High-speed Compressor Research Articles

Multi-Fidelity Aeromechanical Design Framework for High Flow Speed Multistage Axial Compressors

Abstract The development of novel engine architectures is vital in achieving the aviation sector’s net-zero carbon emission target by 2050. With today’s digital decade providing support for an accelerated technology maturation, the challenge for turbomachinery design remains to significantly push the limits of current performance within an ambitious development lead time. In this context, it is essential to adopt a design framework where the predictive models or simulations employed target a sufficiently reliable performance assessment. These models must be tailored to the dynamics of evolving industrial design processes, and therefore continuously balance required design flexibility, robust evaluation, appropriate fidelity (i.e. the level of detail and accuracy they provide), and resulting evaluation time. This paper discusses a framework for designing axial compressors and its application to the aeromechanical optimisation of a high-speed compressor rotor. The design environment integrates geometry parametrisation, modular evaluation with different levels of fidelity for the aerodynamic and structural models, and surrogate-based optimisation (SBO) capabilities. It is shown how the combination of a modular sequencing of the different models and the acceleration enabled by high-performance computing (HPC) and machine learning allows for a more advanced preliminary design. A significant gain in isentropic efficiency is attained while satisfying all structural constraints. At the same time, it is demonstrated that the framework is compatible with the characteristics of the preliminary design phase: both in its ability to adapt to cycle and design changes as well as regarding the turnaround time of the optimisation itself.

Thermodynamic performance and compression characteristics analysis of low GWP refrigerant in compressors: Experimental investigation and 0-D/3-D simulation

The utilization of low global warming potential (GWP) refrigerants is crucial for reducing greenhouse gas emissions. Among these alternatives for hydrofluorocarbons (HFCs), R290 stands out as a natural refrigerant with a low GWP value of 3. Therefore, it is beneficial to promote its widespread adoption and enhance the efficiency of compressors and their systems that utilize R290 to mitigate the greenhouse effect. The present study investigates and compares the thermodynamic performance and compression characteristics of a high-speed compressor employing R290 as a refrigerant with those of an R32 compressor. In contrast to previous studies, this paper presents a novel approach by developing validated the zero-dimensional (0-D) and three-dimensional (3-D) simulation model, along with experiments, to investigate the distribution of performance loss and suction-compression characteristics in high-speed R290 compressors. The results demonstrate that the R290 compressor exhibits superior volumetric efficiency, while excessive compression at high speeds leads to a noticeable reduction in indicated power. The combination of increased over-compression loss and motor loss at high speeds resulted in a 11.7% rise in input power, leading to an 8.4% decline in thermodynamic performance for the R290 compressor under standard heating compared to the R32 compressor.

Experimental study on the effect of fluidic oscillator jet position on the performance of a high speed compressor cascade

In order to further improve the performance of the cascade, this paper focused on a high-load diffuser cascade and a pulsed-type fluidic oscillator for flow control was also applied. Experiments were conducted at design incidence of 0° and near stall incidence of +4°, investigating different jet positions of the fluidic oscillators. The results indicate that at Mach number of 0.67 and design incidence, the pulsed jet effect is optimal when the jet position of the fluidic oscillator is at 35% of chord, resulting in an 8.74% decrease in total pressure loss. At Mach number of 0.5 the total pressure loss decreases by 12.08%. At the Mach number of 0.67 near the stall incidence of +4°, the fluidic oscillator jet position at 7% of chord shows the most significant decrease in total pressure loss, which is 5.3%. When the pulsed jet is positioned at the separation starting point of the corner, the low-pressure region on the suction surface near the endwall decreases, while the high-pressure region on the pressure surface increases, enhancing the pressure expansion capability of the cascade. The pulsed jet can successfully decrease the vorticity in the passage, such as passage vortex, trailing shedding vortex and concentrated shedding vortex, and can resist the transverse secondary flow in the cascade passage, reducing the range of corner separation in the spanwise direction and total pressure loss.

