Total Distortion Research Articles

Aerodynamic investigation of an S-shaped intake employing sweeping jet actuators based on proper orthogonal decomposition

The central curvature change of the S-shaped intake exacerbates the three-dimensional flow separation, resulting in total pressure and swirl distortions at the outlet. In this paper, an efficient active flow control technique, the sweeping jet actuator, was applied to control flow separation. The instantaneous characteristics of the flow field inside and outside the actuator were revealed by using validated numerical simulation methods. In addition, the effect of the sweeping jet on the aerodynamic performance of the S-shaped intake was investigated. Proper orthogonal decomposition (POD), an analysis method used to extract the main feature components of data, was applied to decompose the flow field structure at the S-shaped intake outlet in this study. The results highlight the external flow field characteristics of the actuator, with a jet sweeping range of up to ±40° and a sweeping frequency of 1 500 Hz, corresponding to a Strouhal number of 0.018. When the jet momentum coefficient is only 0.116%, the total pressure loss coefficient and pressure distortion index are reduced by 5.6% and 24.76%, respectively. This study demonstrates the critical role of momentum injection and discretization in inhibiting flow separation in the channel. The POD-based analysis indicates that a sweeping jet with high momentum can significantly enhance the energy in the flow passage and reduce the vorticity intensity of the first three modes. The stable mode structures exist near the outlet, exhibiting excitation frequency and frequency-doubling properties. The findings of this research provide essential input conditions for subsequent distortion studies.

Stall Inception Analysis on Axial Compressors With Different Rotor Loading Distributions Under Radial Inlet Distortions

Abstract Stability studies were conducted on a single-stage, low-speed compressor with different rotor loading-distribution designs under a uniform inlet, 10% intensity, and 20% intensity total tip pressure distortion inlet conditions via numerical calculations, theoretical model predictions, and experimental methods. The steady numerical performance was in basic agreement with experimentally measured performance. The theoretical prediction model showed an error within 1.5%, which is less than that of the steady numerical calculation. The total tip pressure distortion reduced flow stability. Conversely, the design of moving the rotor loading axially rearward significantly improved the flow stability. The blade loading analysis showed that the radial distortion caused a radial redistribution of rotor loading. The increase in the rotor-tip loading due to tip distortion was the main reason for the reduced flow stability. In contrast, the design of moving the rotor loading axially rearward reduced the rotor-tip leading-edge loading, enhancing the flow stability. Moreover, an analysis of the unsteady flow validated the findings of the blade loading analyses. It was found that the periodic evolution of the tip leakage vortex (TLV) had an adverse effect on flow stability. In addition, the modified rotors could prevent the tip leakage flow (TLF) from spilling from the leading edge and prevent the interaction of different diffusing regions, decreasing the probability of flow separation.

Unsteady numerical study on the effects of inlet distortion parameters on the aerodynamic instability of the centrifugal compressor

Total pressure inlet distortion significantly impairs the aerodynamic performance and flow stability of centrifugal compressors. This paper presents a full annulus unsteady numerical simulation to investigate the flow mechanisms under varying inlet distortion parameters. First, the flow characteristics of a uniform inflow is studied as a baseline for comparison with distorted inlet conditions. Results indicate that the interaction between shock waves and tip leakage flow is a primary factor leading to aerodynamic instability. The instability signal in this region is detected through fast Fourier transform and frequency slice wavelet transform (FSWT). Under near stall condition, different distortion parameters are set to research the effects on aerodynamic performance, flow mechanisms, and instability characteristics. The results reveal that distortion intensity has the most significant impact, causing a maximum stall margin loss of 55.43%, followed by distortion angle with a maximum stall margin loss of 43.02%. Total pressure inlet distortion leads to a deterioration in aerodynamic performance, primarily due to premature occurrences of unstable flow phenomena such as leading-edge spillage and trailing-edge backflow. The onset key features triggering aerodynamic instability are identified as leading-edge spillage vortex, tip leakage vortex, and passage vortex. The continuous disintegration of the tip leakage vortex results in low-frequency fluctuating energy exhibiting multipeak characteristics, with pulsation peaks centered around 0.5 BPF, related to the spike stall of the compressor. The high-energy frequency band dissipates over time in the time–frequency spectrum, as shown by FSWT results, indicating the characteristics of instability in the flow.

