Radial Pressure Profiles Research Articles

A Computational Fluid Dynamics Study of Circumferential Groove Casing Treatment in a Transonic Axial Compressor

Numerical investigations were conducted to predict the performance of a transonic axial compressor rotor with circumferential groove casing treatment. The Notre Dame Transonic Axial Compressor (ND-TAC) was simulated at Tsinghua University with an in-house computational fluid dynamics (CFD) code (NSAWET) for this work. Experimental data from the ND-TAC were used to define the geometry, boundary conditions, and data sampling method for the numerical simulation. These efforts, combined with several unique simulation approaches, such as nonmatched grid boundary technology to treat the periodic boundaries and interfaces between groove grids and the passage grid, resulted in good agreement between the numerical and experimental results for overall compressor performance and radial profiles of exit total pressure. Efforts were made to study blade level flow mechanisms to determine how the casing treatment impacts the compressor's stall margin and performance. The flow structures in the passage, the tip gap, and the grooves as well as their mutual interactions were plotted and analyzed. The flow and momentum transport across the tip gap in the smooth wall and the casing treatment configurations were quantitatively compared.

Radial pressure profile of typhoon field near ground surface observed by distributed meteorologic stations

It is a common practice at the international level to predict maximal wind speed for coastal regions prone to strong typhoon occurrence using a typhoon numerical model and Monte-Carlo algorithm. Furthermore, it is necessary to calibrate the radial wind-induced pressure field of a typhoon process by comparison between numerical simulation and actual measurement. This paper developed the analytic model of radial atmospheric pressure distribution originally proposed by Holland and discussed the distribution factor of radial typhoon pressure field (also referred to as Holland parameter β). Some more expressions about radial atmospheric pressure distribution under the condition of typhoon proposed by numerous scholars over the past several decades were also reviewed. Their impacts on prediction of regional extreme wind velocity were studied and compared about the various values of β derived from those formulas. Then, the fitted power exponent about atmospheric pressure field were proposed utilizing a large amount of on-spot observed atmospheric data from several hundreds of national meteorologic stations along Chinese coastal regions according to the Holland empirical analytic model. Since the maximum wind-speed radius, central pressure differential, latitude of typhoon center and even surface temperature of the ocean during typhoon process affect wind-pressure distribution coefficient β more or less, further study and verification are needed to determine the method for calculating β that gives the best precision for the radial atmospheric pressure distribution of a typhoon.

Radio mini-halo emission from cosmic rays in galaxy clusters and heating of the cool cores

It has been proposed that the cool cores of galaxy clusters are stably heated by cosmic rays (CRs). If this is the case, radio mini-halos, which are often found in the central regions of cool core clusters, may be attributed to the synchrotron emission from the CRs. Based on this idea, we investigate the radial profiles of the mini-halos. First, using numerical simulations, we confirm that it is appropriate to assume that radiative cooling of the intracluster medium (ICM) is balanced with the heating by CR streaming. In these simulations, we assume that the streaming velocity of the CRs is the sound velocity of the ICM, and indicate that the heating is even more stable than the case where the streaming velocity is the Alfven velocity. Then, actually assuming the balance between cooling and heating, we estimate the radial profiles of CR pressure in six clusters only from X-ray observations. Since the CR protons interact with the ICM protons, we can predict the radial profiles of the resultant synchrotron radiation. We compare the predictions with the observed radial profiles of the mini-halos in the six clusters and find that they are consistent if the momentum spectra of the CRs are steep. These results may indicate that the cores are actually being heated by the CRs. We also predict broad-band spectra of the six clusters, and show that the non-thermal fluxes from the clusters are small in hard X-ray and gamma-ray bands.

Characteristics of plasma ring, surrounding the Earth at geocentric distances ∼7–10RE, and magnetospheric current systems

There are strong experimental evidences of the existence of plasma domain forming a closed plasma ring around the Earth at geocentric distances ∼7–10RE. In this work, we analyze the main properties of this ring, using the data of the THEMIS satellite mission, acquired between April 2007 and September 2011. We also analyze the contribution of this ring to the storm dynamics. In particular, it is shown that the distribution of plasma pressure at ∼7–10RE is nearly azimuthally symmetric. However, the daytime compression of the magnetic field lines and the shift of the minimal value of the magnetic field to higher latitudes lead to the spreading of the transverse current along field lines and splitting of the daytime integral transverse current into two branches in Z direction. The CRC is the high latitude continuation of the ordinary ring current (RC), generated by plasma pressure gradients, directed to the Earth. We evaluated the contribution of the azimuthally symmetric part of the plasma ring to the Dst index for strong geomagnetic storms using the AMPTE/CCE radial profiles of plasma pressure published before, and showed that the contribution of the ring current including both RC and CRC is sufficient to obtain the observed Dst variation without the necessity to include the tail current system.