Extension and Validation of the Turbomachinery Capabilities of SU2 Open Source Computational Fluid Dynamic Code

Abstract Computational Fluid Dynamic (CFD) tools have revolutionized the way to design engineering systems, but most established codes are proprietary and closed-source, making it difficult, if not impossible, to modify, debug, or add new features to the code. To provide a freely available open-source CFD code for turbomachinery aerodynamics and aeroelasticity, this paper enhances the turbomachinery capabilities of the open-source SU2 code and demonstrates its capabilities of single-passage steady simulation, full-annulus unsteady simulation, and aeroelasticity analysis in two high-speed compressors, namely NASA Stage 35 and TUDa-GLR-OpenStage, and a linear cascade SC1. For the single-passage steady simulation of NASA Stage 35, the SU2 results are validated against the measured data and verified against the commercial solver ansys cfx, and the performance characteristics results are in reasonably good agreement with each other. For the single-passage steady simulation of TUDa-GLR-OpenStage, grid and turbulence model sensitivity studies are performed and results are validated against the measured data, and SU2 can predict both the performance characteristics and the radial profiles with sufficient accuracy. For the full-annulus unsteady simulation of NASA Stage 35, it is demonstrated that SU2 can predict the propagation of inlet distortion equally well as ansys cfx. For the linear cascade, SU2 can predict the unsteady pressure and aerodynamic damping coefficient accurately. The presented results demonstrate the turbomachinery aerodynamics and aeroelasticity capabilities of SU2. The major modifications of SU2 made in this work will be shared with the code maintainer and the community in the future.

Impact of Gas Foil Bearings, Labyrinth Seals, and Impellers on the Critical Speed of Centrifugal Compressors for Fuel Cell Vehicles: A Comprehensive Investigation

The critical speed is a crucial factor that impacts the stability of high-speed compressors. However, limited research has simultaneously considered the influence of gas foil bearings (GFBs), labyrinth seals, and impellers on critical speed. In this study, we develop a rotordynamic model that incorporates the aerodynamic forces of GFBs, labyrinth seals, and impellers to explore the effects of each component on the critical speed. To validate the developed model, experimental tests are conducted on a centrifugal compressor test bed, and the results exhibit a high level of agreement with the model calculations. By comparing the model calculations that include different components, we comprehensively analyze the influence of each component on the critical speed. The findings reveal that, for centrifugal compressors used in fuel cell vehicles, the rotordynamic coefficients resulting from GFBs are significantly larger than those resulting from impellers and labyrinth seals. Thus, it is reasonable to disregard the aerodynamic forces caused by impellers and labyrinth seals when calculating the critical speed. Furthermore, substituting rigid gas bearings for GFBs as a means to simplify the calculations has only a very slight impact on the results. This study aims to optimize the design process of centrifugal compressors for fuel cell vehicles and offers valuable insights for designing compressors of similar sizes.

The effect of tip clearance size on pre-stall flow features of a transonic axial compressor by using throttle model

This paper aims at the numerical analysis of the influence of tip clearance size on the pre-stall flow features of a transonic high-speed compressor by applying the throttle model at the exit of the compressor computational domain. Steady and unsteady calculations have been performed for design, double, and triple tip clearance sizes. The transition of the stall inception type when increasing the tip clearance size and the underlying flow physics has been analyzed in detail. The results show that the stall inception type transforms from spike to modal as the size of the tip clearance changes from design to triple tip clearance. The influence of the tip clearance size on the forward spillage of the tip leakage vortex near the stall limit, which is one of the two criteria for spike stall inception, is crucial for which type of stall inception would appear. For the design clearance case, a remarkable forward spillage of the tip leakage vortex occurs near the stall limit, leading to a typical strong spike stall inception. In the condition of double clearance, the intensity of tip leakage vortex spillage was weakened because the increase in the clearance size allows more low momentum tip leakage flow to go through the clearance instead of spilling from the leading edge. Thus, a weaker spike-type inception containing the content of modal disturbances was induced. Under the triple clearance condition, the high entropy gradient interface is located inside the blade passages all the time; thus, a typical modal-type stall inception appears.

