Main Airflow Research Articles

Portable microwave air plasma device for wound healing

A portable microwave air plasma has been developed for safe and effective wound healing. The device is operated by a fixed microwave power and two different air gas flows (main and cooling air flow). It was found that the speeds of the two air flows determine the stability of the plasma jet and gas temperature and thereby regulate the concentrations of the individual reactive species. Two different regimes, i.e. the NO abundant (0.1 slm main air flow) and ozone abundant regimes (4 slm main air flow), were identified as suitable for wound healing without thermal damage and toxicity. These regimes show similar plasma characteristics (e.g. less than 40 °C at the treatment point, less than 4 ppm of NO2) except for different NO and ozone amounts. Both regimes show more than twice as fast wound healing speed compared with the untreated case without any histological damages. Faster healing speed with intrinsic ozone safety make the NO abundant regime the best operation regime for wound healing. Finally, the stability of the developed device was demonstrated by a one-hour continuous operation test with a 24 V battery.

Simulation of DPM distribution in a long single entry with buoyancy effect

Diesel particulate matter (DPM) is considered carcinogenic after prolonged exposure. With more diesel-powered equipment used in underground mines, miners’ exposure to DPM has become an increasing concern. This paper used computational fluid dynamics (CFD) method to study DPM distribution based on an experiment conducted by the Diesel Emissions Evaluation Program (DEEP) in Canada. Twenty-four cases were simulated where the emissions from both truck and load-haul-dumps (LHDs) were examined. Each vehicle was placed in two stream wise locations, and the vehicles were oriented either facing or with the rear end toward the main fresh airflow. A species transport model with buoyancy effect was then used to examine the DPM dispersion pattern. High DPM regions were identified downstream, around, and even upstream of diesel engines. This can provide guidelines for good working practices and selection of diesel emission reduction technologies underground.

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 9x9 unit coupled with transverse oscillation of the piezoelectric blade had a slightly higher heat-transfer ratio enhancement. The heat-transfer enhancement ratio Nu/Nu0 (Nu0 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 ReL =1200, and with the assistance of the piezoelectric blade, the maximum value of Nu/Nu0 for the 9×9 pin-fin heat sink exceeded 2.

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.

Effect of Nitrogen Dilution on the Lean Blowout Limit and Emissions of Premixed Propane/Air Swirl Flame

The effects of nitrogen dilution on propane/air flame and emissions was investigated using a model gas turbine type swirl flame burner. The burner consists of a six-vane axial swirler and a combustor wall made from quartz tube. Nitrogen was diluted at 5%, 10% and 15% by volume of the total main air flow rate with propane/air mixture at the burner plenum prior to combustion at atmospheric condition. Direct flame imaging was performed using a digital camera to observe the flame shape, intensity and lean blowout phenomenon of premixed nitrogen-diluted propane/air flames. The result shows that nitrogen addition to propane/air flame reduces flame intensity and lean blowout limit, making the nitrogen-diluted flames more susceptible to blowout. Emissions results show that NOx reduce with the increase of nitrogen dilution rate, while the effect on carbon monoxides and unburned hydrocarbons are insignificant.

Sneezing as a mechanical defence - a numerical simulation and analysis of the nasal flow

The nose is responsible for humidification, heating and cleaning of the inhaled air. The sneeze reflex leads to a shock-like cleaning of the nose in strong particle exposure. The aim of this study was the simulation of intranasal air flow of sneezing in a realistic computer model. Based on the CT scan of a 40 year old man a three-dimensional computer model of the nasal cavity and the ethmoid sinuses was created. Flow simulations were performed for different inspiratory and expiratory velocities (± 2 m/s to ± 45 m/s) in order to simulate sneezing. RESULTS were visualized and analyzed by video simulation. During inspiration the main airflow takes place along the middle turbinate. During expiration, the flow is located more cranially. This effect is caused by the shape of the nasopharynx and the posterior portions of the nasal turbinates. During very high speeds (sneezing) also adjacent ethmoid sinuses and the olfactory region are covered by the shock-like expiratory flow. A large vortex formation in the nasopharynx is responsible for a uniform distribution of the airflow also on lower nasal areas. Sneezing is a protective reflex that provides for cleaning of the nose. From a flow rate of 10 m/s, the cranial nasal areas as well as adjacent ethmoid sinuses are covered by the -airflow. Compared to the inspiratory airflow the exhalation is not just vice versa. Particles that deposed in the cranial nasal areas during quiet breathing are removed.

Quantitative Computational Fluid Dynamics Analyses of Particle Deposition on a Transonic Axial Compressor Blade—Part I: Particle Zones Impact

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the microparticles that are not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor 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 areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side (PS). The suction side (SS) is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, stagnation point, and tip leakage vortex, strongly influence the impact location of the particles.

