Radial Pressure Profiles Research Articles

An Experimental Study of Combustor Exit Profile Shapes on Endwall Heat Transfer in High Pressure Turbine Vanes

The design and development of current and future gas turbine engines for aircraft propulsion have focused on operating the high pressure turbine at increasingly elevated temperatures and pressures. The drive toward thermal operating conditions near theoretical stoichiometric limits as well as increasingly stringent requirements on reducing harmful emissions both equate to the temperature profiles exiting combustors and entering turbines becoming less peaked than in the past. This drive has placed emphasis on determining how different types of inlet temperature and pressure profiles affect the first stage airfoil endwalls. The goal of the current study was to investigate how different radial profiles of temperature and pressure affect the heat transfer along the vane endwall in a high pressure turbine. Testing was performed in the Turbine Research Facility located at the Air Force Research Laboratory using an inlet profile generator. Results indicate that the convection heat transfer coefficients are influenced by both the inlet pressure profile shape and the location along the endwall. The heat transfer driving temperature for inlet profiles that are nonuniform in temperature is also discussed.

Migration of Combustor Exit Profiles Through High Pressure Turbine Vanes

The high pressure turbine stage within gas turbine engines is exposed to combustor exit flows that are nonuniform in both stagnation pressure and temperature. These highly turbulent flows typically enter the first stage vanes with significant spatial gradients near the inner and outer diameter endwalls. These gradients can result in secondary flow development within the vane passage that is different than what classical secondary flow models predict. The heat transfer between the working fluid and the turbine vane surface and endwalls is directly related to the secondary flows. The goal of the current study was to examine the migration of different inlet radial temperature and pressure profiles through the high turbine vane of a modern turbine engine. The tests were performed using an inlet profile generator located in the Turbine Research Facility at the Air Force Research Laboratory. Comparisons of area-averaged radial exit profiles are reported as well as profiles at three vane pitch locations to document the circumferential variation in the profiles. The results show that the shape of the total pressure profile near the endwalls at the inlet of the vane can alter the redistribution of stagnation enthalpy through the airfoil passage significantly. Total pressure loss and exit flow angle variations are also examined for the different inlet profiles.

Modelling compressible gas flow near the nozzle of a gas atomiser using a new unified model

In this paper, a unified numerical model is used to simulate the compressible gas flow, during the process of atomisation of liquid, near the atomiser nozzle in gas-only case studies. The flow of the under-expanded gas jets is studied, by analyzing the pressure field, density field and the spatial distribution of Mach number of the gas. The simulated predictions of gas status at the nozzle exit, the radial profile of Pitot pressure, aspiration pressure, and the spatial distribution of the density gradient, are compared with relevant experimental results and an analytical correlation, in order to validate and verify the application of this unified model in the numerical simulation of the gas dynamic behavior during gas atomisation. The simulation results show that the compressible gas flow near the nozzle of a discrete jet atomiser is different from that in a typical annular slit atomiser. Unlike existing models, this new formulation has the potential to be used in future to simulate the simultaneous flow of compressible gas and a weakly compressible liquid metal stream.

A comparison of three different methods for measuring both normal stress differences of viscoelastic liquids in torsional rheometers