Effect of water spray on tip leakage flow in a inlet stage of high-speed compressor

Water spray can reduce the inlet air temperature of the compressor inlet stage of the high-altitude high-speed turbine engine. In this paper, the Euler-Lagrange method is used to simulate the gas-liquid two-phase flow with droplet evaporation in NASA Stage 35. The effects of water spray on the heat and mass transfer characteristics of the stage, the tip leakage vortex structure, the unsteady characteristics of tip leakage flow and compressor performance are analyzed. The results show that the water spray increases the inlet mass flow and tip leakage flow rate of the stage, decreases the tip temperature. The inlet mass flow and tip leakage flow rate increase with the growth of inject mass flow rate and the decrease of droplet size. Water spray increases the scale of the main tip leakage vortex, and deflects the secondary leakage flow in the flow direction. Water spray increases the amplitude of pressure fluctuation at the blade tip. The frequency of pressure fluctuation at dry air condition is 0.2BPF, which decreases to 0.15BPF after water spraying. The leakage vortex weakens the strength of shock wave which causes a decline in the diffusing ability of blade; the leakage vortex is mixed with the main stream, resulting in a large aerodynamic loss. Although the injection of droplets increases the loss of tip leakage flow, it optimizes the performance of NASA stage 35 significantly. Spray increases the total pressure ratio of the R domain from 1.835 to 1.9; the total temperature ratio of the stage reduces from 1.225 to 1.203 and decreases the rotor loss coefficient from 0.12 to 0.08.

Analysis of a Segmented Axial Active Magnetic Bearing for Multi-MW Compressor Applications

In high-speed compressor and turbine applications, active magnetic bearings are employed to increase reliability, reduce maintenance, and provide contact-free and oil-free operation. Evidently, the dynamic performance of active magnetic bearings must correspond to application-specific events like compressor surge or thrust disturbances. This article presents a segmented stator as one of the solutions to increase the bandwidth of axial active magnetic bearings (AMBs) and further improve the stability of the shaft system. We analyze the effects and discuss the tradeoffs of axial active magnetic bearing stator segmentation and slitting to alleviate bandwidth limitations. Finite element method design optimization and control plant modeling methods, open- and closed-loop tests, and identification of the overall thrust AMB–rotor control plant are studied.

Loss reduction in the compressor corner region via blade cooling

With Reynolds number (Re) decreasing to a critical value (approximately 2.0 × 105), the laminar-to-turbulent transition on the blade/endwall surface accelerates the loss generation in the corner region of compressors. Thus, how to effectively control the three-dimensional turbulent mixing loss at a low Re is of great importance. In this study, the mechanism of loss variation in a high-speed compressor cascade as Re decreases from 5.6 × 105 to 1.5 × 105 is investigated by large eddy simulations (LESs). Then, an isothermal cooled wall condition with a constant temperature of 0.8T01 (T01 is the inlet total temperature) is specified on the blade surface to explore the potential of loss reduction via wall cooling at Re=1.5 × 105. At Re=5.6 × 105, the boundary layers on the blade suction surface strongly interact with the endwall boundary layers and multiple passage vortex structures near the spanwise location of x/H = 0.3, inducing a large-scale concentrated shedding vortex (CSV) and determining the loss generation rate in the corner region. With Re decreasing to 1.5 × 105, the blade boundary layers grow much thicker due to the delayed transition. Detailed loss classification result indicates that the stronger interaction between the thickened blade boundary layers and secondary flow accelerates the local generation of turbulent fluctuations, which is mainly responsible for the performance deterioration in the corner region at a low Re. As the blade surface is cooled, the growth of blade boundary layers and the migration of secondary flow in the blade passage can be controlled simultaneously. Thus, the interaction between the blade boundary layers and secondary flow near the spanwise location of x/H = 0.3 is weakened, leading to a reduction in the overall total pressure loss by 13.3%. The results hope to guide in controlling the loss in the corner region of compressors operating at a low Re.

