Radial Flow Gas Research Articles

Formation of ω Centauri from an ancient nucleated dwarf galaxy in the young Galactic disc

We first present a self-consistent dynamical model in which ω Cen is formed from an ancient nucleated dwarf galaxy merging with the first generation of the Galactic thin disc in a retrograde manner with respect to the Galactic rotation. Our numerical simulations demonstrate that during merging between the Galaxy and the ω Cen host dwarf with M B ≃ - 14 mag and its nucleus mass of 10 7 M O ., the outer stellar envelope of the dwarf is nearly completely stripped, whereas the central nucleus can survive from the tidal stripping because of its compactness. The developed naked nucleus has a very bound retrograde orbit around the young Galactic disc, as observed for ω Cen, with apocentre and pericentre distances of ∼8 and ∼1 kpc, respectively. The Galactic tidal force can induce radial inflow of gas to the centre of the dwarf and consequently triggers moderately strong nuclear starbursts in a repetitive manner. This result implies that efficient nuclear chemical enrichment resulting from the later starbursts can be closely associated with the origin of the observed relatively young and metal-rich stars in ω Cen. Dynamical heating by the ω Cen host can transform the young thin disc into the thick disc during merging.

A Unified Approach for Designing a Radial Flow Gas Turbine

Radial flow turbo machines have been used for a long time in a variety of applications such as turbochargers, cryogenics, auxiliary power units, and air conditioning of aircraft cabins. Hence numerous papers have been written on the design and performance of these machines. The only justification for yet another paper is that it would describe a unified approach for designing a single stage inward flow radial turbine comprising a rotor and the casing. The current turbine is designed to drive a direct-coupled permanent magnet high-speed alternator running at 60000 rpm and developing a maximum of 60 kW electrical power. The freedom of choice of the tip diameter and the tip width of the rotor that would be necessary for optimum isentropic efficiency of the turbine stage was restricted by the specified rotational speed and power output. Hence, an optimization procedure was developed to determine the principal dimension of the rotor. The mean relative velocity in the rotor passages in the direction of the flow would be accelerated but flow velocity on the blade surfaces experiences a significant space rate of deceleration. The rate of deceleration can be controlled by means of a proper choice of the axial length of the rotor. A prescribed mean stream velocity distribution procedure was used to spread the rate of deceleration of the mean flow velocity along the meridional length of the flow passages. The nozzle-less volute casing was designed to satisfy the mass flow rate, energy and angular momentum equations simultaneously. This paper describes the work undertaken to design both the rotor and the casing. The work was motivated by the growing interest in developing gas turbine based hybrid power plant for road vehicles. The authors believe that the paper would lead to a stimulating discussion.

8.1. Magnetic phenomena in galactic nuclei

The magnetic environment of the Galactic nucleus contrasts sharply with that of the Galactic disk. The inner few hundred parsecs of our Galaxy appear to be dominated by a strong (~milligauss) and uniform dipole field which dominates the pressure within the central intercloud medium. An attractive hypothesis for the origin of the central vertical field is that it results from the concentration of protogalactic field by radial inflow of gas throughout the Galaxy's lifetime. The predominant orientation of the magnetic field within dense molecular clouds is parallel to the galactic plane, which can be understood in terms of the strong tidal shear to which these clouds are subjected. The contrasting geometries of the cloud and intercloud fields allow for magnetic field line reconnection at cloud surfaces, which, under the right circumstances, could produce the relativistic electrons which delineate the nonthermal radio filaments near the Galactic center with their synchrotron emission. The characteristics of the Galactic center “magnetosphere” should be generalizable to all gas-rich spiral galaxies. Inadequate spatial resolution currently prevents us from exploring magnetic fields in other galactic nuclei to the same depth as in the Galactic center, but existing evidence is consistent with similar magnetic geometries elsewhere.

Molecular Bars in Spiral Galaxies

Images of molecular gas in spiral galaxies show two types of bar structure: large-scale bars, which are correlated with the presence of stellar bars, and generally follow the spiral structure, and nuclear “bars” of a few hundred parsecs in size, which show no direct correlation with the presence of a stellar bar. The dynamical origin of nuclear molecular bars is unclear, although they are consistent with radial inflow of gas into the nucleus, and subsequent evolution of the gas structure.

