Fan Configuration Research Articles

A numerical and experimental test-bed for low-speed fans

An extensive experimental and numerical database provides detailed information on some transition and noise mechanisms encountered in the low-Reynolds-number flows of low-speed axial fans for the first time. Two different similarly instrumented mock-ups built from the same industrial controlled-diffusion airfoil have allowed the first consistent comparison of wall pressure and near-field velocity statistics on the same geometry with and without rotation in perfect similitude of Mach and Reynolds numbers. The experimental and numerical results on the stationary airfoil constitute the largest unique aeroacoustic data set for airfoil trailing-edge noise characterization including installation effects. A similar experimental aeroacoustic database has been built on the rotating controlled-diffusion blade in the Michigan State University-Automotive Fan Research and Development (MSU-AFRD) test facility for different fan configurations, rotational speeds and flow rates. This yields a unique test-bed for fan code validation. The comparisons between the stationary and rotating airfoils suggest that the wall pressure statistics are hardly influenced by rotation in the trailing-edge region, and that the differences in the velocity statistics in the near-wake are a more energetic wake with smaller velocity deficits and diffusion, and a far-less uniform inviscid region in the rotating case.

CFD optimization of jet fan ventilation in a car park by fractional factorial designs and response surface methodology

We propose to solve two important engineering design challenges associated to the optimal placement of jet fans in a car park, by means of CFD. Given a proposed arrangement of jet fans, we provide a simulation framework for rigorous identification of those fan units (if any) that do not contribute to improving the overall air quality in the enclosure. Based on this statistical analysis, we then solve the following constrained optimization problem: Given maximum fan capacities and an air quality level requirement, establish a minimum-cost fan configuration which meets it for the car park in question. The proposed optimization framework is illustrated by an example from an actual car park.

An evaluation of simplified CFD models applied to perimeter fans in air-cooled steam condensers

Modelling air-cooled condensers (ACCs) incorporating hundreds of fans, necessitates the use of simplified fan models when performing a computational fluid dynamics (CFD) analysis of the condenser. The perimeter fans in these ACCs are subjected to distorted inlet flow conditions. This paper compares the accuracy of three different simplified fan models and proposes an improved model, based on numerical and experimental results from representative fan configurations. Three different fan configurations are tested as perimeter fans in a three-fan test facility, and their results compared to CFD results. The experimental evaluation by particle image velocimetry (PIV) reveals the shape of the velocity profiles immediately upstream of the perimeter fan. The accuracy of the CFD-predicted flow field directly upstream of the perimeter fan varies according to the model used to represent the fan as well as the configuration of the specific perimeter fan. The paper indicates a discrepancy of as much as 30% between experimental and simulated volumetric effectiveness values for a specific simulation model and fan configuration. The standard and extended actuator disc fan models perform better than the pressure jump model in predicting the volumetric effectiveness of the perimeter fans, and the extended actuator disc model performs best at predicting fan inlet velocity profiles.

Simulating the Effect of Wind on the Performance of Axial Flow Fans in Air-Cooled Steam Condenser Systems

The use of air-cooled steam condensers (ACSCs) is preferred in the chemical and power industry due to their ability to adhere to stringent environmental and water use regulations. ACSC performance is, however, highly dependent on the prevailing wind conditions. Research has shown that the presence of wind reduces the performance of ACSCs. It has been found that cross-winds (wind perpendicular to the longest side of the ACSC) cause distorted inlet flow conditions, particularly at the upstream peripheral fans near the symmetry plane of the ACSC. These fans are subjected to what is referred to as “two-dimensional” wind conditions, which are characterized by flow separation on the upstream edge of the fan inlets. Experimental investigations into inlet flow distortion have simulated these conditions by varying the fan platform height. Low platform heights resulted in higher levels of inlet flow distortion, as also found to exist with high cross-wind velocities. The similarity between platform height and cross-wind velocity is investigated in this study by conducting experimental and numerical investigations into the effect of distorted inlet flow conditions on the performance of various fan configurations (representative of configurations used in the South-African power industry). A correlation between system volumetric effectiveness, platform height, and cross-wind velocity is derived which provides a means to compare platform height and cross-wind velocity effects.

Noise Reduction on Centrifugal Fan via the Quarter-Wave Resonator

The purpose of this work is to improve flow-induced noise for the centrifugal fan with quarter-wave resonator by design scheme, mockup fabrication, and experimental test. At first, the cascade theory is utilized to generate the three-dimensional fan configuration which is fabricated for performance and acoustic tests later. Next, FFT is applied to measure the noise for comparison and evaluating the effect of quarter-wave resonator. To reduce the fan noise, a set of quarter-wave resonator of this centrifugal fan are designed and fabricated on the centrifugal fan. Consequently, the flow-induced-noise reduction due to the aerodynamics is examined and discussed in details. In conclusions, a comprehensive parametric study on quarter-wave resonator is carried out and summarized for attaining a design guideline for its application on centrifugal fan. The accomplishment of this study provides a systematic scheme of noise reduction for a centrifugal fan with the addition of quarter-wave resonator design.

