Main Airflow Research Articles

Optimization of Noise Reduction Performance for the Muffler in a Heavy Vehicle

The noise reduction performance of the muffler is further optimized in order to study the acoustic performance of the high-performance composite muffler. On the basis of reasonable assumptions, the boundary values of the entrance and exit, which of the inner wall surface of the muffler are set up. The internal acoustic finite element model is established through HYPERMESH, and the transmission loss(TL) is calculated by the SYSNOISE module in Virtual.lab. Then, the effect on noise reduction performance by the main structural parameters of muffler, such as the hole diameter of the perforating tube, the number of expansion chamber, and the position of the main air flow passage are discussed. The experiment proves that the noise reduction performance of the muffler is improved effectively, proves the practicability of this method, and also gives a solution for the design and optimization of complex muffler.

Passive monitoring of particulate matter and gaseous pollutants in Fogo Island, Cape Verde

An air quality monitoring campaign by passive sampling techniques was carried out, for the first time, between November 2016 and January 2017 on the Cape Verdean island of Fogo, whose volcanic mountain rises up to 2829 m. Levels of SO2 and acid gases (HF, HCl, HNO3, H2SO4 and H3PO4) were, in most cases, below the detection limits. Alkylpentanes, hexane, cycloalkanes and toluene were the dominant volatile organic compounds. The m,p-xylene/ethylbenzene ratios revealed that air masses arriving at Cape Verde have been subjected to significant aging processes. High toluene/benzene ratios suggested extra sources of toluene in addition to vehicle emissions. Deposition rates of total settleable dust ranged from 23 to 155 mg/m2/day. On average, organic carbon accounted for 15.6% of the dust mass, whereas elemental carbon was generally undetected. Minerals comprised the dominant mass fraction. The dust levels were mostly affected by two main airflows: the westerlies and the Saharan Air Layer. These air masses contributed to the transport of mineral dust from desert regions, secondary inorganic constituents (SO42−, NO3− and NH4+) and tracers of biomass burning emissions, such as potassium. Sea salt represented 12% of the mass of settleable dust. Scanning electron microscope observations of several particles with different compositions, shapes and sizes revealed high silica mass fractions in all samples, as well as variable contents of carbonates, sulphates, aluminosilicates, Fe, Ti, F and NaCl, suggesting that, in addition to the already mentioned sources, dust is likely linked to industrial emissions in the northern and north-western coast of the African continent. Although some atmospheric constituents presented higher concentrations near the crater, the small fumarolic activity still present after cessation of the eruption in February 2015 has a limited impact on air quality, which is most affected by long range transport and some local sources at specific locations.

Experimental investigations of fuel preparation in a swirling airflow under realistic conditions without reaction in a combustor model with a point fuel source

This paper presents quantitative experimental results of non-reacting spray analysis inside a model combustor at realistic jet engine conditions based on a point fuel source and with using kerosene Jet A-1 for the first time. Therefore, two test conditions with combustor pressures of 0.4 and 1.2 MPa, air preheat temperatures of 440 and 740 K and fuel preheating temperatures of 358 and 467 K were investigated. The basis for this investigation was a specially made combustor model in combination with a burner model similar to a fuel-staged lean burner. The focus was on the main stage with a single decentralised point fuel source. This fuel entry is a liquid jet in cross flow (LJICF) with the jet direction normal to the main air flow. The velocity of the air flow was measured by Laser Doppler Anemometry (LDA). Phase Doppler Anemometry (PDA) was used for the simultaneous measurements of fuel drop size and velocity. Sauter mean diameter (SMD) distributions and drop size dependent velocities were shown for the different axial distances inside the model combustor and were discussed with respect to the distributions and the ability of fuel droplets to follow the airflow. The consequent findings of the drop dispersion were verified by Stokes numbers. The drop diameters, and therefore the Stokes numbers, are heavily dependent on test conditions. With values of 8 < SMD [μm] < 20, the drop sizes were accordingly small. For validating the liquid fuel combustion codes, the dataset is completed by histograms of drop size and the determined Rosin–Rammler (RR) parameters.