A Two-Dimensional Flow Analysis Model for Designing a Nozzle-less Volute Casing for Radial Flow Gas Turbines

This paper describes a two-dimensional model for flow analysis and design of a single entry nozzle-less volute casing for inward flow radial turbines. The model takes into account the cross-sectional shape of the casing by dividing it into a number of segments, which are further subdivided into control volumes. Changes in flow properties are calculated by considering the changes in momenta of fluid in the tangential and radial directions across each control volume. The model has been computerized using Fortran 77 for the IBM AT or 100 percent compatible microcomputers.

High chemical abundances in Virgo spiral galaxies?

Evidence is presented that spiral galaxies in the Virgo Cluster have systematically higher interstellar abundances than comparable field galaxies. This conclusion is based on spectra of H II regions in five Virgo spirals of type Sc. A possible explanation is that abundances in the field spirals are strongly affected by infall of metal-poor gas or by radial inflow of gas from the outer H I disk. These processes are inhibited in the cluster environment, and the Virgo spirals may have evolved more nearly in the manner of the closed box 'simple model of chemical evolution. 59 refs.

Evolution of self-gravitating accretion disks in active galactic nuclei

The evolution of self-gravitating gaseous disks in active galactic nuclei on scales of about 10-1000 pc is investigated. Star formation is a plausible outcome of the Jeans instability operating in a disk which violates the criterion for local stability. Even a low efficiency of star formation would deplete the gaseous disk on a short time scale and create a flat stellar system. These systems can evolve (sphericalize) secularly by means of stellar encounters but this process appears to be too slow to be important. Such flattened stellar systems may be common in the circumnuclear regions of disk galaxies. Conventional viscosities are inefficient in building anew the accretion process even in a cosmological time. Strongly self-gravitating disks are unstable to global nonaxisymmetric modes, which can induce radial inflow of gas in a short dynamical time. The latter effect is studied in a separate paper.

Chemical evolution of viscously evolving galactic discs

The ability of the Lin-Pringle (1987) model of galactic disk formation to reproduce the observed radial distributions of total gas surface density and metals in disk galaxies is investigated. It is found that a satisfactory fit is obtained provided that there exists an outer cut-off to the star-forming disk beyond which gas is allowed to viscously evolve. The metallicity gradient is then established by radial inflow of gas from beyond this cut-off.

Hypersonic, stratified gas flows past an obstacle: Direct simulation monte carlo calculations

Computational studies of the three-dimensional, hypersonic flow of rarefied, strongly stratified gas past an obstacle are carried out, the incident gas stratified in a direction transverse to the mean flow. An “ N-body” computational code based on Monte Carlo techniques is developed for these purposes. Our primary interest is centered on the three-dimensional effects induced in the gas flow by a solid obstacle comparable in size to the gas scale height and collisional mean free path. Of the different types and shapes of obstacles studied, we focus herein on a cylindrical obstacle, assumed to be a diffuse elastic scatterer. The cylindrical obstacle is a short uniform pipe whose upstream end is fully open, facing directly into the flow, and whose downstream end is covered by a flat circular endplate containing an “orifice” at its center. For different choices of “orifice” diameter, the obstacle serves as a useful model of an impact probe (closed orifice) or scoop (closed, partially open, or fully open orifice) in a rapidly rotating strongly stratified gas (as in a gas centrifuge). The computed results show that the obstacle (in all cases studied, spanning the range from completely closed orifice to fully open orifice) induces large systematic motions in the gas, with strong radially inward driven flow in the direction of the gradient of density stratification, and correspondingly large density perturbations in these regions. The radial inflow of gas is prominent not only in the neighborhood of the obstacle and downstream from it but also at considerable distances radially inward from it and at z-heights well above and below. The radially driven gas inflow is a striking three-dimensional effect induced when strongly stratified gas impinges upon an obstacle; it constitutes a major characteristic common to all the hypersonic, stratified flows studied despite differences in Mach number and gas scale height and regardless of whether the obstacle is a flat plate, a “long” solid rod, or a “short” cylindrical pipe. The resultant density distribution of the obstructed molecular gas exhibits a striking “asymmetry” in the (radial) direction of the gradient of density stratification but retains “symmetry” in the z-direction perpendicular to the stratification gradient. The “ r-asymmetry” is in striking contrast to the characteristic rotation-symmetry exhibited about the obstructing pipe's central axis in corresponding cases of unstratified flows investigated. The bow shock that forms near the obstacle exhibits a characteristic thickness that broadens with mean free path in the direction of the gradient of density stratification and a characteristic shape that is substantially warped (in that direction) from the paraboloid-shaped bow shock that forms (with axis of revolution coincident with the pipe's central axis) in corresponding cases of unstratified flows. The redirection of the gas flow at the shock away from the direction of the incident mean flow is particularly strong along that portion of the warped bow shock most closely aligned with the (radial) direction of the stratification gradient; the postshock density ridge in this direction is masked considerably by the strongly stratified density background.