Flow instability control of an ultra-highly loaded transonic compressor rotor using self-excited casing bleed

Flow instability is a common issue encountered by high-speed compressors when they operate outside of their optimal range, especially in highly loaded compressors. This study investigates the potential of an unsteady passive flow control technique, self-excited bleed (SEB), which involves casing modification, to improve the base flow and stability characteristics of an ultra-highly loaded low reaction transonic compressor rotor. Through transient computational fluid dynamics simulations, we demonstrate that SEB can extend the rotor's operating range by up to 14.07%. The physical mechanism underlying this stability enhancement is the suppression of the shock-induced breakdown of the tip leakage vortex (TLV) near the blade leading edge and the attenuation of the double leakage flow by SEB. The unsteady excitation of the bleed effect dominates the tip flow and eliminates the spontaneous closed-loop feedback process based on the dynamic interaction between the TLV breakdown, the tip secondary vortex, and the blade loading. Time-resolved tip-region flow patterns elucidate the self-organization and reconstruction of this feedback mechanism. Frequency spectral analysis further reveals that the self-induced oscillation frequency of the tip leakage flow formed during the feedback process disappears, and the bleed excitation frequency replaces it as the main frequency of the tip flow field. However, increasing the bleed flow rate causes the boundary layer on the suction surface to migrate radially outward, resulting in increased flow blockage at the rear of the tip passage. These two influences of SEB are quantified by a blockage factor, and determining the optimal bleed flow rate requires a trade-off between beneficial and detrimental impacts.

Numerical Study on End Wall Synthetic Jet to Improve Performance and Stability Margin of a High-speed Subsonic Axial Compressor Rotor

Synthetic jet has been confirmed as a novel flow control technology. However, the existing application research on synthetic jet in axial flow compressor is still confined to cascade or low-speed axial flow compressors, and rarely high-speed axial flow compressor. The effects of three vital parameters (i.e., the action position, frequency, peak velocity) on the aerodynamic performance and stability margin are systematically studied, with a high-speed compressor rotor as the object of numerical simulation. An optimal excitation position is determined, corresponding to the core position of the compressor top blockage, as indicated by the results, which increases the stability margin and efficiency of the compressor by 13.2% and 1.15% respectively. The excitation frequency has a threshold ranging from 300Hz to 600Hz. Only when the frequency of synthetic jet exceeds this threshold can it suppress the tip leakage flow. Besides, the jet peak velocity may not have a threshold. However, the higher the peak velocity, the greater the mixing loss between the jet and the mainstream of the compressor rotor will be, thus limiting the further increase of the compressor efficiency.

Half-scale transonic compressor rapid testing rig

High-speed compressor testing is costly due to mechanical complexity and hazardous due to the high energy involved. In the past this has limited the speed and amount of testing. In this paper a new rig architecture is presented that aims to test a scaled transonic compressor stage rapidly. It builds upon the low-speed rapid testing developments made at the Whittle Laboratory and has potential to accelerate technology development. The power input requirement is reduced by testing at half-scale and reduced Reynolds number while maintaining the Mach number. Further power saving and mechanical simplification is achieved by employing a turbo-expander architecture with no shaft-power input, only the aerodynamic losses in system must be overcome. The aerodynamic and mechanical design of the rig is presented. Safe operation and rapid access and rebuild times are critical. The test hardware is machined from solid and bladed disks and rings can be manufactured in days. Only standard instrumentation is required, although a novel control loop is employed to achieve the same accuracy in rotational speed as an electric motor driven compressor rig. Experiments up to 25% design rotational speed were conducted, and the results presented here show that the rig is controllable and inherently safe if the research compressor fails. The rig will be run to full speed in the immediate future and extension to the capability is planned with multi-stage high-speed testing in a second machine.

