Fan Inlet Research Articles

5412 内部円筒を有する直方体空洞の共鳴効果による消音(G09-3 バイオディーゼル,G09 環境工学)

There are some commercial products of ventilator which have their own sound attenuation effect. The ventilator consists of a cylindrical fan unit, a rectangular box as an outer cover, and an orifice plate which faces the fan's inlet. The space surrounded by the outer cover and the orifice plate is supposed to act as a resonance box. In this research, the sound attenuation effect is experimentally verified using a model of rectangular chamber containing an internal cylinder placed in an infinite circular duct. While a simple rectangular chamber with short clearance in duct axis direction in a circular duct shows a typical resonator property, the another model of this research attached additional space between the box and the cylinder shows some peculiar properties as follows: (i) two resonance frequencies are obtained ; (ii) the first resonance frequency is lower than the one of the simple chamber ; (iii) the insertion loss at the first resonance frequency is greater than that of the simple one.

Deconvolution approach for the mapping of acoustic sources (DAMAS) applied to enhance turbofan engine duct mode measurements

Inlet fan noise in turbofan engines is frequently characterized in terms of modal amplitude distribution. The modes can be measured nonintrusively using an array of wall mounted microphones. At high frequency, the number of cuton modes can be much larger than any reasonable number of microphones. This suggests a beamforming analysis technique, rather than a least squares fit, as an appropriate method to extract the mode amplitude from the data. The quality of beamforming output is limited by array resolution and sidelobes. The CLEAN deconvolution algorithm has been used in the past to attempt to improve mode maps from beamforming processing. The recently introduced DAMAS algorithm is a much more comprehensive deconvolution technique, and is well suited to processing mode maps. The benefit of DAMAS is illustrated using simulated mode data. The engine inlet is represented as a cylinder with uniform flow. Two array designs are considered. In each case, several mode distributions are postulated and used to create synthetic array data. Beamforming is applied to create mode maps, and DAMAS is used to deconvolve the array response functions from the mode maps. The results are evaluated by comparing the true mode distributions, the beamform maps, and the deconvolved maps.

Development and testing of rotary dryer for the indigenous cottage sugar industry in nigeria

A 1000kg capacity per day Rotary sugar dryer was designed and fabricated in Nigeria by the National Cereals Research Institute Badeggi in 1989. This was done in order to dry sugar in granulated form in the indigenous small scale sugar plant that was developed in the country. It basically consists of an air inlet fan unit, rotary drum, drying assembly, heating unit, fixed tray and framework. An electric motor of 2.0 Kw was selected as source of power to the rotary drum while a 1.25kw electric motor provided power to the air inlet fan assembly. Also twelve (12) electric heating elements of 1.8kw were installed in the heating unit to provide the required heat energy to dry the sugar. Test results of the dryer shows that the machine had maximum sugar granulated efficiency of 97.8% for 35kg and 45kg of sugar per batch at an initial moisture content of 16.5%. The self sugar discharge mechanisms was very effective and the machine was generally found to be easy to maintain by local artisans due to it’s simple design features.

Numerical investigation of the effect of inlet flow distortions on forced draught air-cooled heat exchanger performance

Forced draught air-cooled heat exchangers (ACHEs) are often arranged into banks consisting of multiple rows of fan-heat exchanger combinations. Fans on the outer edge of the banks are subject to severe cross-flow conditions as the air is swept past en route to fans located deeper within the banks. The cross-flow conditions give rise to increased inlet flow losses. The current investigation seeks to develop a better understanding of the nature of these increased inlet flow losses through the numerical resolution of flow fields associated with systems comprising a single and two banks of ACHEs. For installations comprising two banks of ACHEs it is found that the inlet flow losses of the periphery fan are dominated by flow separation occurring around the inlet lip of the fan inlet section. These flow losses can be reduced by the installation of a walkway at the edge of the fan platform or by the removal of the periphery fan inlet section. For a system comprising of a single bank of ACHEs it is found that the numerical models used accurately reflect the experimentally determined differences in inlet flow losses experienced by systems using either bell-mouth, conical or cylindrical fan inlet sections.

