Yuxin Liu

Brush seals have gained prominence as an effective alternative to conventional labyrinth seals in gas turbine engines due to their superior sealing performance. Their flexible bristles accommodate rotor eccentricity, enhancing sealing adaptability. However, under high pressure load and high rotor rotational speeds, the bristles are susceptible to severe elastic deformation, which can lead to hysteresis effects, instability, and degradation in sealing efficiency. This study designs a high-speed visual brush seal rig and combines it with fluid–structure interaction simulations to investigate the bristle mechanics and leakage behavior under rotational speeds ranging from 0 to 6600 rpm. The effects of front plate and radial clearance between bristle tip and rotor on leakage, windage heating, and hysteresis are then systematically examined. First, for brush seals without a front plate, the results indicate that higher rotational speeds reduce leakage but increase windage heating and suppress the hysteresis behavior of the bristles. Under operating conditions of 3000 rpm and a pressure ratio of 1.55, significant bristle deformation is observed, with the radial clearance increasing by approximately 0.08 mm. When the pressure ratio decreases to 1.34, a closure effect emerges in the rear rows of bristles, accompanied by a distinct stratification phenomenon. Second, the introduction of a long front plate alters the airflow direction, increases the normal aerodynamic force on the bristles, reduces the axial force, and weakens the sealing performance, thereby elevating the leakage risk. Finally, while increasing the radial clearance exacerbates leakage, it contributes to lower windage heating and mitigates bristle hysteresis.

To explore in greater depth how the leakage flow from the shrouded stator cavities affects the performance of the aero-engine compressor, a high-load compressor cascade is taken as the research object, and the specific effects of the radial and circumferential momentum of the cavity outlet leakage flow on the performance of the cascade are analyzed by using the method of numerical simulation and the Self-Organizing Map algorithm. The analysis results show that under the condition of 100% design speed, the leakage flow increases the total pressure loss coefficient of the cascade by 4.54% and the energy loss by 4.16%. Under the condition of 80% design speed, these increases rise to 7.36% and 5.47%. The average radial momentum of the leakage flow at the cavity outlet is positively correlated with the total pressure loss and entropy increase loss of the cascade, and the similarities with the entropy increase loss coefficient are greater than 0.8 under the two speed conditions, which indicate highly correlated. The average circumferential momentum of the leakage flow at the cavity outlet is positively correlated with the entropy increase loss and negatively correlated with the total pressure loss of the cascade. Under the condition of 80% design speed, the circumferential momentum of the leakage flow at the cavity outlet has a greater influence on the two performance parameters, and the similarities can reach 0.56 and −0.52, respectively. Moreover, the influence of the cavity leakage flow at different positions of the cavity outlet surface and different momentum on the performance of the cascade are also different, and there can be a contradictory phenomenon where changes in momentum are beneficial for reducing the total pressure loss coefficient but have a negative impact on reducing the energy loss.

The objective of this research is to delve into the leakage, deflection, and oscillation characteristics of brush seals. To achieve this, the flow characteristics of a brush seal were first analyzed through numerical simulation. Subsequently, a static brush seal test rig was utilized to measure the leakage performance and hysteresis characteristics of brush seals with varying geometric structures under pressure ratios ranging from 1.1 to 3.8. The deflections of bristle during operation were observed using an endoscope, and dynamic pressure sensors were employed to collect data on the airflow dynamic pressure in the free end area of bristles, facilitating the analysis of bristle oscillation characteristics. The results indicated that considering the parameters of this study, the leakage increases with the rise in pressure ratio and radial gap. The long front plate configuration was found to contribute to an increase in leakage. Specifically, under the three radial gap conditions of 0, 0.1, and 0.2 mm, the maximum leakage difference between brush seals with and without the front plate configuration was 4.9%, 4.6%, and 2.6%, respectively. The increase in radial gap and the existence of the front plate were observed to diminish the hysteresis effect of brush seals. At a pressure ratio of π = 2.0, the hysteresis indicator H for structures with a radial gap of 0.2 and 0.1 mm decreased by 45.5% and 63.6%, respectively, compared to the 0 mm gap structure. The existence of the front plate resulted in a 33.3% reduction in H compared to its absence. Additionally, an increase in pressure ratio and radial gap was correlated with an increase in brush oscillation frequency. Under identical pressure ratio conditions, brush seals with the front plate also exhibited higher brush oscillation frequencies than those without.

