Duct Configuration Research Articles

Experimental investigation of the influence of the inlet duct configuration on the unstable operation of a single-stage centrifugal blower

The article is devoted to the experimental investigation of the interactions between the amplitudes and frequencies of surge in a single-stage centrifugal blower and the configuration of its inlet duct. In this work, the term ‘configuration’ implies the combination of the following: the volume of the duct, the presence of the filter inside the duct and the inlet guide vane position. The high-response pressure measurements were performed at three points along the impeller shroud (inlet, middle, outlet) and at a single point downstream the volute outlet and then processed with the use of fast Fourier transform (FFT). The results of the measurements show that the response of the surging system to a change introduced into the duct’s configuration is complex. The closure of the inlet guide vane typically causes a drop in the amplitude and frequency of fluctuating pressure. The introduction of a filter body into the duct most often damps the amplitudes of fluctuations, but leaves the frequencies unaltered. The change of the duct’s volume controls the rate of this damping.

Numerical and Experimental Comparative Study on Nanofluids Flow and Heat Transfer in a Ribbed Triangular Duct

Numerical and experimental investigation is carried out to study the effect of combined vortex generator and nanofluids on turbulent heat transfer and fluid flow characteristics in an equilateral triangular duct. A triangular duct provides a lower heat transfer rate and lower pressure drop compared to other duct configurations. The improvement of heat transfer of these ducts increases their importance for providing higher heat transfer and lower pressure drop. Two different types of nanoparticles, namely Al2O3 and SiO2, suspended in distilled water with two particle concentrations are successfully prepared and experimentally tested. The numerical and experimental results show dramatic heat transfer enhancement by using a vortex generator and nanofluids, simultaneously accomplished with a moderate increase in the friction factor. A low deviation has been seen between the present numerical and experimental results.

Analysis of the acoustical behavior of cavities using impedance functions

The acoustic design of cavities is an important task in a variety of engineering applications, from automotive or aerospace industries to equipment coating designs. In this work, the acoustic impedance functions (a frequency domain model) were calculated using analytical, numerical, and experimental methods. Those different approaches were presented in a unified manner in order to allow comparisons among them. The relationship of the impedance function and a classical frequency response function (FRF) was also established. A circular duct of rigid walls was assumed with different boundary conditions as closed end, as well as opened and absorbed extremities. Three duct configurations were implemented in order to compare analytical, numerical, and experimental results. Finally, it could be possible to evaluate some aspects that are characteristic of a large range of acoustic systems applications as the existence of complex modes and frequency-dependent behavior of absorption material. This study aims the usage of the impedance functions to analyze the acoustic behavior of cavities, as well as to compose the background in order to develop, in the future, an acoustic modeling process using impedance functions.

Analysis of liner performance using the NASA Langley Research Center Curved Duct Test Rig

The NASA Langley Research Center Curved Duct Test Rig (CDTR) is designed to test aircraft engine nacelle liner samples in an environment approximating that of the engine on a scale that approaches the full scale dimensions of the aft bypass duct. The modal content of the sound in the duct can be determined and the modal content of the sound incident on the liner test section can be controlled. The effect of flow speed, up to Mach 0.5 in the test section, can be investigated. The results reported in this paper come from a study to evaluate the effect of duct configuration on the acoustic performance of single degree of freedom (SDOF) perforate-over-honeycomb liners. Variations of duct configuration include: asymmetric (liner on one side and hard wall opposite) and symmetric (liner on both sides) wall treatment; inlet and exhaust orientation, in which the sound propagates either against or with the flow; and straight and curved (outlet is offset from the inlet by one duct width) flow path. The effect that duct configuration has on the overall acoustic performance is quantified. The redistribution of incident mode content is shown, in particular the mode scatter effect that liner symmetry has on symmetric and asymmetric incident mode shapes. The Curved Duct Test Rig is shown to be a valuable tool for the evaluation of acoustic liner concepts.

Thermal analysis for optimization of the optical duct of the ITER core CXRS diagnostics

The First Mirror (M1), as part of the ITER core CXRS diagnostics, is responsible for acquisition and transportation of the optical signal from the plasma to the corresponding spectrometer. The M1 is the most vulnerable component of this system working in severe conditions caused by its location in the direct view of the plasma. Based on the numerical analysis an optimized arrangement of baffles was found for the optical channel. It is shown that such measures like the deeper M1 positioning in the shielding, duct configuration and baffles implementation made it possible to reduce heat loads on the M1 by a factor of about 102–103.

