Duct Configuration Research Articles

Optimal Configuration of An Annular Sector Duct Filled With Porous Media

In the current study, optimal configuration for finned annulus, filled with porous media, have been investigated to maximize the convective heat transfer and minimize the friction effect subject to constant heat flux boundary conditions. Genetic Algorithm (GA) has been employed to find out the optimal geometry out of vast choices of geometrical parameters; ratio of radii of the inner to outer pipe and sector angle of channel. Finite Difference Method (FDM) is applied to solve the governing mathematical model. Chilton-Colburn’s j factor is employed as the objective function and numerical solutions of the momentum and energy equations are used as function values to the optimizer. The results indicate that for a fixed Prandtl number (Pr) the optimal geometry transforms with the variation in permeability of the porous media which is in line with the physics of the problem.

Energy balance analysis of model-scale vessel with open and ducted propeller configuration

This paper focuses on performance analysis of a model scale vessel equipped with an open versus a ducted propeller in self-propulsion using a control volume analysis of energy, applied on Computational Fluid Dynamics (CFD) results. An energy balance analysis decompose the delivered power for each system into internal and turbulent kinetic energy fluxes, i.e. viscous losses, transverse kinetic energy losses, and pressure work and axial kinetic energy fluxes. Such a decomposition can facilitate understanding of system performance and pinpoint enhancement possibilities. For this specific case it is shown that the much higher required power for the ducted propeller configuration to the largest extent is due to higher viscous losses, caused by mainly propeller duct and different rudder configuration. The energy balance analysis is a post-processing tool with the only additional requirement of solving the energy equation, which can be employed with any CFD-code based on commonly available variables.

Taxonomic review of Australian Mecyclothorax Sharp (Coleoptera, Carabidae, Moriomorphini) with special emphasis on the M. lophoides (Chaudoir) species complex

The Australian fauna ofMecyclothoraxSharp (Coleoptera: Carabidae: Moriomorphini) is reviewed, with special focus on species assigned to the monophyletic subgenus Eucyclothorax Liebherr:M.isolatus,sp. n.from Western Australia,M.mooreiBaehr,M.punctatus(Sloane),M.curtus(Sloane),M.blackburni(Sloane);M.eyrensis(Blackburn);M.peryphoides(Blackburn);M.darlingtoni,sp. n.from Queensland;M.jameswalkeri,sp. n.from Western Australia;M.lophoides(Chaudoir); andM.cordicollis(Sloane). The last six species listed above–theM.lophoidesspecies complex–have been the source of long-term confusion for taxonomists, with male genitalic characters providing trouble-free species circumscription. One new subspecies,M.lewisensisestriatus,subsp. n.from Queensland is added to the seven previously described taxa of the monophyletic subgenus Qecyclothorax Liebherr. The balance of the fauna consists of four species in the subgenus Mecyclothorax:1and2, the sister-species pairM.lateralis(Castelnau) andM.minutus(Castelnau);3,M.ambiguus(Erichson); and4,M.punctipennis(MacLeay).Mecyclothoraxfortis(Blackburn),syn. n., is newly synonymized withM.minutus.MecyclothoraxovalisSloane is recombined asNeonomiusovalis(Sloane),comb. n., and a neotype is designated to replace the destroyed holotype. Phylogenetic relationships for the AustralianMecyclothoraxare proposed based on information from 68 terminal taxa and 139 morphological characters. The biogeographic history of AustralianMecyclothoraxis deduced based the sister-group relationship betweenMecyclothoraxand theAmblytelus-related genera, with both groups hypothesized to have originated during the late Eocene. Diversification withinMecyclothoraxhas occurred since then in montane rainforests of tropical Queensland, temperate forest biomes of the southwest and southeast, and in grasslands and riparian habitats adjacent and inland from those forests. Several species presently occupy interior desert regions, though no sister species mutually occupy such climatically harsh habitats. TheM.lophoidesspecies complex exhibits profound male genitalic diversification within the context of conserved external anatomy. This disparity is investigated with regard to the functional interaction of the male internal sac flagellum and female spermathecal duct. Though limited association of flagellar and spermathecal duct configurations can be documented, several factors complicate proposing a general evolutionary mechanism for the observed data. These include:1, the occurrence of derived, elongate spermathecal ducts in three species, two of which exhibit very long male flagella, whereas males of the third exhibit a very short flagellum; and2, a highly derived and exaggerated male flagellar configuration shared across a sister-species pair even though the two species can be robustly diagnosed using external anatomical characters, other significant genitalic differences involving male parameral setation, and biogeographic allopatry associated with differential occupation of desert versus forest biomes.