Quantitative Computational Fluid Dynamics Analyses of Particle Deposition in a Heavy-Duty Subsonic Axial Compressor

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the microparticles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in compressor performance. In the literature, there are some studies related to the fouling phenomena in transonic compressors, but in industrial applications (heavy-duty compressors, pump stations, etc.), the subsonic compressors are widespread. It is highly important for the manufacturer to gather information about the fouling phenomenon related to this type of compressor. This paper presents three-dimensional (3D) numerical simulations of the microparticle ingestion (0.15–1.50 μm) in a multistage (i.e., eight stage) subsonic axial compressor, carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The adopted computational strategy allows the evaluation of particle deposition in a multistage axial compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in the literature. The number of particles and sizes is specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics (velocity and angle) of the impact of micrometric and submicrometric particles with the blade surface are shown. Both blade zones affected by particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability (SP), adopted from the literature. The SP links the kinematic characteristics of particle impact on the blade with the fouling phenomenon. The results show that microparticles tend to follow the flow by impacting on the compressor blades at full span. The suction side (SS) of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena, such as corner separations and clearance vortices, strongly influence the impact location of the particles. The impact and deposition trends decrease according to the stages. The front stages appear more affected by particle impact and deposition than the rear ones.

Distribution and sources of particulate mercury and other trace elements in PM2.5 and PM10 atop Mount Tai, China

The concentrations of particulate mercury (PHg) and other trace elements in PM2.5 and PM10 in the atmosphere were measured at the summit of Mount Tai during the time period of 15 June – 11 August 2015. The average PHg concentrations were 83.33 ± 119.1 pg/m3 for PM2.5 and 174.92 ± 210.5 pg/m3 for PM10. Average concentrations for other trace elements, including Al, Ca, Fe, K, Mg, Na, Pb, As, Se, Cu, Cd, Cr, V, Mo, Co, Ag, Ba, Mn, Zn and Ni ranged from 0.06 ng/m3 (Ag) to 354.33 ng/m3 (Ca) in PM2.5 and 0.11 ng/m3 (Co) to 592.66 ng/m3 (Ca) in PM10. The average concentrations of PHg were higher than those at other domestic mountain sites and cities in other counties, lower than those at domestic city sites. Other trace elements showed concentrations lower than those at the domestic mountain sites. Due possibly to increased control of emissions and the proportion of new energy, the PHg and trace element concentrations decreased, but the PHg showed concentrations higher than those at the Mountain sites, this showed that the reasons was not only severely affected by anthropogenic emissions, but also associated with other sources. The concentration changed trend of the main trace elements indicated that PHg, trace elements and particle matters present positive correlation and fine particulate matter has a greater surface area which was conductive to adsorption of Hg and trace elements to particles. On June 19, June 27 and July 6, according to the peak of mercury and trace elements, we can predict the potential sources of these three days. The results of principal component analysis (PCA) suggested that, crustal dust, coal combustion, and vehicle emissions were the main emission sources of PHg and other trace elements in Mount Tai. The 24-h backward trajectories and potential source contribution function (PSCF) analysis revealed that air masses arriving at Mount Tai were mainly affected by Shandong province. Mount Tai was subjected to five main airflow trajectories. Clusters 1, 2, 3, and 5 represented four pathways for local and regional sources and cluster 4 originated long-distance transportation. Central Shandong was the main source regions of PHg, Pb, Se, As, Cu and Cd. Southeastern and northwestern Shandong province and northern Jiangsu province were the most polluted source regions of Mn, Zn, and Ni. The crustal elements Fe and Ca had similar distributions of potential source regions, suggested by the highest PSCF values in southeastern Shandong and northern Jiangsu.