Исследование фрикционных свойств тормозных колодок с различным рельефом масляных канавок

Some technological operations – stump extraction, preparation of forest roads are made by machines based on powerful caterpillar tractors. One of the problematic units of caterpillar tractors is band brakes of "dry" friction. Typically, friction tape must be changed after two ТО-3. Belt shoe brakes, working in oil, have higher durability (at least one order of magnitude). Apart from the choice of a special friction material for such a brake oil supply system must be ensured and special oil ducts on the working surfaces of the pads. In the literature several fundamental configurations of ducts are known. We, together with specialists from Cheboksary Industrial Tractor Plant have selected cruciform shape of cutting ducts. Due to a variety of factors and difficulties passing on the cutting-friction contact of phenomena analytical method for the selection of the geometry of ducts is difficult. We used full-scale experiment with the previously selected friction asbestos polymer material no. 410-120. Tests were conducted on a combined stand. To simplify this type of test we used not the whole belt of the four pads, but only one pad. To do this, stand design was modified; strain-gage chain was changed to record braking torque. The tests were carried out under braking stops. Different geometries of oil ducts on the different modes of operation were explored. The following parameters were varied: the density of cutting; the width of the ducts; depth of the ducts; angle to the axis of the ducts. Frictional properties and the temperature at the friction surface were evaluated. The best performances of ducts cutting were chosen after tests. mm; mm; mm ; . The results of the work are introduced in production.

Remodeling of alveolar septa after murine pneumonectomy.

In most mammals, removing one lung (pneumonectomy) results in the compensatory growth of the remaining lung. In mice, stereological observations have demonstrated an increase in the number of mature alveoli; however, anatomic evidence of the early phases of alveolar growth has remained elusive. To identify changes in the lung microstructure associated with neoalveolarization, we used tissue histology, electron microscopy, and synchrotron imaging to examine the configuration of the alveolar duct after murine pneumonectomy. Systematic histological examination of the cardiac lobe demonstrated no change in the relative frequency of dihedral angle components (Ends, Bends, and Junctions) (P > 0.05), but a significant decrease in the length of a subset of septal ends ("E"). Septal retraction, observed in 20-30% of the alveolar ducts, was maximal on day 3 after pneumonectomy (P < 0.01) and returned to baseline levels within 3 wk. Consistent with septal retraction, the postpneumonectomy alveolar duct diameter ratio (Dout:Din) was significantly lower 3 days after pneumonectomy compared to all controls except for the detergent-treated lung (P < 0.001). To identify clumped capillaries predicted by septal retraction, vascular casting, analyzed by both scanning electron microscopy and synchrotron imaging, demonstrated matted capillaries that were most prominent 3 days after pneumonectomy. Numerical simulations suggested that septal retraction could reflect increased surface tension within the alveolar duct, resulting in a new equilibrium at a higher total energy and lower surface area. The spatial and temporal association of these microstructural changes with postpneumonectomy lung growth suggests that these changes represent an early phase of alveolar duct remodeling.

Simulation and Validation of Airflow Pressure Patterns in Hopper-Bottom Bins Filled with Wheat

<abstract> <b><sc>Abstract. </sc></b>A non-linear model that can explain the three-dimensional airflow pressure patterns in grains was developed and solved using the finite element method. The model can simulate airflow distribution in both flat-bottom and hopper-bottom bins of different shapes such as square, rectangular, or cylindrical. Resistance to airflow through the grain bed was explained using a modified form of Darcy’s equation. The airflow model was validated against experimental data obtained from studies conducted in a 4.72 m diameter hopper-bottom bin filled with wheat, aerated using a 1.82 m vertical rocket-type aerator. The relative error between the experimental and predicted static pressure values for the entire bin geometry was less than 3.2%, with higher values at regions near the aerator. The validated model can be used to predict the static pressure patterns and airflow distribution (because airflow lines are perpendicular to iso-pressure lines) in various grain beds and can handle variations in product type, moisture content, grain surface configurations, foreign material content, direction of airflow, and aeration duct designs. Using the validated model, airflow pressure patterns in a hopper-bottom cylindrical bin with 10 different duct configurations were predicted and results were discussed for their implications for aeration and near-ambient air drying. The airflow pressure patterns as affected by variations in airflow rate, grain surface configuration (peaked, levelled and conically cored), bin geometry, direction of airflow, and grain bed height (grain filled up to 40%, 60%, and 80% of the bin height) were also simulated and discussed.