Design and aerodynamic performance study of subsonic Y-shaped inlet

Abstract A Y-shaped inlet with a quadrate import was designed by the super-ellipse method in this paper, and according to the variation pattern of the cross-section of the inlet, the variation pattern of the short and long axis of the super-ellipse was deduced. For many different flight situations, the numerical simulations of the Y-shaped inlet were made. The result shows (1) If 0.2≤Ma≤0.8, the total pressure recovery coefficient exceeds 0.96, and the total pressure distortion coefficient is close to 0.1, meeting the criterion of the design; (2) When Ma=0.8, for many different attack angle α=-4°∼22°, the total pressure recovery coefficient is close to 0.97, reaching the level of practical application, and it has little impact on total pressure recovery coefficient and the distortion coefficient. (3) These results demonstrate high total pressure recovery and low distortion coefficients across various flight conditions, indicating its potential for practical applications and future inlet designs.

Free energy formulae for confined nematic liquid crystals based on analogies with Kirchhoff–Routh theory in vortex dynamics

Active nematics are influenced by alignment angle singularities called topological defects. The localization of these defects is of major interest for biological applications. The total distortion of alignment angles due to defects is evaluated using Frank free energy, which is one of the criteria used to determine the location and stability of these defects. Previous work used the line integrals of a complex potential associated with the alignments for the energy calculation (Miyazako and Nara 2022 R. Soc. Open Sci . 9 , 211663 (doi: 10.1098/rsos.211663 )), which has a high computational cost. We propose analytical formulae for the free energy in the presence of multiple topological defects in confined geometries. The formulae derived here are an analogue of Kirchhoff–Routh functions in vortex dynamics. The proposed formulae are explicit with respect to the defect locations and conformal maps, which enable the explicit calculation of the energy extrema. The formulae are applied to calculate the locations of defects in so-called doublets and triplets by solving simple polynomial formulae. A stability analysis is also conducted to detect whether defect pairs with charges ± 1 / 2 are stable or unstable in triplet regions. Our numerical results are shown to match the experimental results (Ienaga et al. 2023 Soft Matter 19 , 5016–5028. (doi: 10.1039/d3sm00071k )).

Impact analysis of uncoordinated electric ferry charging on distribution network

The maritime sector significantly contributes to greenhouse gas emissions, and implementing electric marine vessels can mitigate this emission. Replacing conventional ferries with EFs (Electric Ferries) necessitates dockyard charging stations, making it crucial to analyze the EF's charging impacts on the shore-side distribution network. This research examines the potential effects of uncoordinated EF charging on a regional Australian distribution network. Using OpenDSS (Open Distribution System Simulator) software, power flow impact analysis is conducted on a selected simulated distribution network, integrating BESSs (Battery Energy Storage Systems) as representation of proposed charging stations. The load demand is increased to 50 % and 80 %, given the actual demand is 15 % of the transformers’ capacities. The power flow results without BESSs serve as the base case. In uncoordinated mode, bus voltages decrease by 1 %-3 %, and load currents increase by 2 %-3.5 % compared to the base case. Additionally, lines and transformers near BESS-connected buses see a 1 % rise in power flow with increased total power consumption and loss. THD (Total Harmonic Distortion) and TDD (Total Demand Distortion) are over 5 % and 18 % in uncoordinated charging, which exceeds harmonics limits according to IEEE 519–2022 standards. These results may provide valuable insights for installing EF charging stations in distribution networks.

Numerical investigation of welding deformation diminution for double shell structure using the layered inherent strain

Cyclotron is a key scientific tool and indispensable research platform for conducting cutting-edge research in nuclear equipment development as well as innovative applications of nuclear technology. The shell component has a double-layer thick-walled structure with intricate ribs and high-density, full-penetration welded joints. The mitigation of welding deformation is of profound significance to the performance of the cyclotron. The thick plate joint has many welding layers which will be divided into several steps to complete the backing, filler, and cap welding. The equivalent transverse and longitudinal plastic strains of different layers were extracted by the thermo-elastic-plastic method. The welding deformation generated by each layer of weld can be predicted by using the equivalent plastic strain, and the total distortion can be accumulated layer by layer. Numerical simulation and experimental studies were conducted on the welding deformation of the double shell specimen, and the welding sequence and design of the welding fixture were discussed in detail. The digital photogrammetry system was used to monitor the deformation state of the welded parts in real-time. The measured deformation was compared with the simulation results. Ultimately, the deformation of the specimen is controlled at 2.64 mm. The proposed method can flexibly evaluate the impact of each welding layer on welding deformation for multiple welds, which can provide technical guidance for cyclotron engineering manufacturing.

