Showing papers on "Total pressure published in 2003"

Reduced pumping power and wall temperature in microchannel heat sinks with fractal-like branching channel networks

Abstract: Comparisons are made of the maximum channel wall temperature along, and total pressure drop across, a heat sink with a fractal-like branching channel network with those in a heat sink having a straight channel array. The total channel lengths are identical between the heat sinks, as are the applied heat fluxes. The hydraulic diameter of the straight channel array is equal to that of the terminal branch of the branching channel network. The number of branches per level, number of branching levels, and channel dimensions in the fractal-like network remain fixed. Minor losses are neglected and both hydrodynamic and thermal boundary layers are assumed to reinitiate following each channel bifurcation in the branching flow network. With identical total convective surface areas for both configurations and maintaining a heat sink surface area equal to that of the convective surface area, the fractal-like channel network yielded a 60% lower pressure drop for the same total flow rate and a 30°C lower wall temperatu...

Local Three-dimensional Simulations of Magnetorotational Instability in Radiation-dominated Accretion Disks

Abstract: We examine the small-scale dynamics of black hole accretion disks in which radiation pressure exceeds gas pressure Local patches of disk are modeled by numerically integrating the equations of radiation MHD in the flux-limited diffusion approximation The shearing-box approximation is used, and the vertical component of gravity is neglected Magnetorotational instability (MRI) leads to turbulence in which accretion stresses are due primarily to magnetic torques When radiation is locked to gas over the length and timescales of fluctuations in the turbulence, the accretion stress, density contrast, and dissipation differ little from those in the corresponding calculations, with radiation replaced by extra gas pressure However, when radiation diffuses each orbit a distance that is comparable to the rms vertical wavelength of the MRI, radiation pressure is less effective in resisting squeezing Large density fluctuations occur, and radiation damping of compressive motions converts P dV work into photon energy The accretion stress in calculations having a net vertical magnetic field is found to be independent of opacity over the range explored and approximately proportional to the square of the net field In calculations with zero net magnetic flux, the accretion stress depends on the portion of the total pressure that is effective in resisting compression The stress is lower when radiation diffuses rapidly with respect to the gas We show that radiation-supported Shakura-Sunyaev disks accreting via internal magnetic stresses are likely to have radiation marginally coupled to turbulent gas motions in their interiors

Local Three-Dimensional Simulations of Magneto-Rotational Instability in Radiation-Dominated Accretion Disks

Abstract: We examine the small-scale dynamics of black hole accretion disks in which radiation pressure exceeds gas pressure. Local patches of disk are modeled by numerically integrating the equations of radiation MHD in the flux-limited diffusion approximation. The shearing-box approximation is used, and the vertical component of gravity is neglected. Magneto-rotational instability (MRI) leads to turbulence in which accretion stresses are due primarily to magnetic torques. When radiation is locked to gas over the length and time scales of fluctuations in the turbulence, the accretion stress, density contrast, and dissipation differ little from those in the corresponding calculations with radiation replaced by extra gas pressure. However, when radiation diffuses each orbit a distance that is comparable to the RMS vertical wavelength of the MRI, radiation pressure is less effective in resisting squeezing. Large density fluctuations occur, and radiation damping of compressive motions converts PdV work into photon energy. The accretion stress in calculations having a net vertical magnetic field is found to be independent of opacity over the range explored, and approximately proportional to the square of the net field. In calculations with zero net magnetic flux, the accretion stress depends on the portion of the total pressure that is effective in resisting compression. The stress is lower when radiation diffuses rapidly with respect to the gas. We show that radiation-supported Shakura-Sunyaev disks accreting via internal magnetic stresses are likely in their interiors to have radiation marginally coupled to turbulent gas motions.

A fully hydrodynamic model for three‐dimensional, free‐surface flows

Abstract: The hydrostatic pressure assumption has been widely used in studying water movements in rivers, lakes, estuaries, and oceans. While this assumption is valid in many cases and has been successfully used in numerous studies, there are many cases where this assumption is questionable. This paper presents a three-dimensional, hydrodynamic model for free-surface flows without using the hydrostatic pressure assumption. The model includes two predictor-corrector steps. In the first predictor-corrector step, the model uses hydrostatic pressure at the previous time step as an initial estimate of the total pressure field at the new time step. Based on the estimated pressure field, an intermediate velocity field is calculated, which is then corrected by adding the non-hydrostatic component of the pressure to the estimated pressure field. A Poisson equation for non-hydrostatic pressure is solved before the second intermediate velocity field is calculated. The final velocity field is found after the free surface at the new time step is computed by solving a free-surface correction equation

Fed-batch cultivation of Saccharomyces cerevisiae in a hyperbaric bioreactor.