Fan Interaction Noise Predictions Using RANS-BEM Coupling

A source-to-far-field computation procedure aiming at predicting the noise generated by rotor-stator fan interactions and inlet noise radiation is presented here. It is applied to the NLR turbofan model, tested in DNW-LLF anechoic chamber under the framework of DUCAT project. The unsteady aerodynamic input for the acoustic computation is obtained using a 3D RANS code, CANARI, developed at ONERA for turbomachinery applications. The CFD solutions are coupled, using a modal expansion approach, to a BEM code, solving the Helmholtz equation in an arbitrary bounded space. A single interacting cut-on mode amplitude is either directly deduced from experiment or provided by post-processing the CFD data. With this approach, the predicted noise radiation can be related to the directivity patterns measured at several axial positions upstream of the turbofan inlet. A fairly good agreement is found using both experimental and CFD input data.

Retrofit Constant Speed Fan Laboratory Exhaust Systems Using Multi-Stack and Variable Frequency Drive Techniques

Constant speed fan exhaust systems are the most popular exhaust system in laboratory buildings since they satisfy building architectural requirement, and have low initial costs with reliable performance. The constant speed fan exhaust system maintains constant stack exit velocity to prevent toxic exhaust air downwash back to occupied areas near the building or on the roof top. To achieve constant velocity when the exhaust airflow is less than the design value, makeup air is introduced to the system at the inlet of the exhaust fan. Since the laboratory exhaust airflow is often significantly less than the design airflow, exhaust fans consume significantly more energy than is necessary. Multi-stack and Variable frequency drive techniques can reduce both the make-up airflow rate and fan energy in the constant speed fan exhaust system retrofit. This paper introduces the application principles, describes the optimal methods of stack sizing, and presents an example. The application example showed that the average annual fan power is 50% of the design fan power for a two-stack system, and 47% for a three-stack system.

MEASURING AIRFLOW DISTRIBUTION IN PEANUT DRYING TRAILERS

A method to measure airflow distribution exhausted from a filled peanut drying trailer was developed. Six 6.4-m peanut drying wagons were loaded with dry farmer stock peanuts at a local peanut processing facility. Three wagons had floors with 23% O.A. and three had 40% O.A. Peanuts were leveled on each trailer and peanut depth ranged from 114 to 130 cm. A 76-cm diameter, 1750 rpm, four-blade vane axial dryer with a 91-cm long straightening inlet transition was connected to each peanut drying trailer. The rated airflow capacity of the dryer was approximately 510 m3 min-1 at 124 Pa. Total airflow was measured using a pitot tube traverse across the inlet transition. Static pressure was measured in the wagon plenum using a U-tube manometer. The top of the trailer was divided into 40 sections using a 5 8 cell grid. The airflow through each grid cell was measured using a vane anemometer mounted on a conical transition placed in the center of each grid cell. No significant differences in static pressure, total airflow, or airflow distribution due to the percent O.A. of the perforated drying floor were detected. The average static pressure observed for wagons with the 23 and 40% O.A. was identical at 120 Pa. Total airflow measured at the fan inlet averaged 367 m3 min-1 for the 40% O.A. trailers compared to 366 m3 min-1 for trailers with 23% O.A. The total of the air flow measured as it exhausted from the peanuts was 63% of the flow measured using the pitot tube at the fan inlet.

Study on the Performance of a Sirocco Fan (Flow Around the Runner Blade)

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.