Aerodynamic optimization of double S-duct caret intake by self-adapting non-dominated sorting genetic algorithm

The caret intake could not only provide compressed airflow to the aircraft engine stably but also should have applicable radar stealth performance. Radar stealth means that the echo intensity of the intake should be low when detected by radar, which could be measured by radar cross section (RCS). The airflow distribution of the double S-duct caret intake was numerically optimized to improve aerodynamic performance, with radar stealth performance as constraints. Self-adaptive genetic algorithm and Kriging model were used to improve the optimization efficiency. There could be multiple boundary-layer separations in the S-duct caret intake, resulting in obvious total pressure distortion at the outlet and secondary flow. To suppress these adverse airflow phenomena, the optimization of the double S-duct intake was defined as a problem with two targets and multiple constraints. By defining the probabilities of selection and variation as functions of the iteration number and the fitness, the self-adapting non-dominated sorting genetic algorithm can be applicable for such a problem. Using the Kriging model, which was proven to have satisfactory accuracy in predicting performance parameters, an optimized intake with both excellent aerodynamic and stealth performance was obtained, with a 30% reduction in DC60 value and a 47% reduction in SC60 value compared to the intake before optimization.

Numerical Investigation of Aero-Optical Distortions from High-Speed Turbulent Boundary Layers

Wall-modeled large-eddy simulations of turbulent boundary-layer flows over a flat plate at Mach 3.5, 7.87, and 13.64 were carried out, and the aero-optical distortions resulting from density fluctuations were investigated. The conditions for the Mach 3.5 case match those of a direct numerical simulation in the literature. The Mach 7.87 conditions are representative of the Hypersonic Wind Tunnel at Sandia National Laboratories, and the Mach 13.64 conditions match those of the Arnold Engineering Development Complex Hypervelocity Tunnel 9. The wall-modeled large-eddy simulations were validated using available experimental and DNS reference data. The normalized root-mean-square optical path difference for all three cases is in good agreement with respective data obtained from reference direct numerical simulations and experiments (within 1.53% for M∞=3.5, 1.25% for M∞=7.87, and 12% for M∞=13.64, compared to numerical data). Above M∞=5.0, the normalized path difference obtained from the simulations is above the value predicted by a semi-analytical relationship by Notre Dame University. With increasing Mach number, the bulk contribution to the total optical distortion shifts toward the boundary-layer edge. In addition, a proper orthogonal decomposition reveals that the nature of the dominant density fluctuations, which are located near the boundary-layer edge, changes from three-dimensional to two-dimensional. Understanding how the coherent structures contribute to the optical path difference may pave a way toward devising active flow control strategies geared toward a reduction of the optical path difference.

Inlet distortion of a rear engines concept aircraft and its effect on a fan

Boundary layer ingesting technology (BLI) has been widely developed, but the relevant research on the rear engine concept (REC) still needs to be expanded, especially for the different characteristics of the total pressure distortion and the swirl distortion. The paper investigates the BLI inlet distortion of a REC aircraft and its effect on the fan performance by commercial software CFX. Numerical simulation is conducted to obtain the inlet distortions first and the impact of these distortions on the characteristics of NASA rotor 67 is evaluated. Results show that the distortion tends to increase with the increase of the fluid redistribution effect of the fuselage-propulsor fusion part. Comparatively, the inlet distortion caused by AOS has a more significant influence on the performance of the fan. The swirl distortion is concentrated in the edge region of AIP. The total pressure distortion which coupled higher level of swirl has a more significant effect and is offset in the circumferential direction with the continuation effect of distortion in other leaf channels not obvious.