Abstract: Fed-batch is the dominating mode of operation in high-cell-density cultures of Saccharomyces cerevisae in processes such as the production of baker's yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiae fed-batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO(2). Fed-batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h(-)(1) was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g(-)(1) (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiae cultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability.

Improved interpretation of wireline pressure data

Abstract: Modern wireline pressure data can have resolution and reproducibility sufficient to detect small fluid-density changes and pressure barriers, yet these features are commonly overlooked on conventional pressure-depth plots. The large pressure variation caused by weight of subsurface fluids hides these subtle features. Excess pressure is the pressure left after subtracting the weight of a fluid from the total pressure. This concept is applied to wireline pressure data to remove effects of weight and emphasize subtle pressure differences caused by density variations and pressure barriers. Fluid-density changes of 0.02 g/cm3 or less can be resolved, and within-well pressure barriers in the order of 5 kPa (0.7 psi) can be detected. Using good-quality data, effects of reservoir capillary-displacement pressure can be detected by offset of the free-water level from the petroleum-water contact. This effect can be used to estimate reservoir wettability. Subsurface fluid-density measurements can also be used to evaluate oil or gas quality on a bed-by-bed scale in traps having variable oil or gas composition, to detect compartmentalization by small petroleum density differences, to verify quality of samples for PVT (pressure, volume, temperature) analysis, and estimate salinity or temperature of unsampled water zones.Data quality limits barrier and fluid-contact resolution; thus, quality control is essential. Pressure measurement errors on the 3-kPa (0.5-psi) scale can be detected from behavior of the buildup pressure. Tests having the potential for small amounts of supercharge are identified from the overbalance and formation mobility. Examples illustrate identification of free-water levels and fluid contacts, fluid identification, supercharge identification, and water-zone compartmentalization.

Adsorption Competition Effects in Hydroconversion of Alkane Mixtures on Zeolites

Abstract: In the present work, molecular competition effects in the hydroconversion of alkane mixtures in vapor and liquid phase were studied. The influence of the pore size was investigated by performing catalytic experiments with equimolar heptane/nonane mixtures on a series of bifunctional zeolite catalysts (Pt/H-Y, Pt/H-USY, Pt/H-Beta, Pt/H-MCM-22). Vapor phase catalytic experiments were performed at a total pressure of 4.5 bar, while a total pressure of 100 bar was applied in the liquid phase experiments. The experimental results were analyzed using a lumped adsorption-reaction model. In vapor phase, the longest chain is preferentially converted on all studied catalysts. In liquid phase, the differences in conversion rate were less pronounced. On Pt/H-MCM-22, with active pockets on the surface, and Pt/H-USY having large mesopores, the competition between short and long alkanes in liquid phase reflect the intrinsic reactivities of the reacting molecules. In zeolites with smaller pores (Pt/H-Y, Pt/H-Beta), an inversion of the reactivity order of alkanes of different chain length was observed when increasing the pressure from 4.5 bar and vapor phase to 100 bar and liquid phase. The inversion of apparent reactivity orders is due to changes in physisorption at high pressure, favoring uptake of the smallest molecules.

Absorption cross-sections of NO2: simulation of temperature and pressure effects

Abstract: The measurements of the NO2 absorption cross sections by several authors have been considered in order to derive its temperature and pressure dependences in the 13 200– 42 000 cm −1 spectral range. The temperature dependence is assumed to be linear in the temperature range investigated (217.0– 298.5 K ), whereas the influence of the total pressure is expressed as a temperature-dependent broadening coefficient. From measurements performed with mixtures of NO2 in air and in N2, values of γ air 0 (296 K ) and γ N 2 0 (296 K ) were found to be, respectively, 0.081±0.002 and 0.069±0.003 cm −1 atm −1 . The temperature coefficient n obtained in the present work is 0.8±0.1. The parameterization of the cross sections developed in this work can reproduce measured cross sections within 4%.