The effects of installation configuration and solidity on the power generation of a linear cascade wind turbine

PowerWindow is a Linear Cascade Wind Turbine (LCWT) capable of generating electricity in very low blade speed ratios, which makes it a safe power generator in built environments. The power generation mechanism and aerodynamic performance of PowerWindow were investigated using experimental prototyping and computational fluid dynamic simulations in a previous study. Due to the limited suitable locations for installing the device in grounded configuration, this study investigates elevated and ducted installation configurations. In the elevated configuration PowerWindow is installed on a tower or in between two tall buildings. In ducted configuration it is installed inside a ducted area such as a through-building opening. Aerodynamic performances of the elevated and ducted PowerWindow are investigated and compared, using computational fluid dynamic simulations. It is shown that the coefficient of performance of the ducted PowerWindow with 12% is about 50% higher than the elevated one with 8%. The effect of solidity is also investigated on the flow mechanism and power generation. The results show that increasing solidity results in greater increase in power generation of the ducted configuration compared to the elevated one. This study also investigates effect of increasing solidity on the required pressure gradient and recommends an efficient solidity for each configuration based on the installation circumstances.

Surrogate Model Based Liner Optimization for Aeroengines and Comparison With Finite Elements

Numerical optimizations are very useful in liner designs for low-noise aeroengines. Although modern computational tools are already very efficient for a single aeroengine noise propagation simulation run, the prohibitively high computational cost of a broadband liner optimization process which requires hundreds of thousands of runs renders these tools unsuitable for such task. To enable rapid optimization using a desktop computer, an efficient analytical solver based on the Wiener–Hopf method is proposed in the current study. Although a Wiener–Hopf-based solver can produce predictions very quickly (order of a second), it usually assumes an idealized straight duct configuration with a uniform background flow that makes it arguable for practical applications. In the current study, we employ the Wiener–Hopf method in our solver to produce an optimized liner design for a semi-infinite annular duct setup and compare its noise-reduction effect with an optimized liner designed by the direct application of a numerical finite element solver for a practical aeroengine intake configuration with an inhomogeneous background flow. The near-identical near- and far-field solutions by the Wiener–Hopf-based method and the finite element solvers clearly demonstrate the accuracy and high efficiency of the proposed optimization strategy. Therefore, the current Wiener–Hopf solver is highly effective for liner optimizations with practical setups and is very useful to the preliminary design process of low-noise aeroengines.

The regenerated noise of HVAC elements and its measurement in pipeline track

HVAC systems may spread unwanted noise that needs to be reduced. One of the components of wide range noise can be a regenerated noise which is a secondary sound source usually caused by air flowing through a device. This regenerated noise associated with airflow is indeed a dynamic function of velocity. Therefore, HVAC designers try to prevent these problems by sizing ductwork or duct configurations so that air velocity is low. Nevertheless, in certain situations, this approach is not possible and it is necessary to deal with the regenerated noise further. This article discusses an alternative way of measuring regenerated noise of various duct elements in the pipeline track without being connected to a reverberation chamber. It should be emphasized that this method is not new but information about it is very limited and therefore almost unused.

Performance analysis of different configurations of heating and cooling for a multi-zone building

Multi-zone HVAC designing is important as the considerable amount of the world's energy is used for heating, ventilation, and air conditioning (HVAC) systems. Hospitals are one of the most critical multi-zone buildings. So, proper designing of multi-zone building will lead toward high savings in energy in this sector. Most common types of configurations are; constant volume with reheat (CVHr), dual duct (DD), and variable air volume (VAV) system. The key objective of the current research is to investigate the impact of operational zoning and HVAC system operation strategies on energy performance of a hospital by maintaining the desired comfort conditions. The hospital building is divided into five zones including ward, pharmaceutical, office and OT. The building load is calculated for each zone and optimised for creating the multi-zone building that resulted 52 ton. Then after proper designing of central system based on absorption cooling system to achieve this load, different air distribution system configurations are designed for each zone to determine required air flow rate in terms of cubic fit per min (CFMs). Afterwards, energy simulations are used by developing different models in TRACE 700 for forecasting the best air distribution system for each zone. The results show that COP of absorption chiller is 0.78. Additionally, the economic and cooling capacity analysis of each configuration in terms of net present value (NPV) resulted that the dual duct configuration in most efficient manner for multi-zone buildings such as hospitals.