On Problem of Mathematical Modelling of Thermo-Physical Processes in Regenerative Water-Evaporating Coolers

For cooling the air environment of industrial premises water-evaporating air, conditioners are being increasingly applied. The simplicity of their construction, ecological safety and low power consumption distinguish them from the coolers of other types. Cooling the processed air is due to the loss of energy for the evaporation of moisture from the surface of the water-wetted plates that form air channels. As a result of this process, cooled air is often saturated with moisture, which limits the possibilities for the operation of the coolers of this type. In these cases, more complex coolers of indirect principle without such drawback should be applied. The most effective modification of indirect cooling is the installation of recuperative principle units. The paper presents a mathematical model of heat-mass transfer in such water-evaporating coolers. The scheme of realization of this model based on an iterative algorithm of solution of the system of finite–difference linear equations that takes into account longitudinal and transverse thermal conductivity of the heat transfer plates is suggested. The possibility of obtaining the optimal values of the redistribution of the main and auxiliary air flows through the substantiation of the aerodynamic resistance of the output grid is proved. This allows refusing the inclusion in the additional system cooling fan unit for discharging an auxiliary stream of air.

Airflow Sensitivity Assessment Based on Underground Mine Ventilation Systems Modeling

This paper presents a method for determining the sensitivity of the main air flow directions in ventilation subnetworks to changes in aerodynamic resistance and air density in mine workings. The authors have developed formulae for determining the sensitivity of the main subnetwork air flows by establishing the degree of dependency of the air volume stream in a given working on the variations in resistance or air density of other workings of the network. They have been implemented in the Ventgraph mine ventilation network simulator. This software, widely used in Polish collieries, provides an extended possibility to predict the process of ventilation, air distribution and, in the case of underground fire, the spread of combustion gasses. The new method facilitates an assessment by mine ventilation services of the stability of ventilation systems in exploitation areas and determines the sensitivity of the main subnetwork air flow directions to changes in aerodynamic resistance and air density. Recently in some Polish collieries new longwalls are developed in seams located deeper than the bottom of the intake shaft. Such a solution is called “exploitation below the level of access” or “sublevel”. The new approach may be applied to such developments to assess the potential of changes in direction and air flow rates. In addition, an interpretation of the developed sensitivity indicator is presented. While analyzing air distributions for sublevel exploitation, the application of current numerical models for calculations of the distribution results in tangible benefits, such as the evaluation of the safety or risk levels for such exploitation. Application of the Ventgraph computer program, and particularly the module POŻAR (fire) with the newly developed options, allows for an additional approach to the sensitivity indicator in evaluating air flow safety levels for the risks present during exploitation below the level of the intake shaft. The analyses performed and examples presented enabled useful conclusions for mining practice to be drawn.

Speciation of organic aerosols in the Saharan Air Layer and in the free troposphere westerlies

Abstract. We focused this research on the composition of the organic aerosols transported in the two main airflows of the subtropical North Atlantic free troposphere: (i) the Saharan Air Layer – the warm, dry and dusty airstream that expands from North Africa to the Americas at subtropical and tropical latitudes – and (ii) the westerlies, which flow from North America over the North Atlantic at mid- and subtropical latitudes. We determined the inorganic compounds (secondary inorganic species and elemental composition), elemental carbon and the organic fraction (bulk organic carbon and organic speciation) present in the aerosol collected at Izaña Observatory, ∼ 2400 m a.s.l. on the island of Tenerife. The concentrations of all inorganic and almost all organic compounds were higher in the Saharan Air Layer than in the westerlies, with bulk organic matter concentrations within the range 0.02–4.0 µg m−3. In the Saharan Air Layer, the total aerosol population was by far dominated by dust (93 % of bulk mass), which was mixed with secondary inorganic pollutants ( &lt; 5 %) and organic matter ( ∼ 1.5 %). The chemical speciation of the organic aerosols (levoglucosan, dicarboxylic acids, saccharides, n-alkanes, hopanes, polycyclic aromatic hydrocarbons and those formed after oxidation of α-pinene and isoprene, determined by gas chromatography coupled with mass spectrometry) accounted for 15 % of the bulk organic matter (determined by the thermo-optical transmission technique); the most abundant organic compounds were saccharides (associated with surface soils), secondary organic aerosols linked to oxidation of biogenic isoprene (SOA ISO) and dicarboxylic acids (linked to several primary sources and SOA). When the Saharan Air Layer shifted southward, Izaña was within the westerlies stream and organic matter accounted for ∼ 28 % of the bulk mass of aerosols. In the westerlies, the organic aerosol species determined accounted for 64 % of the bulk organic matter, with SOA ISO and dicarboxylic acids being the most abundant; the highest concentration of organic matter (3.6 µg m−3) and of some organic species (e.g. levoglucosan and some dicarboxylic acids) were associated with biomass burning linked to a fire in North America. In the Saharan Air Layer, the correlation found between SOA ISO and nitrate suggests a large-scale impact of enhancement of the formation rate of secondary organic aerosols due to interaction with anthropogenic NOx emissions.