By brush seal, we mean a type of mechanical seal that uses a large number of closely packed, thin, and flexible bristles to create an outstanding seal between rotating and stationary components in gas turbine engines. However, at high levels of swirling and pressured environments in engines, bristles of brush seals tend to circumferentially slip, which leads to reduced sealing performance and seal failure. In this paper, the effects of upstream–downstream pressure differences Δp (0.2–0.5 MPa), downstream static pressure (0.1–1.0 MPa), and the coverage of bristles by a front plate (0%–90%) on the mechanical characteristics and deflections of bristles of a brush seal at highly swirling inlet were investigated based on a two-way fluid-structure coupling method. A key criterion for bristle instability, based on a simplified two-dimensional (2D) theoretical analysis, is obtained from the fluid-structure coupling simulations. The results indicate that a fundamental reason for the bristle circumferential slip is the ratio of the normal to the axial aerodynamic forces (Fn/Fax) acting on the first row of bristles. When this ratio exceeds 0.9, the bristles will slip circumferentially. The effects of the pressure differential across the seal, the downstream pressure, inlet swirl velocity, and front plate coverage of the bristles on bristle stability can all be explained through their influences on this force ratio. At relatively low outlet static pressure of 0.1 MPa, upstream bristles slip when the inlet swirl is in the range of 230–300 m/s and the bristle slip instability is more likely to occur at higher pressure difference conditions. However, at high downstream pressures, Fn/Fax declines with the growth of Δp, contributing to the stability tendency. With the constant Δp, the value of Fn/Fax significantly increases as the downstream pressure rises, and the critical swirl velocity required to trigger bristle slip is considerably reduced. Additionally, the front plate shields a part of the bristles away from pressure gradient in axial direction but leads to outward radial flow upstream of the bristle pack, thereby increasing the Fn/Fax. Thus, front plate does not offer protection to bristles under high inlet swirl conditions, on the contrary, it may cause early slip of the bristles.

In this study, to reduce the negative impacts of cavity leakage flow on the aerodynamic performance of a shrouded stator, the structure of the seal cavity is optimized. First, the cavity structure is parameterized, and under different cavity design schemes, annular cascades with a cavity structure are simulated numerically to construct a sample database. On this basis, a neural network and genetic algorithm are used to establish the relationship between the modeling parameters and performances to find an optimal solution. Finally, the mechanism whereby the optimized cavity improves the compressor performance is analyzed. The results show that the optimized seal cavity reduces the leakage flow by approximately 30%, while the windage heating through the cavity remains unchanged. Also, the circumferential velocity of the leakage flow at the outlet of the cavity increases, so its ability to resist the boundary layer and pressure gradient extrusion is enhanced in the cascade passage. These two improvements reduce the influence area of the cavity leakage vortex and delay the passage vortex, which can decrease the momentum loss thickness of the boundary layer and reduce the total pressure loss coefficient of the cascade by 2.14%. Furthermore, the changes in the optimized cavity structure exhibit a high degree of consistency with the trends of the correlation analysis. Therefore, according to the structural characteristics and control mechanism of the seal cavity, the proposed optimization method can obtain remarkably effective cavity structures, taking into account the cascade loss minimization as well as the security stability of the inter-stage sealing.

