Showing papers on "Axial compressor published in 2023"

Experimentally Validated Modelling of an Oscillating Diaphragm Compressor for Chemisorption Energy Technology Applications

Abstract: This study presents a detailed dynamic modelling and generic simulation method of an oscillating diaphragm compressor for chemisorption energy technology applications. The geometric models of the compressor were developed step by step, including the diaphragm movement, compressor dimensions, chamber areas and volumes and so on. The detailed mathematical model representing the geometry and kinematics of the diaphragm compressor was combined with the motion equation, heat transfer equation and energy balance equation to complete the compressor modelling. This combination enables the novel compressor model to simultaneously handle the simulation of momentum and energy balance of the diagram compressor. Furthermore, an experimental apparatus was set up to investigate and validate the present modelling and the simulation method. The performance of the compressor was experimentally evaluated in terms of the mass flow rate of the compressor at various compression ratios. Additionally, the effects of different parameters such as the inlet temperature and ambient temperature at various compressor ratios on the compressor performance were investigated. It was found reducing the inlet temperature from 40 to 5 °C at a constant pressure results in the enhancement of the compressor flow rate up to 14.7%. The compressor model proposed and developed in this study is shown to be not only able to accurately deal with the complexity of the dynamic behaviour of the compressor working flow but is also capable of effectively representing diaphragm compressors for analysis and optimisation purposes in various applications.

Numerical Simulation on the Influence of Inlet Flow Characteristics on the Performance of a Centrifugal Compressor

Abstract: Although inlet bent pipes are usually adopted due to limited installation space, the influences of different bend pipes on the inlet flow characteristics and performance of centrifugal compressors are still unclear. The numerical simulation of a centrifugal compressor is established and validated by experimental results with the case of a straight inlet pipe. Then, the internal flow characteristics of the centrifugal compressor with a 90-degree bent pipe (p90) and Z-shaped bent pipe (pz) are simulated and discussed. The results show that the adoption of two inlet bent pipes reduces the performance of the centrifugal compressor to a certain extent, which reduces more greatly with pz, with a maximum reduction of 6.82% in pressure ratio and 14.83% in efficiency, respectively. The pressure ratio and efficiency reduction of the centrifugal compressor both increase with the increment of distortion degree, which maintains the increasing trend as the flow rate increases, and the maximum distortion degree of p90 and pz reaches 0.0351 and 0.0479, respectively. The reduction degree of the pressure ratio shows a power–law relationship with the distortion degree, while the reduction degree of efficiency shows an exponential relationship with it. The flow characteristics at the outlet section of the inlet pipe affect the flow field distribution at the inlet of the impeller, and the distortion area ranges of the total pressure and axial velocity at the inlet of the impeller are near 72°–144° in the circumferential direction for p90, while those of pz are close to 108°–180° and 288°–360°. When the flow with a high distortion degree enters the impeller, a large area with high turbulent kinetic energy is formed in the downstream flow channel, resulting in an increase in the flow loss.

Optimization Design of Aspect Ratio and Solidity of a Heavy-Duty Gas Turbine Transonic Compressor Rotor

Abstract: To investigate the influence of blade aspect ratio and solidity on the performance of heavy-duty gas turbine transonic compressors, a multi-objective optimization design platform was built by adopting the blade parameterization method based on the superposition of thickness distribution on the suction surface, the Kriging surrogate model, and the NSGA-II optimization method. The spanwise distribution of solidity and number of blades were the optimization variables. The multi-objective optimization was carried out with isentropic efficiency and stall margin as the objective parameters for the inlet stage transonic rotor of an F-class heavy-duty gas turbine compressor. The results show that the isentropic efficiency and stall margin at design condition with a constant mass flow rate can be improved by 0.96% and 18.7%, respectively, and the total pressure ratio can also increase. The analysis shows that, for regions where the shock wave–boundary layer interaction is obvious, increasing the solidity can reduce the shock wave loss, the shock wave–boundary layer interaction loss, and the end wall loss, and reducing the aspect ratio can reduce the blade boundary layer loss. The spanwise distributions of solidity and aspect ratio determine the stall margin by affecting the radial matching of the load of each blade section. Tip solidity near the tip region needs to be determined according to the pressure field established by the bulk of the flow.

