Stacking Line Research Articles

Shape optimization of two turbine stages using the deformed polyhedron method and a three-dimensional RANS solver

A combination of the Nelder-Mead deformed polyhedron method with a three-dimensional RANS solver is used in the paper for the constrained optimization of the shape of two selected turbine stages. The objective function is the total stage loss, with the exit kinetic energy also considered a loss. There are constraints imposed on the mass flowrate, exit angle, average reaction and reaction at tip and root. The exit angle and reactions are not allowed to assume values beyond prescribed ranges, whereas a penalty function is imposed on the mass flowrate if it falls outside the required interval. Among the optimized parameters are stator and rotor stagger and twist angles and stator sweep and lean, both straight and compound. The computations of the flowfield are compressible, viscous and three-dimensional. Turbulence effects are taken into account using the modified Baldwin-Lomax model. The process of optimization gives new designs with improved calculated efficiency. Part of the improvementis due to optimization of the stagger angles and blade numbers, as in classical one-dimensional optimization, and part of it is due to the fact that the blades assume new three-dimensional stacking lines.

Fluctuations of the paleomagnetic field during chron C5 as recorded in near‐bottom marine magnetic anomaly data

Near‐bottom magnetic data contain information on paleomagnetic field fluctuations during chron C5 as observed in both the North and South Pacific. The North Pacific data include 12 survey lines collected with a spatial separation of up to 120 km, and the South Pacific data consist of a single long line collected on the west flank of the East Pacific Rise (EPR) at 19°S. The North Pacific magnetic profiles reveal a pattern of linear, short‐wavelength (2 to 5 km) anomalies (tiny wiggles) that are highly correlated over the shortest (3.8 km) to longest (120 km) separations in the survey. Magnetic inversions incorporating basement topography show that these anomalies are not caused by the small topographic relief. The character of the near‐bottom magnetic profile from anomaly 5 on the west flank of the EPR, formed at a spreading rate more than twice that of the North Pacific, displays a remarkable similarity to the individual and stacked lines from the North Pacific survey area. Over distances corresponding to 1 m.y., 19 lows in the magnetic anomaly profile can be correlated between the North and South Pacific lines. Modeling the lows as due to short polarity events suggests that they may be caused by rapid swings of the magnetic field between normal and reversed polarities with little or no time in the reversed state. Owing to the implausibly high number of reversals required to account for these anomalies and the lack of any time in the reversed state, we conclude that the near‐bottom signal is primarily a record of paleointensity fluctuations during chron C5. Spectral analysis of the North Pacific near bottom lines shows that the signal is equivalent to a paleointensity curve with a temporal resolution of 40 to 60 kyr, while measurements of the smallest separations of correctable dips in the field suggest a temporal resolution of 36 kyr.

Design optimization of axial flow compressor blades with three-dimensional Navier-Stokes solver

Numerical optimization techniques combined with a three-dimensional thin-layer NavierStokes solver are presented to find an optimum shape of a stator blade in an axial compressor through calculations of single stage rotor-stator flow, Governing differential equations are discretized using an explicit finite difference method and solved by a multi-stage Runge-Kutta scheme. Baldwin-Lomax model is chosen to describe turbulence. A spatially-varying time-step and an implicit residual smoothing are used to accelerate convergence. A steady mixing approach is used to pass information between stator and rotor blades. For numerical optimization, searching direction is found by the steepest decent and conjugate direction methods, and the golden section method is used to determine optimum moving distance along the searching direction. The object of present optimization is to maximize efficiency. An optimum stacking line is found to design a custom-tailored 3-dimensional blade for maximum efficiency with the other parameters fixed.

A novel 3-dB coupler for MMIC using air-gap stacked microstrip lines

A simple broadside-coupled line structure for MMIC is proposed which uses air-gap stacked microstrip lines and does not require any dielectric process. The analysis and optimization of the coupled line structure were performed by using an electromagnetic simulator. The fabricated 3-dB coupler shows broad-band characteristics (23-45 GHz) with the coupling loss of 3.33/spl plusmn/0.46 dB and the transmission loss of 3.73/spl plusmn/0.43 dB.