Simulation of the Internal Conditions During The Hot-Pressing Process

Abstract: The development of a two-dimensional mathematical model to describe the internal conditions during the hot-compression of wood-based composite panels is discussed. Five primary variables were considered during the model development: air content, vapor content, bound water content, and temperature within the mat, and the extent of the cure of the adhesive system characterized by the cure index. Different heat and mass transfer processes were identified for the transport of the heat and of the moisture phases. The heat was transported by conduction and convection due to a temperature gradient, while the water phases were transported by bulk flow and diffusion due to total pressure and partial pressure gradients. The resulting differential-algebraic equation system was solved by the method of lines. The spatial derivatives of the conduction terms were discretized by central differences, while the spatial derivatives of the convection terms were discretized according to an upwind scheme. The resulting ordinary differential equations in the time variable were solved by a freely available differential-algebraic system solver (DDASSL). The mathematical model predicted temperature, moisture content, partial air and vapor pressures, total pressure, relative humidity, and extent of adhesive cure within the mat structure under a typical hot-compression process. A set of three-dimensional profiles describes the evolution of these variables with time, in the thickness and width dimensions of the mat. The model results allow a better understanding of the interacting mechanisms involved in a complex production process. The model also supports optimization of the hot-pressing parameters for improved quality of wood-based panel products, while reducing pressing time.

Temperature and Pressure Dependence Study of the Reaction of IO Radicals with Dimethyl Sulfide by Cavity Ring-Down Laser Spectroscopy

Abstract: The reaction of IO radicals with dimethyl sulfide was studied using cavity ring-down laser spectroscopy. The reaction rate constant shows both a temperature and pressure dependence. At 100 Torr total pressure, the reaction has reached its high-pressure limit and has a rate constant of (2.5 ± 0.2) × 10-13 molecule-1 cm3 s-1 at 298 K. On the basis of the Arrhenius plot in the region of 273−312 K, the reaction has a negative activation energy (Ea = −18.5 ± 3.8 kJ mol-1). The atmospheric implications of these findings are discussed. In light of these new data, DMS oxidation by IO can compete with oxidation by the hydroxyl radical in the marine boundary layer. Quoted uncertainties are one standard deviation from regression analysis.

Normal Shock/Boundary-Layer Interaction Control Using Aeroelastic Mesoflaps

Abstract: A normal shock/boundary-layer interaction control technique termed mesoflaps for aeroelastic recirculating transpiration has been investigated in a planar Mach 1.37 wind tunnel. In this flow-control system, an array of small flaps is mounted over a cavity; the flaps deflect aeroelastically under the pressure loads imposed by the normal shock, thereby allowing recirculation from downstream of the shock to upstream. Qualitative analysis of the mesoflap control was investigated with spark shadowgraph visualizations and oil-streak surface-flow visualizations, whereas quantitative analysis was achieved by measuring surface pressure distributions and boundary-layer velocity profiles. Nine different mesoflap arrays were investigated, in addition to the solid-wall reference case. It was found that flap thickness and, therefore, transpiration rate, had a demonstrable effect on static and total pressure recovery, in addition to boundary-layer integral properties. Although some of the arrays did not provide a performance benefit, one particular flap array was found to have significantly higher static and total pressure recoveries than the solid-wall reference case, while simultaneously demonstrating a reduction in boundary-layer momentum thickness and unchanged displacement thickness.

Effect of water jet pressure profile and initial web geometry on the physical properties of composite hydroentangled fabrics

Abstract: The effect of a water jet pressure profile (WJPP) and initial web geometry on the properties of hydroentangled fabrics is investigated. Different web structures (obtained by parallel, cross, and air-laid formation) are produced and hydroentangled at the same total pressure but with different water jet profiles. Composite structures are also made by combining different web structures followed by hydroentangling. The fabrics are then characterized in terms of key physical properties. Although the total pressure may be constant, the WJPP influences the tensile properties of fabrics, especially those containing air-laid structures. The results also suggest that to produce high tenacity fabrics, the webs should be hydroentangled on both sides at almost the same total pressure. The MD/CD strength ratios indicate that the most isotropic fabrics are air-laid, composite web struc tures combining cross and parallel-laid webs.