Hydrodynamics of a slot-rectangular spouted bed of biomass particles with simultaneous injection of spouting and pulsating air streams

A study was undertaken to evaluate the operation of a slot-rectangular spouted bed (SRSB) when pulsed air flow at different frequencies and static bed heights was used to spout biomass particles. A pulsed air stream injected at frequencies from 1 to 5Hz was applied simultaneously with the main spouting air flow to fluidize millet particles of mean diameter 1.25mm and particle density 1331kg/m3. Nine static bed heights from 0.15 to 0.55m were studied at room temperature and atmospheric pressure. Pressure fluctuations were recorded at a sampling frequency of 100Hz. The results showed that, at constant average pulsation gas volumetric flow rate and bed depth, a pulsation frequency of 5Hz required the least total air flow to achieve spouting. However, for low pulsation volumetric flow rate, the effect of the pulsation frequency became less evident for deep beds than for shallow ones.

Reliability of turbulence models and mesh types for CFD simulations of a mechanically ventilated pig house containing animals

The use of computational fluid dynamics (CFD) to study the airflow within farm animal buildings is increasing. The choice of turbulence model within CFD is generally considered to be important due to the approximations of the turbulence in varied scales. Although some studies have been conducted on evaluations of turbulence models in simulation of airflow in ventilated rooms, knowledge of airflow in the animal occupied zone (AOZ) with airflow blockage by the animals and knowledge of thermal convection effects are still limited. In this study, five commonly used two-equation turbulence models (standard k – ɛ , realisable k – ɛ , RNG k – ɛ , standard k – ω , and SST k – ω ) were applied to a CFD model of the airflow in a mechanically ventilated pig room with animals housed in pens. In addition to turbulence models, the effects of non-conformal meshing which combines several computational sub-domains and connects the boundary of domains using interfaces, were tested. The effect of mesh ratio on the interface (i.e. ratio of the grid number of the up and down interface) was studied based on fully structural hexahedral mesh (SH). The investigation of mesh type effect was conducted by application of an unstructured tetrahedral mesh (UT) in the AOZ and SH in the rest of the domain. The results showed that the choice of turbulence model did not have a strong effect on the main airflow pattern except for the RNG k – ɛ model. The tested ratios of resolution at interfaces were also found not to strongly impact on the predicted airflow distributions. The use of UT in the AOZ sub domain also provided acceptable results. It was concluded that non-conformal meshes are a feasible alternative for animal buildings with complex geometries to maintain affordable grid numbers and also reduce the difficulties in mesh generation.

Evaluation of Sulfide Control by Air-Injection in Sewer Force Mains: Field and Laboratory Study

