Fan Shroud Research Articles

Development of a Performance-Based Design Technique for an Axial-Flow Fan Unit Using Airfoil Cascades Based on the Blade Strip Theory

Axial-flow fans are widely used as cooling fans in the outdoor units of split-type air conditioners. The design of an axial-flow fan blade involves stacking several airfoils that can be differently designed for each spanwise section. However, the complex flow field around the fan blade, including circumferential and axial flows, presents challenges when applying the single airfoil theory. This study proposed a systematic performance-based design method for axial-flow fans using a cascade of airfoils based on the blade strip theory. The theory characterized the complex three-dimensional flow field driven by an axial-flow fan in terms of a two-dimensional cascade of airfoil flows. Computational fluid dynamics based on finite volume methods were used to predict the flow field and aerodynamic sound sources of an existing low-pressure axial-flow fan partially covered by a fan shroud, and the results were validated against experimental measurements. Three radial locations in the spanwise region from the hub to the blade tip that have a significant impact on aerodynamic performance were selected, and the two-dimensional flow field on a cylindrical surface with a constant radius was extracted from the three-dimensional flow field to characterize the performance of an axial fan. Then, the airfoils at the targeted span locations were optimized for a higher flow rate and greater efficiency via two-dimensional simulations using the cascades of the airfoil, and the selected optimized airfoils were applied to existing fan blades. The effectiveness of the proposed performance-based design method for low-pressure axial-flow fans was validated by the results, which showed that the redesigned fan blades with cascades of airfoils performed as predicted, increasing the intended higher flow rate by about 1%, improving power consumption by 8%, and lowering the overall sound pressure level by 1.5 dBA.

Reduce the Cooling FAN Blade Pass Frequency Noise in Electrical Vehicle

Air duct in the inlet of the cooling fan is often used in EV (electrical vehicle) due to the usage of AGS (active grille system) and profile. It often leads to the unexpected noise of the cooling fan, the overall level and the BPF (blade pass frequency) noise becomes much worse than before significantly. The experimental results shown that the boundary conditions of the cooling fan affect the noise sensitively. So, the whole engine room CAE model is set up to apply the Computational Fluid Dynamics (CFD) and the Computational Aero Acoustics (CAA). Thus, the CFD and CAA synthesis methods are used to predict the fan noise. After theoretical analysis, it is found that the fan shroud is the most sensitive area which significantly affect the BPF noise. Then different shroud proposals are applied to find the best solutions for the BPF noise, The CAA results shown that the BPF frequency peak of the interior noise reduces 5dB (A) for the best shroud case. Then the best proposal one is manufactured and assembled in EV to validate the effects. The Noise in the EV also cut down in 5-8 dB (A). The Experimental and CAE synthesis method for the whole engine room analysis is confirmed to be useful to solve the cooling FAN BPF noise issue. According to the above researches the cooling FAN NVH design rules are drawn and used in EV NVH design.

Tonal noise reduction of an electric ducted fan using over-the-rotor acoustic treatment

This study is concerned with reducing the tonal noise emitted by electric ducted fans which serve as the propulsion system for a variety of unmanned aerial vehicles (UAVs). The underlying concept is utilizing the shroud pressure fluctuation caused by the rotating blades to drive the over-the-rotor (OTR) acoustic treatment and generates a secondary sound field that cancels the primary ducted fan sound field. Experiment shows a considerable destructive effect can be made by meticulous tuning of the strength and phase of the secondary source. In view of the space constraints of a real electric ducted fan, the acoustic treatment is reconfigured as a labyrinth-type acoustic metamaterial that reduces the structure size while maintaining the noise reduction performance at the same time. An advantage of the proposed technique is that each tone can be dealt with by a specifically designed acoustic treatment occupying a small patch on the fan shroud. Hence, a compact multi-tonal noise control solution is possible by circumferentially deploying several OTR acoustic treatments.

Improved Aerodynamics of a Hollow-Blade Axial Flow Fan by Controlling the Leakage Flow Rate by Air Injection at the Rotating Shroud.

Axial flow fans are used in many fields in order to ensure the mass and heat transfer from air, chiefly in the heating, ventilation and air conditioning industry (HVAC). A more proper understanding of the airflow behavior through the systems is necessary to manage and optimize the fan operation. Computational fluid dynamics (CFD) represents a real tool providing the ability to access flow structures in areas that measuring equipment cannot reach. Reducing the leakage flow rate, inherent in operation, by synthetic-jet techniques improves performance. This paper presents the CFD results performed on a hollow blade fan developed by our team. The leakage flow is controlled by blowing air from 16 designated circular holes and arranged on the fan shroud. We discuss the results for two rotational speeds (1000 and 2000 rpm) and two injection rates (400 and 800 L/min). The numerical results consistent with the experimental show, for the low rotation speed and high injection ratio, significant gains in power (53%), torque (80%) and leakage flow rate (80%).

Experiment study of multi-fans cooling module using different shroud structures for advanced vehicle thermal management system

As one of the most important components of the vehicle thermal management system, multi-fans cooling module can potentially be used to optimal the system performance in order to save the energy consumption and reduce the vehicle fuel consumption. In this study, a test rig has been designed, constructed and used to test the heat transfer performance of the multi-fans cooling module using four different fan shroud structures. Results indicate the separated plates, which have limited or worse effect on the performance of the system, are not recommended to be used in the multi-fans cooling module. The optimal shroud structure for multi-fans cooling module has been identified and experimentally tested. By adding shutters at the ventilation part of the fans (Shroud C) can significantly improve the overall performance of the module (Shroud A) by 13.25 % to 69.08 % under various operation conditions.