Passive Noise Reduction for a Contrarotating Fan

There has been renewed interest in the contrarotating (CR) fan configuration in aviation and other applications where size and weight are important design factors. Contra-rotation recovers swirl energy compared with the single-rotor design, but this advantage is not fully harnessed due to, perhaps, the issue of noise. This study explores passive noise reduction for a small, axial-flow, CR fan with perforated trailing-edge for the upstream rotor and perforated leading-edge for the downstream rotor. The fan is designed with simple velocity triangle analyses, which are checked by 3D flow computations. The aerodynamic consequence and the acoustic benefit of such perforated blading are investigated experimentally. The results show that there is a reduction of total pressure compared with the baseline CR fan at the same rotating speeds, but this is easily compensated for by slightly raising the rotating speeds. A reduction of 6–7 dB in overall noise is achieved for the same aerodynamic output, although there is a moderate noise increase in the high frequency range of 12.5–15.0 kHz due to blade perforations. The effect of inter-rotor separation distance is also investigated for the baseline design. A clear critical distance exists below which the increased spacing shows clear acoustic benefits.

Pilot Study on Indoor Flows and Turbulence Statistics of a Vertical Axis Wind Turbine

Turbulence statistics were applied to the downwind flow of a Darrieus-type vertical axis wind turbine (VAWT) to provide insights about VAWT micro-flow characteristics. Micro-turbulence measurements of the flow in front of and behind a VAWT were made using a sonic anemometer. Turbulence data for downwind distances of 0.5 m and 2.0 m from the wind source were collected with and without the VAWT, respectively, using a blower (Type 1 flow) and industrial fans (Type 2 flow) as the wind source. The voltage V, generated by the VAWT was recorded every 15 min. Only the center line of the flow was considered. The Type 2 flow induced a constant spectral power at a high dimensionless frequency range of 0.007 < f < 0.04, perhaps due to the fan configuration, which had a larger wind-swept area. The results show an increase in lateral turbulence, σv, downwind of the VAWT compared to its longitudinal, σu, and vertical, σw, counterparts. Using spectral analysis, the VAWT was found to reduce the horizontal (u and v) turbulent component energies in the dimensionless frequency range of 0.003–1. Interesting dip and peak features were observed for Type 1 flow, but only dip features were observed for Type 2 flow in the resulting spectra. Higher wind speeds increased the voltage generated at a rate of 0.5.

Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine

The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at mid-cruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.

Prediction and optimization of aerodynamic noise in an automotive air conditioning centrifugal fan

The high aerodynamic noise induced by automotive air conditioning systems has important effects on the ride comfort, and the centrifugal fan is the largest noise source in these systems. It is very important to reduce the aerodynamic noise generated by the centrifugal fan. The flow field and the sound field on the whole centrifugal fan configuration have been carried out using the computational fluid dynamics. Simulation results show that the sound pressure level near the outlet of the centrifugal fan is too high. Based on the relationship between flow characteristics and the aerodynamic noise, four parameters of the centrifugal fan, i.e., impeller blade’s outlet angle θ, volute tongue’s gap t, collector inclination angle β, and rotating speed n, were selected as design variables and optimized using response surface methodology. While keeping the function of flow rate unchanged, the peak noise level is reduced by 8 dB or 10.8%. The noise level is satisfactorily reduced.

Thermal performance of plate-fin heat sinks with piezoelectric cooling fan

An experimental method was used to study the thermal-fluid characteristics of plate-fin heat sinks cooled by a piezoelectric fan. The fan configuration, the fan location, and the heat sink dimensions were evaluated in terms of effects on thermal resistance. The experimental results show that, when the piezoelectric fan is vertical, thermal performance is the best with the tip of the fan blade at the center of the heat sink. When the piezoelectric fan is horizontal, thermal performance is the best with the tip of the fan blade at the front edge of the heat sink. In most cases, a vertical piezoelectric fan performs best with low fin heights. When the piezoelectric fan is horizontal, the thermal performance enhances as the fin height increases for three-fin heat sinks. For two-fin heat sinks, however, the correlation with fin height depends on the fin width. Heat transfer efficiency does not increase with fin width when the piezoelectric fan is vertical. However, thermal resistance usually decreases with fin width when the piezoelectric fan is horizontal.

