Fan Outlet Research Articles

Aerodynamic Performance of a Coolant Flow Off-Take Downstream of an Outlet Guide Vane

Within the compression system of a gas turbine engine a significant amount of air is removed to fulfill various requirements associated with cooling, ventilation, and sealing. Flow is usually removed through off-takes located in regions where space is restricted, while the flow is highly complex containing blade wakes, secondary flows, and other flow features. This paper investigates the performance of a pitot style off-take aimed at providing a high pressure recovery in a relatively short length. For this to be achieved some prediffusion of the flow is required upstream of the off-take (i.e., by making the off-take larger than the captured streamtube). Although applicable to a variety of applications, the system is targeted at an intercooled aero-engine concept where the off-take would be located aft of the fan outlet guide vane (OGV) root and provide coolant flow to the heat exchangers. Measurements and numerical predictions are initially presented for a baseline configuration with no off-take present. This enabled the OGV near field region to be characterized and provided a datum, relative to which the effects of introducing an off-take could be assessed. With the off-take present a variety of configurations were investigated including different levels of prediffusion, prior to the off-take, and different off-take positions. For very compact systems of short length, such that the gap between the OGV and off-take is relatively small, the amount of prediffusion achievable is limited by the off-take pressure field and its impact on the upstream OGV row. This pressure field is also influenced by parameters such as the nondimensional off-take height and splitter thickness. The paper analyses the relative importance of these various effects in order to provide some preliminary design rules. For systems of increased length a significant amount of flow prediffusion can be achieved with little performance penalty. However, the prediffusion level is eventually limited by the increased distortion and pressure losses associated with the captured streamtube.

Reducing risk of entry into confined space manure storages

BackgroundDeath from asphyxiation and poisoning when entering confined-space manure tanks is a serious hazard in animal agriculture. Often, multiple fatalities occur when farmers try to rescue friends or relatives overcome...

Heat transfer and performance characteristics of axial cooling fans with downstream guide vanes

This study examines experimentally the effect of stators on the performance and heat transfer characteristics of small axial cooling fans. A single fan impeller, followed by nine stator blades in the case of a complete stage, was used for all the experimental configurations. Performance measurements were carried out in a constant speed stage performance test rig while the transient liquid crystal technique was used for the heat transfer measurements. Full surface heat transfer coefficient distributions were obtained by recording the temperature history of liquid crystals on a target plate. The experimental data indicated that the results are highly affected by the flow conditions at the fan outlet. Stators can be beneficial in terms of pressure drop and efficiency, and thus more economical operation, as well as, in the local heat transfer distribution at the wake of the stator blades if the fan is installed very close to the cooling object. However, as the separation distance increases, enhanced heat transfer rate in the order of 25% is observed in the case of the fan impeller.

Test procedure for drift reducing equipment.

Drift is one of the main paths of plant protection products to non-target organisms. In Germany great efforts are made to reduce drift. Therefore sprayers are tested concerning their drift reducing ability in relation to the German basic drift values which have been determined on the basis of more than 180 drift trials with conventional sprayers. A classification system with classes of at least 50 %, 75 % and 90 % drift reduction has been introduced. Sprayers which meet the requirements of the German guideline are listed in the list of drift reducing sprayers. Nearly all of the sprayers are equipped with air injection nozzles to produce larger droplets. In orchards and hops further measures like shields on fan outlets, green detectors or tunnels are necessary to achieve the respective drift classes. Newer trials show that a drift reduction of 99 % in orchards is possible.

Three Dimensional Velocity Fields at Rotor Outlet of a Semi-Opened Propeller Fan

Three Dimensional Velocity Fields at Rotor Outlet of a Semi-Opened Propeller Fan

The effect of global cross flows on the flow field and local heat transfer performance of miniature centrifugal fans

Centrifugal fans are often integrated into thermal management solutions for a range of applications. Consequently, centrifugal fan designs can be subjected to varying environmental conditions, many of which can alter fan performance characteristics and ultimately influence the heat transfer performance of the cooling solution. Global cross flows are a commonly encountered practical operating condition, particularly in the cooling of electronics. Air-cooled electronic enclosures often incorporate miniature centrifugal fans to maintain reliable component operating temperatures at a local level, while larger system level fans are used to simultaneously control the ambient temperature within the enclosure. This type of operating condition has been investigated by introducing a uniform crossing air flow above a centrifugal fan inlet. Two scaled miniature centrifugal fan designs were selected to fundamentally assess the influence on local velocity field and heat transfer performance. This was achieved experimentally using Particle Image Velocimetry, and a combined infrared and heated-thin-foil technique developed for the accurate measurement of local heat transfer coefficients. the introduction of a crossing air flow above the fan inlet indirectly reduced both the local and global thermal performance of the centrifugal fan, and the resultant distorted inflow shifted the surface heat transfer distribution at the fan outlet from an axisymmetric to asymmetric profile. However, strategic positioning of components relative to a centrifugal fan can maintain the average component heat transfer coefficient at a similar level to a case without any cross flow. Results also indicate issues associated with the implementation of miniature centrifugal fan designs into crossing air flow environments, with reductions in thermal performance of over 30% observed.

