Undistorted Region Research Articles

Effect of radial inlet distortion on aerodynamic stability in a high load axial flow compressor

Radial inlet distortion induced by boundary layer separation can significantly affect the aerodynamic performance of the compressor. The effect of radial inlet distortion on the flow structure is numerically investigated in a high load axial flow compressor. The inlet boundary is determined by the experimental results at the downstream of the distortion generator. The results reveal that tip distortion leads to a reduction in the stall margin, whereas hub distortion extends it. Radial distortion redistributes the main flow toward undistorted region due to the obstructive effect of lattice ring. The deficit in axial velocity with tip radial distortion causes the rotor to operate at a higher incidence angle near the casing, while hub radial distortion alleviates the tip blade loading. The detailed three-dimensional flow field analysis indicates that increased blade loading with tip distortion shifts the trajectories of both primary and secondary tip leakage flow toward the leading edge, thereby expanding the blockage region. Conversely, hub radial distortion unloads the rotor tip region, thereby reducing the blockage region induced by tip leakage flow. Additionally, with hub distortion, the location of separation line on the blade suction surface moves closer to the leading edge, and the flow separation around the trailing edge is intensified.

Partial tip air injection to extend the stall margin in an axial flow compressor with circumferential inlet distortion

As a typical non-axisymmetric inflow, circumferential pressure inlet distortion was experimentally investigated in an axial flow compressor. Based on the obvious decreasing trend of stall margin with the enhancement of distorted intensity, the stall mechanism under the condition of maximum distorted intensity, namely, 24.57 %, was studied in detailed. The casing static pressure over the rotor blade tip along the chord and circumferential direction were measured using a collection of dynamic transducers. Results show that under the circumferential inlet distortion condition, the pressure disturbance is always generated downstream from the distorted region along the rotational direction, and circumferentially propagates until it disappears in the upstream of the distorted region. With the continuous throttling, if the pressure disturbance that has not completely disappeared in the undistorted region enters the distorted region again, its energy will be enhanced, finally induces the stall. Using the above understanding as a foundation to apply partial tip air injection to suppress the disturbance caused by the circumferential inlet distortion, and resist its adverse effect on stall margin to ensure the safe operation of the compressor. It demonstrated that the tip air injection applied in the downstream of the distorted region can obtained the largest stall margin on the premise of the same injected momentum. For the strongest distortion case (DC (60) equals to 24.57 %), the injectors fixed downstream the distorted region can reduce the number and scale of the spike disturbances, suppress the local tip leakage vortex, and decrease the amplitude of the pressure disturbance energy, thus a maximum stall margin improvement of 3.18 % is obtained. However, tip air injection in the undistorted region cannot contribute the stall margin improvement that it leads to stronger tip leakage vortex and earlier stall inception. This study provides a guideline to design the non-axisymmetric tip air injection for circumferential inlet distortion with a help of injected mass flow and energy reduction.

A region-segmentation combinational loss model based on data-driven machine learning for a boundary layer ingestion fan

The boundary layer ingesting (BLI) fan is continuously working under distorted inflows. The rotor blade moves across the distorted and undistorted regions and the resultant off-design condition makes the loss present a notable non-uniform distribution feature. Accurately capturing the loss is very important for evaluations of BLI fan performances in preliminary design stage. However, unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations are extremely computational expensive even though they can well predict the loss, and the traditional empirical or physics-based loss models are usually fade when predicting loss variation trends and absolute magnitudes under complex inflow conditions. This paper develops a data-driven machine learning based region-segmentation combinational loss model to realize a fast and accurate prediction of the aerodynamic loss in a BLI fan rotor. According to the distinctions of loss sources in different spanwise fractions, a region segmentation idea is first used to create local loss model in each sub-region, and then a full-span combinational prediction model is constructed through a data-driven based neural network approach. Results show that the data-driven based region-segmentation combinational loss model presented in this work performs better than the traditional empirical or physics-based loss models in terms of predicting both the loss variation trends and absolute magnitudes. Compared with the high-fidelity URANS simulations, the averaged loss prediction errors in a BLI fan rotor are kept within 10 % under different blade load and inflow distortion conditions.