Thermal and heat transfer behaviors of an inverse diffusion flame with induced swirl

An experimental work was made to investigate the thermal and heat transfer behaviors of a multi-fuel-jet inverse diffusion flame (IDF) with induced swirl. Flame appearances, temperature fields and wall static pressures were compared between the swirling and non-swirling IDFs under identical air/fuel flow rates. Results show that either flame consists of a lower flame base and an upper flame torch where main combustion takes place. However, the main reaction zone in the swirling IDF and is closer to the burner exit and the flame length is much shorter than the non-swirling IDF. Both the radial wall static pressure profile and radial heat flux distribution of the swirling IDF are M-shaped at low nozzle-to-plate distances, and both are influenced by the swirl effect.

Dependence of volumes of magnetic flux tubes on plasma pressure and disturbance in the magnetic field in the axially symmetric case

We have analyzed the applicability of the approximation of the axially symmetric magnetic field created by the dipole field and the currents flowing in the plasma for describing the Dst variation value during magnetic storms and the dependence of the position of the pressure maximum on the volumes of magnetic flux tubes on the plasma pressure. We have determined the dependence of the disturbance in the field on the geocentric distance. We have shown that the experimentally obtained dependence on the position of the pressure maximum on Dst is described in the assumption on the correctness of the adiabatic law on changes in pressure with a change in geocentric distance. We have calculated the values of the magnetic field distortion and the value of the Dst variation for the experimentally determined radial pressure profile for three magnetic storms with Dst ∼ 100 nT. We have shown that, with allowance for nonlinear magnetic field distortions, the axially symmetric part of the ring current makes the main contribution to the value of the Dst variation.

Numerical and Experimental Studies on the Supersonic Coaxial Jet Mixing

Coaxial nozzles are an integral part of many engineering systems where mixing of different fluid streams is required. Single noncircular nozzles have been shown to have better mixing characteristics than their axisymmetric counterparts. Therefore, a combination of such nozzles into coaxial configurations is promising. The aim of the present study is to quantitatively determine the effects of the geometry of the primary supersonic jet on the mixing characteristics with the secondary high speed subsonic jet. Measurements of pressure profiles at several positions along central axis of jets using identical facilities and nominally identical experimental conditions were done. The mixing is dominated by the vortex structures that are present in the inner shear layers. The interaction of the vortex structures govern the growth, and entrainment, and mixing of the jet. Also, the experimental results show that the radial and centerline pressure profiles through various coaxial jets has good correlation with the CFD simulation.

Structure, force balance, and evolution of incompressible cross-tail current sheet thinning

[1] THEMIS five-point observations on April 8, 2009 were used to study thinning of the current sheet in the near-Earth tail that led to the onset of a small substorm. Taking advantage of a fortuitous alignment of the five spacecraft near 2300 LT and 11 RE and within 1.5 RE of the current sheet center, latitudinal gradients are analyzed. A significant latitudinal pressure gradient is present indicating the necessity of a (J × B)z force to maintain the pre-onset equilibrium state. During thinning the total pressure remained approximately constant at all spacecraft rather than increasing. Within the plasma sheet, magnetic field strength increased while plasma pressure decreased due to decreasing temperature. We present a comprehensive explanation for the relationship between the thinning, the stretched structure, and development of intense current density. Our analysis of this event suggests that (1) the thinning in this event is an MHD force-balanced self-evolving process and is not a forced process due to an increased lobe field; (2) the thinning changes flux tube structure in length and curvature but not significantly in volume; (3) the thinning evolves with a change of the radial plasma pressure profile in the near-Earth tail, which is associated with a locally intensified current sheet. The conclusion is that the increased lobe field strength is not the necessary and the primary cause for cross tail current sheet thinning but rather thinning can occur within the plasma sheet as a result of unknown internal processes.