Optimal Area Profiles for Ideal Single Nozzle Air-Breathing Pulse Detonation Engines

Abstract: The effects of cross-sectional area variation on idealized Pulse Detonation Engine performance are examined numerically. A quasi-one-dimensional, reacting, numerical code is used as the kernel of an algorithm that iteratively determines the correct sequencing of inlet air, inlet fuel, detonation initiation, and cycle time to achieve a limit cycle with specified fuel fraction, and volumetric purge fraction. The algorithm is exercised on a tube with a cross sectional area profile containing two degrees of freedom: overall exit-to-inlet area ratio, and the distance along the tube at which continuous transition from inlet to exit area begins. These two parameters are varied over three flight conditions (defined by inlet total temperature, inlet total pressure and ambient static pressure) and the performance is compared to a straight tube. It is shown that compared to straight tubes, increases of 20 to 35 percent in specific impulse and specific thrust are obtained with tubes of relatively modest area change. The iterative algorithm is described, and its limitations are noted and discussed. Optimized results are presented showing performance measurements, wave diagrams, and area profiles. Suggestions for future investigation are also discussed.

Boundary-layer correction for the Busemann hypersonic air inlet

Abstract: A critical aspect of engine design for such flight speeds is total pressure recovery in the inlet, a problem that is exacerbated by boundary-layer development on the inlet walls A profile correcti

Oscillations in pores of a catalyst particle in exothermic liquid (liquid–gas) reactions: Analysis of heat processes and their influence on chemical conversion, mass and heat transfer

Abstract: A theoretical analysis of thermal processes in liquid–gas exothermic reactions in a porous catalyst shows the existence of the alternating motion of liquid in the pore. According to this model, if the released heat in the pore exceeds a certain critical value, the alternating motion of the liquid driven by the formation of the bubble takes place in the pore. Specifically, because of the heating of the liquid in the pore, the partial pressure of vapor saturated in liquid increases until the total pressure of the saturated gas and vapor becomes greater than the maximum possible pressure in the pore (equal to the sum of capillary pressure and pressure in the reactor) and the bubble thereby comes into being. The growing bubble pushes the liquid out of the pore. Since the reagent(s) is no longer in the pore, the reaction ceases and the generated heat dissipates. The liquid penetrates into the pore due to capillary force and the process of bubble formation occurs once again. A detailed analysis of this non-stability is undertaken. This paper seeks to show how this theory can explain some dependencies of the reaction rate observed in practice, mass and heat transfer in the fixed and suspended catalyst as well as some practical recommendations for catalyst development and process intensification. Analogy between oscillation behaviour and the boiling process is considered.

Measurement of pressure

Abstract: This chapter briefly discusses pressure management; there are three categories of pressure measurement: absolute pressure, gauge pressure, and differential pressure. Absolute pressure is the difference between the pressure at a particular point in a fluid and the absolute zero of pressure, that is, a complete vacuum. A barometer is one example of an absolute pressure gauge, because the height of the column of mercury measures the difference between the atmospheric pressure and the “zero” pressure of the Torricellian vacuum that exists above the mercury column. When the pressure-measuring device measures the difference between the unknown pressure and local atmospheric pressure, the measurement is known as gauge pressure. There are three basic methods for measuring pressure. The simplest method involves balancing the unknown pressure against the pressure produced by a column of liquid of known density. The second method involves allowing the unknown pressure to act on a known area and measuring the resultant force either directly or indirectly. The third method involves allowing the unknown pressure to act on an elastic member (of known area) and measuring the resultant stress or strain.

Experimental study on transition between ramjet and scramjet modes in a dual-mode combustor