Numerical study on the effect of distortion of S-duct on flow field and performance of a full annulus transonic fan

Abstract To reveal the influence of distortion of S-duct on the flow field and performance of transonic fan, full annulus unsteady numerical simulation was carried out under S-duct/fan integrated condition. This study focuses on the coupling flow of S-duct/fan integrated condition under peak efficiency (PE) condition and near stall (NS) condition. Results show that, compared with the condition that S-duct or fan is investigated alone, the distortion of S-duct is suppressed under S-duct/fan integrated condition. The curved structure of S-duct is the important reason for the flow migration from undistorted region to distortion region. Higher inlet relative Mach number and more work input of the rotor are observed in the counter-swirl region. The flow separation in S-duct is weakened under NS condition compared with that of PE condition. Counter-swirl region of blade tip has larger region of blockage, and rotating stall inception is most likely to occur in this region.

Experiment investigation on the effect of inlet circumferential non-uniformity on the stall behaviours in a transonic axial compressor with axisymmetric stall precursor

The circumferential non-uniformity is becoming a high risk for jet engines in the future with cutting-edge intake design and undesirable inflow, like crosswind and highly turbulence. This leads to the requirement of a well-designed non-uniformity-tolerant compressor. In those research, the test rigs are mainly low-speed compressors whose stalls are triggered by small length scale disturbance of several blade pitches. The load achieves its maximum value at the trailing edge of the distortion, and spikes tend to emerge from this region. Thus, the circumferential non-uniformity usually deteriorates the stall margin. Unlike the spike, the partial surge shows axisymmetric features in both phase and amplitude since the embryonic period. It is interesting to find out the influence of circumferential uniformity of local disturbance at the hub on the propagation of partial surge. Thus, this paper implemented an experimental method on a transonic axial compressor with an axisymmetric stall precursor originating from the hub, partial surge. The non-uniformity patterns are varied by adjusting the distortion sector with different angles. The stall margin decreased with the sector angle of 90 degrees. In contrast, an unexpected result indicated that the stall margin increased with the sector angle of 120 degrees and 180 degrees, which were affected by two mechanisms, i.e., partial-surge-suppression and embryo-stall-cells-motivation. First, when the sector angle was 90 degrees and 120 degrees, the non-uniformity suppressed the partial surge and the formation of embryo rotating stall cells in the distorted region. With the development of partial surge, the embryo rotating stall cells in the undistorted region grew larger than those in the uniform case. Secondly, the partial surge inception disappeared when the sector angle was further enlarged to 180 degrees. The embryo rotating stall cells at the rotor tip emerged from the distorted region and died out in the undistorted region.

Slope, aspect, and hillshade algorithms for non‐square digital elevation models

AbstractCommon global digital elevation models (DEMs) at 1 to 3 arc‐second resolution use geographic coordinates for grid definition, and while cells are square (equal dx and dy spacing) near the equator, they become increasingly rectangular at higher latitudes. Some GIS software cannot handle rectangular grid cells, but minor modifications to slope, aspect, and hillshade algorithms can handle them. The algorithms can also handle grids with other projections, including Equi‐7, Lambert conformal conic, Lambert azimuthal equal area, and polar stereographic, converting aspect to true north instead of the potentially rotated grid. Computed slope varies with grid spacing with a logarithmic relationship and negative slope. Slope maps and distributions from rectangular DEMs, or DEMs where the actual grid spacing varies from the nominal values because points are far from the undistorted region, have characteristics equal to those of a Universal Transverse Mercator grid with spacing equal to the average dx and dy spacing of the DEM.