A novel pressure sensor plate (normal stress sensor (NSS) from RheoSense, Inc.) was adapted to an Advanced Rheometrics Expansion System rheometer in order to measure the radial pressure profile for a standard viscoelastic fluid, a poly(isobutylene) solution, during cone–plate and parallel-plate shearing flows at room temperature. We observed in our previous experimental work that use of the NSS in cone-and-plate shearing flow is suitable for determining the first and second normal stress differences N 1 and N 2 of various complex fluids. This is true, in part, because the uniformity of the shear rate at small cone angles ensures the existence of a simple linear relationship between the pressure [i.e., the vertical diagonal component of the total stress tensor (Π22)] and the logarithm of the radial position r (Christiansen and coworkers, Magda et al.). However, both normal stress differences can also be calculated from the radial pressure distribution measured in parallel-plate torsional flows. This approach has rarely been attempted, perhaps because of the additional complication that the shear rate value increases linearly with radial position. In this work, three different methods are used to investigate N 1 and N 2 as a function of shear rate in steady shear flow. These methods are: (1) pressure distribution cone–plate (PDCP) method, (2) pressure distribution parallel-plate (PDPP) method, and (3) total force cone–plate parallel-plate (TFCPPP) method. Good agreement was obtained between N 1 and N 2 values obtained from the PDCP and PDPP methods. However, the measured N 1 values were 10–15% below the certified values for the standard poly(isobutylene) solution at higher shear rates. The TFCPPP method yielded N 1 values that were in better agreement with the certified values but gave positive N 2 values at most shear rates, in striking disagreement with published results for the standard poly(isobutylene) solution.

Total ion pressure changes with L shell in the nightside inner magnetosphere

The total ion plasma pressure has been estimated in the equatorial plane of the magnetosphere from the CRRES measurements when the satellite crossed the magnetic shells from L ∼ 2.3 to L ∼ 6.6 in the night sector of ∼20–24 MLT. The data of the LEPA and the EPAS particle detectors as well as the magnetic field data on the CRRES satellite have been used for two events with the AE < 300 nT before the substorm onset. It is found that the gross radial structure of the plasma pressure constructed along the CRRES orbit exhibits a maximum at L ∼ 3 and then a gradual decrease with distance from the Earth. Along with these usual features of the plasma pressure profile, we revealed an additional maximum of the total ion pressure, which appears at L ∼ 4.6–4.9. It is located earthward of the Alfvén boundaries of low‐energy electrons. From the analysis of the energy composition of plasma pressure we conclude that this additional maximum is a result of enhancement of the pressure of ions with energies <30 keV which was observed ∼20 min after a small enhancement of magnetic activity. We suppose that dynamical changes in the electric field and particle density in the plasma sheet are the dominant processes that form the observed peculiarity in the radial profile of the total ion pressure. These dynamical changes lead to a shift of convection boundaries and to acceleration of ion flux which was formed by preexisting quasi‐steady convection.

Simulations of ultrarelativistic magnetodynamic jets from gamma-ray burst engines

Long-duration gamma-ray bursts (GRBs) require an engine capable of driving a jet of plasma to ultrarelativistic bulk Lorentz factors of up to several hundred and into narrow opening angles of a few degrees. We use global axisymmetric stationary solutions of magnetically-dominated (force-free) ultrarelativistic jets to test whether the popular magnetic-driving paradigm can generate the required Lorentz factors and opening angles. Our global solutions are obtained via time-dependent relativistic ideal magnetodynamical numerical simulations which follow the jet from the central engine to beyond six orders of magnitude in radius. Our model is primarily motivated by the collapsar model, in which a jet is produced by a spinning black hole or neutron star and then propagates through a massive stellar envelope. We find that the size of the presupernova progenitor star and the radial profile of pressure inside the star determine the terminal Lorentz factor and opening angle of the jet. At the radius where the jet breaks out of the star, our well-motivated fiducial model generates a Lorentz factor $\gamma\sim 400$ and a half-opening angle $\theta_j\sim 2^\circ$, consistent with observations of many long-duration GRBs. Other models with slightly different parameters give $\gamma$ in the range 100 to 5000 and $\theta_j$ from $0.1^\circ$ to $10^\circ$, thus reproducing the range of properties inferred for GRB jets. A potentially observable feature of some of our solutions is that the maximum Poynting flux in the jet is found at $\theta \sim \theta_j$ with the jet power concentrated in a hollow cone, while the maximum in the Lorentz factor occurs at an angle $\theta$ substantially smaller than $\theta_j$ also in a hollow cone. [abridged]

