Comparison Study on Stage Performance of Centrifugal Compressors With Shrouded and Unshrouded Impellers

The shrouded and unshrouded impellers are two typical kinds of impellers, which are widely utilized in centrifugal compressors of various applications. Centrifugal compressors with unshrouded impellers are generally recognized to display inferior performance to the shrouded impellers with the same geometry. In this paper, a comparative experiment shows some results inconsistent with conventional cognition. Measured performance indicates that the peak efficiency of the centrifugal compressor with an unshrouded impeller is higher than the shrouded one, where the two impellers have the same geometry of meridional profile and blade central plane, and matched the same vaneless diffuser and volute. In order to explore the causes of this divergence, the effects of factors such as blade thickness, surface roughness of components, tip clearance and sealing leakage characteristics on performance are analyzed by CFD code. Numerical results show that reasonable reduction in the blade thickness and improvement on the surface quality of the impeller could effectively increase the peak efficiency and the choke mass flow rate of the shrouded impeller. The unshrouded impeller with arbitrary blade surfaces would be deformed under the action of centrifugal force to achieve a small tip clearance during operation, and then obtains higher efficiency at design speed. The research results are helpful to evaluate the performance potential and sensitive design parameters of shrouded and unshrouded impellers.

The Range of Jupiter's Flow Structures that Fit the Juno Asymmetric Gravity Measurements

<p>The asymmetric gravity field measured by the Juno spacecraft has allowed the estimation of the depth of Jupiter's zonal jets, showing that the winds extend approximately 3,000 km beneath the cloud level. This estimate was based on an analysis using a combination of all measured odd gravity harmonics, <em>J</em><sub>3</sub>, <em>J</em><sub>5</sub>, <em>J</em><sub>7</sub>, and <em>J</em><sub>9</sub>, but the wind profile's dependence on each of them separately has yet to be investigated. Furthermore, these calculations assumed the meridional profile of the cloud‐level wind extends to depth. However, it is possible that the interior jet profile varies somewhat from that of the cloud level. Here we analyze in detail the possible meridional and vertical structure of Jupiter's deep jet streams that can match the gravity measurements. We find that each odd gravity harmonic constrains the flow at a different depth, with <em>J</em><sub>3</sub> the most dominant at depths below 3,000 km, <em>J</em><sub>5</sub> the most restrictive overall, whereas <em>J</em><sub>9</sub> does not add any constraint on the flow if the other odd harmonics are considered. Interior flow profiles constructed from perturbations to the cloud‐level winds allow a more extensive range of vertical wind profiles, yet when the meridional profiles differ substantially from the cloud level, the ability to match the gravity data significantly diminishes. Overall, we find that while interior wind profiles that do not resemble the cloud level are possible, they are statistically unlikely. Finally, inspired by the Juno microwave radiometer measurements, assuming the brightness temperature is dominated by the ammonia abundance, we find that depth‐dependent flow profiles are still compatible with the gravity measurements.</p>

The statistical probability of deep flow structures that fit Jupiter's asymmetric gravity

<div id="magicparlabel-56675" class="abstract"> <div class="abstract_item">Juno's measurements of Jupiter's North-South asymmetric gravity field allowed estimating the depth of the zonal jets trough the relation between the measured density anomaly and the flow field. While the deep zonal jets structure has many degrees of freedom, the gravity measurements are manifested only by four gravity harmonics, which implies that the problem is ill-posed. Hence, any suggested solution for Jupiter's deep jets that fit the gravity measurements is non-unique. Here, we perform a thorough statistical analysis of the deep flow structures' range that is bounded by physical considerations. We begin by examining the vertical range of the deep flow, where the meridional structure of the zonal wind is identical to the measured cloud-level profile. Then, we relax the constraint on the meridional profile and allow reasonable variations from the cloud-level profile along with the varying vertical decay. Finally, we examine random meridional profiles that are independent of Jupiter's measured cloud-level profile and explore the possibility that the interior wind structure, which influences the gravity measurements, is entirely different from the cloud-level flow. A sample population of vertical decay structures is used to compare the statistical likelihood of the various cases. We find that only a relatively narrow envelope of vertical solutions can fit the gravity data. Deep flow profiles constructed from perturbations to the cloud-level winds allow a more extensive range of solutions, yet when the patterns differ substantially from the cloud-level observed wind profile, the ability to match the gravity data reduces significantly. Moreover, only 1% of the tested random zonal wind profiles yield any solution that fits the gravity data. Overall, we find that while interior wind profiles that diverge considerably from those at the cloud-level are possible, they are statistically unlikely. In addition to the gravity measurements, Juno's microwave radiometer (MWR) measurements might reveal information about the wind's structure below the cloud level. Inspired by the MWR's nadir brightness temperature estimations, which are dominated by ammonia abundance, we show that depth-dependent flow profiles are still compatible with the gravity measurements if the variation at depth from the measured cloud-level meridional profile is not too substantial.</div> </div>

