefore, decreasing the radial position could reduce the axial load on the rotating disk without changing the outlet pressure.
Highlights
During the aeroengine design process, the impeller rear cavity differs broadly in the parameters of inlet/outlet conditions because of the different centrifugal compressor and turbine aerodynamic designs and the different demands to ensure adequate cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, and adjusting of rotating assembly axial load
In the aeroengine test process, the deviation between the true matching point of the whole machine and the design matching point will lead to the deviation of pressure distribution in the impeller rear cavity and causes the failure of the functions
The axial velocity and radial velocity are negligibly small, so the equation of the tangential velocity in the NS equation is simplified to the balance of the centrifugal force and the radial pressure gradient
Summary
During the aeroengine design process, the impeller rear cavity differs broadly in the parameters of inlet/outlet conditions because of the different centrifugal compressor and turbine aerodynamic designs and the different demands to ensure adequate cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, and adjusting of rotating assembly axial load. A considerable amount of work about the flow characteristics in the rotor-stator cavity with a centripetal inflow has been carried out by a number of workers [1,2,3,4,5,6]. The results show that for a rotor-stator cavity with centripetal flow, the internal flow conforms to the Batchelor type which consisted of an inviscid core and two Ekman type boundary layers. EI-Oun et al [7] used the pitot tube measurement to obtain the velocity distribution in the rotor-stator cavity with a centripetal flow. Pincombe [8] used the LDV flow field visualization method to measure the velocity profiles in the cavity under different inlet swirl ratio β0 and different rotational Reynolds number Reφ. It is found that the value of β0 has a International Journal of Aerospace Engineering
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