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The objective of this study was to quantify the influence of ventilation methods on children's exposure to indoor particles in a daycare center located in an urban area. The ventilation methods applied to the center were monitored for 1 year. It appears that indoor PM10 and PM2.5 concentrations of the center were basically determined by outdoor conditions. The fluctuations in outdoor particle concentration also affected the ventilation behavior during class. The windows and doors of the classroom were frequently closed during both class hours and nights when the outdoor particle concentrations were at high levels. Statistically significant differences in the I/O ratios were found among the ventilation methods. The PM10 I/O ratio with the closed windows was significantly higher (p < 0.01) than that with the open windows, and when the mechanical fans were operated, the I/O ratio dramatically decreased (p < 0.01). The I/O ratio of PM2.5 showed a similar trend to that of PM10 except for the mechanical fan operation. The filters rated lower than MERV 11 appear to be insufficient to remove submicron particles from the mechanically supplied outdoor air when the PM2.5 concentrations are high, such as during the heating period. [ABSTRACT FROM AUTHOR]

Hospitals tend to have high density of occupancy. Poor indoor environmental quality in hospital buildings can exacerbate the health problems of patients and also harm visitors and staff. This study investigated the environmental characteristics and ventilation affecting the concentration of microorganisms in multiple-bed hospital wards. The measurements were accomplished by using a biosampler and an open plate method at four wards, different positions of electric fans, and different times. Data were analyzed by t-test and MANOVA. The results revealed that the concentrations of airborne bacteria were higher than the concentrations of fungi. There were significant differences in the concentrations of bacteria and fungi between sampling times and between hospital wards (p < 0.05), while no difference was observed by positions of electric fans. Correlations between the concentrations and other environmental parameters indicate that temperature, number of occupants, and humidity were physical factors associated with the concentrations of microorganisms. In addition, mostly, Gram-positive bacteria were observed. This indicates the conditions in buildings in the tropical climate, and regular housekeeping of all room areas is needed to prevent the growth of airborne contaminants and the related risks to patients, visitors, and staff. [ABSTRACT FROM AUTHOR]

This paper describes the investigations performed to better understand two-stage rotor speed matching in a contrarotating fan. In addition, this study develops a comprehensive measuring and communication system for a contrarotating fan using ZigBee network. The investigation method is based on three-dimensional RANS simulations; the RANS equations are solved by the numerical method in conjunction with a SST turbulence model. A wireless measurement system using big data method is first designed, and then a comparison is done with experimental measurements to outline the capacity of the numerical method. The results show that when contrarotating fan worked under designed speed, performance of two-stages rotors could not be matched as the designed working condition was deviated. Rotor 1 had huge influences on flow rate characteristics of a contrarotating fan. Rotor 2 was influenced by flow rates significantly. Under large flow rate condition, the power capability of rotor 2 became very weak; under working small flow rate condition, overloading would take place to class II motor. In order to solve the performance mismatch between two stages of CRF under nondesigned working conditions, under small flow rate condition, the priority shall be given to increase of the speed of rotor 1, while the speed of rotor 2 shall be reduced appropriately; under large flow rate condition, the speed of rotor 1 shall be reduced and the speed of rotor 2 shall be increased at the same time. [ABSTRACT FROM AUTHOR]

The paper reports results of a detailed study of hub- and tip-strong radial inflow distortion on the performance of a low speed, high aspect ratio (3.0) contrarotating fan stage. The distortion screen (placed upstream of the first rotor) covers 1/3 of the span of the blade near the hub and the casing for hub-strong and tip-strong inflow distortions, respectively. The performance of the contrarotating fan was investigated under both the radially distorted inflows and compared with the clean inflow conditions under different speed combinations of rotor-1 and rotor-2. The hub-strong radial distortion reduces the overall performance (pressure rise and efficiency) as well as the operating range by about 2 to 4% under the different speed combinations. On the other hand, it is interesting to observe that the tip covered radial distortion not only improves the pressure rise, but also increases the overall operating range by about 6 to 8%. There was, however, a 6 to 8% decrease in efficiency in this case as compared to 12 to 15% for hubstrong radial inflow distortion. The results reveal the physics of the effects of radial inflow distortion on the overall performance of the contrarotating fan stage. [ABSTRACT FROM AUTHOR]