Performance analysis of different configurations of heating and cooling for a multi-zone building

Multi-zone HVAC designing is important as the considerable amount of the world's energy is used for heating, ventilation, and air conditioning (HVAC) systems. Hospitals are one of the most critical multi-zone buildings. So, proper designing of multi-zone building will lead toward high savings in energy in this sector. Most common types of configurations are; constant volume with reheat (CVHr), dual duct (DD), and variable air volume (VAV) system. The key objective of the current research is to investigate the impact of operational zoning and HVAC system operation strategies on energy performance of a hospital by maintaining the desired comfort conditions. The hospital building is divided into five zones including ward, pharmaceutical, office and OT. The building load is calculated for each zone and optimised for creating the multi-zone building that resulted 52 ton. Then after proper designing of central system based on absorption cooling system to achieve this load, different air distribution system configurations are designed for each zone to determine required air flow rate in terms of cubic fit per min (CFMs). Afterwards, energy simulations are used by developing different models in TRACE 700 for forecasting the best air distribution system for each zone. The results show that COP of absorption chiller is 0.78. Additionally, the economic and cooling capacity analysis of each configuration in terms of net present value (NPV) resulted that the dual duct configuration in most efficient manner for multi-zone buildings such as hospitals.

Modal identification of aeroacoustic systems using passive and active approaches.

The noise generated by a ducted diaphragm configuration, taken in this paper as a prototype aeroacoustic system, is investigated experimentally using a two-port source identification method [Lavrentjev, Åbom, and Bodén (1995) J. Sound Vib. 183, 517-531]. The method requires successively the determination of the so-called passive scattering properties of the ducted diaphragm system using loudspeakers, and the extraction of the active noise that would be emitted by the aeroacoustic source itself in an anechoic duct. These steps involve assembling a non-singular acoustic load matrix based on experimental data, and its inversion. This inversion can present numerical robustness issues, especially when higher-order modes are included as in the present study. Another issue is related to the alteration of the duct-termination reflective properties that external loudspeakers modules can cause, yielding a change in duct scattering characteristics for the active and the passive measurements. The present paper revisits established practices in the field and presents an experimental procedure in which the acoustic load matrix is assembled using the aeroacoustic source instead of the loudspeaker excitations. The proposed approach enables improving the conditioning of the load matrix and accurate determination of the duct termination reflectivity. The use of external loudspeakers however, remains necessary for the measurement of the scattering properties of the source itself.

Design of ducted propeller nozzles through a RANSE-based optimization approach

Marine propellers design requirements are always more pressing and the application of unusual propulsive configurations, like ducted propellers with decelerating nozzles, may represent a valuable alternative to fulfill stringent design constraints. Accelerating duct configurations were realized mainly to increase the propeller efficiency in the case of highly-loaded functioning. The use of decelerating nozzles sustains the postponing of the cavitating phenomena that, in turn, reflects into a reduction of vibrations and radiated noise. The design of decelerating nozzle, unfortunately, is still challenging. The complex interaction between the propeller and the nozzle, both in terms of global flow feature and local (tip located) phenomena, is not yet fully understood. No extensive systematic series, as in the case of accelerating configurations, are available and the design still relies on few measurements and data. On the other hand, viscous flow solvers appear as reliable and accurate tools for the prediction of complex flow fields and their application for the calculation of ducted propeller performance and nozzle flow was almost successful. Hence, using CFD as a part of a design procedure based on optimization, by combining a parametric description of the geometry, a RANSE solver (OpenFOAM) and a genetic type algorithm (the modeFrontier optimization environment), is the obvious step towards an even more reliable ducted propeller design. An actuator disk model is adopted to include efficiently the influence of the propeller on the flow around the duct; this allows avoiding the weighting of the computational effort that is necessary for the calculations of the thousands of geometries needed for the indirect design by optimization. Design improvements, in model scale, are measured by comparing, by means of dedicated fully resolved RANSE calculations, the performance of the optimized geometries with those of conventional shapes available in literature. For both nozzle typologies, dedicated shapes reducing the risk of cavitation and increasing the delivered thrust are obtained, showing the opportunity of customized nozzle design out of usual systematic series. In addition, by analyzing the results of the optimization histories, appropriate design criteria are derived for both accelerating and decelerating nozzle shapes.

