Distortion Index Research Articles

Experimental and numerical investigation of an S-shaped duct using pulsed jet actuators with multiple angles

The complexity and twistiness of the ultra-compact S-shaped ducts with high curvature aggravate the internal flow separation, which affects the intake efficiency. An advanced flow control technology, pulsed jet actuators (PJAs), was implemented to improve the flow condition in the S-shaped duct at a Mach number of 0.4. Based on the considerable control effect obtained from the experimental studies, the influence of the pulsed jet angles on the S-shaped duct was further investigated by utilizing the unsteady Reynolds-averaged Navier–Stokes equations (URANS). The jet angles as a research parameter were set to 15°, 30°, 45°, 60° and 75°, respectively. Moreover, steady jet schemes were adopted to reveal the unsteady flow control mechanism of the pulsed jet. The results showed that the overall performance of the S-shaped duct with the pulsed jet was improved, mainly attributed to the additional kinetic energy and dispersion. The total pressure loss coefficient and distortion index at the aerodynamic interface plane (AIP) were decreased by 7 % and 2.9 % when the pulsed jet angle was 30°. Furthermore, the temperature distortion was significantly improved, with a maximum temperature rise rate of −87.59 K/s. It is concluded that the suitable penetration of the mainstream is the prerequisite for achieving the best flow control effect.

Investigation of the Stability Criterion for Axial Compressor under Circumferential Total Pressure Distortion

The distorted inlet flow that is a widespread flow phenomenon in compressors not only reduces the compressor performance but more seriously deteriorates the compressor stability, thus threatening flight safety. However, quantitatively determining the stability boundary is challenging due to the complexity of the distorted inlet flow. The effective static-pressure-rise coefficient in the stability criterion from Koch, a stability analysis method under clean inlet flow, was applied to explore the compressor stability under circumferential total pressure distortion. Using a series of single-stage axial compressor experiments for aspect ratio and solidity, this study investigated the influence of the distortion index on compressor stability. Subsequently, based on the analysis method under clean inlet flow, a new stability criterion under circumferential total pressure distortion was established to determine quantitatively the stability boundary. In addition, the stability criterion for determining the stability boundary was combined with the body force model for calculating the compressor performance to simulate a five-stage axial compressor under 120° total pressure distortion, and the results were in agreement with the experimental data to verify the stability criterion. Numerical simulation was used to show the internal flow field in the compressor, analyze the load at each stage, and identify the instability stage that induces stall, which can provide a reasonable solution for determining the stability boundary of a multistage axial compressor under circumferential total pressure distortion. The combination can serve as a convenient preliminary design tool to evaluate compressor stability using fewer computational resources.Practical ApplicationsMost stability investigations adopt simple methods such as numerical divergence and specified parameters under circumferential total pressure distortion, which makes the stability boundary inaccurate. Since the stability analysis methods under clean inlet flow have been studied more deeply so far compared to that under distorted inlet flow, a new stability analysis method under circumferential total pressure distortion is established to quantitatively determine the stability boundary based on the stability analysis method under clean inlet flow. Therefore, in the preliminary design phase, the stability analysis method is combined with the model for calculating the compressor performance to scientifically evaluate the stability of the multi-stage axial compressor under circumferential total pressure distortion. Also, the combination simply requires fewer computational resources than the millions of grids in commercial software.

Prediction of soil moisture using BiGRU-LSTM model with STL decomposition in Qinghai-Tibet Plateau.