The design of an intake for a gas turbine engine involves CFD-based investigation and experimental assessment in an intake test rig. In both cases, the engine is represented by a mass flux sink, usually positioned a fewfan radii aft of the real fan face. In general, this approach is sufficient to analyze intake geometry for low distortion at the fan face, because in this case the interaction of the fan with the inlet flow can be neglected. Where there are higher levels of distortion at the fan face, the interaction could become more significant and a different approach would be preferable. One alternative that takes into account the interaction in such cases includes the fan in the analysis of the intake, using either a steady or unsteady flow model approach. However, this solution is expensive and too computationally intensive to be useful in design mode. The solution proposed in this paper is to implement a new boundary condition at the fan face which better represents the interaction of the fan with the flow in the air intake in the presence of distortion. This boundary condition includes a simplified fan model and a coupling strategy applied between the fan and the inlet. The results obtained with this new boundary condition are compared to full 3D unsteady CFD simulations that include the fan. [ABSTRACT FROM AUTHOR]

Tunnel ventilation fans, classically, must have the ability to both supply and extract air from a tunnel system, with the operator's choice dependent on the tunnel ventilation system's operating mode most appropriate at any given point in time. Consequently, tunnel ventilation fans must incorporate a reversible aerodynamic design which limits the maximum fan pressure rise. This paper presents three high pressure reversible fan concepts. These comprise a two-stage counter rotating fan, a single-stage high speed fan, and a two-stage fan with a single motor and impeller on each end of the motor shaft. The authors consider the relative merits of each concept. The third concept offers the most compact fan, transform, silencer, and damper package size. The authors discuss the mechanical design challenges that occur with a two-stage fan with a single motor and impeller on each end of the motor shaft. They present and consider a selectedmotor bearing arrangement and casing design formaintainability. Finally, the authors present both prototype fan and full-scale package aerodynamic and acoustic performance, before discussing the challenges presented by high temperature certification in accordance with the requirements of EN 12101-3: 2012. [ABSTRACT FROM AUTHOR]

This paper describes research involving an in-service failure of a "variable pitch in motion" fan's blade bearing. Variable pitch in motion fans rotate at a constant speed, with the changing blade angle varying the load. A pitch-change mechanism facilitates the change in blade angle. A blade bearing supports each blade enabling it to rotate. The author observed that as the fan aerodynamic stage loading progressively increased, so did the rate of blade-bearing wear. The reported research addressed two separate, but linked, needs. First, the ongoing need to increase fan pressure development capability required an increase in fan loading. This increase was within the context of an erosive operating regime which systematically reduced fan pressure development capability. The second need was to identify the root cause of blade-bearing failures. The author addressed the linked needs using a computational analysis, improving the rotor inflow aerodynamic characteristics through an analysis of the inlet box and design of inlet guide vanes to control flow nonuniformities at the fan inlet. The results of the improvement facilitated both an increase in fan-pressure-developing capability and identification of the root cause of the blade-bearing failures. [ABSTRACT FROM AUTHOR]

This paper describes the development of adaptive acoustic impedance control (AAC) technologies to achieve a larger fan noise reduction, by adaptively adjusting reactance and resistance of the acoustic liner impedance. For the actual proof of the AAC technology III performance, the advanced fan noise absorption control duct liner II was made on trial basis, with the simple control system and the plain device. And, then, the duct liner II was examined for the AAC technology I, II, and III models, using the high speed fan test facility. The test results made clear that the duct liner II of the AAC technology III model could achieve the fan noise reduction higher than O.A. SPL 10 dB (A) at themaximum fan speed 6000 rpm, containing the reduction of fundamental BPF tone of 18 dB and 2nd BPF tone of 10 dB in response to the fan peed change from 3000 to 6000 rpm. [ABSTRACT FROM AUTHOR]

The thickness noise predicted by the Ffowcs Williams and Hawkings (FW&H) equation depends on the normal velocity vn which is very sensitive to the meshing size. Isom showed that in far field a monopolar source is equivalent to a dipolar source induced by a uniform distribution of the load on the entire moving surface. The main objective of this paper is to determine a specific expression of Isom's thickness noise in time and frequency domains for subsonic fans. The scope of the proposed expression of Isom's thickness noise is to define a benchmark test of consistency for thickness and loading noise codes in both time and frequency domains for subsonic fans when using the free field solution of FW&H's equation. [ABSTRACT FROM AUTHOR]