Typhoon wind hazard analysis for southeast China coastal regions

Southeast coastal region is the most developed and populated area in China, and also is one of the regions most seriously impacted by typhoons in the world. In this paper, typhoon wind hazard analysis for 11 major cities, Shanghai, Ningbo, Wenzhou, Fuzhou, Xiamen, Taipei, Guangzhou, Shenzhen, Hong Kong, Zhanjiang, and Haikou, in the southeast China coastal regions, is conducted for the first time. The historical typhoon data from the China Meteorological Administration (CMA) and the State Oceanic Administration is carefully processed and the probabilistic distributions of the key typhoon parameters for the 11 cities are established. The correlations between the key typhoon parameters are carefully evaluated. The wind field model given by Thompson and Cardone is introduced, and the radial pressure profile is properly addressed with validation of the model by six cyclones. Monte Carlo random sampling method is employed to generate virtual typhoons and 1000 years of typhoons are simulated for the 11 cities. Extreme wind speeds of different return periods are then predicted. There is a reasonable agreement between the predictions of wind speed in the code of Hong Kong and available literature, suggesting that the approach is effective in determining the design wind speeds for critical structures in the southeast China coastal regions.

Optical measurements for turbulence characterization in RFX-mod edge

The edge of the reversed field pinch experiment RFX-mod (R=2 m, a=0.46 m) is characterized by a complex magnetic topology and strong pressure gradients. A set of fast spectroscopic diagnostics has been designed to characterize both main plasma edge parameters and turbulence, including coherent structures (blobs) and radial profiles of the thermodynamic variables. Measurements of the edge radial profiles of electron density (n(e)), temperature (T(e)), and pressure (P(e)) are obtained by a thermal helium beam diagnostic, which locally measures the ratios of the spectral lines emitted by a neutral He cloud puffed into hydrogen plasma discharges. A gas puff imaging system allows the high frequency (1 MHz bandwidth) measurement of the fluctuations of He I emissivity in the same positions. The system measures both the intermittent behavior of the edge turbulence and n(e), T(e), and P(e) profiles of the corresponding coherent structures, with a resolution down to 6 μs. The optical diagnostics are complemented by a set of triaxial magnetic coils to simultaneously characterize the edge magnetic field.

Internal mapping of the normal modes of a liquid filled spherical resonator.

We report on the measurements of the pressure fields set up inside a water-filled steel shell over a spectral range (10–50 kHz) that includes 75 modes of the composite system. The 9.5-in.-diameter shell has a wall thickness to radius ratio of h/R = 0.158, which is beyond the thin shell limit. Hydrophone scans of the acoustic pressure fields in the fluid were performed, from which 46 modes of the composite resonator were identified. The modal frequencies are in good agreement with those predicted by Mehl for a fluid-filled shell of arbitrary wall thickness. The radial pressure profiles of the modes are shown to fit the expected spherical Bessel profiles for solutions of the Helmholtz equation under spherical symmetry. The results are interpreted in terms of the idealized rigid shell and empty shell limits.

Internal Magnetic Field Measurements in the TCSU RMF Current Drive Experiment

Detailed magnetic measurements of Field-reversed configurations (FRC) from the Translation Confinement Sustainment Upgrade (TCSU) experiment are presented. A two-axis probe inserted transversely at the axial midplane provides 24 independent measurements of B z (r) and B x (r). Two single-axis 29 channel probes provide axial profiles at the plasma edge. The B x (r) field profiles, oriented to measure Bθ from the rotating magnetic field (RMF), provide details about RMF penetration into the FRC. B z (r) profiles, when combined with the high beta nature of the FRC, interferometric density measurements, and assuming uniform temperature, yield radial density and pressure profiles. Time evolution of these profiles gives insight into plasma dynamics and the n = 1 (wobble) and n = 2 instabilities. Data from 123 and 172 kHz RMF frequencies is presented.

A systematically coarse-grained solvent-free model for quantitative phospholipid bilayer simulations.