Abstract: Air-breathing propulsion has been regarded in recent years as the future solution for spacecraft launchers. Hypersonic flight of vehicles designed for horizontal take-off remains nevertheless a challenging task. Especially the propulsion unit must work over a broad range of flight Mach number: efficiency can be guaranteed only with a system integrating conventional and air-breathing engines and the latter have to be suitable for dualmode operation. The Institute of Flight Propulsion of the Technische Universitat Munchen developed an air-breathing combustor concept, including a novel injection system. The combustion chamber consists of a constant cross section module hosting a strut injector followed by a diverging module which counteracts static pressure peaks consequent to combustion. Hydrogen and air are injected unlike-impinging into the strut wake, where a cylindrical pipe is inserted as flame-holder. The system allows creating a flow recirculation area. Combustion radicals are set free and promote further fuel reaction until a pilot flame stabilizes. Additional hydrogen or methane is injected through the strut sides, pre-mixes with the supersonic air flow (M=2.2) stoked to the combustor and is ignited by means of the pilot flame. The total temperature at the combustor entrance can be varied between 500K and 1200K. First results of wall static pressure measurements and Schlieren imaging demonstrated the possibility of dual-mode combustion. The transition between ramjet and scramjet modes showed to depend on the fuel total injection pressure. This paper presents the results of experiments carried out to define the fuel total injection pressure interval in which the transition occurs. Two injector versions of different thickness (i.e. 3mm and 5mm) have been used. This allowed evaluating the effects of the aerodynamic blockage due to the strut on the overall combustion process, particularly on the transition. ∗ Dipl.-Ing. Sara Rocci Denis, Research Assistant, Institute of Flight Propulsion † Professor Dr.-Ing. Hans-Peter Kau, Director, Institute of Flight Propulsion ‡ Dipl.-Ing. Armin Brandstetter, Systems Engineer, MT12 Mission Dynamics NOMENCLATURE MCC Combustor entrance Mach number MF Flight Mach number pCC Combustor entrance static pressure ptH2A Total pressure of hydrogen injected through system A pW Combustor wall static pressure TSS Flame-holder surface temperature TtCC Combustor entrance total temperature TtH2 Hydrogen injection total temperature φ Equivalence ratio

Two-phase flow through square and circular microchannels - Effect of channel geometry

Abstract: An adiabatic experiment was conducted to investigate the effect of channel geometry on gas-liquid two-phase flow characteristics in microchannels. A mixture of water and nitrogen gas was pumped through a 96 μm × 96 μm square microchannel and the flow pattern, void fraction and pressure drop data were obtained and compared with those previously obtained in a 100 μm circular microchannel. The frictional pressure drop was determined from the measured total pressure drop, and the two-phase flow pattern and void fraction were determined from image analysis of the video recordings. In the square channel, 136 runs were performed over a range of 0.09 ≤ jG,AVG ≤ 62 m/s for the average superficial gas velocity and 0.01 ≤ jL ≤ 4 m/s for the superficial liquid velocity. The frictional pressure drop data showed that the calculations based on a separated–flow model were best at estimating the frictional pressure drop for both microchannels. No particular effect of the channel shape was found for the two-phase frictional pressure drop. The void fraction-to-volumetric quality relationship was also found to be similar for both shapes of microchannels, exhibiting an exponential increase in void fraction with increasing volumetric quality. The empirical correlation that describes the void fraction-to-volumetric quality relationship for the square microchannel was developed earlier from the measured data for the circular microchannel. Observations of the recorded images indicated the two-phase flow patterns to be primarily intermittent with liquid and gas slugs. The liquid film surrounding the gas core displayed a smooth or ring-like structure. The probability of each interfacial structure occurring was examined in detail to develop a novel flow pattern map consisting of four regions named slug-ring flow, ring-slug flow, multiple flow and semiannular flow. Between the square and circular microchannels, the two-phase flow maps exhibited transition boundaries that were shifted depending on the channel shape. The region of ring-slug flow that appears in the circular microchannel collapsed in the square microchannel, possibly due to the suppression of the liquid-ring film in the corners of the square channel.Copyright © 2003 by ASME

Adsorption of Supercritical Carbon Dioxide + 2,6- and 2,7-Dimethylnaphthalene Isomers on NaY-Type Zeolite

Abstract: The surface excess amounts of supercritical carbon dioxide (SC-CO 2 ) on NaY-type zeolite were measured by an isochoric method at 308.2 K. The adsorption amounts of 2,6- and 2,7-dimethylnaphthalene (DMN) isomers dissolved in SC-CO 2 were also measured at 308.2 K by an isochoric method with an ultraviolet detector. The surface excess amounts of CO 2 show a maximum value near the critical pressure of CO 2 and then markedly decrease with increasing pressure and eventually become constant at high pressure. The adsorption amounts of 2,6- and 2,7-DMN gradually decrease with increasing total pressure. The adsorption amounts of 2,7-DMN are about six times higher than those of 2,6-DMN. The separation coefficients in supercritical CO 2 are much higher than those in liquid octane and ethanol. The experimental data were correlated by an extended Radke-Prausnitz equation. The correlated results are in good agreement with the experimental data.