Ali Network data based on the Qinghai-Tibetan Plateau (QTP) can provide representative coverage of the climate and surface hydrometeorological conditions in the cold and arid region of the QTP. Among them, the plateau soil moisture can effectively quantify the uncertainty of coarse resolution satellite and soil moisture models. With the objective of constructing an "end-to-end" soil moisture prediction model for the Tibetan Plateau, a combined prediction model based on time series decomposition and a deep neural network is proposed in this article. The model first performs data preprocessing and seasonal-trend decomposition using loess (STL) to obtain the trend component, seasonal component and random residual component of the original time series in an additive way. Subsequently, the bidirectional gated recurrent unit (BiGRU) is used for the trend component, and the long short-term memory (LSTM) is used for the seasonal and residual components to extract the time series information. The experiments based on the measured data demonstrate that the use of STL decomposition and the combination model can effectively extract the information in soil moisture series using its concise and clear structure. The proposed model in this article has a stable performance improvement of 5-30% over a single model and existing prediction models in different prediction time domains. In long-range prediction, the proposed model also achieves the best accuracy in the shape and temporal domains described by using dynamic time warping (DTW) index and temporal distortion index (TDI). In addition, the generalization performance experiments show that the combined method proposed in this article has strong reference value for time series prediction of natural complex systems.

Manipulating lattice distortion to promote average thermoelectric power factor in metavalently bonded AgBiSe2

Local off-centering of atoms generally leads to high Grüneisen parameters and thus low lattice thermal conductivity, which is considered to be favorable for thermoelectric materials. Nevertheless, such severely distorted local structures may cause strong scattering for electrons and poor electrical performance. Here we demonstrate the relationship between thermoelectric properties and local structure in AgBiSe2 dual alloying with PbTe. It is disclosed that the introduction of Te anions in cubic (AgBiSe2)1−x(PbTe)x can release the distortion index of Bi/Ag/Pb cations in a octahedral shell, which substantially improves the local symmetry and meanwhile the weighted mobility in relevant alloys. More interestingly, it is elucidated that dually-alloyed AgBiSe2 displays a metavalent bonding character, first time reported in n-type cubic TE materials, as collectively verified by atomic coordination number, anomalously increased optical dielectric constant, moderate electrical conductivity, and large Grüneisen parameter. Consequently, a record-high average power factor of 0.52 mW m−1 K−2 between the measurement temperature interval, and a peak zT value of 0.92 at 800 K is obtained for metavalently bonded (AgBiSe2)0.75(PbTe)0.25.

Numerical and Experimental Studies on an Aerodynamic Distortion Grill

An aerodynamic distortion grill is employed to create non-uniform flow from arbitrary uniform upstream flow conditions. Such grills find widespread use in aerodynamic testing applications to generate non-uniform flow conditions. In this paper, the numerical results of the distortion created by one such aerodynamic distortion grill are reported. The computational results were validated against the experimentally observed distortion indices. Further, parametric numerical studies were done by varying the inlet turbulence intensity and by scaling up the geometry of the flow system.

Study on Aerodynamic Design of the Front Auxiliary Inlet

Submerged inlets have been widely used in advanced aircraft due to their excellent stealth characteristics, but they also suffer from poor aerodynamic performance. To improve the aerodynamic efficiency while maintaining stealth capabilities, this paper proposes a design scheme for a front auxiliary inlet with an inlet grille. The front auxiliary inlet is connected to the main inlet to form a composite inlet system. The low-energy upstream airflow that accumulates at the inlet is guided by the front auxiliary inlet to flow into the mainstream, resulting in a stable and high-quality airflow. A certain type of cruise missile was used as the research subject, and intake systems with and without front auxiliary inlets were constructed to compare the inlet performance of the two configurations using the CFD method. Additionally, a sensitivity analysis of the main design parameters of the front auxiliary inlet was carried out. The study reveals that a reasonable design of the front auxiliary inlet can prevent low-energy airflow, which accumulates on the missile body surface, from directly entering the inlet. Moreover, the front auxiliary inlet can inject additional mechanical energy into the low-energy airflow, inhibit airflow separation, and improve the uniformity of the flow field. Under cruise conditions, the total pressure recovery coefficient of the front auxiliary inlet configuration increased by 12.39% compared to the model without a front auxiliary inlet configuration. Furthermore, the total pressure distortion index was reduced by 47.24%.

