The stellar velocity dispersion in nearby spirals: radial profiles and correlations

The stellar velocity dispersion, σ, is a quantity of crucial importance for spiral galaxies, where it enters fundamental dynamical processes such as gravitational instability and disc heating. Here we analyse a sample of 34 nearby spirals from the Calar Alto Legacy Integral Field Area (CALIFA) spectroscopic survey, deproject the line-of-sight σ to σR and present reliable radial profiles of σR as well as accurate measurements of ⟨σR⟩, the radial average of σR over one effective (half-light) radius. We show that there is a trend for σR to increase with decreasing R, that ⟨σR⟩ correlates with stellar mass (M⋆) and tested correlations with other galaxy properties. The most significant and strongest correlation is the one with M⋆: $\langle \sigma _{R}\rangle \propto M_{\star }^{0.5}$. This tight scaling relation is applicable to spiral galaxies of type Sa–Sd and stellar mass M⋆ ≈ 109.5–1011.5 M⊙. Simple models that relate σR to the stellar surface density and disc scale length roughly reproduce that scaling, but overestimate ⟨σR⟩ significantly.

Numerical Analysis of the Influences of Balance Hole Diameter on the Flow Characteristics of the Back Chamber of Centrifugal Pump

The flow characteristic inside a pump chamber is the core problem in the study of the thrust force of a centrifugal pump. A numerical study on the IS150-125-315-type centrifugal pump with four different balance hole diameters was conducted. By selecting clear water as the medium, the time-averaged continuity equation with relative coordinates and the Navier-Stokes equation are established on the basis of the FLUENT software. The RNG k–ε equation turbulence model and the SIMPLEC algorithm are used to conduct a numerical simulation. The numerical results match the accuracy of the design values on the performance of the pump. The test results match the accuracy of the numerical results on the pressure of the back chamber and clearance leakage of the back seal ring. The influence of balance hole diameters is revealed in the flow field of the back chamber of the centrifugal pump. In detail, the patterns of the axial and radial distributions of the dimensionless tangential and radial velocities and the spanwise distribution of their average values in the back chamber of the centrifugal pump with different balance hole diameters are investigated. The relationship is also obtained between fluid rotational angular velocity in the back chamber of the centrifugal pump and rotational angular velocity of the impeller. The results reveal that the turbulent boundary layer and core region of the flow always exist in the pump chamber, even if there are no balance holes. The increase in diameter of the balance holes is associated with the increase in the radial component in the core region velocity and the decrease in the value range of its tangential component. At a certain radius and angular position, the diameter of larger balance holes leads to higher normalized tangential velocity in the core region. At the same time, a higher absolute value of the normalized radial velocity near the pump cover corresponds to greater radial leakage. At the same balance hole diameters, the rotating speed of the core region fluid generally keeps constant along the axial direction, whereas a significant difference is observed along the radial and tangential directions. The dimensionless radial and tangential velocities are significantly influenced by the flow of the volute chamber in the pump and are rarely influenced by the changes in the balance hole diameters, and vice versa. The dimensionless radial velocity will exert more power on large sections, such as sections 5 and 7, than the dimensionless tangential velocity, and vice versa. For cases with balance hole diameters less than its design value, dimensionless tangential average velocity is less than 0.5 with increases and dimensionless radial average velocity is less than 0 with decreases along the radial direction in the flow core area. Otherwise, dimensionless tangential average velocity is approximately equal to 0.59 and dimensionless radial average velocity is approximately equal to 0 in the flow core area. The balance hole diameter changes from 0 mm to 12 mm, and the rotating speed of the core region fluid is 0–0.8 times, rather than half, that of the impeller.

Test and Analysis of Machine Center's Principal Spindle Dynamic Errors

The form of principal spindle's dynamic errors is analysed firstly. Principal spindle's radial average errors and asynchronous errors, axial average errors and asynchronous errors, minimum radial separation center of some vertical machine center are all tested with SPN-300 of API. Three vertical machine centers are tested and every machine center is tested three times at different rotating speed. The test results and the influences of all errors are analysed at last.