Using multi-stack and variable-speed-drive systems to reduce laboratory exhaust fan energy

In buildings that contain laboratories, fume hoods are normally used to control contaminant concentrations. Exhaust stacks with a constant exit velocity are required to make sure that dangerous concentrations do not occur in occupied areas near the building or on the roof top. To achieve constant velocity when exhaust flow rates are less than design, makeup air is introduced to the system at the inlet of the exhaust fan. Since laboratory exhaust airflow is often significantly less than the design airflow, exhaust fans consume significantly more energy than is necessary. To reduce exhaust fan energy, techniques involving multiple exhaust stacks and a variable speed drive (VSD) can be applied to laboratory exhaust systems. The potential fan energy savings depend on optimal selection of the number of stacks, the sizes of the stacks, and the exhaust system ductwork design. This paper introduces application principles, describes the optimal methods of stack sizing, and presents an example to demonstrate these methods. Published in 2005 by John Wiley & Sons, Ltd.

Effect of inlet duct contour and lack thereof on the noise generated of an axial flow fan

This study concerns the unsteady flows in turbomachines in general, and the aeroacoustics of fans in particular. The principal objective of this paper is the determination of the influence of the upstream environment on the acoustic and aerodynamic behavior of axial fans. After analysis of the various sources of noise present in turbomachines, interest is focused on the influence of the disturbances of the velocity field at the suction. Accordingly, the effect of the presence of a contoured duct and a lack thereof at the inlet of an axial flow fan is analyzed . The results show the strong involvement of the upstream turbulence level in the generation of the noise, and in particular, of broadband noise.

Computation of Engine Noise Propagation and Scattering off An Aircraft

The purpose of this paper is to demonstrate the feasibility of computing the fan inlet noise field around a real twin-engine aircraft, which includes the radiation of the main spinning modes from the engine as well as the reflection and scattering by the fuselage and the wing. This first-cut large-scale computation is based on time domain and frequency domain approaches that employ spectral element methods for spatial discretization. The numerical algorithms are designed to exploit high-performance computers such as the IBM SP4. Although the simulations could not match the exact conditions of the only available experimental data set, they are able to predict the trends of the measured noise field fairly well.

Effect of cross-flow on the performance of air-cooled heat exchanger fans

In large-scale applications such as arrays of axial fans in air-cooled heat exchanger systems, edge–proximity and wind-induced cross-flow may decrease the flow through some fans by causing the flow to enter them at off-axis angles. In this study, such off-axis inflows were introduced by inserting inlet pipe sections between the plenum chamber of a standard test facility and one of three different scale model test fans of 1542 mm diameter. Fan power consumption turned out to be completely independent of off-axis inflow angle up to 45°. Fan total-to-total pressure rise was found to be independent of off-axis inflow angle, and the decrement in fan pressure rise was equal to the dynamic pressure based on the cross-flow velocity component at the fan inlet. Analysis showed that for model fans to represent the cross-flow behaviour of their prototypes, they should have the same ratio of dynamic pressure to pressure rise, and the same dimensionless characteristic slope at their operating points. The performance of a row of fans operating at off-axis inflow conditions representing a cooling system was well predicted by a simple model assuming that the fans farther from the edges induce cross-flows over the fans closer to the edges.

Unsteady Pressure Field Investigation of an Axial Fan—Inlet and Outlet Unsteady Pressure Field Measurement

The unsteady pressure characteristics at inlet and outlet of an axial fan were measured in this study. A 1.829 m (6 ft) diameter axial fan was operated at 1770 rpm in a laboratory. The unsteady pressure field was obtained at three axial positions each with seven radial locations. The results showed that there was a relatively long response time for pressure drop both in the inlet and outlet during fan start-up. The measurements also showed that, due to the vortex shedding from the trailing edge of each fan blade, the fan outlet pressure oscillation frequency was related to the fan operating frequency. A theoretical analysis was also conducted in order to understand the measurements. The unsteady pressure measurements helped improve the fan performance and contributed to the understanding of the vibrational behavior of the fan unit. The complete set of the measurements obtained can be used as a database for computational fluid dynamics (CFD) codes validation and modeling.