Test Analysis on Flow Field of Exhaust Hood in Commercial Kitchen

Making exhaust hood model in laboratory according to exhaust hood in commercial kitchen, steam instead of fume, and characteristics of flow field are studied in kitchen exhaust hood. The distribution of velocity and temperature at typical planes was measured at valve opening of 45 degrees when water boiling. Results show that in a certain range, air velocity of exhaust hood decreases when air from the exhaust opening distance increases, velocity reduces with x and y increasing, steam velocity reaches maximum value close to exhaust outlet of fan.

Research on the Variable Static Pressure Control Used Iterative Algorithm in a VAV System

In a VAV system the static pressure can be reseted based on the change of load. At low load conditions the duct static pressure can be adjusted lower, that make VAV terminal air valves in large opening as far as possible.And lower fan outlet pressure can effectively reduce fan energy consumption. This paper presents a method using iterative algorithm to control the fan frequency. It can improve the dynamic quality of the control system. Satisfying the requirements under lower static pressure so as to achieve the purpose of energy-saving.

Parameter Optimization and Numerical Simulation of Dust-Collecting and Dedusting System with Air Curtain in Heading Face

A new type of dust-collecting and dedusting system with air curtain was developed to solve the problems of the dust-prevention in mine tunnel. The speed of air-curtain fan, the structure size and pressure of dedusting duct are the critical factors, which effect dust control of the whole system. In order to achieve optimal efficiency of dust control, the simulation was conducted with FLUENT(computational fluid dynamics software) to analyse the air-curtain fan surface path lines and dust particle tracks at different wind speeds of air curtain fan, dedusting duct diameters and outlet pressures. We obtained the law of fan speed, the diameter and outlet pressure of dedusting duct, which effect the whole system on dedusting. This law would play a guiding role on the structural optimization of dust-collecting and dedusting system with air curtain.

Aero-mechanical optimisation of a structural fan outlet guide vane

The aero-mechanical optimisation of a fan outlet guide vane (OGV) in the bypass duct of a modern turbofan engine is presented. The purpose of the described outlet guide vane arrangement is to remov...

Automatic Monitoring System of Centrifugal Fan Performance

The centrifugal fan performance experiment system was introduced. The structure, function, measuring principle of the system is analyzed. The experimental system consists of centrifugal fan, air hose, computer and test software. The experiment system can automatically measure and process centrifugal fan performance parameters. The distribution of gas velocity at fan outlet can be measured by five hole probe device.

Performance of a half‐height, innovative cooling fan

An innovative cooling fan with distinguishing features such as ultra thinness, high performance, and quietness is proposed for notebook computers. In particular, the configuration of the proposed fan allows it to suck the largest volume of hot air from surfaces along the vertical direction and expel exhaust air onto the side surface along the horizontal direction, therefore, thinner notebook PCs can be designed. In order to achieve these characteristics, unique designs are required; a 13‐blade impeller is designed for the centrifugal fan in stead of the common conventional design for axial fans, which is a complicated centrifugal blade shape design. A flat rectangular casing for the fan is designed with external dimensions of 89 mm × 76 mm × 13 mm. The casing contains a rotor impeller and a volute; the design of curved throat of the volute is complicated. The top and bottom surfaces, each, have one circular inlet hole. The side surfaces each have a long rectangular outlet hole. In this study, we focus on the P‐Q performance curves of this centrifugal cooling fan designed for notebook PCs, the P‐Q curves are obtained by numerical analysis and tests based on the AMCA standard 210–85. When this fan is subject to real operating conditions, with regard to the maximum flow rate to the near cut‐off point, the pressure P gradually increases from the fan inlet to the fan outlet. The average percentage (%) error in the flow rate Q was determined by both numerical analysis and AMCA test. Additionally, from the result of the standard CNS‐8753 noise test, the fan noise level is 30∼33 dBA and the flow field around the inlet, the outlet and the flow passage can be visualized by Particle Interference Visualization (PIV). Finally, according to the P‐Q curve, it can be inferred that this cooling fan outperforms other comparable regular products available. The noise level is satisfactory, and the heat removal is good; hence this design is proposed for application in industry.