Strongly swirling flows in a cylindrical separator

This paper describes a numerical study of two-phase, strongly swirling flow in a cylindrical separator with double vortex generators to predict the separation efficiency of a mixture consisting of oil as the primary phase and sand, with a specific diameter, as the secondary phase. The mixture-granular multiphase and RNG k– ε turbulence models are implemented in this study. The analytical predictions are compared against experimental data; i.e., the mean tangential velocity and the mean radial pressure profiles. The overall agreement between the experimental data and the predictions obtained with the RNG k– ε model are reasonably good. The numerical procedure has the ability to capture a narrow localized residence zone for the solid particles at a periphery location near the mid-separator where the two vortices merge and the suspension process occurs. Moreover, the analysis has proven to be useful in predicting the internal flow structure of the primary phase, thereby, the separation of the particulate phase. The separated particles are forced to remain near the periphery of the cylindrical separator and being concentrated at the mid-separator as a result of the strong centrifugal force.

Radial distribution of the inner magnetosphere plasma pressure using low-altitude satellite data during geomagnetic storm: The March 1–8, 1982 event

Plasma pressure distribution in the inner magnetosphere is one of the key parameters for understanding the main magnetospheric processes including geomagnetic storms and substorms. However, the pressure profiles obtained from in-situ particle measurements by the high-altitude satellites inside the plasma sheet and other regions of the magnetosphere do not allow tracking the pressure variations related to the storms and substorms, because a time interval needed to do this generally exceeds the characteristic times of them. On the contrary, fast movement of low-altitude satellites makes it possible to retrieve quasi-instantaneous radial or azimuthal profiles of plasma pressure along the satellite trajectory, using the precipitating particle flux data in the regions of isotropic plasma pressure. For this study, we used the low-altitude polar-orbiting Aureol-3 satellite data for plasma pressure estimation, and the IGRF, Tsyganenko 2001 and Tsyganenko 2004 storm time geomagnetic field models for the pressure mapping into the equatorial plane, and for the evaluation the corresponding volume of the magnetic flux tube. It was found that during quiet geomagnetic condition the radial pressure profiles obtained coincide with the profiles, obtained previously from the high-altitude measurements. On the contrary, the plasma pressure profiles change significantly during the development of storms and substorms. Nevertheless, three geomagnetic field models gave significantly different geomagnetic field profiles, those points out the necessity to develop a magnetically self-consistent model for description of the inner magnetosphere geomagnetic field. However, the common features observed for all models are: during geomagnetic storm the plasma pressure profiles became sharper; the position of the maximum of plasma pressure corresponds to expected one for given D st minimum; the maximum value of inner magnetosphere static pressure correlates with the solar wind dynamic pressure. Increase in the plasma pressure profiles indicates the possibility to consider the interchange instability as one of important factors for the development of the main phase of geomagnetic storm.

“Effective” Negative Surface Tension: A Property of Coated Nanoaerosols Relevant to the Atmosphere

Atmospheric aerosols play a very important role in atmospheric processes and have a major influence on the global climate. In this paper, we report results of a molecular dynamics study on the unique properties of organic-coated water droplets. In particular, we find that, for particles preferring an inverted micelle structure, the lower chain-chain interaction, with increasing radial distance from the water-organic interface, results in a negative internal radial pressure profile for the organic layer. As a result, a coated particle behaves as though the surface tension is "negative" and implies that such a particle will inherently have an inverse Kelvin vapor pressure effect, resulting in increased water condensation.

Hydrodynamic model of wind field in a moving typhoon

An algorithm is developed for solving the hydrodynamic equations describing wind field structure in a typhoon. The specific feature of the algorithm consists in solving an overdetermined set of equations: given radial profiles of pressure and vertical velocity component, horizontal wind components are found. Projection of angular momentum on tangential direction plays a role of “error of closure.” The calculated wind fields in resting and moving typhoons are presented. As an example, the whole lifecycle of Typhoon Ivan (September 2–17, 2004) is described in detail.