We present an implicit solvent coarse-grained (CG) model for quantitative simulations of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers. The absence of explicit solvent enables membrane simulations on large length and time scales at moderate computational expense. Despite improved computational efficiency, the model preserves chemical specificity and quantitative accuracy. The bonded and nonbonded interactions together with the effective cohesion mimicking the hydrophobic effect were systematically tuned by matching structural and mechanical properties from experiments and all-atom bilayer simulations, such as saturated area per lipid, radial distribution functions, density and pressure profiles across the bilayer, P2 order, etc. The CG lipid model is shown to self-assemble into a bilayer starting from a random dispersion. Its line tension and elastic properties, such as bending and stretching modulus, are semiquantitatively consistent with experiments. The effects of (i) reduced molecular friction and (ii) more efficient integration combine to an overall speed-up of 3−4 orders of magnitude compared to all-atom bilayer simulations. Our CG lipid model is especially useful for studies of large-scale phenomena in membranes that nevertheless require a fair description of chemical specificity, e.g., membrane patches interacting with movable and transformable membrane proteins and peptides.

Radial profile of pressure in a storm ring current as a function of D st

Using satellite data obtained near the equatorial plane during 12 magnetic storms with amplitudes from −61 down to −422 nT, the dependences of maximum in L-profile of pressure (Lm) of the ring current (RC) on the current value of Dst are constructed, and their analytical approximations are derived. It is established that function Lm(Dst) is steeper on the phase of recovery than during the storm’s main phase. The form of the outer edge of experimental radial profiles of RC pressure is studied, and it is demonstrated to correspond to exponential growth of the total energy of RC particles on a given L shell with decreasing L. It is shown that during the storms’ main phase the ratio of plasma and magnetic field pressures at the RC maximum does not practically depend on the storm strength and Lm value. This fact reflects resistance of the Earth’s magnetic field to RC expansion, and testifies that during storms the possibilities of injection to small L are limited for RC particles. During the storms’ recovery phase this ratio quickly increases with increasing Lm, which reflects an increased fraction of plasma in the total pressure balance. It is demonstrated that function Lm(Dst) is derived for the main phase of storms from the equations of drift motion of RC ions in electrical and magnetic fields, reflecting the dipole character of magnetic field and scale invariance of the pattern of particle convection near the RC maximum. For the recovery phase it is obtained from the Dessler-Parker-Sckopke relationship. The obtained regularities allow one to judge about the radial profile of RC pressure from ground-based magnetic measurements (data on the Dst variation).

Convectively stable pressure profile in magnetic confinement systems with internal rings

A convectively stable pressure profile in a long multiple-mirror (corrugated) magnetic confinement system with internal current-carrying rings is calculated. The plasma energy content in the axial region can be increased by using an internal ring that reverses the on-axis magnetic field direction and gives rise to an average magnetic well near the axis. The pressure profile in the outer region—outside the magnetic well—is considered in detail. It is shown that, in the radial pressure profile, a pedestal can be formed that leads to a higher pressure drop between the center and the plasma edge. The pressure profile is calculated from the Kruskal-Oberman criterion—a necessary and sufficient condition for the convective stability of a collisionless plasma. The revealed pedestal arises near the boundary of the average magnetic well in the region of the smallest but alternating-sign curvature of the magnetic field lines due to a break in the convectively stable pressure profile. Such a shape of the stable pressure profile can be attributed to the stabilizing effect of the alternating-sign curvature of the field lines in the multiple-mirror magnetic confinement systems under consideration.

Kinematic deprojection and mass inversion of spherical systems of known velocity anisotropy

Traditionally, the mass / velocity anisotropy degeneracy (MAD) inherent in the spherical, stationary, non-streaming Jeans equation has been handled by assuming a mass profile and fitting models to the observed kinematical data. Here, the opposite approach is considered: the equation of anisotropic kinematic projection is inverted for known arbitrary anisotropy to yield the space radial velocity dispersion profile in terms of an integral involving the radial profiles of anisotropy and isotropic dynamical pressure. Then, through the Jeans equation, the mass profile is derived in terms of double integrals of observable quantities. Single integral formulas for both deprojection and mass inversion are provided for several simple anisotropy models (isotropic, radial, circular, general constant, Osipkov-Merritt, Mamon-Lokas and Diemand-Moore-Stadel). Tests of the mass inversion on NFW models with these anisotropy models yield accurate results in the case of perfect observational data, and typically better than 70% (in 4 cases out of 5) accurate mass profiles for the sampling errors expected from current observational data on clusters of galaxies. For the NFW model with mildly increasing radial anisotropy, the mass is found to be insensitive to the adopted anisotropy profile at 7 scale radii and to the adopted anisotropy radius at 3 scale radii. This anisotropic mass inversion method is a useful complementary tool to analyze the mass and anisotropy profiles of spherical systems. It provides the practical means to lift the MAD in quasi-spherical systems such as globular clusters, round dwarf spheroidal and elliptical galaxies, as well as groups and clusters of galaxies, when the anisotropy of the tracer is expected to be linearly related to the slope of its density.