Effect of partial bypass on the heat transfer performance of dehumidifying coils

This study extends a so called “partial bypass” concept to dehumidifying fin-and-tube heat exchangers. Tests are performed for a 2-row and 4-row fin-and-tube heat exchangers having plain fin configuration. The inlet dry bulb temperature is fixed at 25°C while the inlet relative humidities are 50% and 80%, respectively. Test results showed that for a 2-row coil under RH=50%, the corresponding heat transfer augmentation ratio (QR) and pressure penalty ratio (PR) decrease with the rise of bypass ratio (BR). At a smaller frontal velocity, the regime of appropriate bypass ratio where QR>1 and PR<1 is more apparent. The effect of partial bypass decreases as the velocity increases. As the velocity gets close to 2ms−1, it shows that the performance at high bypass ratio becomes more efficient. At the same time, when bypass ratio becomes lager, the tendency of the decreasing of ΔP is more drastic than the decreasing of Q. Nevertheless, not for all the cases that the performances get better as the bypass ratio increases. For Vfr=4ms−1, the experiment results show that the overall effect is less efficient than at Vfr=2ms−1. The major reason is caused by the flow pattern. The rise of bypass airflow is quite large which may act as an air curtain to distort the main airflow, and result in higher pressure drop. This implies that the design of the bypass design is quite imperative in the practice of real applications. For a 4-row heat exchanger, the experiment data of QR and PR for the 4-row coil performs better than a 2-row coil.

A Case Study on the Air Flow Characteristics of the Hirobo-FALCON 505 Controllable Helicopter's Main Rotor Blade

The aerodynamics of the helicopter rotor is one of the most elating and exigent tribulations faced by the aerodynamicists today. Study through flow visualization process plays a key role in understanding the airflow distinctiveness and vortex interaction of the helicopter main rotor blade. Inspecting and scrutinizing the effects of wake vortices during operation is a great challenge and imperative in designing effective rotor system. This study aimed to visualize the main rotor airflow pattern of the Hirobo-FALCON 505 controllable subscale helicopter and seek for the vortex flow at the blade tip. The experimental qualitative data is correlated with quantitative data to perform scrupulous study on the airflow behavior and characteristics along with its distinctiveness spawned by the main rotor blade. Simulation using design software is performed in analogous stipulations to endow with comparability between the flow visualization results. Throughout the blade span several dissimilar flow patterns have been identified. The main rotor hub has turbulent flow at its center due to low energy of air amassed in this region whereas in the middle portion of the rotor blade, the air encompasses high kinetic energy with a clear straight streamline pattern.

Review of Control Strategies Employing Neural Network for Main Steam Temperature Control in Thermal Power Plant

Main steam temperature control in thermal power plant has been a popular research subject for the past 10 years. The complexity of main steam temperature behavior which depends on multiple variables makes it one of the most challenging variables to control in thermal power plant. Furthermore, the successful control of main steam temperature ensures stable plant operation. Several studies found that excessive main steam temperature resulted overheating of boiler tubes and low main steam temperature reduce the plant heat rate and causes disturbance in other parameters. Most of the studies agrees that main steam temperature should be controlled within ±5 Deg C. Major factors that influenced the main steam temperature are load demand, main steam flow and combustion air flow. Most of the proposed solution embedded to the existing cascade PID control in order not to disturb the plant control too much. Neural network controls remains to be one of the most popular algorithm used to control main steam temperature to replace ever reliable but not so intelligent conventional PID control. Self-learning nature of neural network mean the load on the control engineer re-tuning work will be reduced. However the challenges remain for the researchers to prove that the algorithm can be practically implemented in industrial boiler control.

Finite Element Analysis of the Drum-Shape Cavity Fluidic Gyroscope Sensitive Mechanism

Against the deflect that the existing fluidic gyroscope airflow channel structure was easy to cause the flocculating flow. This paper presented a kind of elliotic-drum flow cavity structure. Using the finite element method, calculated the flow field in the closed cavity at different angular velocity input. The results showed that the gas flow path of the main airflow distribution was streamlined, there did not form the vortex area which could reduce the energy additional losses, when the angular rate input changed, then the jet flow field distribution didnt keep equal and symmetrical, the jet speed difference at the hot sensitive wire changed with angular velocity, thus revealing the drum-shape cavity fluidic gyroscope sensitive mechanism.