Experimental investigation of the aerodynamics of a UAV inlet with double 90° bends

Unmanned aerial vehicle (UAV) inlets commonly have a compact S-shaped inlet structure for the sake of stealth. Most of the current studies on subsonic inlets have focused on S-shaped configurations with relatively gentle transitions of the flow channel. In this study, the aerodynamic performance and swirl flow characteristics of a UAV inlet, which has double 90° bends in the duct and is integrated with an aircraft fuselage and a volute, are studied both experimentally and numerically. The influences of angle of attack, sideslip angle, AIP (Aerodynamic Interface Plane) Mach number, and freestream airspeed are analyzed. A measure of adding two deflectors in front of the first bend and a baffle at the bottom of the volute is proposed to improve the total pressure distortion and swirl distortion characteristics of the inlet. Finally, a practice of shape optimization is performed to further improve the aerodynamic performance and swirl flow characteristics on the basis of the baseline configuration. The results indicate that the maximum and minimum total pressure recovery coefficients of the baseline inlet configuration are 0.982 and 0.969, respectively, as well as the maximum total pressure distortion index of –0.0814 and the maximum swirl distortion index of 32.1 % under normal operating conditions. Through a total of 8 iterations of optimization, the total pressure recovery coefficient is eventually improved by 0.21 % of that of the baseline configuration, as well as the total pressure distortion index, swirl distortion index and maximum swirl angle reduced by 43.6 %, 4.6 % and 11.1 %, respectively.

Effect of Fluid-Solid-Thermal Coupling on the Performance of S-Duct in Hypersonic Inlet

This article studies the effects of multi-field coupling on the S-duct by a self-developed fluid-solid-thermal bi-directional coupling code. The flow field inside the S-duct is complex with various vortices as the airflow turns. The results indicate that the total pressure recovery coefficient and the total pressure distortion index (DI) change rapidly at the beginning and reach a steady state at about 100s. The σ decreases by 12%, and the DI increases by 2% compared to the starting point. Structural deformation, size of separation zone, and wall temperature changes over time, and stabilizes around 100 s. The deformation mainly occurs at the outlet, with a maximum displacement of 3.65 mm for up-warping and 4.60 mm for expansion. The values of the total pressure recovery coefficient with S-ducts of bias distance with 20, 40, and 60 mm drop by 2.5%, 8.6%, and 12.1%, and the values of the total pressure distortion index increases with S-ducts of bias distance with 20, 40, and 60 mm increase by 10.8%, 15.1%, and 1.7%. The S-duct with a larger aspect ratio has larger separation zones and a smaller total pressure recovery coefficient.

Measurement and analysis of the distortion of factor prices in China.

This study uses the extended C-D production function method to measure the total distortion of factor prices and the distortion of capital, labor and land factor prices in China's provinces and cities. The results indicate that between 2000 and 2019, due to factors such as the dual economic structure between urban and rural areas, human intervention in the capital market, and lagging land marketization reform, both capital and land factor prices showed negative distortions, except for positive distortions in labor factor prices. The degree of this positive distortion began to gradually weaken, and even showed a negative distortion trend in some regions.

High-performance passive impedance network model for grid-tie inverters in steady state

Nowadays, the high penetration of inverter-interfaced distributed energy resources (DERs) has raised a well-founded concern regarding the interaction of these devices with the upstream grid. The harmonic interaction phenomenon between these players can be described by time-domain simulations, using high computational effort switched and/or average models often impractical for large power systems. This paper proposes an innovative low-computational-burden model named passive impedance network (PIN), capable of accurately representing DERs in electric power systems (EPSs). Through passive RLC components, the PIN model can describe DER dynamic behavior at a certain frequency of interest, making it able to represent harmonic flow within the EPS nodes. The proposed model is compared with the switched model, average model, and an experimental setup under different grid distortions and injected current profiles. A comparison of the total demand distortion (TDD) between the proposed PIN model and the experimental results is carried out. The effect of DER parameter deviations on PIN model accuracy is addressed, in which the absolute error of the PIN model TDD values are 0.65% and 0.06% for the experimental and switched model, respectively. Besides, the PIN model presents an improved computational performance compared to the time-domain-based switching model, requiring 99% less computational burden.