Enhanced Li+ conductivity of Li7La3Zr2O12 by increasing lattice entropy and atomic redistribution via Spark Plasma Sintering

Cubic Li7La3Zr2O12 (c-LLZO) is an ideal solid-state electrolyte for Li-ion batteries. The Li diffusivity at 24d site is a rate-determining step of the ionic conductivity. Aluminium is commonly used to synthesise c-LLZO. However, Al3+ prefers to occupy the 24d over 96h. To improve the ionic conductivity of Al-doped LLZO, minimizing the occupation of Al at 24d is shown to be crucial. In this work, SPS (Spark Plasma Sintering) is employed primarily due to its capability of metastable phase stabilization via a non-equilibrium process and ion redistribution related electromigration process. X-ray powder diffraction refinement reveals that occupancy of Al at 24d site decreased and lattice distortion index increase of SPS processed Al-doped c-LLZO. The lattice distortion index is closely tied to lattice entropy, i.e., configuration and vibrational entropy. Increasing lattice entropy can reduce the energy barriers between Al and Li’s 24d and 96h sites, stabilising Al3+ occupancy at 96h site. After SPS parameter optimisation, the high ionic conductivity of 2.6 × 10–4 S·cm-1 and low electronic conductivity of 10–7 S·cm-1. This study offers a new perspective on using SPS to modify the lattice structure, with potential benefits beyond simply densifying the samples. Highlighting the importance of high lattice entropy is favourable in enhancing ionic conductivity.

Effects of Inlet Pressure Distortion on the Performance and Flow Field of a Centrifugal Compressor at Design Condition

The present paper presents experimental results on the effects of inlet total pressure distortion on the performance and flow field of a centrifugal compressor. The total pressure at inlet is artificially distorted by means of a perforated sheet, which is supported by a support mesh. A total of eleven configurations, including clean inlet configuration, are tested. Performance measurements and impeller inlet and exit flow studies are carried out. The distorted inlet flow causes loss of energy, reduction in the maximum flow coefficient and perceptible decrease in the stable operating range of the compressor when compared with undistorted inlet flow. The reduction in stable operating range is the highest for 150° Distortion and the least for 4x22.5° Distortion. In radial distortion group, tip distortion has more detrimental effect on the operating range, energy coefficient and efficiency. The mass averaged total pressure at the impeller exit is the highest for clean inlet and the lowest for Hub+90° Distortion. The circumferential distortion has more adverse effect than the radial distortion on the flow parameters. The combined radial and circumferential distortion (Hub+90°) has the worst effect on the mass averaged flow parameters. As the Distortion Index (DI) increases, the mass averaged total pressure at exit stations decreases. Distortion sector angle of 60° having the lowest total pressure is found to be the critical sector for circumferential distortion configurations. As the Distortion Correlation parameter, DC(60) increases, the mass averaged total pressure for circumferential distortion configuration decreases.

Study on the aerodynamic performance of nacelle inlet under crosswind

Flow separation will occur in the nacelle inlet under crosswind operation, which will result in engine intake distortion and even engine surge. To study the reference characteristics of the flow field of the short tank inlet separation under the influence of crosswind, this paper observed the cloud map of the total price loss coefficient by changing the flow deflection Angle and flow velocity, made a qualitative analysis of the total pressure distortion degree, then calculated the average total pressure loss coefficient and distortion index, and conducted a quantitative analysis to explore the improvement of the total pressure distortion under different flow field factors. The results show that the degree of total pressure distortion is improved with the increase of incoming flow velocity at a small inlet deflection Angle, but with the increase of incoming flow deflection Angle, the ability of incoming flow velocity to improve the total pressure distortion gradually weakens until it disappears. The inlet deflection Angle plays a decisive role in the improvement effect of incoming flow velocity on the total pressure distortion.