Simulating Natural Ventilation in and Around Buildings by Fast Fluid Dynamics

Natural ventilation is a sustainable technology that can provide a well-built environment and also save energy. The application of natural ventilation to buildings requires a careful approach in the early design phase, and fast, simple design tools are greatly needed. Fast fluid dynamics (FFD) can provide useful airflow information at a speed much faster than CFD so that it is a potential design tool for natural ventilation. This study thus validated FFD with test cases representing different types of natural ventilation. The results showed that FFD was capable of predicting the main air flow feature and ventilation rate with reasonable accuracy for wind-driven or buoyancy-driven natural ventilation. FFD simulation can reflect the influence of wind direction and surrounding buildings on natural ventilation.

Application of the mechanical ventilation in elevator shaft space to mitigate stack effect under operation stage in high-rise buildings

Even though the measures to minimize the stack effect in high-rise buildings were taken that include a revolving door on the lobby floor, additional barriers to the passage of air in the lower part of the building, and air-tightness reinforcement for elevator doors, the stack effect is still present during cold season in Korea. However, it is difficult to fully apply the measures for stack effect under occupied condition in high-rise buildings. In this study, as an advanced method to lower the stack effect in high-rise buildings under occupied condition, mechanical ventilation in elevator shaft space, which cools the shaft space with outdoor air and reduces the temperature or pressure differences between indoor air in shaft and outdoor air, was proposed. In this paper, the application details and performance analyses of the installed shaft cooling system in a completed building in Korea were described. Also, as a measure to improve the performance of the applied system, concentrated cooling in the lower part of the elevator shaft where there is a main air flow passage was proposed. As a result, cooling effect of mechanical ventilation system in elevator shaft was improved and the extent of stack effect in winter was decreased effectively.

Automatic Airway Analysis on Multidetector Computed Tomography in Cystic Fibrosis

To evaluate the fully automatic quantification of airway dimensions on chest multidetector computed tomography (MDCT) performed in cystic fibrosis (CF) patients. Airflow indices including predicted forced expiratory volume in 1 second (FEV1%) were used to study the impact on regional lung function. MDCT data of patients with CF (14 children and 23 adults) and of control patients (11 children and 22 adults) were used to compute total diameter (TD), lumen area (LA), and wall thickness (WT) using dedicated software. Pulmonary function testing including FEV1% was performed in parallel and correlated with MDCT parameters in a generation-based analysis. TD was largely increased in CF patients (third-generation to fourth-generation airways in children, first to ninth in adults; P<0.05). LA remained unchanged, but WT was also larger in CF compared with controls (third generation to sixth generation in children, first to eleventh in adults; P<0.05). In adult CF patients significant negative correlations for TD, LA, and WT with FEV1% were found for intermediate airways (fifth to seventh generation; r=-0.7 to -0.9) but not in pediatric CF patients and controls. Automatic airway analysis succeeded in quantifying specific pathologies such as airway dilatation and wall thickening in CF patients at different ages. Moreover, our results indicate a shift in main airflow resistance to intermediate airways in cases of chronic CF. The objective computational parameters TD, LA, and WT should be considered for assessment and follow-up of CF airway disease.

Experimental investigation into the impact of crossflow on the coherent unsteadiness within film cooling flows

Film cooling is regularly used to cool the surface of components within the turbine stage of an aero engine. This enables them to withstand the high air temperatures that are required for maximising aero engine cycle efficiency. It is known that the mixing of a film cooling flow with the main high temperature air flow through a turbine passage is an unsteady process, with coherent unsteady features occurring across a range of blowing ratios. Upon an aero engine the cooling holes on a turbine blade commonly have a crossflow at the hole inlet. Previous work has shown that crossflow at the hole inlet modifies the time-mean flowfield downstream of a cooling hole compared to the case without crossflow.The current paper investigates the impact of spanwise orientated crossflow on the coherent unsteadiness within film cooling flows. Both cylindrical and shaped cooling holes, located on a blade pressure surface, are studied. The range of blowing ratios considered is 0.7–1.8 and the crossflow velocity is up to 0.8 times the bulk jet velocity. High Speed Photography and Hot Wire Anemometry are used to observe the presence of coherent unsteadiness, both immediately downstream of the hole exit and within the cooling hole tube.The results show that the coherent unsteadiness downstream of the hole exit is persistent and its occurrence is not significantly affected by the magnitude of spanwise crossflow. Within the cooling hole tube the existence of coherent unsteadiness is presented for the first time, inside both cylindrical and shaped holes, with a Strouhal number of 0.6–1.2. The pattern of this in-hole coherent unsteadiness is seen to change with increasing the crossflow velocity.