Hydrodynamic modeling of a circulating fluidized bed

Hydrodynamics plays a crucial role in defining the performance of circulating fluidized beds (CFB). The numerical simulation of CFBs is very important in the prediction of its flow behavior. From this point of view, in the present study a dynamic two dimensional model is developed considering the hydrodynamic behavior of CFB. In the modeling, the CFB riser is analyzed in two regions: The bottom zone in turbulent fluidization regime is modeled in detail as two-phase flow which is subdivided into a solid-free bubble phase and a solid-laden emulsion phase. In the upper zone core–annulus solids flow structure is established. Simulation model takes into account the axial and radial distribution of voidage, velocity and pressure drop for gas and solid phase, and solids volume fraction and particle size distribution for solid phase. The model results are compared with and validated against atmospheric cold bed CFB units' experimental data given in the literature for axial and radial distribution of void fraction, solids volume fraction and particle velocity, total pressure drop along the bed height and radial solids flux. Ranges of experimental data used in comparisons are as follows: bed diameter from 0.05–0.418 m, bed height from 5–18 m, mean particle diameter from 67–520 μm, particle density from 1398 to 2620 kg/m 3, mass fluxes from 21.3 to 300 kg/m 2s and gas superficial velocities from 2.52–9.1 m/s. As a result of sensitivity analysis, the variation in mean particle diameter and superficial velocity, does affect the pressure especially in the core region and it does not affect considerably the pressure in the annulus region. Radial pressure profile is getting flatter in the core region as the mean particle diameter increases. Similar results can be obtained for lower superficial velocities. It has also been found that the contribution to the total pressure drop by gas and solids friction components is negligibly small when compared to the acceleration and solids hydrodynamic head components. At the bottom of the riser, in the core region the acceleration component of the pressure drop in total pressure drop changes from 0.65% to 0.28% from the riser center to the core–annulus interface, respectively; within the annulus region the acceleration component in total pressure drop changes from 0.22% to 0.11% radially from the core–annulus interface to the riser wall. On the other hand, the acceleration component weakens as it moves upwards in the riser decreasing to 1% in both regions at the top of the riser which is an important indicator of the fact that hydrodynamic head of solids is the most important factor in the total pressure drop.

A Puzzling Merger in A3266: The Hydrodynamic Picture fromXMM‐Newton

Using the mosaic of nine XMM-Newton observations, we study the hydrodynamic state of the merging cluster of galaxies Abell 3266. The high quality of the spectroscopic data and large field of view of XMM-Netwon allow us to determine the thermodynamic conditions of the intracluster medium on scales of order of 50 kpc. A high quality entropy map reveals the presence of an extended region of low entropy gas, running from the primary cluster core toward the northeast along the nominal merger axis. The mass of the low entropy gas amounts to approximately 2e13 solar masses, which is comparable to the baryonic mass of the core of a rich cluster. We test the possibility that the origin of the observed low entropy gas is either related to the disruption a preexisting cooling core in Abell 3266 or to the stripping of gas from an infalling subcluster companion. We find that both the radial pressure and entropy profiles as well as the iron abundance of Abell 3266 do not resemble those in other known cooling core clusters (Abell 478). Thus we conclude that the low entropy region is subcluster gas in the process of being stripped off from its dark matter halo. In this scenario the subcluster would be falling onto the core of A3266 from the foreground. This would also help interpret the observed high velocity dispersion of the galaxies in the cluster center, provided that the mass of the subcluster is at most a tenth of the mass of the main cluster.

A New Method of Assessing Anal Sphincter Integrity Using Inverted Vectormanometry