Effects of Stage Loading on Performance and Flow Field of a Centrifugal Compressor With Inlet Pressure Distortion

The paper presents experimental results on the effects of inlet total pressure distortion on the performance and flow field of a centrifugal compressor. The total pressure at the inlet is artificially distorted by means of a perforated sheet, which is supported by a support mesh. A total of eleven configurations, including clean inlet configuration, are tested. Performance measurements and impeller inlet and exit flow studies at three flow coefficients, one near design flow coefficient, one below design flow coefficient and one above design flow coefficient, are carried out. The present paper presents and discusses results at the three flow coefficients and the effects of stage loading on the distortion effects are presented. A new parameter, Distortion Index (DI) is introduced. As DI increases, the mass averaged total pressure at exit stations decreases. Distortion sector angle of 60° having the lowest total pressure is found to be the critical sector for circumferential distortion configurations. As the Distortion Correlation parameter, DC (60) increases, the mass averaged total pressure for circumferential distortion configuration decreases, except in the case of low flow coefficient where the mass averaged total pressure is nearly constant. DC (60) also increases with sector angle. The static pressure normalized with static pressure for clean inlet decreases as the distortion sector angle is increased. Distortion attenuates the static pressure as the flow passes through the vaneless diffuser. The attenuation increases with the distortion sector angle.

Prepositive Synergistic Bulge Design for Improving Aerodynamic Performance of Submerged Inlet

A submerged inlet has good stealth characteristics and a low external drag, but it also has the disadvantage of low internal flow efficiency. In view of this, a new efficiency enhancement method based on the prepositive synergistic bulge of the inlet’s anterior lip is proposed. Taking the submerged inlet of an aircraft as the baseline configuration, a miniature bulge with a square bottom and an outer convex form is designed in front of the inlet’s anterior lip. Through the convex shape of the bulge, part of the low-energy boundary layer airflow is diverted away from the inlet’s entrance, so that the airflow greatly reduces the flow separation after entering the inlet, and the internal flow performance of the entire submerged inlet is improved. Taking the flow field of an aircraft in the classic cruise state as an example, the simulation analysis results show that the flow field characteristics of the entire submerged inlet are obviously improved after adding the synergistic bulge. The total pressure recovery coefficient of the new inlet configuration increased by 1.36%, the total pressure distortion index decreased by 10.86%, and the body drag only increased by 0.37% compared with the baseline case. According to calculations of synergistic bulge inlet configurations with different design parameters, the effect of this configuration is relatively stable, whereby the aspect ratio of the bulge has the greatest impact on the performance, and its value should not be less than 0.75. In addition to the advantages of not requiring additional components or occupying space and being easy to manufacture, the method of adding a synergistic bulge can improve the aerodynamic performance of the baseline inlet under most cruise flight conditions, and its additional drag is small, which gives it a wide applicability range.

Flow Separation Control of Nacelle Inlets in Crosswinds by Dielectric Barrier Discharge Plasma Actuation

Crosswinds will lead to large-scale flow separation in the nacelle inlets, which seriously affects the flight safety of the aircraft; there is an urgent need to develop flow control measures. As a plasma flow control method, the application of surface dielectric barrier discharge in the field of nacelle inlet separation control is of great significance for improving the intake quality. Based on the characteristic law of the baseline flow field, the flow control effect of the nacelle inlet separation flow field experiments with NS-DBD, and the influence of the actuation frequency on the flow control is discussed. A comparative experimental study of NS-DBD and AC-DBD is carried out. Finally, the flow control mechanisms for both are discussed. The results show that under the condition that the flow velocity of the wind tunnel is 35 m/s and the crosswind angle is 10°, the average total pressure loss coefficient and distortion index decrease by 29.62% and 44.14% by NS-DBD actuation. At the same time, exists an inherent optimal coupling frequency in NS-DBD, and the control effect of NS-DBD is better than that of AC-DBD. NS-DBD mainly through shock waves and induced vortices, while AC-DBD mainly through the induced generation of near-wall jets to reduce the inverse pressure gradient and improve nacelle flow separation.

