Cantilevered Stators Research Articles

Study on the Tip Leakage Loss Mechanism of a Compressor Cascade Using the Enhanced Delay Detached Eddy Simulation Method.

The leakage flow has a significant impact on the aerodynamic losses and efficiency of the compressor. This paper investigates the loss mechanism in the tip region based on a high-load cantilevered stator cascade. Firstly, a high-fidelity flow field structure was obtained based on the Enhanced Delay Detached Eddy Simulation (EDDES) method. Subsequently, the Liutex method was employed to study the vortex structures in the tip region. The results indicate the presence of a tip leakage vortex (TLV), passage vortex (PV), and induced vortex (IV) in the tip region. At i=4°,8°, the induced vortex interacts with the PV and low-energy fluid, forming a "three-shape" mixed vortex. Finally, a qualitative and quantitative analysis of the loss sources in the tip flow field was conducted based on the entropy generation rate, and the impact of the incidence on the losses was explored. The loss sources in the tip flow field included endwall loss, blade profile loss, wake loss, and secondary flow loss. At i=0°, the loss primarily originated from the endwall and blade profile, accounting for 40% and 39%, respectively. As the incidence increased, the absolute value of losses increased, and the proportion of loss caused by secondary flow significantly increased. At i=8°, the proportion of secondary flow loss reached 47%, indicating the most significant impact.

Detailed Simulations of a Three-Stage Supercritical Carbon Dioxide Axial Compressor with a Focus on the Shrouded Stator Cavities Flow

This paper describes the findings of detailed simulations performed to investigate the impact of seal teeth cavity leakage flow on the aerodynamic and thermal performance of a three-stage supercritical CO2 axial compressor. The study compares a shrouded stator configuration (with cavities) to a cantilevered stator configuration (without cavities) to highlight their differences. High-fidelity computational fluid dynamics simulations were performed using non-linear harmonic (NLH) and mixing plane assumptions, considering various possible rotor/stator interface configurations for mixing plane calculations. The key performance parameters for each case were compared, and the best-performing configuration selected for further analysis. The individual stage performance parameters are also examined and compared between the cantilevered and shrouded configurations. It was observed that in the shrouded case, the leakage flow enters the cavity downstream of the stator trailing edge and gets entrained into the primary flow upstream of the stator, leading to boundary layer changes at the hub and degradation of stator and downstream rotor performance. Vortical flow structures were also observed in the stator wells, which tended to change the flow angles around the region, thereby affecting mixing and velocity distribution, resulting in a slight deterioration of compressor performance. Additionally, the study examines windage heating due to shear work from rotating walls, including the seal teeth surface. The amount of shear work done on the leakage flow and the corresponding rise in fluid temperature were quantified, tabulated, and further compared with a simple analytical model, showing good agreement between them and, hence, validating the numerical approach used.

Flow characteristics of a low-solidity cantilevered stator embedded in a 4-stage low-speed research compressor

This research presents the influence of the low-solidity design on the loss and stability of the cantilevered stator and the evolution of the hub leakage vortex. The highly loaded 4-stage low-speed research compressor (LSRC) with an embedded cantilevered stator (CS) of Stator 3 (S3) was experimentally measured at the blade row outlet and in the S3 passage, respectively, and the URANS simulation method was calibrated accordingly. Then, the prototype CS blade number was reduced, namely low-solidity cantilevered stator (LSCS), to increase the blade loading. The diffusion factor ( DF) of LSCS at the midspan at the design working condition is 5.2% higher than that of CS. The URANS results show that LSCS provides higher efficiency for the 1.5 stage compressor with a consistent stall margin. For S3, the total pressure loss of LSCS is lower than CS at the design point (DP) working condition, but it is the opposite at the near stall (NS) working condition. For LSCS at the NS point, the blockage region becomes large and occupies the lower half of the fore blade passage because the low-solidity stator could not provide the enough flow turning ability, and the core of the hub leakage vortex (HLV) moves forward and the intensity is strengthened. The high loss region of LSCS at the near stall condition is consistent with the size of two hub leakage vortices. The first HLV breakdown is caused by unsteady mixing flow, and then it twists downstream and contacts with the trailing edge of the adjacent blade pressure surface. The study of the hub leakage flow characteristics of the low-solidity cantilevered stator can help designers to control flow better.