Simulation of 3D Co-Flow Jet Airfoil with Integrated Micro-Compressor Actuator at Different Cruise Mach Numbers

Abstract: This paper presents a 3D Co-Flow Jet (CFJ) active flow control airfoil with an integrated micro-compressor at different flight conditions that make the micro-compressor actuator work at different operating conditions. The simulations are performed at Mach 0.25, 0.3, and 0.4 with the angle of attack varying around the cruise condition. The RPM of the embedded micro-compressor is controlled to achieve a variety of operating conditions to satisfy the different flight conditions. The micro-compressor actuator is designed for high efficiency at a required mass flow rate in order for the CFJ airfoil to maintain a desired momentum coefficient (Cµ). For each Mach number, different operating points are studied by fixing the compressor RPM at different values and varying the angle of attack (AoA) of the CFJ airfoil. The aerodynamic performance, CFJ mass flow rate, energy expenditure, and 3D flow field are studied for each case. Results show the micro-compressor mass flow rate linearly increases with the CFJ airfoil AoA until the airfoil stalls. The CFJ airfoil will stall before the micro-compressor chokes. Airfoil stall decreases the mass flow rate going through the compressor, preventing the compressor from obtaining a higher mass flow. The aerodynamic performance of the CFJ airfoil shows a maximum CL/CD of 625.9 and a maximum corrected aerodynamic efficiency (CL/CD)c of 66.7 for the case of M = 0.25 at compressor RPM 27,000 and AoA = 0° where the micro-compressor efficiency (η) is 76.6%. As a comparison with the baseline airfoil at cruise AoA of 5°, the integrated CFJ airfoil achieves an increase of CL, CL/CD, (CL/CD)c, and (C2L/CD)c by 26%, 89%, 1.2%, and 27% respectively. This indicates that the CFJ airfoil can indeed be used for efficiency cruise with high cruise lift coefficient. For large AoAs leading to airfoil stall, the micro-compressor RPM needs to be increased to shift the micro-compressor operating line towards a higher mass flow rate and Cµ. This study is a virtual simulation of the integrated system of the CFJ airfoil and the micro-compressor actuator to examine the aerodynamic performance and show how the CFJ airfoil can be controlled within a flight envelope at different operating conditions.

Leakage Flow Impact on Shrouded Stator Cavity Flow Topology and Associated High-Speed Axial Compressor Stage Performance

Abstract: Abstract This paper presents the investigation of realistic cavity leakage flow for the von Karman Institute for Fluid Dynamics H25 axial compressor stage, equipped with a shroud cavity of average Reynolds number Rer = 2.2 * 106 and average aspect ratio G = 0.06. On top of overall performance measurements, time averaged data from unprecedented experimental dataset are used to characterize the stator hub shroud cavity flow field and its interaction with the power stream. The sensitivity of the stage performance and stability as well as the cavity flow topology is evaluated against injection conditions, compressor throttling, and compressor speed. Parametric steady RANS simulations of the stage under injection are used to support the findings and state on the relevance of such approach in the preliminary design phase of axial compressor components. As an example, a stage efficiency reduction of 0.97% for a leakage fraction of 0.56% at design point is retrieved. This performance drop is attributed to the effect of cavity flow on: the blockage ratio, the boundary layer skewness, and total temperature increase at stator row inlet. It is also presented that there is a mutual interaction between the cavity geometry and the cavity flow field organization. The injection homogenizes the cavity flow field and the associated pressure gradient. The various operating conditions presented also demonstrate that the cavity flow studied is, on average (i.e., time), sensitive to changes in compressor rotation speed and changes in stage loading.

Mechanism study on the effect of self-circulating casing treatment with different circumferential coverage ratios on the axial compressor stability

Abstract: To reveal the mechanisms underlying the effect of self-circulating casing treatment with different circumferential coverage ratios on the stability of the axial compressor, a three-dimensional unsteady numerical was hereby conducted on Rotor 35. The circumferential coverage ratios of self-circulating casing of 20%, 40%, 60%, and 80% were designed, respectively. The calculated results point out that all the schemes effectively expand the stable working range of the compressor and that the expansion effect is positively correlated with the circumferential coverage ratio. The self-circulating casing with an 80% circumferential coverage ratio exhibits the highest stall margin improvement at 14.83%. The internal flow field analysis shows that the underlying mechanism for the compressor stability increasing with the increase in the circumferential coverage ratio is that after the flows with a higher circumferential speed component enter the self-circulating casing suction port, sufficient circumferential space is required to complete the transformation in the flow direction, so that the flows can smoothly enter the self-circulating casing and subsequent development can be carried out. The larger circumferential size of the self-circulating casing creates favorable conditions for more airflows to enter the self-circulating casing. With the increase in the circumferential coverage ratio, the suction effect of self-circulating casing on low-speed fluid at the blade tip and the bleeding mass flow rate is larger, and a better compressor expansion effect is thereby achieved.