Biased Technological Progress, Factor Price Distribution, and Overcapacity: A Case from China

This study aims to investigate the effects and mechanisms of biased technological progress on China’s industrial overcapacity. Using a time-varying stochastic frontier model, standardized supply-side system method, and the production function method, we measure the capacity utilization rate, biased technological progress index, and factor price distortion index in China’s industrial sector. Additionally, we employ a mediation effect model to analyze the impact of biased technological progress on overcapacity through factor price distortion. The findings suggest that biased technological progress can alleviate overcapacity, while factor price distortion exacerbates the problem. Biased technological progress alleviates overcapacity through capital price distortion, with a more significant effect in heavy industries than in light industries. Based on the results, we propose a series of policy recommendations, including optimizing the bias towards technological progress, improving the factor market, and enhancing the original innovation capability.

BFIP: an online tool to calculate the best fitted idealized polyhedron

Distortion of polyhedra is frequently used in the structure–property analysis of inorganic materials. The commonly used Baur distortion index (BDI) loses efficacy in dealing with equi-length polyhedra. This work provides an online calculator to characterize the polyhedral distortion on the basis of the best fitted idealized polyhedron (BFIP) method. This method can determine any subtle change between distorted and corresponding idealized polyhedra. It works by fitting an idealized oriented polyhedron of user-selected type to a collection of center and vertex coordinates on an orthonormal basis. The input only needs the coordinates of the center and ligand atoms. It can be accessed at http://bfip.crystalstructure.cn. The function is demonstrated using a distorted MgO6 octahedron. Examples of the application and comparison with the BDI are given, including a tetrahedron, octahedron, eight-vertex triangular dodecahedron/cube and cuboctahedron.

Methods for Comprehensive Calibration of a Low-Frequency Angular Acceleration Rotary Table

The total harmonic distortion (THD) index and its calculation methods are presented to calibrate the sinusoidal motion of the low-frequency angular acceleration rotary table (LFAART) and make up the incomprehensive evaluation based on the angular acceleration amplitude and frequency error indexes. The THD is calculated from two measurement schemes: a unique scheme combining the optical shaft encoder and the laser triangulation sensor and a regular scheme using the fiber optical gyroscope (FOG). An improved reversing moments recognition method is presented to upgrade the accuracy of solving the angular motion amplitude based on optical shaft encoder output. The field experiment shows that the difference in the THD values achieved using the combining scheme and FOG is within 0.11% when the signal-to-noise ratio of the FOG signal is higher than 7.7 dB, indicating the accuracy of the proposed methods and the feasibility of taking THD as the index.

Forecasting the Distortion in Solar Radiation during Midday Hours by Analyzing Solar Radiation during Early Morning Hours

Knowing the fluctuation of solar radiation is essential for reliable and safe operation of power systems with a high share of solar PV power plants. This paper introduces a novel method for forecasting the distortion in global solar radiation during the midday time (during the peak of solar radiation at which the generation of the PV plants is maximum), by analyzing the solar radiation during the very early hours. This paper shows that there is a strong relation between the condition of the solar radiation during the very early minutes of the day (when the generation of the PV plants is low) and the condition of the solar radiation during the midday hours (when the output of the PV plants is enormous). This relation can be utilized to help power systems operators in determining the safe share of PV plants that can be fed to power systems. We analyzed real data of one complete year for two sites in Saudi Arabia to approve this approach. The difference between each two readings was calculated for the hours 7 a.m. and 8 a.m. Then, the negative, zero, and amplitude of the difference was used to formulate a distortion index (DI) that predicts the distortion/fluctuation in the global radiation. It was concluded that the DI could classify the days into three categories: clean, distorted, and medium level according to the value of the DI. The accuracy of this approach was 85.2% and the error was 14.8%.