Application of All-Ceramic Nozzle to Radial Flow Turbine

An all-ceramic turbine nozzle offers the capability for improved erosion resistance and up-rated turbine inlet temperature. This yields significant improvement in engine durability and performance. Results of ceramic turbine nozzle engine tests and engine simulator tests for a small radial flow gas turbine are presented. The effects of erosive particles and ingested sea salt on the ceramics are included in this work.

Paper 8: Calculations of the Flow Distribution within a Radial Turbine Rotor

The distribution of pressure and velocity within the rotor of a radial flow gas turbine is computed using a two-dimensional streamline curvature method. Solutions are obtained on the meridional plane and also on three blade-to-blade surfaces at the hub, mid-blade position, and at the shroud. The torque, as calculated from the blade-to-blade flows, agrees with the measured torque over a speed range of approximately 2:1 with sufficient accuracy to support the usefulness of the flow structure as indicated by two-dimensional calculation methods applied to radial turbomachines.

Paper 23: An Investigation of the Losses in the Rotor of a Radial Flow Gas Turbine at Zero Incidence under Conditions of Steady Flow

The performance of a radial flow turbine, operating on compressed air, is measured over a range of pressure ratio and speed. Separate tests on the nozzle assembly alone enable the rotor performance to be separated from the overall characteristics. In particular, the conditions at each pressure ratio for which the nozzle exit whirl velocity is equal to the rotor tip speed may be deduced. Also, it is possible to evaluate the enthalpy ‘loss’ in the rotor, that is, the difference between the specific enthalpy drop actually occurring in the rotor and its isentropic value. An attempt is then made to relate this loss with the relative velocities within the rotor passages as predicted by inviscid, two-dimensional analytical techniques. The method developed by Stanitz and co-workers has been programmed to analyse the rotor internal fluid flow properties in the blade-to-blade plane for the conditions of zero incidence. The region investigated does not include the whole rotor, but extends from a boundary upstream of the blade tip to a downstream boundary at a radius equal to 72 per cent of the tip radius. The analysis is performed for overall turbine static to static pressure ratios of 1·2 to 1·6. The result of the theoretical analysis is to show that the variable ratio of rotor outlet to inlet specific volume with changing pressure ratio is accommodated almost entirely without any change in the flow distribution; that is, over the region of the impeller investigated, and at overall turbine pressure ratios up to 1·6, the compressible flow through the rotor may be considered as being through stream tubes of fixed geometry. There is thus a sound basis for the correlation of rotor loss coefficient in terms of parameters which describe compressible flow with friction along variable area pipes. Consideration is given to the manner in which the zero incidence loss coefficient may be defined in order to remain constant at varying pressure ratios.