Influence of Axial Installation Deviation on the Hydraulic Axial Force of the 1000 MW Francis Runner in the Rated Operating Condition

Abstract: To study the influence of the axial installation deviation of the runner on the hydraulic axial force of the 1000 MW Francis turbine unit, geometric models of the full flow passage of the Francis turbine with the runner sinking in the axial direction by 0, 0.5, 1, 1.5, 2.5, 4, and 5.5 mm were established. The geometric models of the upper crown clearance, lower band clearance, and pressure balance pipes were also built. The SST turbulence model was used in the CFD setup to numerically simulate the flow in the Francis turbine with different runner installation sinking values. The results show that the hydraulic axial force on the inner surface of the runner remains stable when the runner is lowered. The hydraulic axial force on the entire runner surface and the outer surface of the lower band decreases, and the hydraulic axial force on the outer surface of the upper crown clearance increases. All of these hydraulic axial forces gradually tend to stabilize as the amount descending from the runner increases. To study the reasons for the changes in hydraulic axial forces, the streamlines and fluid fields of different sections in the flow passage were analyzed in detail. It was found that periodic changes of vortices were generated in the clearance due to the influences of the geometric shape and wall rotation. These vortices affect the distribution of velocity and pressure and, thus, determine the hydraulic axial forces. The runner axial installation deviation has little influence on the streamlines, pressure, and velocity distribution in each flow passage, and only changes the velocity and pressure in the upper crown clearance and lower band clearance. Therefore, the axial installation deviation of the runner has a great effect on the hydraulic axial force on the outer surface of the upper crown and lower band and has a smaller impact on the runner passage and the hydraulic axial force on the inner surface of the runner. The conclusions in this study can be adopted as references for the installation accuracy control of other hydraulic Francis turbine units.

A Combined Artificial-Intelligence Aerodynamic Design Method for a Transonic Compressor Rotor Based on Reinforcement Learning and Genetic Algorithm

Abstract: An aircraft engine’s performance depends largely on the compressors’ aerodynamic design, which aims to achieve higher stage pressure, efficiency, and an acceptable stall margin. Existing design methods require substantial prior knowledge and different optimization algorithms to determine the 2D and 3D features of the blades, in which the design policy needs to be more readily systematized. With the development of artificial intelligence (AI), deep reinforcement learning (RL) has been successfully applied to complex design problems in different domains and provides a feasible method for compressor design. In addition, the applications of AI methods in compressor research have progressively developed. This paper described a combined artificial-intelligence aerodynamic design method based on a modified deep deterministic policy gradient algorithm and a genetic algorithm (GA) and integrated the GA into the RL framework. The trained agent learned the design policy and used it to improve the GA optimization result of a single-stage transonic compressor rotor. Consequently, the rotor exhibited a higher pressure ratio and efficiency owing to the sweep feature, lean feature, and 2D airfoil angle changes. The separation near the tip and the secondary flow decreased after the GA process, and at the same time, the shockwave was weakened, providing improved efficiency. Most of these beneficial flow field features remained after agent modification to improve the pressure ratio, showing that the policy learned by the agent was generally universal. The combination of RL and other design optimization methods is expected to benefit the future development of compressor designs by merging the advantages of different methods.

An Experimental Facility with the High-Speed Moving Endwall for Axial Compressor Leakage Flow Research

Abstract: The moving endwall has a great influence on the development and stability of axial compressor leakage flow. This paper presents a novel experimental facility with a high-speed moving endwall for studying axial compressor leakage flow. The uniqueness of the design concept is that using a large disk simulates the high-speed moving endwall. When R/Cx = 16, theoretical analysis shows that the maximum linear velocity difference is about 2.5% while the maximum axial velocity difference of the mid-three passages is less than 5%. Single-passage simulations show that the disk radius of R/Cx = 16 can achieve an acceptable accuracy in terms of static pressure, total pressure, and density flow. Seven-passage simulations confirm that the mid-three passages have small errors from the axial velocity difference. Subsequently, preliminary experimental results obtained from the experimental facility are presented. The results reveal that the moving endwall significantly changes the distributions of the total pressure loss and static pressure coefficient. The relative difference in the averaged total pressure loss between the experiment and CFD is 11.33% and 7.69% for the static and moving endwall, respectively. It is expected that the experimental facility will make more useful contributions to the understanding of axial compressor leakage flow in the future.