Reliability analysis for stall warning methods in an axial flow compressor

The reliability of widely studied four stall warning methods, namely, auto- and cross-correlation, Root-Mean-Square (RMS), and fast wavelet analysis, were experimentally studied in a low-speed axial flow compressor. Unsteady pressures used for stall warning were measured by time-resolved sensors mounted on the casing along axial and circumferential spatial resolution. Three influence factors of rotational speed fluctuation, circumferential and axial location of pressure sensors for the stall warning reliability were analyzed and discussed. The rotational speed fluctuation that inevitably exists in the actual aero-engine would lead to the phase shift of phase-locked pressure data and thus deteriorates the stall warning reliability using the auto-correlation and RMS analysis methods. The circumferential location of pressure sensors would affect the reliability of proposed stall warning methods due to the uneven tip clearance distribution. Auto-correlation, RMS, and fast wavelet methods are more effective at the large tip clearance location than at the small tip clearance location. For the cross-correlation method that needs two symmetrically-arranged pressure sensors, the negative effect caused by the circumferential unevenness of tip clearance size can be avoided. The ideal axial location of the sensor installation for stall warning is near the rotor leading edge where the strong tip leakage flow fluctuation exists. In addition, considering the actual complex inflow condition, the stall warning methods' reliability with inlet circumferential distortion was studied. In the distorted region, the adverse effect of distortion on stability can be detected by above four methods. In the undistorted region, only cross-correlation coefficient correspondingly decreased to reveal the stability margin deterioration caused by circumferential distortion. Considering the random circumferential position of distortion, cross-correlation method was proved to have a promising application compared to others.

Reconstructing 3D digital model without distortion for poorly conductive porous rock by nanoprobe-assisted FIB-SEM tomography.

Oil and natural gas prospecting requires precise pore characterisation of insulating rock samples, which involves severe charging problems in the state-of-art FIB-SEM tomography, such as overexposure, drift and distortion. For weak cemented samples with very poor conductivity, the conventional ways such as decreasing accelerating voltage or current as well as coating a thin layer of carbon or gold fail to eliminate all the detrimental effect, leading to image distortion in the form of lateral shift and longitudinal stretching. A new nanoprobe-assisted method is explored in FIB-SEM tomography to address this problem and improve image quality. To be specific, a metallic nanoprobe is induced and attached on the sample surface to create an express path for the export of excess electrons near the region of interest, which effectively removes distortion and drift when imaging. Two adjacent areas were characterised and reconstructed into 3D digital models by FIB-SEM tomography with nanoprobe-assisted method applied to one region only. The lateral shift creates zigzag feature for distorted region and the longitudinal stretching of undistorted object can reach 14%. Average pore size of distorted region is larger than that of the undistorted region, however considering the longitudinal stretching, the average pore size of distorted region can be corrected to the same level as the undistorted region. The systematic error caused by distortion for poorly conductive porous rock is hazardous for digital rock physics analysis. Therefore, the nanoprobe-assisted FIB-SEM tomography should be regarded as a one of the optional and feasible procedures in case decreasing accelerating voltage or current as well as coating a thin layer of conductive material does not work.

Structural and optical characteristics investigations in oxygen ion implanted GaN epitaxial layers

This paper presents the lattice disorder-induced effect by oxygen ion implantation in GaN epitaxial layers. Oxygen ion implantation in GaN epitaxial layers is done with fluencies 5 × 1014 cm−2 and 5 × 1015 cm−2 at 120 keV energy on two different pieces of a GaN sample. Unimplanted and implanted GaN layers are investigated by High-resolution X-ray diffraction (HRXRD), Optical absorption and Raman spectroscopy. The in-plane and out of plane lattice parameters (i.e. a and c) of the distorted and undistorted region in the GaN samples are determined from the respective XRD peak positions. Due to the incorporation of oxygen ions in GaN layers up to implantation depth, lattice parameters are extended, as a result, the samples are under hydrostatic strain. Raman spectroscopic studies on the unimplanted and oxygen ion-implanted GaN samples are done by green and ultra-violet (UV) lasers. Raman spectroscopy results indicate that the broadening of the E2 (High) peak and intensity of A1 (LO) peak increases with increasing fluence. A doublet in A1 (LO) peak is found in UV excited Raman spectra in unimplanted and implanted GaN samples. The occurrence of the A1 (LO) doublet is due to surface defects and phonon-plasmon coupled-mode generated due to nonequilibrium photoexcited carriers. In this article, the origin of doublet has been studied and reported.