Heat Transfer From a Shrouded Rotating Disk With Film Cooling

A study of the cooling effect of secondary fluid injection on the heat transfer between a shrouded rotating disk and a radially inward main flow stream is presented. The investigation is intended as a model study of film-cooled, radial-flow gas turbines. The film-cooling method is reviewed, and the nondimensional parameters governing the heat transfer are obtained. Experimental results, covering the range of radial-flow, gas-turbine operating conditions, were obtained from a film-heated, rotating-disk facility. The heat-transfer behavior of the main stream only was determined separately, and the film-cooling results are presented as ratios of the heat transfer obtained with film cooling to the heat transfer obtained with only the single radial inflow.

Heat Transfer From a Shrouded Rotating Disk to a Single Fluid Stream

This paper presents the initial results of a model study to determine the heat-transfer characteristics of radial-flow gas turbines. A test facility was constructed and several unconventional experimental techniques were developed for use in the facility. An idealized model consisting of a shrouded rotating disk with a single radially inward airflow was studied. The flow pattern and heat-transfer behavior were analytically and experimentally determined. The experimentally determined heat transfer is correlated by an algebraic expression over the range of nondimensional parameters characteristic of radial-flow gas-turbine operation.

Theoretical Assessment of the Performance Characteristics of Inward Radial Flow Turbines

While the simple centrifugal compressor has been widely used over a considerable period of time and in a variety of applications, in particular aircraft gas turbines and aero-engine superchargers, and its behaviour is therefore reasonably well understood, the inward radial flow gas turbine has only recently begun to attract the attention of engineers. As a result, its characteristics are not understood as fully as those of the centrifugal compressor.Inward radial flow turbines have a number of attractive features, such as robustness, cheapness, and relative immunity from thermal stresses, which render them particularly suitable, where the mass throughput and overall pressure ratio are moderate.While the assessment of performance and flow conditions at the design point presents no very great difficulties, the evaluation of performance under conditions of reduced speed and pressure ratio, knowledge of which is essential in most applications, does not appear to have been attempted hitherto.An analytical treatment of part-load conditions is outlined in this paper. In addition, the influence of the various design parameters on the overall characteristics is examined, and tentative suggestions are made for the best combination of these parameters for particular applications.

On a Theory of Radial-Flow Gas Turbine : 2nd Report, Mixed-Flow Turbine

In the 1st report radial-inflow turbines of purely radial-flow type were investigated. in this report, in order to introduce design data and to explain various performances of radial-inflow turbines of mixed-flow type, by investigating relations between the isentropic heat drop in the impeller and the distribution of the static pressure at the outlet of the impeller, a general formula of efficiency was introduced adopting such parameters as used in the 1st report. The characteristics of radial turbines of mixed-flow type, when the ratio of the diameter at the outlet of the impeller to the outer diameter of the impeller was about 0.6, were calculated and effects of several factors on efficiency were investigated. Then a radial turbine of mixed-flow type was designed for supercharging diesel-engines and the velocity diagram and the dimensions of the designed rotor were shown.

On a Theory of Radial-Flow Gas Turbine

A general fromula of an efficiency of radial-flow gas turbine, including the rotationary loss was introduced by adopting three parameters-the flow factor, the ratio of radial components of absolute velocities at the inlet and the outlet of the impeller and the ratio of the inner and the outer diameters. When the angle of the impeller at the outlet was given or the absolute velocity at the outlet of the impeller was radially directed, the relations at the optimum and the maximum efficiency were given. The characteristics of radial-flow gas turbine, when the ratio of the inner and the outer diameters was 0.6, were shown, the effect of the rotationary loss was discussed and the case when the absolute velocity at the outlet of the impeller was radially directed, was proved to be not optimum. Then a radialflow gas turbine for supercharging a diesel-engine was designed and the velocity diagram was shown with the dimensions of its impeller.

Radial-Flow Compressors and Turbines for the Simple Small Gas Turbine

Abstract This paper describes the procedure followed in developing an acceptable radial-flow turbine for use with a lightweight gas-turbine-driven fire pump for the Navy Bureau of Ships. In the course of this work considerable data were accumulated on general design information and practice on radial compressors and turbines. A review is given of these data as well as the current design approach for a simple cycle radial-flow gas turbine. A discussion of the factors and variables which affect the performance of radial turbomachines is included.