Vectorgraphy as an integrated mapping of radial pressure profiles of the anal canal has been used to attempt identification of pressure-related defects with doubtful reliability since vectorgraphs bear no resemblance to endoanal ultrasound scans at similar levels in the anal canal. This study aimed to devise a technique to enable vectorgraphy to be more representative of sphincter function and integrity. Vectormanometry was performed in 50 patients with anorectal disorders using an Arndorfer pneumohydraulic system. "Normal" three-dimensional manometric images of each 0.5 cm of the anal sphincter were computer-generated by plotting anal pressures at rest and during squeeze radially around a central zero axis. The graphs were replotted with zero at the periphery and maximal anal pressure at the center. Both this ("inverted") and "normal" vectorgraphs were compared with endoanal ultrasound images at similar levels, assessing both internal and external anal sphincters. Standard vectormanometry produced excellent pictures of pressures throughout the anal canal; the anatomy however bore no resemblance to the pictures produced by endoanal ultrasound. The inverted vectographs showed a much better correlation with endoanal ultrasound at each 0.5-mm level of the anal canal, for both squeeze pressure graphs and external sphincter correlations and for resting pressure graphs and internal sphincter correlations. Accurate assessment of sphincter integrity is not possible when interpreting the vectormanometry graphs in the current format; however, inverted vectorgraphy gives good correlations with endoanal ultrasound and provides combined functional (pressure measurement) and anatomic (three-dimensional profile) information regarding the anal canal.

The effect of the shear-thickening transition of model colloidal spheres on the sign of N1 and on the radial pressure profile in torsional shear flows

A novel rheometer plate was used to measure radial pressure profiles during cone-and-plate and parallel-plate shearing flows of a concentrated colloidal dispersion of poly(methyl methacryalate) spheres suspended in dioctyl phthalate. There is a long history of using suspensions of this type as a model rheological system. The measured pressure profile can be used to calculate N1 and N2, and also provides a check on the flow field in the rheometer. At shear rates just below onset of shear thickening, our measurements show that N1 is positive as predicted by Stokesian dynamics simulations of model Brownian hard spheres, but we are unable to determine the sign of N2. After the onset of thickening, we find that in both flow geometries the pressure increases sharply with radial position. This is in striking contrast to the pressure profiles ordinarily observed for viscoelastic liquids (with the exception of certain liquid crystal polymers), for which the pressure decreases with radial position. Under these cond...

Reynolds Stress Model in the Prediction of Confined Turbulent Swirling Flows

Strongly swirling vortex chamber flows are examined experimentally and numerically using the Reynolds stress model (RSM). The predictions are compared against the experimental data in terms of the pressure drop across the chamber, the axial and tangential velocity components, and the radial pressure profiles. The overall agreement between the measurements and the predictions is reasonable. The predictions provided by the numerical model show clearly the forced and free vortex modes of the tangential velocity profile. The reverse flow (or back flow) inside the core and near the outlet, known from experiments, is captured by the numerical simulations. The swirl number has been found to have a measurable impact on the flow features. The vortex core size is shown to contract with the swirl number which leads to higher pressure drop, higher peak tangential velocity, and deeper radial pressure profiles near the axis of rotation. The adequate agreement between the experimental data and the simulations using RSM turbulence model provides a valid tool to study further these industrially important swirling flows.

Comprehensive Modeling of Gas Fluidized-Bed Reactors Allowing for Transients, Multiple Flow Regimes and Selective Removal of Species

A multiphase reaction engineering model is being developed to investigate the dynamic and steady state behaviour of fluidized-bed catalytic reactors. It accounts for transients, axial and radial dispersion, temperature and pressure profiles, interphase mass and heat transfer, different hydrodynamic flow regimes, catalyst deactivation, reactions with changes in molar flows and various energy options. The model is general enough that it can treat catalytic systems, subject to mass and energy transfer resistances within the phases, as well as permeating membranes. It is able to handle multiple phases and regions (low-density phase, high-density phase, freeboard region and permselective membranes). The model reduces as special cases to a number of simpler fluidized bed reactor models previously reported in the literature, allowing evaluation of the influence of different simplifying assumptions. As a case study, the model is shown to simulate oxy-chlorination fluidized-bed reactors for the production of ethylene dichloride from ethylene, extending a recent paper by Abba et al. (Chem. Eng. Sci., (2002) 57, 4797-4807).