Interacting Effects in a Multistage Axial Compressor Using Shrouded and Cantilevered Stators

This paper describes the analysis of the flowfield in a four-stage low-speed axial compressor at the design point investigated both numerically and experimentally, with particular emphasis on the impact of stator hub flow leakage in a section of the machine featuring a change of stator configuration. The goal of the work is to give insight into the effect of the stator hub configuration on the aerodynamic performance in terms of loss and efficiency of downstream blade rows as well as the resulting stage matching effects. The investigation is focused on aerodynamic behavior and stage interaction, which the stator hub configuration of a given stage induces in a downstream stage with respect to its performance and flowfield. Two shrouded and one cantilevered stator hub configurations, such as those commonly employed in industry, are investigated and discussed with respect to local flow phenomena and stagewise aerodynamic effects. The results show that the stator hub configuration of a given stage has a drastically high impact on the downstream rotor aerodynamic performance, whereas the downstream stator as well as the upstream rotor are only slightly influenced by the stator hub configuration.

Using forward end-sweep to reduce transonic cantilevered stator losses to improve compressor performance

ABSTRACTThe complicated flows in a transonic cantilevered stator would cause serious aerodynamic losses and reducing these losses would contribute much to improving the overall aerodynamic performance of a compressor. The paper conducts an overview study of the potential aerodynamic losses in a transonic cantilevered stator and presents a systematic numerical study for the effects of forward end sweep on reducing aerodynamic losses. A 2-D stator blade is used to throw light upon the physical mechanism of the forward end sweep on reducing the losses. At the casing region, forward end sweep has led to a redistribution of the blade load along the chordwise direction, higher in the front part and lower in the rear part. This result leads to a lower pressure gradient from the 30% chord location to the trailing edge and can be beneficial for the reduction of the corner separation. At the hub region, on one aspect, forward end sweep reduces both the peak Mach number and the size of the high-Ma region of the blade suction surface, thus decreasing the shock loss near the hub. On the other aspect, it also reduces the peak load and the strength of the leakage vortex, therefore alleviating the flow blockages. Simultaneously, the forward end sweep is applied to a commercial and high-performance multistage compressor to further validate its feasibility. When the technique is applied to the transonic first four stator rows, an improvement of adiabatic efficiency is achieved by ∼ 0.85% and the compressor stable operating range is slightly increased. The results suggest that the forward end-swept transonic cantilevered stators have a significant potential for reducing the stator losses. They would provide guidelines to advance the cantilevered stator design and further improve the compressor aerodynamic performance.Abbreviations: h, stagnation enthalpy; , stagnation pressure; p, static pressure; U, blade rotational speed at tip; V, velocity; , non-dimensional wall distance; , total pressure loss coefficient; , flow coefficient (Vx/U); , stage load coefficient (Δh/U2); , adiabatic efficiency; , total pressure ratio; in, inlet; out, outlet; LE/TE, leading/trailing edge; PS/SS, pressure/suction surface

Optimization of cantilevered stators in an industrial multistage compressor to improve efficiency

This paper presents an optimization of transonic cantilevered stators based on the combination of sweep and lean in a 5-stage axial compressor to improve its adiabatic efficiency and maintain its total pressure ratio by employing a time-saving integrated optimization design system. The system combines design of experiment with artificial neural network and computational fluid dynamics. The optimization is focused on the first stator stage and the motivation is to understand the mechanism of the performance improvement. It shows that the effect of combinational sweep and lean not only reduces the size of the transonic regions on the blade suction surface near the leading edge but also decreases the leakage loss, thus resulting in lower aerodynamic losses in hub region. Simultaneously, the downstream rotor achieves a higher aerodynamic performance due to a better matching for the improvement of the inlet working conditions. After optimization, the stator loss is reduced by 3.7%, whereas the adiabatic efficiency of the downstream rotor is increased by 0.64%, thus achieving an increment of 0.22% of peak efficiency of the entire compressor. The results show that cantilevered stators with the characteristic of sweep and lean have a significant potential to improve the performance of multistage axial-flow compressor.