Endwall geometric uncertainty and error on the performance of TUDA-GLR-OpenStage transonic axial compressor

Abstract: The hub and casing walls of axial compressors are often modeled as smooth continuous surfaces in CFD simulations, but in real geometries, non-smooth pinches, steps and leakage cavities may exist. In the GPPS first Turbomachinery CFD Workshop, a comprehensive validation and verification campaign of RANS flow solvers was conducted, and all the simulation results consistently over-predicted the total pressure ratio at the rotor exit near the casing and the stator exit near the hub. From a recent examination of the test rig geometry, a pinched casing wall over the rotor and a leakage cavity below the stator were found, which were not considered in the workshop. In this paper, the effects of these endwall geometric uncertainties and errors are analyzed via numerical simulation. When considering the rotor casing pinch of the test geometry, the predicted total pressure ratio and choke mass flow of the compressor stage are smaller than that without the pinch, leading to better agreement with the measured data. When considering a stator hub cavity with a leakage flow rate of about 0.2% of the compressor inlet mass flow, the near-hub total pressure ratio distribution matches slightly better with the experimental data, but the effects on the global compressor stage characteristics are not visible. The relevant mechanisms of these changes in performances are analyzed in detail. The updated geometries and grids will be released to the public as a benchmark test case for turbomachinery CFD validation and verification.

Design optimization and flow analysis of discrete tip injection in a transonic compressor based on nonlinear harmonic method and endwall blockage attenuation

Abstract: Discrete tip injection (DTI) shows great promise for improving the operating stability of transonic axial flow compressor (AFC) rotors. However, the design optimization of DTI remains a challenging task because of both the reliance on computationally expensive unsteady simulations to calculate its effects and the lack of a flow physics-based index for assessing operating stability. The present study introduces a nonlinear harmonic method for the rapid simulation of the dominant unsteady effects caused by a DTI device, and it proposes the unsteady shroud endwall blockage attenuation as an operating stability optimization index for DTI design based on analyzing the stall flow mechanism in transonic AFCs. On this basis, an efficient optimization method for DTI design is proposed in combination with an adaptive kriging-based optimization technique. This design optimization method is validated by the Coandă injector design for the transonic rotor National Aeronautics and Space Administration Rotor 37, with improved operating range and reduced injection mass flow pursued simultaneously by a comprehensive objective function. The optimal DTI design significantly reduces the stalling flow coefficient of the compressor by 4.46% at a small injection mass flow (0.72% of the compressor stalling mass flow), with a slight increase in the aerodynamic performance of the compressor. Detailed unsteady flow-field analysis shows that the main reason for the improved operating stability of the transonic AFC is a significant attenuation and delayed recovery of shroud endwall blockage, and the underlying flow mechanism is elucidated well.

Evolution of unsteady vortex structures in the tip region of an axial compressor rotor

Abstract: The evolution of unsteady vortex structures in the tip region of an axial compressor rotor is investigated based on delayed detached eddy simulation. The vortex structures are identified by the [Formula: see text] method, and the velocity fields are visualized by the particle tracing method. The results show that the evolution of the tip leakage vortex (TLV) can be divided into three phases: the generation phase, the development phase, and the dissipation phase. The unsteadiness of the flow field mainly appears in the dissipation phase as a consequence of the unsteady secondary tip leakage. There are three primary unsteady vortex structures caused by the tip leakage flow (TLF), and these vortex structures are related to each other as a feedback loop. The intermittent formation of the vortex ropes leads to the breakdown of the TLV and thus results in the roll-up of the backflow vortex (BFV) due to the radial velocity gradient. The secondary leakage of the BFV locally enhances the TLF jet and affects the formation of the vortex ropes in turn. This feedback loop causes the unsteady behavior of the TLF and has great impacts on the performance and stability of the compressors.

