Axial Flow Research Articles

Low-order MIMO controller for turbomachinery supported by active magnetic bearings

In industry, the operation of turbomachinery supported by active magnetic bearings (AMBs) requires a robust and simple controller to meet increased performance requirements and stringent regulations. This study proposes an innovative low-order Multiple-Input Multiple-Output (MIMO) controller. Its structure is derived from the decentralized augmented Proportional-Integral-Derivative (PID) controller, enhanced with fixed terms in the skew-diagonals of the controller matrix. The resulting controller couples the information acquired by the AMB sensors on the same control axis to enhance the overall performance. The parameters of the new MIMO structure are tuned using a model-based procedure that exploits a non-smooth optimization algorithm, with the rotor model adjusted on experimental measurements to represent the real dynamics of the system. The novel controller performance is evaluated through two case studies: first, an expander-compressor system; second, a centrifugal turbo compressor designed for oil and gas applications, facing challenges associated with the observability and controllability of the second bending mode. The performance is then compared with that obtained using a decentralized augmented PID controller whose parameters have been tuned with the same non-smooth optimization algorithm. The new controller demonstrates a significant reduction in vibration caused by rotor bending modes. For example, in the analyzed case studies, unbalance responses were reduced by up to a factor of 10. Moreover, the proposed controller increases robustness compared to the decentralized case, as demonstrated by the second case study where controllability and observability issues are addressed.

Load split design strategy of tandem stators in a highly loaded micro axial compressor

Load split design strategy of tandem stators in a highly loaded micro axial compressor

Design and Stability Study of a Distortion-Tolerant Axial Compressor Based on an Alternating Stator Layout

To effectively suppress flow separation in the corner regions of a compressor, improve aerodynamic performance, and enhance distortion tolerance, this study focuses on a single-stage high-load transonic axial flow compressor and introduces a novel and effective unconventional stator design known as an alternating stator (AS) vane layout. This study examines the relationship between the AS layout and the flow separation in the corner regions from a fluid dynamics perspective and investigates the enhancement effects of different AS designs on the compressor's aerodynamic performance and stability margin (SM). Numerical investigations indicate that the alternating layout scheme, which is developed by locally adjusting the inlet geometric angle of the stator vanes, can effectively improve the aerodynamic performance and stability of the compressor. Compared to the original compressor design, the scheme with a 12° adjustment in the blade tip's geometric angle significantly increases both the total pressure ratio and efficiency. This scheme also enhances the SM by 34.69%. With this alternating layout, the novel stator arrangement induces differentiation in the flow field structure among adjacent passages. Internally, an alternating separation forms at the top and root corner regions of the adjacent stator passages, effectively preventing extensive flow separation from occurring at the top or root corner regions of the compressor and thereby delaying a compressor stall. When this design is applied to the compressor stage with inlet distortion conditions, the AS scheme with a 12° adjustment in the blade tip's geometric angle effectively improves the compressor's aerodynamic performance and distortion tolerance and holds significant potential for expanding the stable operating range of the compressor with inlet distortion conditions. Relative to the original design, the SM of the AS compressor can be increased by 83.09%.

Response and stall mechanism for axial compressor under rotating inlet distortion

For multi-shaft aero-engines, the downstream compressor inlet will be exposed to rotating inlet distortion once rotating stall occurs in the upstream fan or low-pressure compressor. In this paper, an experimental study is carried out on six axial compressors under rotating inlet distortion, aiming to clarify the effects of rotating inlet distortion and reveal the stall mechanism. The result under rotating inlet distortion shows that the rotational speed of distortion strongly affects the stability of the compressor. Within a certain band of distortion speeds, i.e., in the dangerous distortion speed band, the stability margin of the compressor decreases extremely severely. Comparing the results from the six compressors, it is discovered that the left boundary of the dangerous distortion speed bond coincides with the propagation speed of rotating stall, whereas the right boundary is associated with the distortion angle. When introduced rotating inlet distortion, flow separation is prone to occur in the high-load region, which consequently induces stall disturbance. The reason for the varying stability margin with the distortion speed is that the distortion zone at different speeds affects the spatiotemporal evolution of the stall disturbance. Within the dangerous distortion speed bond, the intensified effect of the distortion zone accelerates the evolution of stall disturbance into rotating stall. At the end of this paper, a model is proposed to explain the impact of distortion speed and distortion angle on compressor stall.