The effect of heavy deformation on the precipitation in an Al-1.3Cu-1.0Mg-0.4Si wt.% alloy

This work has investigated the effect of the combination of natural ageing and 80% pre-deformation after solution heat treatment on precipitation during subsequent artificial ageing in an Al-1.3Cu-1.0Mg-0.4Si wt.% alloy. It was found that a combined use of atomic resolution aberration corrected high-angle annular dark-field scanning transmission electron microscopy and scanning precession electron diffraction enabled a detailed characterisation of precipitates in heavy pre-deformed materials. The dominant phase in the undeformed condition was the L phase. L was also found to be nucleated in the undistorted regions of the Al matrix in the pre-deformed conditions. Two phases with high aspect ratios were nucleated on dislocations: The C phase and a previously reported phase, which we named here the ‘E phase’. The crystal structure of E was solved experimentally as monoclinic with core composition Mg6Al2Si2Cu4, supported by density functional theory calculations. It was determined that the order of pre-deformation and natural ageing had an influence on the relative fractions of the aforementioned phases formed during artificial ageing. An increased fraction of C+E relative to L was found in the condition where the pre-deformation was applied after natural ageing as compared to the condition where the pre-deformation was applied before natural ageing.

Isometric deformations of unstretchable material surfaces, a spatial variational treatment

The stored energy of an unstretchable material surface is assumed to depend only upon the curvature tensor. By control of its edge(s), the surface is deformed isometrically from its planar undistorted reference configuration into an equilibrium shape. That shape is to be determined from a suitably constrained variational problem as a state of relative minimal potential energy. We pose the variational problem as one of relative minimum potential energy in a spatial form, wherein the deformation of a flat, undistorted region D in E2 to its distorted form S in E3 is assumed specified. We then apply the principle that the first variation of the potential energy, expressed as a functional over S∪∂S, must vanish for all admissible variations that correspond to isometric deformations from the distorted configuration S and that also contain the essence of flatness that characterizes the reference configuration D, but is not covered by the single statement that the variation of S correspond to an isometric deformation. We emphasize the commonly overlooked condition that the spatial expression of the variational problem requires an additional variational constraint of zero Gaussian curvature to ensure that variations from S that are isometric deformations also contain the notion of flatness. In this context, it is particularly revealing to observe that the two constraints produce distinct, but essential and complementary, conditions on the first variation of S. The resulting first variation integral condition, together with the constraints, may be applied, for example, to the case of a flat, undistorted, rectangular strip D that is deformed isometrically into a closed ring S by connecting its short edges and specifying that its long edges are free of loading and, therefore, subject to zero traction and couple traction. The elementary example of a closed ring without twist as a state of relative minimum potential energy is discussed in detail, and the bending of the strip by opposing specific bending moments on its short edges is treated as a particular case. Finally, the constrained variational problem, with the introduction of appropriate constraint reactions as Lagrangian multipliers to account for the requirements that the deformation from D to S is isometric and that D is flat, is formulated in the spatial form, and the associated Euler–Lagrange equations are derived. We then solve the Euler–Lagrange equations for two representative problems in which a planar undistorted rectangular material strip is isometrically deformed by applied edge tractions and couple tractions (i.e., specific edge moments) into (i) a bent and twisted circular cylindrical helical state, and (ii) a state conformal with the surface of a right circular conical form.

Precision and accuracy of acetabular size measures in fragmentary hominin pelves obtained using sphere‐fitting techniques