A Post-Swirl Maneuvering Propulsor Application to Undersea Vehicles

A method to generate vehicle maneuvering forces from a propulsor alone has been applied to a generic undersea vehicle. Open and ducted post-swirl propulsors were configured with an upstream rotor and downstream stator row. During normal operation, the downstream stator blades are all situated at the same pitch angle and generate a roll moment to counter the torque produced by the rotor. By varying the pitch angles of the stator blade about the circumference, it is possible to generate a mean stator side force that can be used to maneuver the vehicle. In addition, the side force can be increased with increasing thrust producing side forces at very low vehicle velocities enabling low-speed maneuvering capability. The viscous, 3-D Reynolds-averaged Navier–Stokes (RANS) commercial code Fluent was used to predict the vehicle and propulsor component forces as well as the velocity field. Open and ducted geometric configurations were studied and force coefficients computed and compared with currently used control surface forces. Computations predicted that the maneuvering propulsor generated side forces equivalent to those produced by conventional control surfaces with side force coefficients on the order of 0.25 for the open propulsor at the self-propulsion point. This translates to 50% larger forces than can be generated by conventional control surfaces on 21 $^{\prime \prime}$ unmanned undersea vehicles. The ducted configuration produces maximum side force coefficients on the order of 0.15, which is still sufficient for vehicle control. Both configurations produced side forces for the Bollard pull condition indicating low-speed maneuvering capability.

Numerical Investigations of Fan-in-Wing Aerodynamic Performance with Active Flow Control

Aerodynamic performance of a fan-in-wing configuration in hover is numerically investigated using a high-fidelity three-dimensional unsteady Reynolds-averaged Navier–Stokes flow solver based on unstructured grid technology. Fan-in-wing or ducted fan configurations offer the advantage of hover capability with enhanced thrust comparing to open fans, but they suffer from reduced efficiency and thrust levels at offdesign conditions. In this study, the aerodynamic performance and flowfield of a fan-in-wing configuration in hover are numerically investigated over a range of blade pitch angles at two operating speeds. The maximum thrust, peak efficiency, and stall margin of the system are among the main interests of this investigation. An innovative concept using an active flow control is introduced in this study to enhance the operating efficiency and thrust level of the system by increasing the circulation and duct mass flow rate in the fan-in-wing system. Numerical investigations indicate a 25–55% increase in the maximum system thrust, achieved without suffering the peak efficiency loss, when using the proposed active flow control concept. This potentially provides a viable technology to significantly enhance the aerodynamic performance of lift fan devices such as the ducted fans or fan-in-wing configurations to support the research of vertical takeoff and landing aircraft.

Performance study of ducted nozzle Savonius water turbine, comparison with conventional Savonius turbine

Savonius turbine presents an attractive, environmentally friendly and cost effective electric generation in low velocity regions. However, this turbine has not been fully explored, as researchers are still searching for solution for the main problem of low efficiency of Savonius turbine configuration. This research paper proposes a novel system of ducted nozzle configuration around Savonius rotor to increase the efficiency of the turbine. In this study, six different duct nozzle designs had been investigated. A numerical investigation was carried out in this research work using finite volume Reynolds-Averaged Navier-Stokes Equations (RANSE) code ANSYS Fluent with Reynolds numbers of 1.32×105. Consequently, validation was carried out following previous experiments. Flow characteristics through augmented configuration, and performance of the Savonius turbine had been studied, and it was found that the water flow speed had been enhanced by the developed ducted nozzle system. The maximum power coefficient of the ducted nozzle turbine was increased by 78% compared to the conventional modified rotor. The maximum power coefficient was 0.25 at tip speed ratio (TSR) of 0.73. The use of this system is expected to contribute towards a more efficient utilization of flows in rivers and channels for electrical generation in rural areas.