Aerodynamics of inter-spool duct under the influence of an upstream transonic compressor stage

The compressor inter-spool duct (ISD), with its offset and profiled curvature, is an inherent part of the turbofan system due to large density gradients and substantial area changes across each spool. The aerodynamic performance of the ISD is highly dependent on the upstream flow conditions, and hence its design process must account for the upstream effects. In the present investigation, the inter-spool duct design is carried out, suiting an existing high-speed transonic compressor stage, forming an integrated system. The emphasis of this investigation is to assess the effect of upstream secondary flow structure, i.e., shock losses, tip leakage vortices, blade wakes, and corner-separated flow, on the aerodynamic performance of the duct. The compressor stage performance is presented with the help of experimental and numerical data at design and off-design conditions. The inter-spool duct is numerically analyzed considering uniform inlet flow and the flow coming from the upstream high-speed compressor stage. This investigation reveals that the duct with uniform inlet flow is free from any severe flow separation; consequently, minimum loss. However, the losses are observed to increase significantly with the upstream compressor stage. The majority of the losses are incurred at the duct inner wall due to large wake structures emanating from the stator hub section. The stage exit swirl throughout the duct in the outer wall region, in combination with the hub-separated flow, results in the low-pressure region at the duct-inner wall, causing flow reversal at the exit. This creates flow blockage resulting in a decrease in the choke margin of the integrated system. The overall efficiency of the integrated system is also reduced owing to the losses encountered within the duct.

The Horizontal Mode Natural Frequency of a Floating Pile in Layered Soil: Full-Scale Field Test Vs Mathematical Models

Pile supported structures can be subjected to a variety of man-made and naturally occurring dynamic loads. Dynamic loads such as those from rotating machinery include a considerable lateral component. The natural frequency of a pile in the horizontal mode becomes a key parameter in the design of dynamically sensitive equipment foundations. It is not uncommon for structural engineers to estimate the natural frequency of piles using quick linear methods using available soil investigation data before advanced laboratory tests on soil samples can be performed to calibrate nonlinear numerical models. This paper presents results from free and forced vibration tests on a full-scale single pile, designed for a high-speed compressor unit, in Hazira, India. Two different fast mathematical models, one following the Beam on Dynamic Winkler Foundation (BDWF) method, and another involving an FEM–BEM based numerical method were used in predictions against experimental results. The BDWF method was found to produce a preliminary estimate of pile stiffness at low strain levels. However, the selection of soil stiffness and damping models are crucial for the accuracy of BDWF models. It was found that the FEM–BEM model was able to simulate the nonlinear pile response with a moderate overestimation of vibration amplitudes.

Experimental and Computational Investigation of an Advanced Casing Treatment in a Single-Stage High-Speed Compressor

Abstract An advanced casing treatment (CT) design was tested in a single-stage, high-speed axial compressor. The geometry of the casing included bent-axial slots applied near the rotor leading edge. Compressor performance and stall margin (SM) measurements were acquired for both casing treatment and for the smooth wall case at four different corrected speeds. The measurements also included rotor-exit radial traverses of unsteady total pressure. The results indicated an increase in rotor pressure ratio at all operating conditions with the application of the casing treatment. The stall margin also increased at all rotor speeds. Efficiency increases were observed with the casing treatment at design conditions and some off-design conditions. Numerical simulations of the IGV, rotor, and stator were conducted with and without the casing treatment. These results served to validate the efficacy of the part-wheel unsteady Reynolds-averaged Navier–Stokes (URANS) simulations to predict the effects of the casing treatment. The simulations also allowed a detailed study of the flow physics related to the interactions between the rotor and casing.

Development of flow-vibroacoustic coupled numerical methods for prediction of noise radiation due to flow-born vibration of compressor discharge piping system

The compressor and fan in air conditioner outdoor unit are the core component which deter-mines noise performance as well as cooling or heating performance. Among these, the com-pressor has larger contribution to the noise of outdoor units. For high efficiency air condition-er, the size and operating speed of compressor are smaller and faster. The high-speed com-pressor causes loud noise which is complaints for the customer. Traditionally, it is well-known that the vibration of compressor and connected duct is main noise source. However, as the compressor speed increases, the refrigerant flow in the compressor discharge duct also emerged as a major noise source. To reduce the compressor noise operating at high speed, it is necessary to analyze vibrational and acoustic characteristics of compressor discharge duct. This duct noise has the two-types source: structure born noise and flow induced noise. The structure born noise is generated by the duct vibration caused by compressor movement. For the flow induced noise, the static pressure field of refrigerant flow in the duct is vibrational source. In this paper, the compressor discharge duct noise considering two mechanisms was investigated. The refrigerant flow is solved using CFD and duct vibration and noise radiation are computed by FE-BE method.