Influence and Analysis of Temperature Rise to Principal Spindle's Rotating Error Test

The form of principal spindle's dynamic errors is analysed firstly. Scientific test scheme is designed to analyse the influence of rotating speed to rotating errors and decrease temperature rises influence. Principal spindle's radial average errors and asynchronous errors, axial average errors and asynchronous errors, minimum radial separation center of some vertical machine center are all tested with SPN-300 of API. Test method is rise speed-test-stop & cooling-rise speed. Three vertical machine centers are tested and every machine center is tested three times at different rotating speed. The test results and the influences of all errors are analysed at last.

The Measurement and Process of Aeroengine Inlet Total Pressure Field

It’s important to measure inlet total pressure field for aeroengine. Firstly, test scheme is discussed. Three pectinate total pressure probes, which can be rotated with an additional straight ring segment around the engine axis, are used to measure the total pressure field. The radial distribution of test points is designed via Tchebycheff integral method. Radial average and circumferential average are calculated according to the field data via area averaging method. At last the total pressure field is visualized via mapping the data to colors. Test results show that the total pressure distribution in main airflow is evener than that in boundary layers and the thickness of inner and outer ring boundary layer can be estimated.

Numerical Investigation of Enhanced Dilution Zone Mixing in a Reverse Flow Gas Turbine Combustor

An advanced method for dilution zone mixing in a reverse flow gas turbine combustor was numerically investigated. For long mixing lengths associated with reverse flow combustors (X/H > 2.0), pattern factor was found to be mainly driven by nozzle-to-nozzle fuel flow and/or circumferential airflow variations; conventional radially injected dilution jets could not effectively mix out circumferential nonuniformities. To enhance circumferential mixing, dilution jets were angled to produce a high circumferential (swirl) velocity component. The jets on the outer liner were angled in one direction while the jets on the inner liner were angled in the opposite direction, thus enhancing turbulent shear at the expense of jet penetration. Three-dimensional CFD calculations were performed on a three-nozzle (90 deg) sector, with different fuel flow from each nozzle (90, 100, and 110 percent of design fuel flow). The computations showed that the optimum configuration of angled jets reduced the pattern factor by 60 percent compared to an existing conventional dilution hole configuration. The radial average temperature profile was adequately controlled by the inner-to-outer liner dilution flow split.

Pattern Factor Reduction in a Reverse Flow Gas Turbine Combustor Using Angled Dilution Jets

An advanced method for dilution zone mixing in reverse flow gas turbine combustors was experimentally investigated. To enhance circumferential mixing, dilution jets were injected with a high circumferential (swirl) velocity component. The jets on the outer liner were angled in one direction while the jets on the inner liner were angled in the opposite direction. To demonstrate reduced pattern factor, AlliedSignal Engines’ F109 combustor was tested at sea level takeoff conditions. For the baseline (conventional) configuration, the experimental results showed that large scale circumferential temperature non-uniformities at the turbine inlet were caused primarily by fuel flow variations from nozzle to nozzle. These temperature variations were significantly reduced by angled dilution jets. A pattern factor of 0.102 was achieved compared to the best case pattern factor of 0.163 for the baseline configuration. The only combustor modification was the dilution hole configuration. The radial average temperature profile produced by angled dilution jets was very similar to the profile produced by the baseline configuration.

Numerical Investigation of Enhanced Dilution Zone Mixing in a Reverse Flow Gas Turbine Combustor

An advanced method for dilution zone mixing in a reverse flow gas turbine combustor was numerically investigated. For long mixing lengths associated with reverse flow combustors (X/H > 2.0), pattern factor was found to be mainly driven by nozzle-to-nozzle fuel flow and/or circumferential airflow variations; conventional radially injected dilution jets could not effectively mix out circumferential non-uniformities. To enhance circumferential mixing, dilution jets were angled to produce a high circumferential (swirl) velocity component. The jets on the outer liner were angled in one direction while the jets on the inner liner were angled in the opposite direction, thus enhancing turbulent shear at the expense of jet penetration. 3-D CFD calculations were performed on a three-nozzle (90°) sector, with different fuel flow from each nozzle (90%, 100% and 110% of design fuel flow). The computations showed that the optimum configuration of angled jets reduced the pattern factor by 60% compared to an existing conventional dilution hole configuration. The radial average temperature profile was adequately controlled by the inner-to-outer liner dilution flow split.