Probabilistic failure assessments for integrally bladed disks are system reliability problems where a failure in at least one blade constitutes a rotor system failure. Turbine engine fan and compressor blade life is dominated by High Cycle Fatigue (HCF) initiated either by pure HCF or Foreign Object Damage (FOD). To date performing an HCF life assessment for the entire rotor system has been too costly in analysis time to be practical. Although the substantial run-time has previously precluded a full-rotor probabilistic analysis, reduced order models make this process tractable as demonstrated in this work. The system model includes frequency prediction, modal stress variation, mistuning amplification, FOD effect, and random material capability. The model has many random variables which are most easily handled through simple random sampling. [ABSTRACT FROM AUTHOR]

In this work a simple method is developed to evaluate the design parameters of a horizontal-axis wind turbine (HAWT). The method applies the available data of an axial fan to a HAWT for the same arc profile blade in both machines. The method is illustrated by a numerical example with a complete design procedure in which the pitch angle and the chord of the blade are calculated. These calculated results agree with the measured data of a commercial HAWT blade. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Initially in this research, effects of blade inlet and outlet angles on the performance were considered by measuring performances. Twelve impellers with various blade angles were used for the measurements. The most suitable inlet and outlet angles and the inclination angle were acquired. Then, measurements on the inlet and outlet flows and their axial and circumferential distributions were taken for various operating conditions at the various measuring positions. The turning angles through the blade were calculated from these measured results. The inlet and outlet flows of the sirocco fan are not uniform around the circumference. The distributions of the flow have some relations with the development of flow in the inlet part and in the casing. Discussions were made on the flow to have a improved performance. [ABSTRACT FROM AUTHOR]

A study was conducted in the NASA Glenn Research Center (NASA-GRC) linear cascade on the intermittent flow on the suction surface of an airfoil section from the tip region of a modern low aspect ratio fan blade. Experimental results revealed that, at a large incidence angle, a range of transonic inlet Mach numbers exist where the leading-edge shock-wave pattern was unstable. Flush-mounted, high-frequency response pressure transducers indicated large local jumps in the pressure in the leading edge area, which generates large intermittent loading on the blade leading edge. These measurements suggest that for an inlet Mach number between 0.9 and 1.0, the flow is bi-stable, randomly switching between subsonic and supersonic flows. Hence, it appears that the change in overall flow conditions in the transonic region is based on the rate of switching between two stable flow states rather than on the continuous increase of the flow velocity. To date, this flow behavior has only been observed in a linear transonic cascade. Further research is necessary to confirm this phenomenon occurs in actual transonic fans and is not the by-product of an endwall restricted linear cascade. [ABSTRACT FROM AUTHOR]

We carried out investigations for the purpose of clarifying the rotor outlet flow fields with rotating stall cell in a diagonal-flow fan. The test fan was a high-specific-speed (n s = 1620) type of diagonal-flow fan that had 6 rotor blades and 11 stator blades. It has been shown that the number of the stall cell is 1, and its propagating speed is approximately 80% of its rotor speed, although little has been known about the behavior of the stall cell because a flow field with a rotating stall cell is essentially unsteady. In order to capture the behavior of the stall cell at the rotor outlet flow fields, hot-wire surveys were performed using a single-slant hot-wire probe. The data obtained by these surveys were processed by means of a double phase-locked averaging technique, which enabled us to capture the flow field with the rotating stall cell in the reference coordinate system fixed to the rotor. As a result, time-dependent ensemble averages of the three-dimensional velocity components at the rotor outlet flow fields were obtained. The behavior of the stall cell was shown for each velocity component, and the flow patterns on the meridional planes were illustrated. [ABSTRACT FROM AUTHOR]

A novel fan that operates as an air moving device as well as a filter has been investigated. The unit utilizes a brush disk, instead of bladed impellers, within a centrifugal fan casing and is known as a ‘mop fan’. The performance of the mop impellers as fans was tested and their characteristic curves were found to be similar to those of centrifugal fans. The characteristics of the mop fan in terms of airflow rate, pressure, and efficiency were tested using a standard method, BS 848. The tests allowed mops of different fibre number and fibre diameter to be constructed and so optimize mop fan performance. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]