Simulation and Validation of Airflow Distribution Patterns in Bins Filled with Canola

A non-linear model that can explain three dimensional airflow pressure patterns in bins filled with canola was developed using the finite element method. Resistance to airflow through the porous matrix (canola) was described using a modified form of Darcy’s equation. The airflow model was validated against experimental data obtained from studies conducted in a flat bottom bin of 4.6 m diameter containing‘Tobin’ canola, aerated using a fully perforated floor. The average relative error between the experimental and predicted values for the entire bin geometry was 1.8 per cent. Relative error values decreased with increasing grain bed height and bin diameter. The airflow pressure patterns resulting from eight other duct configurations were simulated. The model can be used to predict the airflow distribution in various grain beds and has the capability to handle variations in product type, moisture content, foreign material content, direction of airflow and aeration duct designs.

Effects of the gas outlet duct length and shape on the performance of cyclone separators

In most published studies regarding the numerical simulation of cyclone separators, the gas outlet duct is usually treated as a short straight duct, differing considerably from the experimental apparatus, in which a relatively long duct followed by a curve, or vice versa, is generally used. This work focuses on the influence of length and shape of the outlet duct on the grade efficiency and pressure drop inside a small cyclone separator. The results are obtained through Large Eddy Simulation of the fluid flow inside the separator, coupled with a concomitant Lagrangian description-based on Newton’s second law-of the dispersed phase. More than thirty different outlet duct configurations, including different lengths, curves, curves positions and curvature radii were simulated. The results show that the cyclone gas outlet duct may affect the cyclone performance: the pressure drop initially decreases with duct length until a minimum is reached, and from this point on it monotonically increases with duct length. As for the cut off diameter, the relation showed itself much more complex.

Evaluating Daylighting Performances of Anidolic Light-Duct Systems Using RADIANCE with Photon Map Algorithm in Terms of Light Duct Index

Various types of daylighting systems have been developed to save electric energy for interior illumination in modern buildings by effectively admitting natural light into the space. Among the daylight systems, anidolic light- duct systems are developed to admit direct sunlight at the light collector located on the side walls, normally south- facing wall, transport to the admitted sunlight through light duct with high-reflectance interior surfaces, and illuminate indoor spaces by light diffuser. The efficiency of anidolic light duct system is affected by various design variables including the aperture size of the light collector, geometric configuration and reflectance of the light guiding duct and the diffusing character of the light diffuser. In this study, the efficiency of illumination in terms of illuminance levels were tested by different geometric configuration of the light duct. The geometric configuration of light duct was expressed by LDI(Light Duct Index) which is the same as the Well Index of atrium spaces. The illuminance level were calculated for equinoxes and summer and winter solstices by the RADIANCE program with Photon map algo- rithm. Then, the illuminance classes defined by KS A 3011 were identified for the different LDIs. The result showed that for the LDI values from 2.17 to 26.00, when LDI was increased by 8.3% daylighting performance was reduced to 85%~95%. The simulation results also showed that for all the working hours during day times, except for 4 o'clock on the winter solstice, the light ducts having the LDI lower than 13 provided enough daylight for conference which requires illuminance class F.

Acoustically Consistent Investigation of Combustion Instabilities in a Dump Combustor

An acoustically consistent, linear modal analysis-based analytical method is presented to predict the longitudinal and transverse combustion instabilities in a two-dimensional Cartesian dump combustor. At first, rigorous acoustical analysis (without combustion) is performed of two duct configurations with one and two discontinuities in the cross-sectional area. Novel, acoustically consistent jump or matching conditions are developed and applied at the duct cross-sectional interface(s), with distinct forms for the purely axial and nonaxial modes. The effects of uniform and nonuniform mean flows, cross-sectional area ratio, as well as of different types of boundary conditions on the duct acoustic modes are investigated. Acoustic modal frequency predictions are in excellent agreement with the analytical and numerical results of Meissner (“Effect of Cross-Sectional Area Discontinuities in Closed Hard-Walled Ducts on Frequency of Longitudinal Modes,” Archives of Acoustics, Vol. 35, No. 3, 2010, pp. 421–435). In the second part, combustion instabilities of a two-dimensional Cartesian dump combustor are investigated. The instability analysis employs the developed acoustically consistent jump conditions instead of the conventional mass, momentum, and energy balance-based conditions. Effects of the fluctuating heat-release source term in the acoustic wave equation are incorporated directly into the longitudinal wave number, obviating the need for a separate energy matching condition across the flame. A detailed investigation of the parametric space and boundary conditions affecting combustion instabilities is undertaken, and the consistency of the modal analysis with the Rayleigh criterion is explicitly demonstrated. Further, the present approach enables the consideration of arbitrary mean flame shapes in determining the unstable modes. Instabilities are demonstrated for the fundamental longitudinal mode and its harmonics, as well as for the fundamental transverse mode. The effects of the cross-sectional area ratio and flow Mach number on the unstable-mode growth rates are also presented.