Within the engine air system, the sealing is pivotal for augmenting engine thrust and efficiency. The brush seal, a contact-based sealing structure, exhibits commendable sealing efficacy. Nevertheless, the supple bristles tend to slip circumferentially in swirl inlet, diminishing the seal's stability and thus constraining its applicability. This study employs a fluid–structure interaction approach to initially dissect the flow field dynamics within the bristles in swirling conditions, examining the aerodynamic behavior across various bristles and their consequent motion and deformation. Leveraging the Design of Experiment method, typical geometric variables of brush seals, such as the diameter, length, inclined angle, rows, radial clearance of bristles, and the spacing between bristles, are scrutinized, and their influence on aerodynamic force distributions on the first row of the bristles and the interplay among these parameters assessed. It was observed that under the swirl inlet imposed, the first row of bristle pack experiences diminished axial forces compared to no-swirl. The diameter of bristle emerged as a primary factor impacting axial aerodynamic force, contributing 33% of the force, and there exists a linear correlation between diameter and axial aerodynamic force. Notably, the interplay between bristle diameter and inclined angle significantly influences axial forces and bristle deformation. The critical factors influencing the normal aerodynamic force acting on the bristles were identified as the spacing and diameter of the bristles, with respective contribution rates of 27.4% and 27.3%. A linear escalation in the normal aerodynamic force is seen with increasing spacing and diameter. Additionally, a substantial inverse relationship between diameter and inclined angle was discerned.

When subject to highly swirling inlet flow, the bristles on the upstream face of a brush seal in gas turbine engines tend to slip circumferentially, which may lead to aeromechanical instability and seal failure. In this article, a new design of the front plate of brush seal, which mitigates this effect, is presented. Angled ribs on the upstream side of the front plate are used to reduce the swirl of the flow impacting on the bristle pack. The effects of the rib geometry, including angle of inclination and height-to-spacing ratio, are investigated using computational fluid dynamics, and a bulk porous medium model of the bristle pack, on a simple seal geometry. Results show that the ribs can effectively regulate the flow upstream of the bristle pack, reducing the swirl and channeling flow radially inward to the sealing section, resulting in decreased circumferential forces on the bristles. Ribs inclined at 20° to the radial direction and with height-to-spacing ratio of 0.4 were selected as the most effective of those investigated for the seal geometry under study. A model of an aeroengine preswirled cooling air chamber was created to give insight into the inlet swirl boundary conditions that a preswirl seal brush seal could be subjected to at a range of leakage flow rates and inlet swirl velocities. The new design and upstream roughness feature substantially reduced inlet swirl velocity incident on the bristle pack. The findings in this work could have a significant impact on brush seal design and, in particular, mitigate a significant operational risk of swirl-induced instability in high-pressure, high-speed shaft seal locations.

Advanced brush seal technology has a significant impact on the performance and efficiency of gas turbine engines. However, in highly inlet swirling environments, the bristles of a brush seal tend to circumferentially slip, which may lead to aerodynamic instability and seal failure. In this paper, seven different front plate geometries were proposed to reduce the impact of high inlet swirl on the bristle pack, and a three-dimensional porous medium model was carried out to simulate the brush seal flow characteristics. Comparisons of a plane front plate with a relief cavity, plane front plate with axial drilled holes, anti-“L”-type plate and their relative improved configurations on the pressure and flow fields as well as the leakage behavior were conducted. The results show that the holed front plate can effectively regulate and control the upstream flow pattern of the bristle pack, inducing the swirl flow to move radially inward, which results in decreased circumferential velocity component. The anti-“L” plate with both axial holes and one radial hole was observed to have the best effect on reducing the swirl of those investigated. The swirl velocity upstream the bristle pack can decline 50% compared to the baseline model with plane front plate, and the circumferential aerodynamic forces on the bristles, which scale with the swirl dynamic head, are reduced by a factor of 4. This could increase the bristle stability dramatically. Moreover, the front plate geometry does not influence the leakage performance significantly, and the application of the axial hole on the front plate will increase the leakage slightly by around 3.5%.