A matrix to evaluate the conjugate cooling of a heaters' array

Circuit boards are usually cooled by forced airflow and the heat transfer from the discrete electronic components may be enhanced by conductive boards. The conjugate forced convection-conduction cooling of an array of N heaters mounted on a conductive substrate was described by means of dimensionless conjugate coefficients g+kj grouped in a N-square matrix G+. Experiments were performed with one or two rows of protruding heaters mounted on the conductive lower wall of a rectangular duct, made of either Aluminum or Plexiglas. One end of the duct was closed and the heaters were cooled by two impinging airflows exiting from square holes at the duct upper wall. For each substrate plate, the conjugate coefficients were obtained from tests with a single active heater at a time and expressed as functions of a Reynolds number in the range from 2000 to 7000. Additional tests with two or three active heaters at a time were then performed and the measured temperature increase of each heater above the flow inlet temperature was predicted quite well using the previously obtained coefficients matrix G+. These results showed that the conjugate coefficients are invariant with the conjugate cooling rates from the heaters. The conjugate coefficients were also used to predict the allowable conjugate cooling rates for an array of heaters, in order to keep their temperature within reliable limits. Numerical simulations were performed for a duct configuration similar to that of the experiments, but with flush mounted heaters. The numerical results were thus distinct from those of the experiments with protruding heaters, but they showed similar trends of change with the Reynolds number and they indicated a perspective of the effects of the heaters height.

Detailed velocity profiles in close-coupled elbows—Measurements and computational fluid dynamics predictions (RP-1682)

This article presents a systematic study to measure detailed velocity profiles in close-coupled five-gore elbows having nominal diameters of 305 mm (12 in) and turning radii r/D = 1.5, and to, likewise, predict the velocity profiles using computational fluid dynamics. The purpose of the testing was to study the physics of the flow in complex geometries and to provide data that can be used to verify the accuracy of computational fluid dynamics modeling predictions. The close-coupled elbow combinations comprised either a Z-shape or a U-shape configuration. In every instance the duct length separating the center-points of the elbows was systematically varied. Detailed velocity profile measurements were performed at one traverse plane located one duct diameter upstream of the first elbow and at one duct diameter downstream of the second elbow, and at various axial locations in the straight section between the close-coupled elbows. Velocity profiles results are compared to computational fluid dynamics Reynolds Stress Model and Large Eddy Simulation predictions for the effect of separation distance of the elbows in Z-shape duct configurations. Reynolds Stress Model turbulence modeling predicted the velocity trends correctly with a maximum error of 15%. However, Large Eddy Simulation modeling failed to predict the trend and the magnitude of the velocities, thus Large Eddy Simulation approach is not suitable for this type of flow.

Experiments and Numerical Simulations of Pressure Effects in Apartment Fires

The fire induced pressure and its influence on ventilation flows within a compartment have not been studied in detail previously. In this research work, we have investigated the development of gas pressure and the resulting flows in compartment fires first experimentally, by burning a series of heptane pool and polyurethane mattress fires inside a real, 58.6 m^2 by 2.57 m high, apartment and then by carrying out numerical simulations of the experiments with the FDS code. The experiments were conducted with three different ventilation duct configurations to simulate three different airtightness conditions. The peak heat release rates were less than 1 MW and the burning times were about 180 s. The experimental results indicate that the gas pressure in relatively closed apartment can become high enough to revert the flows of the ventilation system, prevent escape through inwards-opening doors, and even break some structures. The peak gas temperatures under the ceiling of the burn room were about 300°C. The pool fires remained well-ventilated. The pressure ranges encountered in the experiments were between 100 Pa to 1650 Pa and the pressure occured within 50 s of ignition. We also report the FDS validation for this type of simulations and discuss the process of modelling the ventilation system and leakages.

Radiation of sound in a semi-infinite hard duct inserted axially into a larger infinite lined duct

This article examines sound radiation from a hard semi-infinite duct placed symmetrically inside an acoustically lined duct. We introduce a wake on right handed region of the duct configuration to analyze sound radiation process for the trailing edge situation. The integral transforms together with Wiener–Hopf techniques render the solution of underlying problem. However expressions for field intensity involve infinite sums/products that enable solution using truncation approach. The sound radiation analysis is then observed graphically while using different choice of some pertinent parameters. It is worth mentioning that results of leading edge situation can be recovered as a limiting case.