Flight Control of TUAV with Coaxial Rotor and Ducted Fan Configuration by NARMA-L2 Controllers for Enhanced Situational Awareness

Flight Control of TUAV with Coaxial Rotor and Ducted Fan Configuration by NARMA-L2 Controllers for Enhanced Situational Awareness

Optimization of Backward Curved Aerofoil Radial Fan Impeller Using Finite Element Modelling

This paper deals with optimizing the design of radial fan impeller using finite element analysis. Most manufacturing concerns spend more than a 60% of their money for materials. The design of turbo machinery has been practiced in the last half of the previous century with increasing degree of sophistication. This trend of development is not complete because design of any turbo machine is interdisciplinary process involving aerodynamics, thermodynamics, fluid dynamics, stress analysis, vibration analysis, the selection of materials, and the requirements for manufacturing. So, products have not reached a level of full maturity. Today there is considerable room for further development of most turbo machinery products when looked at with the perspective of the broadest possible design world and when it comes to development at the design stage then various types of analysis of every component are performed on computer before the first prototype is built. Among these the major one end the most frequently used in the manufacturing of any mechanical part is stress analysis. As the mass of the fan is directly related to the thickness of the impeller parts hence our objective in this project is to minimize the thickness, keeping in consideration the operating restrictions and design parameters.This work concentrates on to generate the finite element model of backward curved aerofoil radial fan impeller which behaves mathematically like structure model & carry out stress analysis using ANSYS software. The analysis was carried out using the default thickness of the impeller of the radial fan. This results in massive weight of the fan, leading to large vibrations and one of the reasons to failure. Ways were found out to reduce all these things, so the analysis was carried using various reduced thicknesses of the impeller and the optimum thickness of the impeller parts found for the safe stress and strain limits.This value analysis/Engineering results in material reduction, cost reduction with reduced vibrations for the desired design and operating conditions. The basic procedures and issues involved in the Finite Element Analysis of a radial fan are also outlined. The design configuration of the radial fan has been provided by Boiler Auxiliaries Plant.

Fan selection and stack design for open-cathode polymer electrolyte fuel cell stacks

The design of open-cathode polymer electrolyte fuel cell (PEFC) stacks with forced-air convection from one or several fans requires careful consideration of the characteristic curves of the stack and the fan(s). Ideally, the intersection – the operating point – between the stack and the fan characteristic curves should be located in the optimal operating region of the fan; and be sufficiently far away from any unstable region. In this paper, the effect of various fan and stack configurations, operating conditions and their impact on the fan and system characteristic curves as well as stack performance are investigated with a model considering two-phase flow and conservation of mass, momentum, species, charge, and energy in the PEFC stack and ambient; the fans are treated as interface conditions. The results indicate that the fan power rating, fan type, single fan or fans in series, fuel cell length, and separate air-coolant channels have a significant impact on the operating point and resulting stack performance – these factors therefore have to be accounted for when designing the PEFC stack and selecting fans. Furthermore, the results suggest that the stack characteristic curve can be secured by straight-forward air-flow simulations instead of solving a detailed, mechanistic fuel-cell model, allowing for more efficient model-based design studies of fans interacting with a PEFC stack.

Model for predicting performance of cooling fans for thermal design of electronic equipment (Modeling and evaluation of effects from electronic enclosure and inlet sizes)

AbstractThis study describes the performance of cooling fans in terms of the P–Q curve and the maximum flow rate under various environmental conditions. It focuses on the relationship between fan performance and configuration factors such as the electronic enclosure. The presence of an enclosure wall increased the pressure characteristic of the fan performance. The presence of a narrow inlet decreased the flow rate. When the inlet area of the enclosure became smaller than twice the fan flow area, the flow rate was decreased. The maximum flow rate depended on the ratio of the inlet area to the fan flow area. A model for predicting pressure rise and flow rates in the enclosure is proposed. The model is used in a thermal analysis of a PCB model set in an enclosure. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20347

An integrated study of the design method for small axial-flow fans, based on the airfoil theory

This research is aimed to establish an integrated design scheme through combining the cascade theory and inverse design method for the small axial-flow fans. At first, a reliable set of low-Reynolds-number aerodynamic characteristics for National Advisory Committee for Aeronautics airfoils is constructed to serve as the fan design database via the computational fluid dynamics (CFD) calculation incorporated with a dependable turbulent model. Then, with the inputs of design conditions and few geometric settings, this design program can generate a fan configuration to meet with the desired performance requirement. Furthermore, by changing the operating flowrate for this fan geometry, this design approach can also yield the axial velocity and the pressure distributions for various operating points over the entire performance curve. Consequently, this feature enables the design engineer to foresee the actual fan performance delivered under different system resistances. Thereafter, a computer numerically controlled fabricated prototype and a three-dimensional numerical model are chosen to validate the design prediction of fan performance via both test and CFD approaches. As a result, a slight deviation among the designed, experimental, and numerical outcomes is observed throughout the P Q performance curve. In conclusion, this systematic and user-friendly inverse design program not only provides the fan engineer's design ability to meet with the performance requirement at the on-design point, but also the predicting capability on the off-design characteristics.

