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Rotating holes are widely used in jet engine internal air systems as an important kind of throttling element. The flow characteristics of rotating holes are of great importance in the design of the internal air system. This paper aims to investigate the influence of pumping effect on the flow characteristics of axial rotating holes. Pumping effect refers to the flow phenomenon induced by a rotating plate which characterized by a radial outflow. There are altogether two types of holes considered in the paper: round hole and square hole. A 1/25 (14.4-degree) sector model is used to carry out the numerical investigation using the commercial software ANSYS CFX. In the simulation, the SST turbulent model is used. Meanwhile, a non-rotating method using the relative frame of reference is used. In the non-rotating method, an initial incidence angle is given at the inlet instead of setting the plate to be rotating, thus the pumping effect induced by the rotating plate can be eliminated. The non-rotating method results are compared with the conventional reference frame results to investigate the influence of pumping effect. The results show that due to the influence of the pumping effect-induced radial outflow, the theoretical two-dimensional incidence angle becomes three-dimensional, which has negative effects on the hole discharge coefficient. At the same time, due to a larger circumferential length, square holes will undermine the pumping effect, thus has a higher discharge coefficient than the round holes.

Purge flow is of great importance in cooling turbine disks and sealing rotor-stator disc cavity to reduce hot gas ingestion in gas turbines. The amount of cooling air extracted from the compressor is crucial to engine efficiency. Excessive sealing air will cause not only a reduction in work transfer but also an increase in aerodynamic losses caused by the mixing of main and sealing flow. In order to simplify rim seal structure while ensuring high sealing efficiency, the current paper optimizes the flow path of the secondary air system and presents a new rim seal structure with auxiliary sealing holes transporting a certain amount of secondary sealing flow. The new structure was compared with the conventional counterpart using validated CFD methods, showing that the additional secondary sealing flow is possible to improve sealing efficiency in disk cavity. The current paper investigates the secondary sealing flow with and without swirl (the angle of auxiliary sealing hole inclination is 0° and 45° respectively), while maintaining the total amount of the sealing flow, flowrate ratio of sealing air (main sealing flow rate versus secondary sealing flow rate=1:1, 2:1, 3:1, 4:1), found that both two parameters have essential impacts on sealing efficiency. The relationship between these two parameters and sealing efficiency was obtained, and it provides a new philosophy for the design of rim seal in gas turbines.

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.

Unsteady flow structures have been observed and reported in a number of recent rim-sealing investigations. These unsteady flow structures will influence the cavity pressure distribution, therefore influence the sealing efficiency. As a result, it is important to determine the mechanisms of these unsteady flow structures and how they influence the hot gas ingestion and sealing efficiency. A two-sector axial rim seal model is used to carry out the numerical investigation. The simulation is performed using the URANS method by the commercial CFD code ANSYS CFX, in which the SST turbulent model is applied. The mechanism and influence of the unsteady flow structures are analyzed. It was found that two different types of unsteadiness are observed inside the wheel space cavity: radial large flow structures dominated by the mainstream pressure distribution and inertia wave, and circumferential Kelvin-Helmholtz vortexes induced by circumferential velocity discontinuous distribution. The number and rotating speed of the radial and circumferential flow structures can be calculated using a cross-correlation method, and it was found that they can lead to a deeper ingress. By increasing the sealing flow rate, the pressure fluctuation inside the wheel space cavity is suppressed and the rotating speed of the flow structures is deaccelerated; thus, the sealing flow stabilizes the flow inside the wheel space cavity. Meanwhile, the K-H vortices’ position is lifted by the increased sealing flow rate, and the strength of the K-H vortices is suppressed, thus the sealing efficiency inside the wheel space cavity is also improved.

Secondary sealing flow is of great importance in the turbine disk cooling and sealing system. The amount of cooling air extracted from the compressor is crucial to engine efficiency. To determine a minimum amount of cooling air, the flow characteristic of the rim seal should be investigated. Numerical simulation is carried out to investigate the flow field near the rim seal region. Both RANS and URANS numerical simulation methods are used in the commercial CFD code ANSYS CFX to analyze axial and radial rim seals. In the simulation, a 1/33 sector is selected as computing region to simulate the flow field and the SST turbulent model is used. The steady and unsteady simulation results of pressure distribution and seal efficiency are analyzed and compared. The computed results show that due to the different geometry configuration, the pressure distribution also shows inconsistency. Unsteady phenomena are observed in both axial and radial type of rim seals. Radial sealing lip can suppress the inherent unsteadiness and interaction between main flow and sealing flow, thus showing higher sealing efficiency. Comparing to steady results using the RANS method; unsteady simulation, using the URANS method, can capture the pressure difference and seal efficiency fluctuation at the disk rim more efficiently. Also, the interaction between the rotor and stator is considered in unsteady simulation, so the unsteady simulation is recommended. The results obtained in the current paper are useful to the investigation and design of turbine rim seals.