Anatomic variations of the pancreatic duct and their relevance with the Cambridge classification system: MRCP findings of 1158 consecutive patients.

BackgroundThe study was conducted to evaluate the frequencies of the anatomic variations and the gender distributions of these variations of the pancreatic duct and their relevance with the Cambridge classification system as morphological sign of chronic pancreatitis using magnetic resonance cholangiopancreatography (MRCP).Patients and methodsWe retrospectively reviewed 1312 consecutive patients who referred to our department for MRCP between January 2013 and August 2015. We excluded 154 patients from the study because of less than optimal results due to imaging limitations or a history of surgery on pancreas. Finally a total of 1158 patients were included in the study.ResultsAmong the 1158 patients included in the study, 54 (4.6%) patients showed pancreas divisum, 13 patients (1.2%) were defined as ansa pancreatica. When we evaluated the course of the pancreatic duct, we found the prevalence 62.5% for descending, 30% for sigmoid, 5.5% for vertical and 2% for loop. The most commonly observed pancreatic duct configuration was Type 3 in 528 patients (45.6%) where 521 patients (45%) had Type 1 configuration.ConclusionsVertical course (p = 0.004) and Type 2 (p = 0.03) configuration of pancreatic duct were more frequent in females than males. There were no statistically significant differences between the gender for the other pancreatic duct variations such as pancreas divisium, ansa pancreatica and course types other than vertical course (p > 0.05 for all). Variants of pancreas divisum and normal pancreatic duct variants were not associated with morphologic findings of chronic pancreatitis by using the Cambridge classification system. The ansa pancreatica is a rare type of anatomical variation of the pancreatic duct, which might be considered as a predisposing factor to the onset of idiopathic pancreatitis.

Morphology of the distal thoracic duct and the right lymphatic duct in different head and neck pathologies: an imaging based study.

BackgroundThe purpose of this study was to assess the influence of head and neck pathologies on the detection rate, configuration and diameter of the thoracic duct (TD) and right lymphatic duct (RLD) in computed tomography (CT) of the head and neck.MethodsOne hundred ninety-seven patients were divided into the subgroups "healthy", "benign disease" and "malignant disease". The interpretation of the images was performed at a slice thickness of 3 mm in the axial and coronal plane. In each case we looked for the distal part of the TD and RLD respectively and subsequently evaluated their configuration (tubular, sacciform, dendritic) as well as their maximum diameter and correlated the results with age, gender and diagnosis group.ResultsThe detection rate in the study population was 81.2 % for the TD and 64.2 % for the RLD and did not differ significantly in any of the subgroups. The predominant configuration was tubular. The configuration distribution did not differ significantly between the diagnosis groups. The mean diameter of the TD was 4.79 ± 2.41 mm and that of the RLD was 3.98 ± 1.96 mm. No significant influence of a diagnosis on the diameter could be determined.ConclusionsThere is no significant influence of head/neck pathologies on the CT detection rate, morphology or size of the TD and RLD. However our study emphasizes that both the RLD and the TD are detectable in the majority of routine head and neck CTs and therefore reading physicians and radiologists should be familiar with their various imaging appearances.

Robust Flight Control Using Nonsmooth Optimization for a Tandem Ducted Fan Vehicle

AbstractThis work addresses the aerodynamic modeling and near‐hover‐flight control design for an unconventional aerial robot of the tandem ducted fan configuration, which is intended to be prototypical of a flight service vehicle. The main model elements of this novel unmanned vehicle, which exhibit highly nonlinear and unstable open‐loop modes, are presented. A frequency‐domain controllability analysis concerning the plant's behavior around the hovering flight condition is then adopted to determine the expected control performance, which is of important practical significance to controllability improvement through vehicle design changes. A robust controller that stabilizes the unmanned vehicle under wind disturbances is designed using a newly developed nonsmooth optimization algorithm, which rigorously and efficiently tunes the arbitrarily predefined structured controller against multiple control requirements. A successive two‐loop architecture is employed in the designed controller. In this architecture, the inner loop provides stability augmentation and decoupling, and the outer loop guarantees the desired velocity tracking performance. Simulation results under stochastic wind gusts are presented to verify the performance of the proposed controllers. Preliminary flight tests are also carried out to demonstrate the performance of the system.