Ice Object Exclusion Characteristics of Turboshaft Engine Inlet under Helicopter/Inlet Integration Conditions

In this study, the influence laws of different parameters on the exclusion characteristics of hailstone and ice flake, and on the aerodynamic performance of the inlet are studied by numerical method. The motion of the hailstone and ice flake is simulated using the 6-DOF method. Results show that the inhalation of hailstone in the inlet decreases total pressure distortion by about 20%, and the total pressure recovery coefficient is essentially unchanged. Icing of the upper lip decreases the total pressure distortion of the inlet by about 22%, and the total pressure recovery coefficient decreases by 0.6%. The ice flakes on the inner and outer lip, when shed and brake by collision with the center body, will cause damage to the engine duct. The shedding and breaking of ice flake at an angle of 150° to the lip can result in a large amount of ice flake debris entering the engine duct, threatening the performance and structure of the engine in the rear. The motion characteristics of hailstone and ice flake under helicopter fuselage/rotor/inlet integration conditions are revealed. It also provides a reference on the numerical methods for the numerical study of hailstone/ice flake exclusion characteristics of helicopter fuselage/rotor/inlet integration conditions.

Unsteady Aerodynamic Forcing Due to Distortion in a Boundary Layer Ingesting Fan

Abstract Boundary Layer Ingestion (BLI) is a concept with the potential to reduce energy consumption needed for aircraft propulsion. For the fan this results in a need to work well in an environment of increased continuous distortion. The objective of this study is to increase the understanding of unsteady aerodynamic forces due to total pressure distortion in a BLI fan. This is done by using computational fluid dynamics to analyze a fan design intended for a BLI installation. Results include low subsonic to transonic operating speeds and distortion in a wide range of wave numbers. The forcing exhibits a significant dependency on the aeroacoustic cut-on/cut-off condition. This is in particular true at part speed where the normalized unsteady force rises sharply before dropping suddenly as the corrected speed or engine order increases. Unsteady pressure in the blade passage is observed to exhibit the same increase in level followed by a sudden drop once the cut-on limit is passed and undamped pressure waves propagating out from the blade row appear. The unsteady forces on the first three modes exhibit different sensitivities to the distortion wavelength but all are affected by the acoustic condition. By comparing results for the reference fan to a similar fan design with a higher blade count the cascade properties of the blade row are found to dominate the interaction. A result of this is that a higher blade count fan may be less affected by the distortion, and be less prone to propagate noise due to low engine order distortion.

Association of cortical gyrification, white matter microstructure, and phenotypic profile in medication-naïve obsessive-compulsive disorder.

Obsessive-compulsive disorder (OCD) is thought to arise from dysconnectivity among interlinked brain regions resulting in a wide spectrum of clinical manifestations. Cortical gyrification, a key morphological feature of human cerebral cortex, has been considered associated with developmental connectivity in early life. Monitoring cortical gyrification alterations may provide new insights into the developmental pathogenesis of OCD. Sixty-two medication-naive patients with OCD and 59 healthy controls (HCs) were included in this study. Local gyrification index (LGI) was extracted from T1-weighted MRI data to identify the gyrification changes in OCD. Total distortion (splay, bend, or twist of fibers) was calculated using diffusion-weighted MRI data to examine the changes in white matter microstructure in patients with OCD. Compared with HCs, patients with OCD showed significantly increased LGI in bilateral medial frontal gyrus and the right precuneus, where the mean LGI was positively correlated with anxiety score. Patients with OCD also showed significantly decreased total distortion in the body, genu, and splenium of the corpus callosum (CC), where the average distortion was negatively correlated with anxiety scores. Intriguingly, the mean LGI of the affected cortical regions was significantly correlated with the mean distortion of the affected white matter tracts in patients with OCD. We demonstrated associations among increased LGI, aberrant white matter geometry, and higher anxiety in patients with OCD. Our findings indicate that developmental dysconnectivity-driven alterations in cortical folding are one of the neural substrates underlying the clinical manifestations of OCD.