Chemical and biological processes consume dissolved oxygen (DO) in urban wastewater during transportation along sewer systems. Anaerobic conditions (DO &lt; 0.2 mg/L) are easily reached, leading to sulfide (S2−) generation. Release of free sulfide, hydrogen sulfide gas (H2S), from the liquid to the gaseous phase, causes odor, corrosion of pipes and supposes a risk for health of people working in sewers. These issues get worse in force mains, due to inability to take oxygen from the gaseous phase of pipe. Air injection is a suggested practice to control H2S emission in force mains. That technique aims to keep aerobic conditions in wastewater in order to avoid sulfide generation and favor a decrease of Biochemical Organic Demand (BOD). However, several force mains with air injection are not achieving their goals due to a limited oxygen transfer. Field measurements of dissolved oxygen in urban wastewater are presented in an existing force main with air injection during the summer of 2014 in the southeast of Spain. A laboratory scale model is constructed to quantify two-phase flow conditions in pipe due to air injection for different incoming flows rates of water and air. Particularly, for the case of plug flow, also known as elongated bubble flow. Velocity field measurement of water phase in laboratory allows estimating turbulent diffusivity of oxygen in the water, Em, and inter-phase mass transfer coefficient KL(T). In the laboratory, flow and air depth, bubble length, water velocity field, pressure inside force main and water and airflow rates are determined experimentally. These variables are used to assess DO in water phase of force main by comparison with those obtained from field measurements. This work allows assessing air injection efficiency in wastewater, and, therefore, to predict DO in wastewater in force mains.

An Innovative Method for the Evaluation of Particle Deposition Accounting for Rotor/Stator Interaction

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the microparticles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in the compressor performance. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0.15–1.50 μm) in a transonic axial compressor stage, carried out by means of a commercial computational fluid dynamic code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by the flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. A particular computational strategy is adopted in order to take into account the presence of two subsequent annular cascades (rotor and stator) in the case of particle ingestion. The proposed strategy allows the evaluation of particle deposition in an axial compressor stage, thanks to its capability of accounting for rotor/stator interaction. NASA Stage 37 is used as a case study for the numerical investigation. The compressor stage numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in the literature. The blade zones affected by the particle impact and the kinematic characteristics of the impact of micrometric and submicrometric particles with the blade surface are shown. Both blade zones affected by the particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability, adopted from the literature. The sticking probability links the kinematic characteristics of particle impact on the blade with fouling phenomenon. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side of rotor blade and stator vane. Both the rotor blade and stator vane suction side are only affected by the impact of smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, shock waves, and tip leakage vortex, strongly influence the impact location of the particles. The kinematic analysis shows a high tendency of particle adhesion on the suction side of the rotor blade, especially for particles with a diameter equal to 0.15 μm.

Wind-break walls with optimized setting angles for natural draft dry cooling tower with vertical radiators

To get larger cooling performance enhancement for natural draft dry cooling tower with vertical cooling deltas under crosswind, setting angles of wind-break walls were optimized. Considering specific structure of each cooling delta, an efficient numerical model was established and validated by some published results. Aerodynamic fields around cooling deltas under various crosswind speeds were presented, and outlet water temperatures of the two columns of cooling delta were exported as well. It was found that for each cooling delta, there was a difference in cooling performance between the two columns, which is closely related to the characteristic of main airflow outside the tower. Using the present model, air inflow deviation angles at cooling deltas’ inlet were calculated, and the effects of air inflow deviation on outlet water temperatures of the two columns for corresponding cooling delta were explained in detail. Subsequently, at cooling deltas’ inlet along radial direction of the tower, setting angles of wind-break walls were optimized equal to air inflow deviation angles when no airflow separation appeared outside the tower, while equal to zero when outside airflow separation occurred. In addition, wind-break walls with optimized setting angles were verified to be extremely effective, compared to the previous radial walls.

Redox (pro-oxidant/antioxidant) balance in the spray drying of orange peel extracts

ABSTRACTPhenolic compounds have been reported to show both antioxidant and pro-oxidant properties. The effects of spray drying conditions on the balance between antioxidant and pro-oxidant properties of orange peel extract have been evaluated in this work. The inlet drying temperatures (ranging between 100 and 175°C) gave no significant effect on the redox recoveries. On the other hand, the main air flow rate (between 28 and 38 m3/h) and feed pump rate (between 4 and 7 mL/min) significantly affected the pro-/antioxidant recovery ratio. The ratios of pro-/antioxidant recovery were found to be between 1.00 and 1.13, and the pro-oxidant and antioxidant recoveries in this study were found to be between 87–96 and 83–93%, respectively.