Analysis and application of a new type of sweep optimization on cantilevered stators for an industrial multistage axial-flow compressor

Sweep is often applied to transonic rotors to reduce the shock loss and to stator vanes to reduce the end-wall separation loss. In this paper, a new type of sweep is created for cantilevered stators in a 5-stage axial-flow compressor through a combined use of sensitivity analysis and an integrated optimization design method. The shape of sweep is focused on the stator hub region according to sensitivity analysis, and the new swept stator design is beneficial for reducing the stator loss at hub end and improving the compressor aerodynamic performance. Firstly, the optimization design of a single first stator row is conducted in the multistage environment, and the aerodynamic benefits gain is mainly due to two aspects. On the one hand, the effect of sweep near the hub reduces the stator inlet Mach number and further reduces the size of supersonic regions and the peak Mach number on the suction surface, thus decreasing the aerodynamic losses. On the other hand, the sweep also reduces the loading in the front part of the blade near the hub and weakens the leakage flow, thus reducing the flow blockage and decreasing the secondary losses in the hub region. After the optimization, the stator loss is reduced by 7.4%, leading to an increment of 0.21% of adiabatic efficiency of the multistage compressor. Secondly, the same optimization strategy is then applied to the remaining stator rows to maximize the aerodynamic benefits gain. The optimized compressor achieves an approximately 1% improvement of adiabatic efficiency over than the baseline one and also performs better over the whole operating range. Simultaneously, the operating range of the multistage compressor is widened. The results indicate that cantilevered stators with the type of sweep in this work have a significant potential to improve the performance of multistage axial-flow compressor.

An Experimental Verification of a New Design for Cantilevered Stators With Large Hub Clearances

Proportionally large relative radial clearances can be found within the rear stages of multistage axial compressors of gas turbines and aero engines, with significant impact on their efficiency. A new three-dimensional design for cantilevered stators in axial compressors is presented, with the aim of improving the overall efficiency and losses of rear stage vanes with large relative hub clearances. The new vane design comprises an unconventional dihedral, with special consideration to reduce the losses caused by the hub clearance vortex. The design was tested in a 4-stage low speed axial research compressor under rear stage conditions. The results are compared to the nominal design to validate the reduction of hub clearance losses and blockage. For both designs, the hub clearances over the third and fourth stator were varied from 1.5% up to 6.0% of span. Overall performance data and flow field traverses upstream and downstream of stator 3 and rotor 4 will be presented in this article in comparison with 3D CFD results.

Study on the effects of end-bend cantilevered stator in a 2-stage axial compressor

Leading edge recambering is applied to the cantilevered stator vanes in a 2-stage compressor in this paper. Different curving effects are produced when the end-bend stator vanes are stacked in different ways. Stacking on the leading edge induces a positive curving effect near the casing. When it is stacked on the centre of gravity, a negative curving effect takes place. The numerical investigation shows that the flow field is redistributed when the end-bend stators with leading edge stacking are applied. The variations in the stage matching for the mainstream and near the hub have an impact on the performance of the 2-stage compressor. The isentropic efficiency and the total pressure ratio of the compressor are increased near the design condition. The compressor total pressure ratio is decreased near choke and near stall. The maximum flow rate is reduced and the stall margin is decreased.

Flow visualization study of tip leakage flows across cantilevered stator blades

A test program has been conducted to study tip leakage flows associated with cantilevered stator blades in axial flow compressor systems. A low-speed single-stage test rig has been developed to simulate flows characteristically found in middle-stage axial flow compressors. The test rig is designed specifically to accommodate flow visualization techniques in the study of cantilever stator blade tip leakage flows. Extensive testing demonstrates that the test rig simulates axial compressor stage performance characteristics. Data taken include both onand off-design operating conditions. Data reduction and analysis of high-speed film footage provides actual tip leakage path lines and velocities for four different tip treatments. The tip treatments investigated are baseline (no tip treatment), pumping groove, double winglet, and pressure side winglet. Of the four tip treatments tested, the pumping groove proved to be the most effective in reducing tip leakage.