Swirling Inflow Within the Narrow Gap of Two Disks

The results of an analytical study dealing with the asymptotic swirling inflow, generated within the gap of two closely placed parallel disks, are presented. It is shown that the radial velocity component can be expressedby a single parameter, which combines the reduced Reynolds number and radial position. The latter velocity is found to flatten at the midgap position with the Reynolds number producing a plateau that progressively expands toward the walls. Under the action of viscous diffusion, the axial distribution of the tangential velocity is found to exhibit a similar property. The radial profile of the static pressure is shown to depend on the relative vortex strength and the Reynolds number. As inertia begins to dominate the viscous forces, the mid-channel tangential velocity curvature in the axial direction is found to tend asymptotically to zero, thus, encouraging the centerline velocity to approach the free-vortex profile. The results of the analytical study compare favorably with previous and present experimental evidence.

On Flow Development in Jet-Driven Vortex Chambers

This work presents the study of the flow in a jet-driven vortex chamber over a wide range of Reynolds numbers, contraction ratios, inlet angles, area and aspect ratios. Dimensional analysis furnishes the general functional relationships between the fundamental dimensionless quantities. Application of the integral equations of continuity and energy over the control volume, along with the minimum-pressure-drop or maximum flow rate postulate, provide the required analytical means to relate the predominant non-dimensional parameters such as the chamber geometry, the core size, pressure drop, Reynolds number, and viscous losses. Both the n = 2 vortex model, with reverse and non-reverse flow, and the free vortex model have been used at the vortex chamber exit plane. The theoretical results are found to successfully capture most of the salient properties of the flow. The influence of vortex chamber geometry, such as contraction ratio, inlet angle, area ratio, aspect ratio, and Reynolds number, on the flow field has been analyzed and compared with the present experimental data. A parametric study explores how the pressure coefficient and the core size vary with the different dimensionless properties. The observations show the pressure drop to decrease with the length. At first this appears to be counterintuitive since one habitually expects the pressure drop to be larger for longer pipes. A closer examination however, reveals that in addition to the radial-axial plane flow there is also a substantial centrifugal force, which decays with the length, thus shaping the development of the overall flow-field. The pressure drop across the vortex chamber differs from that in pipe flow, due to the mechanism of swirl flow. It depends mainly on intensity of tangential velocity. If the chamber length is increased, the vortex decay factor decreases, which leads to less pressure drop. The current theory confirms that the previous published models are only applicable for high Reynolds numbers where the inertia dominates the viscous forces. Based on the present theory, a new approach to determine the tangential velocity and radial pressure profiles inside the vortex chamber is developed and compared with the available experimental data. The n = 2 vortex model with reverse flow gives better results for strongly swirling flow.

Molecular dynamics computation of the work of ion solvation: comparison of two models of water

Clusters of the TIP4P water model with 125 and 256 molecules and with the K+ or K− ions were simulated by the molecular dynamics method. The radial profiles of local density, energy, normal pressure and molecular orientation were obtained. The work of cluster formation was calculated from the normal pressure profile. The results for the TIP4P and SPC/E model of water are discussed in comparison with each other. A divergence in behaviour of water molecules in the two models was discovered.

Cone angle effects, radial pressure profile, and second normal stress difference for shear-thickening wormlike micelles

Many dilute surfactant solutions containing long, thin, wormlike micelles undergo a shear-thickening transition at which the apparent viscosity jumps to a much higher value due to the formation of shear-induced structures. However, the behavior of the normal-stress differences N1 and N2 has not been studied at the low-shear rates and shear stresses (<0.1 Pa) at which shear thickening occurs in most of the commonly studied systems, such as aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSS). For dilute equimolar solutions of CTAB/NaSS, the validity of measurements of the shear flow properties η, N1 and N2 via cone-and-plate rheometry is assessed by systematically varying the cone angle, and by measuring the pressure profile during cone-and-plate flows. The dependence on the cone angle of the apparent viscosity value is consistent with a stratified fluid structure, as shown to occur in Couette rheometers by Hu and co-workers [Hu, Y. T. et al., J. Rheol. 42, 1209–1226 (199...