The Effect of a Piezoelectric Fan on Forced Air Heat Transfer in a Pin-Fin Heat Sink

An investigation was carried out on the effect of airflow from the blade of a piezoelectric fan on the main cooling airflow across a pin-fin heat sink. The study considered the respective orientation and distances between the piezoelectric blade and the heat sink in a rectangular channel where the airflow was uniform and axial. Three different pin-fin heat sinks with in-line pin-fin arrays were used: 5´5, 7´7 and 9´9. Variable parameters included the Reynolds number of the main airflow and the relative position of the piezoelectric blade and the heat sink. The results showed that the smaller the horizontal distance between the blade and the heat sink, or the greater the vertical distance between the piezoelectric blade and the channel floor, the better the total heat transfer enhancement. Of the three heat sinks used, the 9´9 unit coupled with transverse oscillation of the piezoelectric blade had a slightly higher heat-transfer ratio enhancement. The heat-transfer enhancement ratio Nu/Nu 0 (Nu 0 is the Nusselt number of the system without the piezoelectric blade) will gradually approach 1 with an increase of the Reynolds number of the main flow. At Re L =1200, and with the assistance of the piezoelectric blade, the maximum value of Nu/Nu 0 for the 9´9 pin-fin heat sink exceeded 2.

Field tests of centralized and decentralized ventilation units in residential buildings – Specific fan power, heat recovery efficiency, shortcuts and volume flow unbalances

The energy efficient operation of mechanical ventilation systems depends on various parameters. In Luxembourg, field tests with 20 centralized and 60 decentralized mechanical ventilation systems in single- and multi-family homes were conducted in order to measure the actual performance of those systems in occupied buildings. The considered parameters were: Main air flows, internal and external recirculation, sensitivity to differential pressure, specific fan power and heat recovery efficiency. In many cases, the performance of the ventilation units was lower than expected. The systems showed deviations between supply and exhaust flows of up to 60%. In particular, the air flow in decentralized units was strongly influenced by pressure differences between the inside and outside due to wind or stack effects which leads to a decreased heat recovery efficiency. The total mean recirculation ratio was 6.5%, with a standard deviation of 12.5% for centralized and 13±6.2% for decentralized devices. As a consequence, the delivered flow of fresh air is smaller by the amount of recirculation. The specific fan power, the ratio between air flow and power consumption, was measured with 0.475±0.37Wh/m3 for centralized and 0.22±0.023Wh/m3 for decentralized systems. The lower value for the decentralized systems can be explained by lower pressure losses due to the lack of ductwork. The heat recovery efficiency was 0.65±0.24 for centralized systems and 0.7±0.17 for decentralized systems which is significantly lower than nominal values provided by the manufacturers. The results of this study show that the overall energy efficiency of ventilation devices installed in residential buildings under real working conditions are often lower than expected. These findings could possibly serve as indicators for future research & development at manufacturer and commissioning level.

Experimental and Numerical Investigation of Fuel–Air Mixing in a Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustor

This paper presents the results of an investigation in which the fuel/air mixing process in a single slot within the radial swirler of a dry low emission (DLE) combustion system is explored using air/air mixing. Experimental studies have been carried out on an atmospheric test facility in which the test domain is a large-scale representation of a swirler slot from a Siemens proprietary DLE combustion system. Hot air with a temperature of 300 °C is supplied to the slot, while the injected fuel gas is simulated using air jets with temperatures of about 25 °C. Temperature has been used as a scalar to measure the mixing of the jets with the cross-flow. The mixture temperatures were measured using thermocouples while Pitot probes were used to obtain local velocity measurements. The experimental data have been used to validate a computational fluid dynamics (CFD) mixing model. Numerical simulations were carried out using CFD software ansys-cfx. Due to the complex three-dimensional flow structure inside the swirler slot, different Reynolds-averaged Navier–Stokes (RANS) turbulence models were tested. The shear stress transport (SST) turbulence model was observed to give best agreement with the experimental data. The momentum flux ratio between the main air flow and the injected fuel jet, and the aerodynamics inside the slot were both identified by this study as major factors in determining the mixing characteristics. It has been shown that mixing in the swirler can be significantly improved by exploiting the aerodynamic characteristics of the flow inside the slot. The validated CFD model provides a tool which will be used in future studies to explore fuel/air mixing at engine conditions.