Wide total pressure range probe with hemi-spherical tip

Abstract: A highly reliable air data pressure probe having an accurate, sensitive and linear Angle of Attack and Angle of Sideslip measurement, while simultaneously providing for an increased range of and increased accuracy of total air pressure measurements while further ensuring proper de-icing and anti-icing of the air data pressure probe.

Steady and Unsteady Casingwall Flow Phenomena in a Single-Stage Low-Speed Compressor at Part-Load Conditions

Abstract: This article describes an investigation of the casingwall flow phenomena in a single-stage, axial-flow, low-speed compressor at part-load conditions, utilizing an oil-flow technique to visualize the boundary layer development and highfrequency sensors to measure ensemble-averaged velocity and flow-angle distributions as well as unsteady total pressure distributions. Representative results are shown and discussed. The results enable different sources of endwall blockage to be identified and changes with flow rate to be determined.

Optimization of blade—diffuser interaction for improved turbine performance:

Abstract: Flowfields within turbines are generally three-dimensional and unsteady. Typically, the flowfields in the interaction zone between the last stage and the diffuser are strongly inhomogeneous. This nonuniformity strongly limits the downstream diffusion process, so that significant improvement can be achieved by making the total pressure field in this zone more uniform. One way to achieve this is by using kinks in the endwall contours and, if necessary, one or two splitters. The use of balance-based space averaging and modelling procedures can help to characterize these flows, and to develop an optimum interaction zone and diffuser geometry. In the study described here, as an example the interaction zone of high-pressure/ intermediate-pressure (HP/IP) and low-pressure (LP) diffusers of steam turbines were numerically and partly experimentally optimized for a fixed blading and exhaust. The operating conditions were also kept constant except that for low pressures the flowfield was studied for a range of back pressures (i.e. exhaust velocities). The optimization process starts with an initial flowfield in the interaction zone generated numerically or experimentally. Using these data a design procedure is applied that creates both a much more uniform total pressure field at the last stage exit and a diffuser geometry possibly with one or two splitters and proven for an earlier LP design experimentally. It was demonstrated that, depending on the inhomogeneity of the flow from the upstream stage, a performance improvement of several percentage points could be achieved.

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers:

Abstract: The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of t...

Interferometric Rayleigh Scattering and PIV Measurements in the Near Field of Underexpanded Sonic Jets

Abstract: ∗ Assistant Professor, Member AIAA † Professor, Senior Member AIAA ‡ Vice President, Associate Fellow AIAA ABSTRACT Velocity measurements were made in the near field of underexpanded sonic air jets using particle image velocimetry (PIV), interferometric Rayleigh scattering and total pressure tubes. The two main objectives were to study the effect of underexpansion ratio on the flow structure and to determine the suitability of the PIV technique in high-speed flows with shock waves. The jets were produced by a convergent nozzle connected to a settling chamber. Different underexpansion conditions were obtained by changing the chamber (jet total) pressure against the atmospheric ambient. Jet exit-toambient pressure ratios, u = pe/pa, ranged between 1 and 20.32 corresponding to fully-expanded jet Mach numbers between Mj = 1 and 3.03. The PIV measurements of the streamwise and transverse velocities in the near field up to x/D = 10 (where D is the nozzle diameter) were made. From these data, distributions of mean velocities, turbulence intensities and turbulent shear stress were obtained. In order to check the accuracy of the PIV measurements (particularly, the particle lag effects) an interferometric Rayleigh scattering technique was also used to obtain the streamwise velocity for certain jet conditions. Additionally, some pressure measurements were made using a total pressure tube to provide a comparison with the two optical techniques. In general, the PIV method provided good velocity data in the jet near field and allowed the identification of flow structures and their respective locations such as shock waves, expansion regions, slip lines and shear layers. However, when compared to the Rayleigh scattering data, the effect of particle inertia was evident in certain locations in the jets. This effect was most dramatic just downstream of the Mach disk (barrel shock) in the case of highly underexpanded jets.