Oral Pressure and Nasal Flow on /m/ and /p/ in 3- to 5-Year-Old Children without Cleft Palate

Objectives : (1) To compare oral pressure and nasal airflow in 3- to 5-year-olds versus older children and adults; (2) to describe stability of these measures in 3- to 5-year-olds at two recording times; and (3) to report participation rates of 3- to 5-year-olds for the aerodynamic protocol. Design : Prospective, nonrandomized, convenience samples in four age groups. Setting : University clinic. Participants : A total of 105 individuals without cleft palate and with normal speech for their age who were 3 to 5 (n = 45), 7 to 9 (n = 20), 11 to 13 (n = 20), or 20 to 30years old (n = 20). All had normal nasal resonance and absence of nasally obstructive conditions on the testing day. Main Outcome Measures : Oral pressure and nasal airflow on /p/ and /m/ in syllable series and the word "hamper." Results : Oral pressure was significantly higher on /p/ for 3- to 5-year-olds versus the two oldest groups. Nasal airflow on /p/ occurred infrequently across groups. Oral pressure on /m/ was significantly higher for 3- to 5-year-olds versus adults. Nasal airflow on /m/ increased significantly with age. Oral pressure and nasal flow did not differ at two measurement times for the 3- to 5-year-olds. Of the 3- to 5-year-olds, 88% completed the protocol. Conclusions : Oral pressure decreased on /p/ and nasal airflow increased on /m/ from early childhood into adulthood. Nasal air escape on /p/ occurred rarely for speakers of any age; when it did occur, the magnitude was limited. Most preschool-aged children should be able to complete a velopharyngeal aerodynamic protocol, and measures are stable even for these young speakers.

Characteristic size research of human nasal cavity and the respiratory airflow CFD analysis

To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters for nasal structure, thirty three-dimensional, anatomically accurate representations of adult nasal cavity models were reconstructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated using the fluid dynamics with the finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to varying airflow distribution in the nasal cavities and the main airflow passed through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than a half of overall resistance. The characteristic model of nasal cavity was extracted based on the characteristic points and dimensions deducted from the original models. It showed that either the geometric structure or the air-flow field of the two kinds of model was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that properly represented the original model in research for nasal cavity.

Spray Combustion Characteristics of Palm Biodiesel

The potential of palm methyl esters (PME) as an alternative fuel for gas turbines is investigated using a swirl burner. The main air flow is preheated to 623 K, and a swirling spray flame is established at atmospheric pressure. The spray combustion characteristics of PME are compared to diesel and Jet-A1 fuel under the same burner power output of 6 kW. Investigation of the fuel atomizing characteristics using phase Doppler anemometry (PDA) shows that most droplets are distributed within the flame reaction zone region. PME droplets exhibit higher Sautermean diameter (SMD) values than baseline fuels, and thus higher droplet penetration length and longer evaporation timescales. The PME swirl flame presents a different visible flame reaction zone while combusting with low luminosity and produces no soot. NOx emissions per unit mass of fuel and per unit energy are reduced by using PME relative to those of conventional fuels.

Flow Measurements Using Particle Image Velocimetry in the Ultracompact Combustor

The potential for the ultracompact combustor (UCC) lie in future research to reduced fuel consumption and improved engine performance. Velocity measurements performed on the UCC test rig at the Air Force Institute of Technology revealed flow patterns and time-averaged turbulence statistics for data taken burning hydrogen fuel in a straight and a curved cavity vane configuration. Over an equivalence ratio from 0.7 to 1.5, the straight vane configuration showed spanwise velocity decreased linearly with distance from the cavity vane over the width of the main channel. Increasing the flow rates and holding the equivalence ratio and ratio of cavity to main airflow rates constant, flow velocities in the main channel showed an increase with the curved circumferential configuration but a decrease with the straight circumferential configuration. Turbulence intensity is expected to be a major contributing factor, specifically since measured at 15% and 21% in the main channel for the straight and curved configurations, respectively. The results also show how the radial vane cavity (RVC) created strong vorticity throughout the main flow supporting a recirculation zone for mixing. Peak vorticity occurred farthest from the cavity vane suggesting the angle of the radial vane cavity is effective in generating increasing flow rotation.

The Measurement and Process of Aeroengine Inlet Total Pressure Field

It’s important to measure inlet total pressure field for aeroengine. Firstly, test scheme is discussed. Three pectinate total pressure probes, which can be rotated with an additional straight ring segment around the engine axis, are used to measure the total pressure field. The radial distribution of test points is designed via Tchebycheff integral method. Radial average and circumferential average are calculated according to the field data via area averaging method. At last the total pressure field is visualized via mapping the data to colors. Test results show that the total pressure distribution in main airflow is evener than that in boundary layers and the thickness of inner and outer ring boundary layer can be estimated.