On the early stagnation point during transient acoustic cavitation

We explore an acoustofluidic phenomenon, in an aqueous environment, of an emerging early stagnation point that consistently positions itself at a distance of two times the ultrasonic horn tip diameter 2D, regardless of the tip size. This was initially captured numerically in a two-dimensional domain of horn-type reactors of diameters D = 3, 6, 13, and 16 mm in a 107 × 50 mm cuvette. We deduced that the axial extension of the bubble cluster influences the rate of decay of axial flow; however, it does not affect the stagnation point. Cavitation attenuation was scrutinized by mathematically modeling the time-averaged axial flow during the cavitation transient state and solving the flow using Newman's subroutine. During fast streaming, acoustic force attenuation α decreases exponentially at a maximum rate of ≈1.70 with the doubling of Reynolds number Re. However, an inverse trend was demonstrated by the dimensionless attenuation Γ=−2αD, as it increased by a factor of ≈1.28. Similarly, Γ exponentially increased with the doubling of Re during slow streaming suggesting direct proportionality between Γ and Re. This emphasized the underlying role of the term 2D in amplifying attenuation induced by morphing structures of inertial bubble clusters. Moreover, tracking the bubble population along the horn axis revealed that mushroom-like structures formed under small horn tips have a linear bubble distribution, while cone-like structures under larger tips maintained an exponential distribution. This may suggest that a linear distribution may enhance attenuation and justify the aforementioned trends.

Design, optimization, and aerodynamic interactions of inter-spool duct with an upstream tip-critical transonic axial flow compressor stage

Design, optimization, and aerodynamic interactions of inter-spool duct with an upstream tip-critical transonic axial flow compressor stage

Gas–liquid separation mechanisms and bubble dynamics in a helical axial multiphase flow pump

Gas–liquid separation mechanisms and bubble dynamics in a helical axial multiphase flow pump

Parametric investigation of inlet flow cooling on axial compressor performance in different operating conditions

Parametric investigation of inlet flow cooling on axial compressor performance in different operating conditions

CFD Analysis of Straightener Designs on Overall Performance of the Axial Flow Blood Pump

CFD Analysis of Straightener Designs on Overall Performance of the Axial Flow Blood Pump

Numerical Characterization of an High Pressure Compressor Stage Equipped With a Closed Shrouded Stator Cavity

Abstract In axial compressors, shrouded stator cavity flows are responsible for performance degradation due to their interaction with the power stream. The present paper aims at exploring the possibility of employing a single-stage high-pressure axial compressor as a test vehicle for cavity flows investigations. In a first step, the robustness of the adopted RANS approach is tested against experimental data on the closed-cavity baseline configuration (i.e., no downstream-to-upstream recirculation). In a second phase, the effect of different hub cavities layouts of different levels of realism is numerically investigated. The focus is set on the representativeness of a closed cavity configuration with injection. The cavity flow topology and impact on the overall performance are considered in the analysis. At its final extent, this paper provides numerical and experimental guidelines for the robust assessment of cavity flows topology and performance effects.

Effect of active/passive flow control based on synthetic jet of stator blades on a single stage axial compressor

Effect of active/passive flow control based on synthetic jet of stator blades on a single stage axial compressor

Correction: Impact of Additive Manufacturing Surface Roughness on the Aerodynamic Performance of Axial Compressor Blades

Correction: Impact of Additive Manufacturing Surface Roughness on the Aerodynamic Performance of Axial Compressor Blades

Flow and Heat Transfer in Ribbed Swirl Tubes with a Tangential Inlet Jet for Gas Turbine Blade Leading Edge Cooling

The heat transfer and flow structure behaviors in ribbed swirl tubes with a single tangential inlet jet were widely predicted to be applicable for cooling the leading edge of the gas turbine blade. This study tested two cross-sectional areas under the same length of 500 mm. The essential ratios of rib height and pitch were all set to 0.376 and 10. The ribbed angles of attack were 60° and 90°. The realizable turbulent kinetic energy – epsilon model was adopted for the computational study under the Reynolds number varying from 5000 to 30,000. The results demonstrated axial backflow in the middle of the tube and substantial axial flow in the near wall region. While the longitudinal vortex developed in the case of 60° ribs, significant vortex flow at the tube center, accelerated by the ribs and cross-sectional area, appeared in the case of 90° ribs. In all cases, there was an increase in the heat transfer rate as the Reynolds number rose, and the 90° ribs experienced a pressure penalty greater than 37.4%. In addition, the thermal performance in the Type (A) 90° rib case was approximately 21.2% higher than that of the 60° rib case.