The influence of the design parameters of centrifugal fans on the difference between outlet and inlet noise levels

The operation of the industrial centrifugal fans is accompanied by the air-borne noise generation thanks to such phenomenon as: vortex formation within blade channels of impeller (because of flow separation in channel) and interactions between vortex wakes (at outlet of impeller) and cut-off of fan casing. Sound waves, which are formed at outlet of blade channels and within fan casing, propagate as through outlet side of casing, as in opposite direction: through rotating blade channels of impeller and inlet cone of casing. As it follows from theoretical analysis and experimental research the noise levels at outlet side of centrifugal fan are higher than noise levels at inlet of fan (as for broadband as for tonal noise), because of noise reduction, which is caused by sound wave propagation through inhomogeneous channel, consisted of impeller and inlet cone of casing. The efficiency of the noise reduction depends on the design parameters of impeller and casing. In particular, according to results of research the difference between levels of noise, radiated from outlet and inlet sides of fan, depend on: shape of blade channels, relation between width of casing and impeller.

Calculation of the Time-Averaged Flow in Squirrel-Cage Blowers by Substituting Blades With Equivalent Forces

Radial fans of the squirrel-cage type are used in various industrial applications. The analysis of such fans via computational fluid mechanics can provide the overall fan performance coefficients, as well as give insights into the detailed flow field. However, a transient simulation of a 3D machine using a sliding grid for the rotating blades still requires prohibitively large computational resources, with CPU run times in the order of months. To avoid such long simulation times, a faster method is developed in this paper. Instead of solving the transient Navier–Stokes equations, they are first averaged over one impeller rotation, and then solved for the mean flow since only this flow is of practical interest. Due to the averaging process, the blades disappear as solid boundaries, but additional equation terms arise, which represent the blade forces on the fluid. An innovative closure model for these terms is developed by calculating forces in 2D blade rows with the same blade geometry as the 3D machine for a range of flow parameters. These forces are then applied in the 3D machine, and the resulting 3D time-averaged flow field and performance coefficients are calculated. The 3D flow field showed several characteristic features of squirrel-cage blowers, such as a cross-flow pattern through the fan at low flow coefficients, and a vortexlike flow pattern at the fan outlet. The 3D fan performance coefficients showed an excellent agreement with experimental data. Since the 3D simulation solves for the mean flow, it can be run as a steady-state problem with a comparatively coarse grid in the blade region, reducing CPU times by a factor of about 10 when compared to a transient simulation with a sliding grid. It is hoped that these savings in computational cost will encourage other researchers and industrial companies to adopt the new method presented here.

Acoustic absorbers for use with computer cabinet fans and other cooling systems

Systems and methods for absorbing acoustic noise generated by computer cabinet cooling fans are described herein. In one embodiment, an acoustic absorber for use with a fan carried by a computer cabinet in a room includes a first acoustic panel spaced apart from a second acoustic panel. The first acoustic panel is configured to be positioned proximate to an outlet of the fan and at least approximately parallel to a flow of cooling air discharging from the outlet. The second acoustic panel is also configured to be positioned proximate to the outlet of the fan and at least approximately parallel to the flow of cooling air discharging from the outlet. The first and second acoustic panels together form an opening configured to direct the flow of cooling air away from the fan outlet and into the surrounding room. In a further embodiment, the opening formed by the first and second acoustic panels can be configured to extend at least approximately 360 degrees around the fan.

CFD prototyping of an air-assisted orchard sprayer aimed at drift reduction

The environmental contamination due to off-target deposition of pesticide droplets can be minimized by using optimum design and operating parameters of sprayers. A three-dimensional computational fluid dynamics (CFD) model was developed and used to evaluate concepts of boom sprayer setup to orchard spraying to reduce drift without a decrease in biological efficacy. To track the path of the droplets, a Lagrangian particle tracking multiphase flow model was used, combined with spray atomization models and taking into account the velocity variation at the fan outlet. The studied sprayer settings included: sprayer ground speed, fan speed (air jet velocity), number, type, size, position and orientation of nozzles and liquid pressure. To account for the speed of the tractor, a moving coordinate system was implemented. For the boom sprayer setup, nozzles were employed that produce a flat fan spray pattern (110° Turbo Teejet and 85° Teejet off-centre air induction nozzles). Boom-type spraying was compared to conventional orchard spraying using 80° hollow cone nozzles. There was a good similarity between the vertical spray distribution profile patterns produced from the boom and orchard sprayer setups; however, the boom sprayer setup produced lower droplet concentration to the highest positions and could therefore offer possibilities for drift reduction at long distance, while providing good coverage at a short range. There was a good agreement between measured and predicted vertical spray distribution patterns.