Comparison of Sweep and Dihedral Effects on Compressor Cascade Performance

The influence of two stacking lines, namely sweep and dihedral, has been investigated in a linear compressor cascade. Both types of blade considered are symmetric about midspan and consist of a straight central section with either swept or dihedral sections toward the endwalls. Two types of experiment have been carried out. First, a parametric study was performed by changing both the magnitude and the extent of the sweep or dihedral. In the case of swept blades, those with forward sweep (SWF), for which the stacking line is swept in the upstream direction toward the endwall, were found to have better performance than backward-swept blades. Subsequently, four sets of SWFs were compared. In the case of dihedral blades, it is well known that the dihedral is advantageous when the angle between the suction surface and the endwall is obtuse, i.e., positive dihedral. Thus, four sets of positive dihedral blades (DHP) were compared. In both SWF and DHP blades, those configurations that have better efficiency than straight blades were determined. Second, detailed three-dimensional measurements inside the blade passage were performed in the cases that showed the best performance in the parametric study. Both SWF and DHP showed significant effects on the flowfield. In the SWF case, a vortex, which has the opposite sense to the passage vortex, was observed in the forward portion inside the blade passage. This vortex supplies high-energy fluid to the endwall region and reduces the corner stall. The secondary flow is greatly reduced. In the DHP, the blade loading was reduced at the endwall and increased at the midspan. Reduction of the corner stall and the secondary flow was also observed.

Characterization of Defect Structures in Lely 6H-SiC Single Crystals Using Synchrotron White Beam X-Ray Topography

AbstractDefect structures in Lely SiC single crystals have been studied using synchrotron white beam X-ray topography. Basal plane dislocations and stacking faults probably generated during post-growth cooling are clearly revealed. For both perfect dislocations and partial dislocations bounding the stacking faults, Burgers vectors and line directions are determined from contrast extinction analysis as well as projected direction analysis on different topographic images. The fault planes and fault vectors of the stacking faults were determined using contrast extinction analysis. Possible dislocation generation mechanisms are briefly discussed.

Phase Displacement Acceleration of High Intensity Stacks in the CERN ISR

In the ISR high intensity stacks of more than 25 A are accelerated by phase displacement from 26.6 to 31.4 GeV/c. Phase displacement is the only known means of accelerating stacks of such large momentum spread (?p/p = 3%) with the existing low power RF system. Acceleration in this way may produce loss of intensity due to RF and power supply magnet noise, momentum blowup of the stack, closed orbit and working line variations, and changes in the RF bucket size while traversing the stack. The existing instrumentation allows close control of all relevant parameters during acceleration and has resulted in reducing the intensity losses to as little as 10%. In this way, luminosities significantly in excess of the ISR design luminosity are achieved in an operational way, making 31.4 GeV/c one of the standard ISR momenta for physics data taking and giving an equivalent nomentum of greater than 2,000 GeV/c when related to stationary target machines.

Seismic velocities in the Lewisian metamorphic complex, northwest Britain—‘in situ’ measurements

Synopsis Sixteen reversed seismic refraction profiles, each 1 km long, in Sutherland between Kylesku and Durness have demonstrated a difference in P-wave velocity between the northern and central belts of the mainland outcrop of the early Precambrian Lewisian rocks. The variably-retrogressed pyroxene granulites of the central belt (of andesitic-dioritic composition) yielded a velocity of 6.34 ± 0.17 km/s (6 observations); the quartzo-feldspathic gneisses of the northern belt yielded a velocity of 5.64 ± 0.18 km/s (6 observations); the rocks of the boundary region, near the Ben Stack line, yielded a velocity of 5.28 ± 0.23 km/s (4 observations). Correlations are made with the velocity layering of crustal models derived for the area, confirming the wide occurrence in the upper crust of granulite-facies rocks. Such high values of velocity in surface rocks place strict limits on velocity gradients in such rock types in the deeper continental crust.