Attenuation of Inlet Distortion Effects on Fans Using Asymmetric Inlet Guide Vanes

Abstract This research proposes and preliminarily analyzes a novel concept to passively reduce the negative impact of deep inlet distortion on the fan of an aero-engine. It consists of placing a row of non-axisymmetric inlet guide vanes (IGVs) just upstream of the fan rotor to induce a spatially varying swirl distribution. The swirl distribution is tailored so as to reduce flow incidence in the distorted flow region and increase it in the undistorted flow region to decrease the fluctuation in aerodynamic force on the fan blades under large inlet distortion that can lead to blade failure, as well as attenuate the negative effect of flow non-uniformity on fan/engine aerodynamic performance. A computational study is carried out on a high-speed (transonic) fan rotor (NASA Rotor 67) from a published distortion study using full-annulus unsteady 3D computational fluid dynamics (CFD) simulations. The asymmetric IGV is designed through a process of manual iterations and CFD simulations to take into account the change in flow redistribution with IGV geometry. The asymmetric IGV design, though not optimized, reduces the aerodynamic force variation amplitude by around two-thirds. Moreover, it allows the fan to recover over half of the loss in total pressure rise due to inlet distortion. The asymmetric IGV is also able to reduce the total pressure distortion at the fan rotor exit. Spanwise analysis indicates that the effectiveness of the asymmetric IGV can be improved on all three metrics if better 3D IGV shaping is performed.

Innovative hierarchical control of multiple microgrids: Cheetah meets PSO

The expansion of microgrids (MGs) comes from the increasing integration of renewable energy resources (RES) and energy storage systems (ESs) into distribution networks. However, effective integration, coordination, and control of Multiple Microgrids (MMGs) during energy transition from microgrid to grid, and vice versa presents a formidable challenge. This arises from the necessity to ensure smooth operation, coordination, and control of MMGs for stability and efficiency during transitions. The dynamic operation of MMGs due to intermittent renewable energy in microgrids and load variations presents an additional challenge for hierarchical control techniques. This paper provides an Artificial Intelligent (AI)-based control technique and introduces an innovative hybrid optimization technique, denoted as HYCHOPSO, derived from the fusion of Cheetah Optimization (CHO) and Particle Swarm Optimization (PSO) techniques, and the quantitative findings of extensive benchmark testing, constitute key aspects of novelty. The strategic choice of this novel optimization technique, coupled with a Proportional-Integral (PI) controller, provides key insights. HYCHOPSO is tested within benchmark functions and reaches its optimal score before 50 iterations as compared with optimization algorithms namely CHO, GWO, PSO, Hybrid-GWO-PSO, and SSIA-PSO which reaches after approximately 200 iterations. HYCHOPSO consistently exhibits the lowest mean values, indicating its robust convergence capabilities. The proposed control technique results in a significant reduction of the microgrid's Current Total Demand Distortion to 1.1%, meeting acceptable limits for a 600 V-bus According to IEEE519–2014 standard, even under nonlinear loads. Additionally, precise regulation of voltage and frequency is achieved with0.19%−+ deviations and a frequency overshoot of 1.9%. Furthermore, optimization contributes to seamless energy transition from microgrid to grid, achieving synchronization in less than 5 s. This enhances the real application's reliability, flexibility, scalability, and robustness. Furthermore, HYCHOPSO is introduced as an AI-based technique to facilitate control parameter design under dynamic conditions, with substantial simulation cases demonstrating control feasibility

Influence of combinational distortion generator geometrical parameters on the steady and dynamic components of the total pressure distortion

To construct a method for designing a total pressure distortion generator with adjustable, steady, and dynamic components, we experimentally investigated the influences of combinational distortion generator geometrical parameters on the steady and dynamic components of the total pressure distortion based on an indraft wind tunnel. Different types of annular plates and cylindrical rods were installed upstream of a traditional baffle total pressure distortion generator; the total pressure distortion was then measured using rotatable total pressure rakes. The installation of cylindrical rods upstream of the baffle plate could maximally reduce the ratio of steady and dynamic components of total pressure distortion by 30%. Increasing the number and height of the rods, as well as the axial distance between the rod and baffle plate, were effective methods of reducing the steady components of total pressure distortion. Similarly, changing the geometrical parameters of the annular plate was also an effective method for adjusting the ratio of steady and dynamic components of total pressure distortion. The ratio of the steady and dynamic components of total pressure distortion first experienced a decrease and then increased variance law with the increase in the height and circumferential scale of the annular plate. During this procedure, the steady and dynamic components ratio of total pressure distortion could be maximally reduced by 24% and maximally increased by 20%.