Comparative analysis of different catalytic baskets for dual-bed catalytic reactor based on CFD simulations

Catalytic baskets used to support catalyst beds can have different designs. For industrial practice, reactors with axial and radial gas flow direction through the catalyst bed are commonly used. Based on CFD simulations, the influence of the tail gas distribution in a dual-bed catalytic reactor on the linear gas flow velocity and pressure drop across the catalyst bed was analysed. CFD simulations were performed for the reactor's use in a pilot nitric acid plant for axial-radial and radial catalytic basket designs. The calculation results indicated a significant influence of the basket design on the linear gas flow velocity profile and pressure drop distribution in a dual-bed catalytic reactor. The most advantageous solution was the coaxial arrangement of the catalyst beds without separating them with a space, which can affect the reliability of the reactor. The lowest linear flow velocity and gas flow resistance values in a dual-bed catalytic reactor were obtained for the mixed axial and radial gas flow through the catalysts beds, separated only with a porous baffle.

Flow distribution of supercritical hydrocarbon fuel in parallel regenerative cooling channels under non-uniform heat flux

Regenerative cooling technology is an important approach for thermal protection in scramjet engines. Non-uniform axial and circumferential heat flow distribution on the combustor leads to improper flow distribution, resulting in reduced cooling efficiency and localized overheating, potentially causing thermal protection failure. To effectively utilize the fuel heat sink and enhance cooling efficiency, it is necessary to investigate the mechanism of flow distribution in the channels under different heat flow conditions. This study investigates the flow and heat transfer characteristics in single cooling and parallel channels under various heat flux. The heat transfer characteristics, flow resistance changes, and the influence of heat flux on heat transfer deterioration are analyzed. There are two types of heat transfer deterioration in channels, caused by the inlet effect and the mutation of fuel supercritical properties. Furthermore, the mechanism behind flow deviation induced by non-uniform heat flux in parallel channels is investigated. When a supercritical process occurs, non-uniform heat flux induces temperature deviations, resulting in density distribution variations. This, in turn, influences velocity distribution and leads to disparities in flow resistance distribution. Consequently, flow deviation occurs, and the cracking reaction amplifies flow deviation while reducing temperature deviation.

Structural design optimization and vibration assessment of a base frame for a 3 MW turbo compressor

This study focuses on the design and analysis of a base frame for a 3 MW turbo compressor, aiming to develop a robust and reliable structural framework. The design process included comprehensive simulations, incorporating static stress-strain and dynamic vibration analyses to assess the base frame’ performance under operational conditions. The static analysis evaluated the total deformation and strain behavior of the base frame, ensuring it can withstand the maximum load without yielding or excessive deformation. Dynamic vibration analysis was performed to identify the natural frequencies and potential resonance issues, minimizing the risk of vibrations that could compromise operational stability. Results from the static analysis revealed that the initial design exhibited a maximum total deformation of 0.24 mm, which was reduced to 0.09 mm in the final design—a 62.5% improvement. Elastic strain values were within safe operational limits for both designs. The effective mass ratio analysis showed significant results at frequencies close to 0 Hz, with negligible impact across the operating frequency range. Based on these analyses, an optimized base frame model was developed, meeting the design criteria for mechanical strength and vibrational stability. The results highlight the importance of integrating deformation, strain, and vibration assessments in the structural design of heavy-duty turbo compressor base frame, contributing to enhanced durability and performance.

Critical Factors in Parabolic Nozzle Design and Performance Analysis with CFD

Abstract This study presents a comprehensive analysis of contoured nozzle designs using the Method of Characteristics (MOC) and Fluent simulations. The study aims to compare the performance and flowfield predictions of these methods and explore the influence of various design param- eters on nozzle performance. Initial investigations validate the MOC algorithm’s accuracy against commercial software, highlighting its rapid computational capability despite limita- tions in handling real gas effects. Fluent simulations consistently predict slightly lower specific impulse values due to differing exit pressure predictions but align closely with MOC results in inviscid flow conditions. The research explores the role of the initial circular arc in defin- ing the nozzle’s expansion and straightening sections, finding that smaller circular arcs create larger property gradients, necessitating quicker expansions and leading to potential isentropic losses, which were almost imperceptible in the Fluent case, in fact, a more axial flow was deliv- ered. Variations in design parameters, such as the contour’s exit angle and cone nozzle fraction, demonstrate their impact on nozzle performance, with higher exit angles generally improving specific impulse, contrary to expectation. For some pairs of design options, longer nozzles al- low smoother expansions, resulting in lower average exit angles and improved specific impulse. The findings emphasize the contemporary relevance of the MOC for preliminary nozzle studies, highlighting the balance between accuracy and computational cost.