Acoustic scattering in a small centrifugal compressor based on the use of linearized equations in a rotating frame

Numerical solutions of acoustic wave scattering are often used to describe sound propagation through complex geometries. For cases with flow, various forms of the convected equation have been used. A better alternative that includes vortex-sound interaction is instead to use the linearized and harmonic forms of the unsteady fluid flow governing equations. In this paper, a formulation of the linearized equations that include rotational effects, in an acoustic computation using a rotating frame of reference in a stationary geometry, is presented. We demonstrate that rotational effects can be important, e.g., when computing the transmission loss through high-speed compressors. The implementation of the proposed addition to the existing schemes is both simple and numerically inexpensive. The results are expected to have an impact on the research and development related to noise control of high-performance turbo-machinery, e.g., used in automotive or aviation applications at operating conditions that can be represented by steady background flows.

Experimental validation of a three-dimensional through-flow model for high-speed compressor surge

This paper describes the validation of surge simulations produced using the low-order code ACRoSS with experimental data from a 4. 5-stage high-speed rig, representative of the front stages of a modern high-pressure compressor (HPC). ACRoSS is an unsteady, 3D through-flow code developed at Cranfield University to predict compressor performance during stall events. The experimental data was derived during the Rig250 build 6B test campaign, carried out in 2016 by the DLR Institute of Propulsion Technology. To correctly represent the surge events, the ducting of the testbed upstream and downstream of the compressor is included in the simulation.The results from the low-order model are compared with measurements from unsteady probes for two surge events at design speed with different downstream plenum sizes. The surge frequency and pressure profiles in time are closely reproduced by the low-order model. Analysis of the unsteady pressure measurement and the acoustic waves modelled by ACRoSS indicates that the surge period is likely to be influenced by the reflection of the initial surge wave in the inlet duct.Using the ACRoSS model, surge can be accurately reproduced both in 3D and 2D. Two-dimensional, axisymmetric simulations are shown to be sufficient for the cases investigated, and surge can be simulated with a computational cost of less than one hour per event using just 40 CPUs. This represents over an order of magnitude improvement in computational power and time required to simulate surge, compared to traditional URANS 3D CFD.

High Speed Compressor based Adder using XOR-XNOR Gate: A Study

High Speed Compressor based Adder using XOR-XNOR Gate: A Study

The Characteristics and Mechanisms of High-Intensity Sound in a High-Speed Multistage Compressor

An experiment with a multistage high-speed compressor is conducted to investigate the high noise with abnormal blade vibration. Different points are selected to monitor the noise in the compressor and the amplitude of blade vibration. The evolution rhythm of sound frequency and sound pressure level against speed is captured. The relation between the vibration and the noise is obtained. A research method based on an acoustic analogy is developed to investigate the characteristics and mechanisms of high-intensity sound in a rectangular cavity pipeline. The calculated distribution of the first four-order acoustic mode inside the rectangular cavity pipe is consistent with the results in the literature, and the maximum calculation error of the acoustic mode frequency value is 2.7%, which certifies the effectiveness of the method. A simplified compressor model is established to study the vortex system and the sound field characteristics of this method when high-intensity sound occurs. The results present the motion law of shedding vortices with high-intensity sound, and the calculation error of the frequency corresponding to the high-intensity sound is 3.6%. The “frequency-locked phase-locked” characteristics (i.e., character frequency) keep constant at a range of velocities, showing similarity with the phenomenon obtained in experiment above, and beta mode forms of Parker are captured. The study in the present paper makes a contribution for the cognition of mechanisms with high-intensity sound in aeroengine compressors.