Enhancement of a cylindrical separator efficiency by using double vortex generators

The present article describes a numerical study of multiphase, strongly swirling flow in a cylindrical separator with double vortex generators to predict the separation efficiency of mixture consisting of oil as the primary phase and sand with several sizes as the secondary phases. Solids are classified by the separation process and the feed is split into coarse and fine fractions (with the fine fraction usually remaining in suspension). The mixture-granular multiphase and renormalization group (RNG) of k − ɛ turbulence models are implemented in this study. The predictions are compared against the experimental data of mean tangential velocity and mean radial pressure profiles. The overall agreement between the measurements and the predictions obtained with RNG k − ɛ model is reasonably good. The present models based on computational fluid dynamics (CFD) techniques have ability to capture a narrow localized residence zone for solid particles at location near the mid-cylinder where the two vortices merge and the suspension process can take place. Furthermore, they have proven to be useful in predicting the internal flow structure of the continuous phase thus the separation of the particulate phases. Most of the larger particles to be separated are forced to remain near the periphery of the separator and concentrated at the mid-separator as a result of strong centrifugal force. On the other hand, the finer particles with less inertia are not affected too much and are subsequently dispersed over the separator. The separation process does not end by the arrival of the particles onto a collecting zone. If the process is to be continuous, the collected particles have to be transported and discharged from the separator.

APPLICATION OF A SELF-SIMILAR PRESSURE PROFILE TO SUNYAEV-ZEL'DOVICH EFFECT DATA FROM GALAXY CLUSTERS

We investigate the utility of a new, self-similar pressure profile for fitting Sunyaev-Zel'dovich (SZ) effect observations of galaxy clusters. Current SZ imaging instruments - such as the Sunyaev-Zel'dovich Array (SZA) - are capable of probing clusters over a large range in physical scale. A model is therefore required that can accurately describe a cluster's pressure profile over a broad range of radii, from the core of the cluster out to a significant fraction of the virial radius. In the analysis presented here, we fit a radial pressure profile derived from simulations and detailed X-ray analysis of relaxed clusters to SZA observations of three clusters with exceptionally high quality X-ray data: A1835, A1914, and CL J1226.9+3332. From the joint analysis of the SZ and X-ray data, we derive physical properties such as gas mass, total mass, gas fraction and the intrinsic, integrated Compton y-parameter. We find that parameters derived from the joint fit to the SZ and X-ray data agree well with a detailed, independent X-ray-only analysis of the same clusters. In particular, we find that, when combined with X-ray imaging data, this new pressure profile yields an independent electron radial temperature profile that is in good agreement with spectroscopic X-ray measurements.

A Solvent-Free Coarse-Grained Model for Quantitative POPC Bilayer Simulations

We presented an implicit solvent CG model in a bottom-up scheme for simulations of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer membranes. The usage of implicit solvent enables membrane simulations on large length- and time-scale at modest computational expense. Despite an improved computational efficiency, the model preserves chemical specificity and quantitative accuracy in comparison with top-down solvent-free CG bilayer models. In the CG model, each of the CG sites was associated with the center-of-mass of a specific group of atoms in the all-atom representation of POPC. The bonded and non-bonded interaction parameters together with the effective cohesive interactions mimicking the hydrophobic effect were systematically derived by matching radial distribution functions, density and pressure profiles of the bilayer, and self-assembly of lipids in all-atom simulations of POPC phospholipids. The CG model is especially useful for studies of large-scale phenomena in membranes which require a detailed description of chemical specificity, e.g. membrane patches interacting with movable and transformable membrane proteins/peptides.

On Interpreting the Diamagnetism of a Compact Plasmoid

A set of formulas for interpreting the diamagnetic measurements of compact plasmoid in a conducting chamber is derived. The formulas are written in the form of an integral transformation relating the magnetic flux to the radial pressure profile of the plasmoid. An inverse transformation is also found. Particular examples of applying the newly derived formulas to the SHIP experiment are given. They show that the conductive chamber has essential effect on the result of the measurements. The optimization of the loop geometry that allows maximizing the measured signal is also described.