The range of flow structures fitting Jupiter's asymmetric gravity field

<div>Jupiter's North-South asymmetric gravity field, measured by the Juno spacecraft, allowed estimating the depth of the zonal jets trough the relation between the measured density anomaly and the flow. This analysis was based on a combination of all four measured odd gravity harmonics, so the direct effect of each of them on the flow profile has not been investigated. Moreover, past calculations assumed that the cloud-level zonal wind maintains its meridional structure with depth; However, the Juno microwave radiometer measurements imply that a vertically dependent meridional profile might be more suitable, due to the reasonable relation between the Nadir brightness temperature profile and the zonal wind. In this study, we analyze in detail the possible range of structures of Jupiter’s deep jet-streams, fitting each of the Juno's measured asymmetric gravity harmonics. Specifically, we examine the possible vertical structure of Jupiter’s deep jet streams, different meridional structures of the cloud-level zonal wind and depth-dependent meridional profile compatible with the Nadir temperature tendency. We find that each odd gravity harmonic constrains the flow at a different depth, with J3 being the most dominant at depths below 3000 km, where the electrical conductivity becomes significant. J5 is the most restrictive harmonic overall, and J9 does not constrain the flow at all if the other odd harmonics are within the measurement range. Deep flow profiles constructed from perturbations to the cloud-level winds allow a more extensive range of solutions, yet when the patterns differ substantially from the cloud-level observed wind profile, the ability to match the gravity data reduces significantly. Random zonal wind profiles, unconnected to the cloud-level profile allow almost no solutions for the gravity data, and only 1% of the tested wind profiles yield any solution. Overall, we find that while interior wind profiles that diverge considerably from those at the cloud-level are possible, they are statistically unlikely. Finally, we find that meridional smoothing of the wind with depth, according to the Juno MWR brightness temperature profile, still allows fitting the measured gravity signal within the uncertainty range.</div>

Radial Inflow Turbine Geometry Generation Method Using Third Order Bezier Curves for Blade Design

Radial inflow turbines offer larger efficiency performance for small power applications due to its geometric configuration in which flow varies its radial position along the flow path. The geometry configuration of radial-inflow turbines demands a careful and adequate design of the flow path, since a 90° change of direction occurs from the radial inflow to the axial outflow. The blade camberline also requires attention since it defines the tangential flow direction along the meridional coordinate and any variation in its geometry affects the turbine performance. In this paper, a method for meridional profile and camberline geometry generation is proposed and tested through CFD. The method consists in using fourth order Bezier curves for defining the hub, shroud and mid-height blade meridional profile and third order Bezier curves for defining the relative flow velocity angle along the meridional coordinate, which leads to the camberline angular position in the rotor considering radial fibered blades. The blade thickness is set to vary linearly along the meridional coordinate and along the blade height. Different configurations of blade geometry are proposed and analyzed. These configurations are fixed to satisfy the design parameters. The code is programed in Python and adjusts the geometry data in files that are readable by meshing software. Thereby numerical calculations are performed to verify which configuration of camberline results in better performance. The calculations are done in models with the same boundary conditions and geometric data except for the variation of relative flow velocity angle along the meridional coordinate but setting the inlet and outlet angle to a fixed value. This way, the most suitable camberline geometry can be selected. The CDF model used for this analysis was validated with the experimental results reported by Kang et al. [1]

RESPONSE OF THE NEUTRAL WIND TO INTENSE GEOMAGNETIC STORMS

Perturbations of the ionosphere related to geomagnetic storms have been an object of a close attention of ionospheric researchers for several decades and therefore are relatively well known. Effects of geomagnetic storms to atmospheric parameter have been studied. Mustel et al.,(1977) summarized a decrease of pressure after strong sporadic geomagnetic storms, while Pudovkin and Veretenko (1992) summarized changes of the meridional profile of the zonal atmospheric pressure during geomagnetic strom. Recently, Gustavo A. Mansilla (2011) obtain that atmospheric parameters such as wind speed and temperature could be affected by geomagnetic storms. In this paper we examine the possible connection between neutral wind speed from Meteor Wind Radar Kototabang and intense geomagnetic storms occured in 2003 and 2004. By statistical method we compare storm time value of neutral wind speed over Kototabang with their standard deviation obtained from quiet time value. The results shows that geomagnetic storms influence neutral wind speed over Kototabang.

Exact calculation of axisymmetric capillary bridge properties between two unequal-sized spherical particles

A calculation method for the meridional profile of axisymmetric bridges between two spheres of different size is introduced in this manuscript. From geometrical data of the capillary bridge, such as the neck radius and boundary conditions (filling and contact angle), the shape of the capillary bridge is calculated analytically as a solution of the Young–Laplace equation. Its free surfaces, of constant mean curvature, may be classified into portions of nodoid, unduloid, and other limit cases. Moreover, other properties of the liquid bridge can be computed analytically, such as the associated capillary force exerted on the solid surfaces, liquid volume, mean curvature, and free surface area.

A Simulation of Equatorial Plasma Bubble Signatures on the 016300 Å nightglow Meridional Profile Over Brazilian Low Latitude

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An analytical theory for the capillary bridge force between spheres

An analytical theory has been developed for properties of a steady, axisymmetric liquid–gas capillary bridge that is present between two identical, perfectly wettable, rigid spheres. In this theory the meridional profile of the capillary bridge surface is represented by a part of an ellipse. Parameters in this geometrical description are determined from the boundary conditions at the three-phase contact circle at the sphere and at the neck (i.e. in the middle between the two spheres) and by the condition that the mean curvature be equal at the three-phase contact circle and at the neck. Thus, the current theory takes into account properties of the governing Young–Laplace equation, contrary to the often-used toroidal approximation. Expressions have been developed analytically that give the geometrical parameters of the elliptical meridional profile as a function of the capillary bridge volume and the separation between the spheres. A rupture criterion has been obtained analytically that provides the maximum separation between the spheres as a function of the capillary bridge volume. This rupture criterion agrees well with a rupture criterion from the literature that is based on many numerical solutions of the Young–Laplace equation. An expression has been formulated analytically for the capillary force as a function of the capillary bridge volume and the separation between the spheres. The theoretical predictions for the capillary force agree well with the capillary forces obtained from the numerical solutions of the Young–Laplace equation and with those according to a comprehensive fit from the literature (that is based on many numerical solutions of the Young–Laplace equation), especially for smaller capillary bridge volumes.