Experimental and Numerical Calculation of Turbulent Timescales at the Exit of an Engine Representative Combustor Simulator

To deepen the knowledge of the interaction between modern lean burn combustors and high pressure (HP) turbines, a nonreactive real scale annular trisector combustor simulator (CS) has been assembled at University of Florence (UNIFI), with the goal of investigating and characterizing the combustor aerothermal field as well as the hot streak transport toward the HP vanes. To generate hot streaks and simulate lean burn combustor behaviors, the rig is equipped with axial swirlers fed by a main air flow stream that is heated up to 531 K, while liners with effusion cooling holes are fed by air at ambient temperature. Detailed experimental investigations are then performed with the aim of characterizing the turbulence quantities at the exit of the combustion module, and specifically evaluating an integral scale of turbulence. To do so, an automatic traverse system is mounted at the exit of the CS and equipped to perform hot wire anemometry (HWA) measurements. In this paper, two-point correlations are computed from the time signal of the axial velocity giving access to an evaluation of the turbulence timescales at each measurement point. For assessment of the advanced numerical method that is large Eddy simulation (LES), the same methodology is applied to a LES prediction of the CS. Although comparisons seem relevant and easily accessible, both approaches and contexts have fundamental differences: mostly in terms of duration of the signals acquired experimentally and numerically but also with potentially different acquisition frequencies. In the exercise that aims at comparing high-order statistics and diagnostics, the specificity of comparing experimental and numerical results is comprehensively discussed. Attention is given to the importance of the acquisition frequency, intrinsic bias of having a short duration signal and influence of the investigating windows. For an adequate evaluation of the turbulent time scales, it is found that comparing experiments and numerics for high Reynolds number flows inferring small-scale phenomena requires to obey a set of rules, otherwise important errors can be made. If adequately processed, LES and HWA are found to agree well indicating the potential of LES for such problems.

The effect of "Pyriform Turbinoplasty" on nasal airflow using a virtual model.

A new procedure, pyriform turbinoplasty, is described and nasal airflow is measured before and after this procedure in a virtual model. Pyriform turbinoplasty is the submucosal reduction of the bone of the frontal process of the maxilla and the lacrimal bone. It opens part of the lateral margin of the nasal valve area with minimal damage to nasal mucosa. The resection of bone in this area can be extended by "nasal wall lateralization" when the lacrimal bone that joins the uncinate process behind the lacrimal duct as well as the base of the inferior turbinate and the edge of the maxilla at the rim of the pyriform aperture are removed. Nasal airflow was simulated using computational fluid dynamics and ANSYS Fluent solver. Analysis using fluid dynamics showed that these procedures help ventilation in the main airflow areas without substantially altering the normal pattern of airflow. The changes after performing a pyriform turbinoplasty seem to be an improvement when compared to the changes after inferior turbinate surgery that can misdirect the airflow largely through the inferior meatus.

An Analysis of Effect of Wing Walls on Natural Ventilation

Background/Objectives: The air flow inside a building due to natural ventilation consists of recirculation regions and a main flow between the inlet and outlet. Recirculation regions are characterized by low velocities resulting in thermal discomfort for the occupants. Winged walls are basically protrusions from external walls to improve the process of natural ventilation. Existing literature on wing walls is on main air flow pattern only. Methods/Statistical Analysis: In this paper, CFD was used to compare effectiveness of configurations suggested in the literature. Information was also obtained about the recirculation regions. Further conventional wing walls were modified and its effectiveness presented. Findings: Valuable information on recirculation regions can be accomplished through this innovation. Optimum dimension of wing walls to improve natural ventilation has also been achieved through the research. More than all these, the information obtained from this research can be used for designing energy efficient buildings.