Hip joint diameter is highly correlated with body size in primates and so can potentially provide important information about the biology of fossil hominins. However, quantifying hip joint size has been difficult or impossible for many important but fragmentary specimens. New three-dimensional technologies can be used to digitally fit spheres to the acetabular lunate surface, potentially allowing hip joint diameter estimates for incomplete joint surfaces. Here we evaluate the reliability of sphere-fitting to incomplete lunate surfaces in silico using three-dimensional polygonal models of extant anthropoid hipbones. Measurement error in lunate sphere-fitting was assessed at the individual observer level, as well as between observers. Prediction error was also established for acetabular sphere size estimates for smaller divisions of the lunate surface. Sphere-fitting techniques were then applied to undistorted regions of lunate surface in Plio-Pleistocene hominin pelves, with a range of diameters constructed from extant error estimates. The results of this study indicate that digital sphere-fitting techniques are precise and that the lunate does not need to be completely preserved to accurately infer hip dimensions, although some aspects of joint size and morphology can influence sphere size estimates. Joint diameter is strongly predicted by spheres fit to the cranial and caudal halves of the lunate in all anthropoids. We present new hip joint size estimates for a number of fossil hominins, and outline additional applications for digital sphere-fitting as a morphometric technique.

A predictive approach to the in-plane mechanical properties of stitched composite laminates

ABSTRACT This contribution attempts to model the alteration of the in-plane elastic properties in laminates caused by stitching, and to predict the in-plane effective tensile strength of the stitched composite laminates. The distortion of in-plane fibers is considered to be the main cause that affects the in-plane mechanical properties. A fiber distortion model is proposed to characterize the fiber misalignment and the fiber content concentration due to stitching. The undistorted region, the fiber distortion region, the resin-rich pocket and the through-thickness reinforcement section are taken into account. The fiber misalignment and inhomogeneous fiber content due to stitching have been formulated by introducing two parameters, the distortion width and maximum misalignment. It has been found that the ply stress concentration in stitched laminates is influenced by the two concurrent factors, the stitch hole and inhomogeneous fiber content. The stitch hole brings about the stress concentration whereas the higher fiber content at the local region induced by stitching restrains the local deformation of the composite. The model is used to predict the tensile strength of the [0/45/0/–45/90/45/0/–45]2s T300/QY9512 composite laminate stitched by Kevlar 29 yarn with different stitching configurations, showing an acceptable agreement with experimental data.

Electromagnetic and microstructural investigations of a naturally grown 8° [001] tilt bicrystal of Bi2Sr2CaCu208 + x

Electromagnetic characterization and high resolution transmission electron microscopy have been conducted on the same 8° [001] symmetrical (010) tilt boundary in a naturally grown, bulk-scale bicrystal of Bi2Sr2CaCu2O8 + x (BSCCO-2212). The resistive transition showed excess resistance above and below Tc, suggesting some weak coupling at the boundary, but the inter- and intragranular voltage-current characteristics, irreversibility fields, and critical current density (Jc) values were very similar and characteristic of strongly coupled grains and grain boundary. The misorientation was accommodated by a set of partial dislocations with the Frank spacing of 1.9 nm. The dislocation cores appeared to be separated by relatively undistorted regions of crystal. The Jc, values at 25 K exceeded 103 A/cm2 in fields of several tesla, more than two orders of magnitude larger than that found earlier in [001] twist boundaries of BSCCO-2212. This result is consistent with the view that low angle [001] till boundaries play an important role for current transport in polycrystalline BSCCO tapes.

Rod-like Polymers in Nematic Solvents: Mechanically and Electrically Driven Frederiks-like Transitions

A layer of short, grafted, main chain liquid crystalline polymers in a nematic solvent is confined to a slit. The polymers are modeled as bendable rods. This system can undergo a number of distortional transitions induced either by applied pressure or by an electric field. As well as Frederiks-like transitions the system can also exhibit columnar transitions in which the distorted domains are separated by undistorted regions. The coupling between the rods and nematic solvent implies that the system has an effective modulus due to both contributions. A combination of pressure and electric fields allows for the lowering of the Frederiks transition voltage to arbitrarily low values.