Experimental Investigation of a Forward Swept Rotor in a Multistage Fan with Inlet Distortion

Previous studies of transonic swept rotors in single stage fans have demonstrated the potential of significant improvements in both efficiency and stall margin with forward swept blading. This paper extends the assessment of the payoff derived from forward sweep to multistage configurations. The experimental investigation compare two builds of an advanced two-stage fan configuration tested alternately with a radial and a forward swept stage 1 blade. In the two-stage evaluations, the testing was extended to include the effect on inlet flow distortion. While the common second stage among the two builds prevented the overall fan from showing clean inlet performance and stability benefits with the forward swept rotor 1, this configuration did demonstrate superior front stage efficiency and tolerance to inlet distortion. Having obtained already low distortion sensitivity with the radial rotor 1 configuration relative to current production military fan standards, the sensitivity to inlet distortion was halved with the forward swept rotor 1 configuration. In the case of the 180-degree one-per-rev distortion pattern, the two-stage configuration was evaluated both with and without inlet guide vanes (IGVs). The presence of the inlet guide vanes had a profound impact in lowering the two-stage fan's sensitivity with inlet distortion.

Effects of Swirl Velocities From Fan Assemblies Mounted on Lifting Surfaces

The penetration of a jet of fluid into a traversal moving stream is a basic configuration of a wide range of engineering applications, such as film cooling and V/STOL aircrafts. This investigation examines experimentally the effect of blowing ratio of fans in crossflow, and numerically, the effect of the swirl velocity of jets in crossflow, downstream of the injection hole. The experimental results indicated an agreement with typically straight jets in crossflow (no vorticity), illustrating that the trace of the jet, remains close to the wall and subsequently enhance cooling at low blowing ratios in the case of turbine blade applications. However, the rotation of the jet results in an imparity between the two parts of the counter rotating vortex pair and as a consequence, the injected fluid not only bends in the direction of the main stream but also diverts in the direction of the rotation in order to conserve its angular momentum. The induction of the swirl velocity on the injected jet destructs one of the two parts of the kidney vortex, which entrains fluid from the crossflow to the jet promoting the mixing between the two fluids while the trace of a swirled jet remains closer to the wall downstream of the injection hole. Finally, the use of contrarotating jet or fan configurations reduces the wall shear stress in a very great extent, leading to better thermal protection of turbine blades, as well as cancels out the yaw torques of each fan separately, resulting in better flight control of typical lift surface.

Impact of Fan Gap Flow on the Centrifugal Impeller Aerodynamics

The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related computational fluid dynamics (CFD) analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown.

Numerical and experimental study of a cross-flow fan for combine cleaning shoes

Computational Fluid Dynamics (CFD) and measurements using hot-wire anemometers were used to study the flow configuration and performance of a cross-flow fan (CFF) used for grain cleaning. Four CFFs with the same rotor and casing but different vortex wall positions were studied using CFD. Special attention was paid on the effect of the vortex wall position on the performance of the fan and on achieving a balanced airflow division between the two outlets. It was demonstrated that two-dimensional CFD model can predict fan performance up to an acceptable level. Moreover, it was shown in general that the position of the vortex wall plays a crucial role for the performance of the CFF and in particular the airflow division between the two outlets. A more uniform air division was obtained by the changes made to the position of the vortex wall. It was observed that the mass flow rate division between the two outlets can be greatly influenced by the rotor outlet opening.

Autonomous takeoff and landing control for a prototype unmanned helicopter

In this paper, an autonomous takeoff and landing control strategy is designed and implemented for a prototype coaxial unmanned helicopter with ducted fan configuration. The control strategy is designed such that longitudinal and lateral controls use ground forces, attitude and drifting feedbacks. Vertical control employs takeoff and landing decision and vertical velocity control is based on altitude tracking. Ground forces feedback is used to balance longitudinal forces and moments during liftoff effectively cancelling all ground forces. Attitude and drifting feedbacks are used to balance the longitudinal and lateral movements of the helicopter during takeoff and landing. The flight control strategy is successfully verified during flight tests.