Effect of different axial deflected angles of reversed blade-angle slots on the axial flow compressor performance and stability

Abstract: The aim of the paper is to explore the influence of the reversed blade-angle slot casing treatment (RBSCT) and its axial deflected angle (ADA) on the compressor performance and stability, and to reveal the mechanism that the change in ADA of the RBSCT influences the effect to broaden the compressor stable working range. The NASA Rotor 35 is used as the object of the investigation, and four RBSCTs with ADA of −15°, −30°, −45° and −60° are designed and investigated by unsteady numerical simulation. The results show that as the absolute value of the axial deflected angle increases, the capacity to improve the compressor stability of the RBSCT increases and then decreases. The unsteadiness of the injection and suction flows formed by the reversed blade angle slot plays an important role in the removal of the low-velocity zone. When ADA is −30°, the unsteadiness amplitude of the injection and suction flows is significantly higher than those of the other three. Consequently, the RBSCT with −30° ADA obtains the maximum stall margin improvement of 17.41% and the maximum design point efficiency improvement of 1.06% among the four RBSCTs.

A novel experimental control method to suppress instability in a centrifugal compressor with two counter and co-rotating rotors

Abstract: The use of a counter-rotating rotor in turbomachines can be a solution to improve performances by allowing reduction in size and weight, especially compared to multistage configuration. The present study aims are to demonstrate another advantage of the counter-rotating rotors: their application to expand the operating range of centrifugal compressors toward extremely low flow rates based on an active control method. This method was performed on two different counter-rotating configurations. The principle of the active control method is to adjust independently the rotation speed of each rotor to push back the instability appearance. Experimental results show that reducing the rotation speed of the upstream-rotor while fixing the speed of the downstream rotor can push the instability phenomenon toward a lower mass flow rate while decreasing the pressure rise and efficiency. Co-rotating mode is applied to push further the stable region toward low mass flow rates allowing a significant extension of the operating range. The experimental results reveal that the map width is shifted by about 50% over the studied range toward a lower mass flow rate for both counter-rotating centrifugal compressors when using the control method. This can be achieved when the absolute value of the upstream-rotor speed is within the range of 48%–61% of the rotational speed of the downstream rotor.

Adaptive feedback control of stability in an axial flow compressor with circumferential inlet distortion

Abstract: The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a lowspeed axial compressor. Three flat-baffles with different span heights are used to simulate circumferential distorted cases. Compared with auto-correlation and root-mean-square analysis, cross-correlation analysis used to predict early stall warning does not depend on the circumferential distortion position. Hence, the cross-correlation coefficient was used to monitor the stable status of the compressor when suffering from different circumferential distortions and was also selected as the feedback signal in the active control strategy. Based on the stall margin improvement of tip air injection obtained under different distorted intensities and the sensitivity analysis of cross-correlation coefficients to injected momentum ratios, tip air injection was adopted as the actuator for adaptive feedback control. The designed digital signal processing controller was applied to achieve adaptive feedback control in distorted inflow conditions. Results show that the adaptive feedback control on stability can obtain approximately identical stall margin improvement as the steady injection under different distortion intensities with a reduced injection mass flow. Thus, the proposed adaptive feedback control is ideal for the engine operation with circumferential distorted inflow, which frequently occurs in the flight.

Accounting for Circumferential Flow Nonuniformity in a Multistage Axial Compressor

Abstract: Abstract The flow field in a compressor is circumferentially nonuniform due to geometric imperfections, inlet flow nonuniformities, and blade row interactions. Therefore, the flow field, as represented by measurements from discrete stationary instrumentation, can be skewed and contributes to uncertainties in both calculated one-dimensional performance parameters and aerodynamic forcing functions needed for aeromechanics analyses. Considering this challenge, this article documents a continued effort to account for compressor circumferential flow nonuniformities based on discrete, undersampled measurements. First, the total pressure field downstream of the first two stators in a three-stage axial compressor was measured across half of the annulus. The circumferential nonuniformities in the stator exit flow, including vane wake variability, were characterized. In addition, the influence of wake variation on stage performance calculations and aerodynamic forcing functions were investigated. In the present study for the compressor with an approximate pressure ratio of 1.3 at the design point, the circumferential nonuniformity in total pressure yields an approximate 2.4-point variation in isentropic efficiency and 54% variation in spectral magnitudes of the fundamental forcing frequency for the embedded stage. Furthermore, the stator exit circumferential flow nonuniformity is accounted for by reconstructing the full-annulus flow using a novel multiwavelet approximation method. Strong agreement was achieved between experiment and the reconstructed total pressure field from a small segment of measurements representing 20% coverage of the annulus. The analysis shows the wake–wake interactions from the upstream vane rows dominate the circumferentially nonuniform distributions in the total pressure field downstream of stators. The features associated with wake–wake interactions accounting for passage-to-passage variations are resolved in the reconstructed total pressure profile, yielding representative mean flow properties and aerodynamic forcing functions.