THREE-DIMENSIONAL OPTIMIZATION DESIGN OF HUNDRED-PERCENT REVERSIBLE SUBWAY FAN

Optimization design of a hundred-percent reversible axial fan is conducted by the method of three-dimensional optimization design based on design of experiment, flow analysis and blade profile modification. The results show that the performance of the fan is improved significantly without changes of diameter, rotation speed and tip clearance. At designed condition, the efficiency of positive rotating fan is 82.3% by 9.1% improved and the efficiency of negative rotating fan is 79.1% by 3.3% improved. The internal flow field of the fan is reasonable without obvious separations and back flows. The total pressure distribution at the fan outlet is improved as well. The performance of the fan at different flow rate is fine with the smooth performance curve. The three-dimensional optimization design of the axial fan is successfully validated by the experimental results.

Computation of rotor wake turbulence noise

A major source of fan broadband noise is the interaction of rotor wake turbulence with the fan outlet guide vanes. A broadband noise model that utilizes computed rotor flow turbulence from a Reynolds averaged Navier–Stokes code is used to predict fan broadband noise spectra. The noise model is employed to examine the broadband noise characteristics of the 22-in source diagnostic test fan rig for which broadband noise data were obtained in wind tunnel tests at the NASA Glenn Research Center. A 9-case matrix of three outlet guide vane configurations at three representative fan tip speeds are considered. For all cases inlet and exhaust spectra of acoustic power are computed and compared with the measured spectra where possible. The acoustic power levels and shape of the predicted spectra are in good agreement with the measured data for the fan exhaust duct radiation at approach condition where direct comparisons are possible. The predicted spectra show the experimentally observed trends with fan tip speed, vane count and vane sweep. The results also demonstrate the validity of using computational fluid dynamics based turbulence information for fan broadband noise calculations.

Design and performance of a dynaniic gas flux chamber.

Chambers are commonly used to measure the emission of many trace gases and chemicals from soil. An aerodynamic (flow through) chamber was designed and fabricated to accurately measure the surface flux of trace gases. Flow through the chamber was controlled with a small vacuum at the outlet. Due to the design using fans, a partition plate, and aerodynamic ends, air is forced to sweep parallel and uniform over the entire soil surface. A fraction of the air flowing inside the chamber is sampled in the outlet. The air velocity inside the chamber is controlled by fan speed and outlet suction flow rate. The chamber design resulted in a uniform distribution of air velocity at the soil surface. Steady state flux was attained within 5 min when the outlet air suction rate was 20 L/min or higher. For expected flux rates, the presence of the chamber did not affect the measured fluxes at outlet suction rates of around 20 L/min, except that the chamber caused some cooling of the surface in field experiments. Sensitive measurements of the pressure deficit across the soil layer in conjunction with measured fluxes in the source box and chamber outlet show that the outflow rate must be controlled carefully to minimize errors in the flux measurements. Both over- and underestimation of the fluxes are possible if the outlet flow rate is not controlled carefully. For this design, the chamber accurately measured steady flux at outlet air suction rates of approximately 20 L/min when the pressure deficit within the chamber with respect to the ambient atmosphere ranged between 0.46 and 0.79 Pa.

홴 후방 유동장을 고려한 홴싱크 설계에 관한 연구

A numerical and experimental study on the flow fields behind the fan outlet was carried out to improve the performance of a conventional fan-sink(fan and heat sink). Conventional fan-sinks have a heat sink of which fin configurations tend to increase the flow resistance, thus decreasing the performance and the cooling capabilities of a fan-sink. Lining surface method is used for the prediction of flow fields behind the fan outlet. Oil-dot flow visualization technique is applied for the validation of numerical results. The numerical results and experimental data show agreement each other. A conventional heat sink is modified and redesigned using flow patterns behind the fan outlet. The newly designed heat sink has the configuration of curved fins which minimize flow resistance. It showed improvements in both cooling capabilities and volumetric flow rate compared to the conventional one.