Surge margin monitoring of one turboshaft engine with inlet distortion

In order to explore the engine surge when inlet distortion index and engine surge margin, the relationship between the parameter characteristics of research engine surge, strengthen safety monitoring assessment engine, this paper designed a kind of a certain type of engine bench test surge monitoring system, and unstable flow field of a certain type of vortex axis engine working parameters for monitoring and analysis. In this paper, a plug-plate distortion generator is used to induce a surge engine, and the circumferential static pressure changes of the inlet and outlet of the engine, the axial compressor and the centrifugal compressor under different working conditions are obtained. The changes of circumferential unevenness and mean turbulence, the pressure ratio at working point and the converted air flow rate at working point are analyzed with the increase of the height of the plug-plate under different working conditions. The results show that the distortion index of the working point increases and the surge margin decreases with the increase of the height of the plug-plate at the same rotating speed. When the height of the plug-plate is similar, the higher the speed is, the greater the distortion index of the working point is, and the smaller the surge margin is.

Effect of Sb-induced oxygen octahedral distortion on piezoelectric performance and thermal stability of Pb(In,Nb)O3-Pb(Hf,Ti)O3 ceramics

The combination of excellent thermal stability and outstanding electrical performance is of great significance for piezoelectric ceramics. Herein, we have prepared 0.11Pb(In0.5Nb0.5)O3-0.89Pb(Hf0.47Ti0.53)O3-Sb2O5 (PIN-PHT-xSb) ceramics by solid-phase method and investigated the effect of oxygen octahedral lattice distortion on microstructure and macroscopic electrical properties. The distortion index of oxygen octahedra is studied by Rietveld refinement, showing that optimal octahedral distortion can soften B-O repulsion, disrupt long-range ordered ferroelectric domains, and enhance local heterogeneities, significantly increasing piezoelectric properties. Moreover, outstanding thermal stability and ultrahigh piezoelectric response of PIN-PHT-1.2Sb ceramics are realized under the synergistic influence of octahedral distortion, excellent density, and large grain size. Compared with PIN-PHT ceramics, PIN-PHT-1.2Sb ceramics exhibit ultrahigh piezoelectric responses (d33 = 706 pC/N, kp = 0.68, εr = 3244), a high Curie temperature (TC) of 300 °C, excellent thermal stability, and anti-fatigue properties.

Design and examination of a turboprop inlet with scavenge duct

The inlet with scavenge duct is an important part of turboprop aircraft engine. This type of inlet normally has a complex shape, of which the design is challenging and directly affects the flow field quality of the engine entrance and thus the engine performance. In this paper, the parametric design method of a turboprop aircraft inlet with scavenge duct is established by extracting and controlling the transition law of the critical characteristic parameters. The inlet’s performance and internal flow characteristics are examined by wind-tunnel experiment and numerical simulation. The results indicate that a flow tendency of winding up on both sides is formed due to the induction of the inlet profile, as well as a vortex pair on the back side of the power output shaft. The vortex pair dominates the pressure distortion index on the Aerodynamic Interface Plane (AIP). In addition, with the increase of freestream angle of attack, the total-pressure recovery coefficient of the inlet increases gradually while the total pressure distortion index decreases slightly. On the basis of the experimental results under different working conditions, the parametric design method proposed in this paper is feasible.

A new intake distortion design system for research

The intake distortion experiment is one of the important methods for aero-engine aerodynamic stability assessment. In this paper, in order to overcome the shortcomings of traditional design methods such as low accuracy in approximating the target distortion map and many experimental iterations, a design system is proposed to design the target map distortion network using Fluent based on the mapping relationship between screen distance and porous media. Finally, the steady-state total pressure test system is designed, and the physical design of the distortion generator and wind tunnel test are completed, with the error of distortion index of less than 1.5%. The test results show that the design system can simulate the distortion requirements with high accuracy and efficiency.