極超音速空気吸い込み式エンジン用予冷却器（プリクーラ）の開発研究

Here is presented an experimental and analytical study on a precooler for hypersonic air-breathing engines. Precooling of the incoming air breathed by an air-inlet gives extension of the flight envelope and improvement of the thrust and specific impulse. Three precooler models were installed into an air-turbo ramjet engine and tested under the sea level static condition. When the fan inlet temperature was down to 180K, the engine thrust and specific impulse increased by 2.0 and 1.2 times respectively. Thick frost formed on the tube surfaces at the entrance part of the precooler blocked the air-flow passage. On the other hand, very thin frost formed at the exit part because the water vapor included in the air was changed to mist particles due to the low temperature of the air in this part. Parametric studies on the precooler design values and a sizing analysis were also performed. Decrease of tube outer diameters on the precooler is only way to increase heat exchange rates without increase of its weight and pressure loss.

Active Control of Discrete-Frequency Noise Generated by Rotor-Stator Interactions

Discrete-frequency tones generated by unsteady blade row interactions are of particular concern in the design of advanced turbine engines. In the annular fan inlet and exit duct, the acoustic waves generated at the multiples of the rotor blade pass frequency must have circumferential periodicity. The rotor-stator generated discrete-frequency noise is characterized as a summation of these circumferentially periodic acoustic waves or spatial modes over the multiples of the rotor blade pass frequency. Only the spatial modes that propagate to the far field represent the discrete-frequency noise received by an observer. A series of fundamental discrete-frequency noise source control experiments is described. Active airfoil source control is utilized to generate propagating spatial modes to interact with, and simultaneously cancel, the upstream and downstream propagating spatial modes generated by the rotor-stator interaction. The active airfoil source control is optimized for the control of the propagating spatial modes. The active noise control system incorporates the active airfoil source control with in-duct spatial mode measurements. Data are acquired and analyzed that demonstrate the viability of this unique active noise control technique. Significant simultaneous noise reductions are achieved for the upstream and downstream propagating spatial modes. The control system is successfully demonstrated over a range of rotor blade pass frequencies.

Experimental Study on the Aerodynamic Characteristics of a Two-Stage and a Counter-Rotating Axial Flow Fan

Experiments were done for the comparison of performance and flow characteristics between a two -stage axial flow fan and a counter-rotating axial flow fan. Each stage of the two -stage axial flow fan used fur the present study has an eight bladed rotor and thirteen slater blades. The front and the rear rotor of the counter - rotating axial flow fan have eight blades each and are driven by coaxial counter ro latins shafts through a gearbox located between the rear rotor and the electric motor. Both of the two axial fan configurations have identical rotor blades and the same operating condition fur the one -to-one comparison of the two. Performance curves of the two configurations were obtained and compared by varying the blade pitch angles and axial gaps between the blade rows. The fan characteristic curves were obtained following the Korean Standard Testing Methods for Turbo Fans and Blowers (KS B 6311). The fa n flow characteristics were measured using a five-hole probe by a non-nulling method. The velocity profiles between the hub and tip of the fans were measured and analyzed at the particular operating condition s of peak efficiency, minimum and maximum pressure coefficients. The peak efficiency of the counter-rotating axial fan was improved about 2% respectively, compared with the two stage axial fan. At the minimum pressure coefficient point of the two stage axial fan, the fan inlet flow patterns show that axial velocity highly decreased in the vicinity of the blade tip region. Also, the reverse flow took place at the blade tip.

Multidomain Spectral Computations of Sound Radiation from Ducted Fans

A time-domain method for acoustic propagation and its application to tone noise radiated from rigid-wall fan inlets are presented. The noise propagation phenomena are modeled by the nonlinear time-dependent Euler equations written in conservative form. The equations are solved numerically using a staggered-grid multidomain Chebyshev discretization for the spatial terms and a Runge-Kutta scheme for time integration. Various types of radiation boundary conditions are implemented and Investigated on generic benchmarks. The resulting code is optimized on parallel machines with shared memory. The method is first validated on noise radiation from two-dimensional and axisymmetric flat ducts with no mean flow for which analytical data exist. The full potential of the method is then tested by computing the sound field radiated from an axisymmetric bell-mouth duct in a nonuniform mean flow. Three-dimensional computations of the sound field in a bent pipe, on which both experiments and computations using a boundary integral method have been carried out at ONERA, are also presented.