The effect of calcium spray on leaf and bract distortion, bound:Unbound calcium ratio, and calcium distribution in two poinsettia cultivars

Abstract To deteimine if direct Ca sprays could affect the distribution and binding of Ca in the leaves and the severity of leaf/bract distortion in two varieties of poinsettia (Euphorbia pulcherimma Willd.), we applied either 100 mg.l‐1 or 400 mg.l‐1 of Ca either one time or weekly to leaves of distortion‐ susceptible ('V‐14 Glory') and nonsusceptible ('Annette Hegg Dark Red,’ AHDR) cultivars. Only weekly spraying with 400 mg.l‐1 Ca reduced distortion in V‐14 plants, compared to controls or AHDR plants. Both bound and unbound Ca concentrations were higher in AHDR leaves than in V‐14 leaves, but these differences were not correlated with distortion severity. EDX analysis demonstrated that distorted regions of V‐14 leaves and bracts had lower Ca concentrations than did undistorted regions or AHDR leaves; weekly spraying with 400 mg.r1 Ca produced relatively uniform leaf Ca distribution in V‐14 leaves. Localized Ca deficiencies appear to produce the bract/leaf distortion in ‘V‐14 Glory plants, and these deficiencies can be partially overcome by weekly Ca spray applications.

The effect of calcium spray on leaf and bract distortion, bound:unbound calcium ratio, and calcium distribution in two poinsettia cultivars

Abstract To determine if direct Ca sprays could affect the distribution and binding of Ca in the leaves and the severity of leaf/bract distortion in two varieties of poinsettia (Euphorbia pulcherimma Willd.), we applied either 100 mg.l‐1 or 400 mg.1‐1 of Ca either one time or weekly to leaves of distortion‐ susceptible ('V‐14 Glory') and nonsusceptible ('Annette Hegg Dark Red,’ AHDR) cultivars. Only weekly spraying with 400 mg.l‐1 Ca reduced distortion in V‐14 plants, compared to controls or AHDR plants. Both bound and unbound Ca concentrations were higher in AHDR leaves than in V‐14 leaves, but these differences were not correlated with distortion severity. EDX analysis demonstrated that distorted regions of V‐14 leaves and bracts had lower Ca concentrations than did undistorted regions or AHDR leaves; weekly spraying with 400 mg.l‐1 Ca produced relatively uniform leaf Ca distribution in V‐14 leaves. Localized Ca deficiencies appear to produce the bract/leaf distortion in ‘V‐14 Glory’ plants, and these d...

Analysis of Lattice Modulations in the Tweed Structure of an Fe–Pd Alloy by Image Processing of a High-Resolution Electron Micrograph

Computer-image processing of a high-resolution electron micrograph was carried out to extract information on the lattice distortions associated with the tweed structure of an Fe–Pd alloy which is a precursor phenomenon in the fcc-fct martensitic transformation. It was proven that the distorted and undistorted regions formed alternating layers parallel to {110} planes, as predicted by the continuum elasticity theory in a previous paper. The distorted layers contained tetragonally distorted strain centers with the tetragonality of about 0.97. This result coincides well with the `embryo model' proposed previously by the present authors' group.

X-Ray Diffraction Microscopy Technique for the Study of Aluminium Single Crystals

By the use of Soller slit in the primary beam and a line source of characteristic X-rays, the X-ray diffraction microscopy is extended to allow the detection of imperfection in a crystal lattice. A Soller slit creates a set of virtual X-ray sources. A large number of rays cross at the center of each cell, so that the vertically divergent beam emerging from each cell may be said to issue from the virtual source located at the center of each cell. At the same time the rays are diverging horizontally from the actual source, so that the virtual source is actually a short horizontal line through the center of each cell, there being one virtual source for each cell of the Soller slit.This technique has the advantage of allowing the diffraction patterns from distorted and undistorted region in a crystal lattice to be recorded on the large surface by taking a single photograph.This new technique is applied in the present investigation to a study of the deformation of aluminium single crystal, and it is revealed that the clustered slip regions are rotated relative to matrices after tensile deformation.

Studium von Einzelversetzungen in nahezu idealen Kristallen mit einer R�ntgenmethode

The integrated intensities of X-ray diffraction for theLaue and theBragg case have been calculated for both an ideal and a mosaic crystal. The ratio of both intensities is thought to be a measure for the contrast of topographic X-ray work. Concerning to the Laue case, in thin crystals the distorted regions around dislocations have a higher diffraction intensity than the undistorted regions. In thick crystals the contrast is reverted. That is the case of anomalous transmission in ideal crystals.