Rb-Sr isotopic studies near the major Precambrian junction, between Scourie and Loch Laxford, northwest Scotland.

The nature and significance of the Precambrian junction between Scourie and Loch Laxford, that separates pyroxene granulites and retrogressed equivalents of the Kylesku group to the south (Khoury 1968; Bowes et al. , 1971) from quartzofeldspathic gneiss of the Rhiconich group to the north (Dash 1969; Chowdhary and Bowes 1972; Gillen 1975), has been the subject of widely differing interpretations. However in all interpretations, chronological considerations relating to the c 2.5 km wide zone of highly deformed rocks immediately south of the Rubha Ruadh granite sheet (Gillen 1975) and the coincident ‘Ben Stack Line’ of Lambert and Holland (1972) play an important role. Development of the junction associated with gneiss formation during the Laxfordian episode ( c 1950–1700 m.y.) was suggested by Sutton and Watson (1951, 1962). Bowes (1969), on the other hand interpreted the evidence as indicative of major tectonic movements which deformed the gneisses of the Rhiconich group during the latter part of the Laxfordian episode. These differences are, in part, related to the chronological significance of basic minor intrusions in the zone. Formation of the junction during the Inverian episode ( c 2200 m.y.), before the emplacement of the Scourie dyke suite, was suggested by Lambert and Holland (1972), Bott et al. (1972) and Park (1973). Beach et al. (1973) also place the intense deformation shown in this zone before the emplacement of the Scourie dyke suite and after the granulite facies metamorphism of the Scourian episode that has been dated at 2700 ± 20 m.y. by Pidgeon and . . .

Geophysical evidence concerning the structure of the Lewisian of Sutherland, N.W. Scotland

Interpretation of two new gravity profiles across the Ben Stack line and of the I.G.S. aeromagnetic map indicates that the Lewisian biotite-gneisses occurring to the north of this line are underlain at a depth of about 3 km or less by rocks possessing similar density and magnetic properties to the pyroxene-granulites which crop out south of the line. The Ben Stack line forms the fundamental division between these two metamorphic assemblages of the Lewisian and its plane dips steeply towards the south. The gravity profiles also indicate that both the biotite-gneisses and pyroxene-granulites in the vicinity of the Ben Stack line are anomalously low in density. This is attributed to the penetration of both formations by granitic and pegmatitic intrusions of low density. The evidence suggests that the granitic material concentrated in the vicinity of the Ben Stack line occupies too great a volume to be derived solely from the host biotite-gneisses in the immediate vicinity and may therefore possibly be of more extensive origin.

Discussion

Dr J. T arney said that while he accepted that the simplest interpretation of the geophysical data to the north of the Ben Stack line suggested a model in which the Laxfordian gneisses were a supracrustal series underlain by a pyroxene-granulite basement at a depth of about 3 km, he wondered whether a model in which there was a gradational increase in density with depth would be equally compatible with the data. Would this not allow for a larger amount of suitable material to be present at depth from which to derive the granitic intrusions in the vicinity of the Ben Stack Line ? Is it not possible that granulite facies metamorphism of such material at a depth of, say, 6 km could yield granitic fluids plus a higher density granulite facies residuum ? Nevertheless he agreed with the general point that higher density granulite facies gneisses must underlie the Laxfordian grey gneisses and that the latter were not simply ‘made-over’ Scourian. Work which Mr. S. J. Moorhouse has been doing on the Lewisian inliers in the Moines, near Tongue, immediately to the east of the area, has shown that many of the Lewisian slices there correspond geochemically with the Laxfordian grey gneisses of the Rhiconich area. However in the Borgie inlier, some of the Lewisian granulites have the high K/Rb and Ba/Rb and low Rb/Sr, K/Ba and K/Sr ratios characteristic of the Scourian assemblage. This area is structurally well to the north of the Ben Stack Line. The evidence suggestes