Surface effects on the diagnostic of carbon/nitrogen low-pressure plasmas studied by differentially pumped mass spectrometry.

In this work, the characterization of the species produced in reactive plasmas by differentially pumped mass spectrometry is addressed. A H2/CH4/N2 mixture (90 : 5 : 5) was fed into a direct current glow discharge and analysed by conventional and cryo-trap assisted mass spectrometry. The gaseous mixture was chosen because of its particular relevance in the inhibition of tritium-rich carbon film deposition in fusion plasmas (scavenger technique) and in the deposition of amorphous hydrogenated carbon films by plasma-assisted chemical vapour deposition. Important changes in the composition of the detected species upon surface modification of the reactor walls (stainless steel or covered by an amorphous hydrogenated carbon layer) or in the way they are sampled (length and spatial configuration of the stainless steel duct) were detected. They are analysed in terms of radical formation and recombination on the reactor walls or into the sampling duct, thus providing some insight into the underlying chemistry. In general, when the reactor walls are covered by an amorphous hydrogenated carbon layer, more hydrocarbons are produced, but the radical production is lower and seem to be less reactive than in stainless steel. Also, two sources of oxygen contamination in the plasma have been identified, from the native oxide layer in stainless steel and from unintended water contamination in the chamber, which modify considerably the detected species.

Eigenfrequency of a Helmholtz resonator at the wall of a rectangular duct

The eigenfrequency of a Helmholtz resonator fixed at the wall of a rectangular duct is estimated. Special attention is given to determining the attached length of the resonator neck as viewed from the duct. The dependences of the attached neck length and the eigenfrequency on the duct configuration are analyzed. Theoretical results are compared with the data of numerical calculations performed by the finite-element method.

Performance evaluation of ducts with non-circular shapes: Laminar fully developed flow and constant wall temperature

Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase fully developed laminar flow through bundle of ducts with non-circular shape – rectangular, isosceles triangular, elliptical, trapezoidal and hexagonal. The bundle of circular tubes has been used as a reference heat transfer unit. Constant wall temperature has been selected as the thermal boundary condition. The performance characteristics of the bundles with non-circular ducts have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the hydraulic diameter of the duct has been specified.The results clearly show that the rectangular, trapezoidal or hexagonal duct configuration can compete, in some cases, with the circular tube configuration. The choice of the tube shape and geometrical details depends on the constraints imposed and the objectives pursued. The results obtained from the present study revealed that they differed from those obtained with a common constraint of specified cross sectional area.

Numerical Studies of Supersonic Flow in Bell-Shaped Micronozzles

In this study, numerical computations are performed that examine the thrust production and efficiency of supersonic micronozzles with bell-shaped expanders. The bell geometry is favored on the macroscale for its flow alignment. To date, concerns over microfabrication challenges of the contoured geometry have limited its consideration for microscale applications. Three different bell expander configurations are examined (100% full bell, 80%, and 60%) for two-dimensional and three-dimensional duct configurations of varying depths (), and a decomposed monopropellant is used as the working fluid, and the associated throat Reynolds numbers range from 15 to 800. Owing to the inherently low Reynolds numbers on the microscale, substantial viscous subsonic layers develop on the walls of the nozzle expander, retard the bulk flow, and reduce the nozzle performance. The thrust production and specific impulse efficiency are computed for the various flow scenarios and nozzle geometries to delineate the impact of viscous forces on the nozzle performance. Results are also compared to the inviscid theory and to two-dimensional and three-dimensional results for 30 deg linear nozzle configurations. It is found that the flow alignment of the bell nozzle comes at the expense of increased viscous losses, and, on the microscale, a 30 deg linear nozzle offers a higher efficiency for in two-dimensional micronozzles and over the majority of Reynolds numbers in three-dimensional simulations. The simulation results indicate that a short micronozzle outperforms a longer nozzle at a given Reynolds number, and this result is supported by existing micronozzle studies in the literature.