Investigating the cooling effect of the inlet flow on the axial compressor performance in different operating conditions

In this article, the compressor performance in wet compression conditions is compared with that of dry compression. Wet condensation has been done through droplets with one-micron diameter and a three percent mass flow rate. The flow inside the compressor is steady and three-dimensional, using the software ANSYS CFX has been simulated. In the case of wet compression, the discrete phase transition model has been used along with the application of active input forces from the continuous phase. The comparison of the present simulation results for dry states with the experimental data reports a good agreement. The results indicate that applying wet compression in the compressor improves adiabatic efficiency by 7.21% in near-stall conditions, 5.21% in design conditions, and 1.78% in choking conditions. The use of wet compression significantly reduces the mass flow rate under operational conditions of choking, it is not recommended to use this method in the operational conditions of choking in the compressor. The results indicate that the compressor stable performance range is reduced by 18.31% with wet compression compared to dry compression, which is unfavorable. Also, the stall margin of the process of wet compression and dry compression was obtained as 2.38% and 8%, respectively. The results of the study showed that with flow injection, the stall margin of the wet compression process was reduced by 5.62% compared to the dry compression process.

Electro-osmotic flow in channel: effects of superhydrophobic surface structures sizing

Abstract Numerical study on electro-osmotic flow over superhydrophobic transverse grooves and ribs have been explored. With uncharged liquid-gas interface, smaller electro-osmotic axial flow is attained. The electro-osmotic axial flow is found to be significantly influenced by the gas area fraction and the normalized groove-rib spacing. In the presence of the liquid-gas interfaces, slip flows are observed over these interfaces, consistent with that reported in pressure-driven flow. As the flow is permitted in the vicinity of the liquid-gas interface, flow redistribution is observed along the channel. Higher bulk flow with reducing flow magnitude is observed close to the wall when solid wall is present, and vice versa. Despite the alteration of the axial flow, conservation of flow along axial direction is attained. To estimate the normalized electro-osmotic axial flow for this flow condition, a new correlation formulation is proposed to accurately predict the averaged axial flow magnitude for different values of gas area fraction and normalized groove-rib spacing in the range between 0.1 and 4.

Advancement of the Dragon Heart 7-Series for Pediatric Patients With Heart Failure.

Safe and effective pediatric blood pumps continue to lag far behind those developed for adults. To address this growing unmet clinical need, we are developing a hybrid, continuous-flow, magnetically levitated, pediatric total artificial heart (TAH). Our hybrid TAH design, the Dragon Heart (DH), integrates both an axial flow and centrifugal flow blood pump within a single, compact housing. The axial pump is embedded in the central hub region of the centrifugal pump, and both pumps rotate around a common central axis, while maintaining separate fluid domains. In this work, we concentrated our design and development effort on the centrifugal blood pump by performing computational modeling. An iterative process was employed to improve the DH design. The pressure generation, scalar stress levels, and fluid forces exerted on the magnetically levitated impellers were computationally estimated. A shaft driven centrifugal prototype was also manufactured and tested using a hydraulic flow loop circulating a water-glycerol blood analog. Pressure and flow performance of the pump prototype was measured for a given rotational speed for comparison to computational predictions. Our design achieved the target pump pressures of 60-140 mm Hg for flow rates of 1-5 L/min, and strong agreement in pressure rise was demonstrated between the experimental data and simulation results (less than 10% deviation on average). Fluid stress levels were, however, found to exceed thresholds in the outflow region of the pump, and fluid residence times were less than 600 ms. The findings of this work demonstrate that the more compact, next-gen DH's centrifugal pump design is able to achieve pressure-capacity requirements. Next steps will require a focused strategy to reduce hemolytic potential and to integrate magnetic suspension components for full rotor levitation.