Improved precision in field measurements of sound from large ID fans

An electric utility was receiving complaints about noise from their power plant from residences nearly 2 miles away. An onsite and off-site noise survey confirmed the neighbors complaints, and indicated that the sound was coming from the plant ID fans via the stack. Most of the complaints occurred when the plant went to low load at night. A study was therefore undertaken to determine how the fan sound level varied with plant load. A simple, reliable, and inexpensive means was sought to make repeatable fan sound pressure level measurements without penetrating the stack. Both narrow-band and 1/3-oct band measurements were taken from fixed and scanned microphone locations at the fans, in the stack annulus, and on the boiler roof during boiler ramp ups and ramp downs. A sampling methodology was developed with a high degree of precision allowing reliable measurements of ID fan blade pass frequency tone level versus plant load. Subsequent noise measurements evaluated modifications to the fan inlet, cutoff, blade tips, and fan speed with a relatively high degree of precision.

A nondestructive method for measuring the airflow resistance of locally reacting jet engine nacelle components

As a noise control measure to reduce inlet fan noise of jet engines, the nacelles are often equipped with a locally reacting absorber formed by a thin resistive wire mesh placed over a honeycomb structure. Historically there has been a problem to measure, in nondestructive fashion, the airflow resistance of repaired or refurbished nacelle parts for the purpose of demonstrating OEM compliance. ASTM-C522 is the traditional airflow resistance test method and is destructive, requiring a sample be cut from the specimen and fit into an apparatus where the flow velocity due to a constant pressure drop can be measured. This paper presents the theory and practical considerations of a nondestructive test method to measure the airflow resistance using an ASTM-E1050 impedance tube placed against the wire mesh of the complete specimen. Transfer matrix theory is used to describe the combined impedance of the wire mesh and air cavity. It is shown that at the air cavity resonance frequency the measured system impedance will be that of the wire mesh with the real part being the airflow resistance. Airflow resistance estimates obtained using the presented method and the ASTM-C522 test method are shown to be in excellent agreement.

Development Study on ATREX Engine

This is the status report of the development study on ATREX engine (Air Turbo Ramjet) that is now under way in the Institute of Space and Astronautical Science (ISAS) cooperation with the Ishikawajima Harima Heavy Industries (IHI), the Kawasaki Heavy Industries (KHI), the Mitsubishi Heavy Industries (MHI). ATREX engine will be applied for the propulsion system of fly-back booster of TSTO space plane. ATREX is the combined cycle (a fan-boosted ramjet) engine providing the effective thrust from sea level static to flight Mach number 6. ATREX is worked on the expander cycle with precooling the incoming air as shown in Fig. 1 . ATREX employs the tip turbine configuration which allows the compactness and the light weight of turbo machinery and the variable geometry airintake and plugnozzle which allow the wide range operation conditions.From 1990 to 1992, “ ATREX-500“ has been tested at the sea level static conditions. ATREX-500 is the 1/4-scale model of which fan inlet diameter is 300mm and overall length 2,200mm. From 1992 have been performed the wind tunnel tests on the primary components of ATREX, the axisymmetric variable geometry airintakes, the precoolers and the variable geometry plug nozzles. In parallel to the windtunnel tests, the ram combusters have been tested simulating the hypersonic flight conditions and the application studies on advanced carbon-carbon composite for the tip-turbine and fan assembly has been proceeded.In 1994 initiated the flight test plan in which ATREX will be verified in the practical flight conditions by using an unmanned flying test bench.In 1995 will be tested ATREX-500 installing the precooler under the sea level static conditions to examine the engine performance and the icing on the precooler.The present paper addresses the high loading ram combuster experiment using the mixer with skewed lobes to generate swirl flow and the analytical studies and the designs on the precooler and the precooled ATREX engine and the flight test plan.