Numerical and experimental investigation of conventional and un-conventional preswirl duct for VLCC

This paper shows the study of preswirl duct as an effective energy saving devices that have been devised and reviewed to support the propeller performance, especially for the ship of VLCC with large block coefficients. From the bare hull wake measurements, typical upper/lower asymmetry of hull wake at the propeller disk was found. The 2 kinds of pre-swirl duct, Unconventional half circular duct and Conventional circular pre-swirl duct have been designed and reviewed to recover the loss of propeller running in that condition. The general function of the pre-swirl duct was set to work against this asymmetry of wake and generate pre-swirled flow into the propeller against the propeller ro-tating direction. The optimum self propulsion tests with various angle configurations were carried out and the best configuration was decided. Accordingly, cavitation test was carried out with best configuration of unconventional half circular duct. The blade surface and tip vortex cavitation behaved smoother when the duct was mounted. The hull pressure amplitudes reflected this difference, so the hull pressure amplitude with duct was smaller than that of without duct.

Analytical Study on Stall Stagnation Boundaries in Axial-Flow Compressor and Duct Systems

Stall stagnations in the system of axial-flow compressors and ducts occur in transition from deep surge conditions to decayed or converged stall conditions. The present study is concerned with the boundaries between the deep surges and the stagnation stalls on the basis of analytical results by a code on surge transients analysis and simulation. The fundamental acoustical-geometrical stagnation boundaries were made clear from examinations of the results on a variety of duct configurations coupled with a nine-stage compressor and a single stage fan. The boundary was found to be formed by three parts, i.e., B- and A-boundaries, and an intermediate zone. The B-boundary occurs for the suction-duct having a length of about a quarter of the wave-length of the first resonance in the case of very short and fat plenum-type delivery duct. On the other hand, the A-boundary occurs for the long and narrow duct-type delivery flow-path having a length about a fifth of the wavelength and relatively small sectional area in the case of short and narrow suction ducts. In addition to this, the reduced surge-cycle frequencies with respect to the duct lengths are observed to have respective limiting values at the stagnation boundaries. The reduced frequency for the B-boundary is related with a limiting value of the Greitzer's B parameter. The tendency and the characteristic features of the related flow behaviors in the neighborhood of the boundaries were also made clearer.

Shape optimization of a general bypass duct for tone noise reduction using continuous adjoint method

A novel continuous adjoint-based acoustic propagation method is proposed for low-noise turbofan duct design. A fan bypass duct tonal noise propagation model that is verified by comparison with an analytical solution of the modal radiation from a semi-infinite duct with the shear layer is enhanced with its continuous adjoint formulation, having been applied to design the bypass duct. First, this article presents the complete formulation of the time-dependent optimal design problem. Second, a continuous adjoint-based acoustic propagation method for two-dimensional bypass duct configurations is derived and presented. This article aims at describing the potential of the adjoint technique for aeroacoustic shape optimization. The implementation of the unsteady aeroacoustic adjoint method is validated by comparing the sensitivity derivative with that obtained by finite differences. Using a continuous adjoint formulation, the necessary aerodynamic gradient information is obtained with large computational savings over traditional finite-difference methods. The examples presented demonstrate that the combination of a continuous-adjoint algorithm with a noise prediction method can be an efficient design tool in the bypass duct noise design problem.

Flow and performance characteristics of an Allison 250 gas turbine S-shaped diffuser: Effects of geometry variations

The S-shaped diffuser which connects the exit of the compressor to the inlet of the combustion chamber of the Allison 250 gas turbine has been investigated using the Shear-Stress Transport turbulence model (SST) and the commercial code ANSYS-CFX. The diffuser geometry includes an initial conical diffuser which smoothly transitions into a constant cross-section S-duct. The numerical model and setup were validated using both in-house processed experimental data and experimental data from the literature on a similar geometry. The stream-wise velocity profile was observed to flatten in the initial divergent section, and then the region of the flow with the highest velocity is pushed toward the outer surface of the first bend, with a secondary-flow in the plane of the cross-section. This distortion of the stream-wise velocity intensified when the inlet turbulence intensity was decreased or when the Reynolds number was increased. An increase of the Reynolds number also translated into higher static pressure recovery potential and lower wall friction coefficients. Six variations of the diffuser geometry were considered, all having the same total cross-sectional area ratio and centreline offset. The qualitative results were the same as those of the Allison 250 diffuser, but unlike the base geometry, all the considered variants showed separated-flow regions (and reversed-flow regions in some cases) of different sizes and at different locations. The performance indicators for the Allison 250 S-shaped diffuser were the highest overall. Most interestingly, the current duct geometry outperformed its variant with a cross-sectional area expansion extending over its entire length, which is the most common inlet duct configuration.