Application of the aeroacoustic analogy to a shrouded, subsonic, radial fan

A study was conducted to investigate the predictive capability of computational aeroacoustics with respect to a shrouded, subsonic, radial fan. A three dimensional unsteady fluid dynamics simulation was conducted to produce aerodynamic data used as the acoustic source for an aeroacoustics simulation. Two acoustic models were developed: one modeling the forces on the rotating fan blades as a set of rotating dipoles located at the center of mass of each fan blade and one modeling the forces on the stationary fan shroud as a field of distributed stationary dipoles. Predicted acoustic response was compared to experimental data measured at two operating speeds using three different outlet restrictions. The blade source model predicted overall far field sound power levels within 5dB averaged over the six different operating conditions while the shroud model predicted overall far field sound power levels within 7dB averaged over the same conditions. Doubling the density of the computational fluids mesh and using a scale adaptive simulation turbulence model increased broadband noise accuracy. However, computation time doubled and the accuracy of the overall sound power level prediction improved by only 1dB.

Design features of fan assembly in automobiles

Nowadays in the engine cooling system and in air-conditioning system of passenger compartment and cabin of tractor is applied a great variety of designs of fan units for the supply of cooling air. A distinctive feature of fan units of automobiles is that they need not only to supply cooling air, but also must make efficient use of air flow. This is not an easy task, because these two functions are almost always in conflict. The problem becomes even more complicated when a car air conditioner is installed. Efficiency factor of the incident flow is higher than the efficiency of the fan. It is therefore necessary to use more efficient the incoming air flow. The article analyzes the most common fan assemblies of automobiles used for the operation of the engine cooling and passenger compartment air conditioning system. Its strengths and weaknesses were evaluated. There were evaluated the most important characteristics: the effectiveness of the fan use, the rational use of air flow when the vehicle is moving, mass-dimensional characteristics and the noise produced by the fans in their work. The conclusions and recommendations for improving the fan installations were given. When choosing one or another variant of the fan assembly it is needed to take into account the features of the automobile design. High efficiency of fan can be obtained when the fan shroud has a full coverage of the radiator. In this case, for rational use of incoming flow is necessary to install in the fan cover the valves of a large cross-section in contrast to traditional, these valves must be driven to forced opening and closing.

Trends in engine cooling systems

This paper deals with engineering highlights engine cooling system components by dividing them into three groups: (1) components on the engine side - water jacket, water pump, thermostat and V–bell; (2) those on the vehicle body side - radiator and radiator cap; and (3) those concerned with airflow–cooling fan, fan shroud, and body front–end shaping. It also presents the latest applications of high performance engines using as examples certain Japanese manufactured models. Additionally it cites recent trends of automotive cooling systems by outlining a cooling method used far turbocharger bearings installed to achieve higher output as well as for an intercooler for boosting the turbocharger efficiency.

Optimising the natural frequencies of a fan shroud in a powertrain cooling system with modal iteration method

The durability of a fan shroud is determined by its vibration response to the road, which in turn is determined by its natural frequencies relative to the frequencies from road excitation. The objective of the current study is to develop an optimisation algorithm that increases a specific structure's natural frequency such that it separates itself from the main band of the road excitation. The optimisation algorithm uses a series of iterations of modal analyses in a commercially available Finite-Element Analysis (FEA) software package. After each modal analysis, the key characteristics that contribute to the structural deformation are identified and evaluated. The thickness of each element is then adjusted in accordance with the contribution. As demonstrated in a case study of a fan shroud used in a sports vehicle, the optimisation algorithm works well in enhancing the fan shroud's natural frequency.

Phenomenon of labyrinth seal with low static pressure difference and large clearance

This paper discusses the straight-through type labyrinth seal. This labyrinth seal is used for axial flow fans, which have an outer ring at the blade tip to seal the clearance between the ring tip and the fan shroud, in order to prevent the reverse flow or leakage. These fans are used for the cooling of automobile radiators. In these cases, the labyrinth seal is used in an extremely low static pressure difference and a large clearance. A significant decrease of the leakage rate was reported even when the labyrinth seal rotated in comparatively low speed in this unique condition according to the authors' former report. However, this phenomenon is different from past research. Furthermore the cause of this phenomenon has not been determined. Therefore, the internal flow was depicted with Computational Fluid Dynamics (CFD) in order to clarify the cause of this phenomenon. The results of CFD show that the leakage rate decreases significantly because the carry-over flow is intercepted in the expansion groove. This is the newly discovered phenomenon which occurs under the unique condition of an extremely low differential pressure. It has not been pointed out before as the reason why the rotation decreases the leakage rate.

Phenomenon of labyrinth weal with Low static pressure difference and large clearance

The low pressure axial flow fans with an outer ring, used for cooling automobile radiators, have a significantly large tip clearance between the ring tip and the fan shroud. It has been found that the turbulent reverse flow, or leakage flow, which occurs at the tip clearance, greatly affects the fan performance and noise level. Therefore, in order to improve the fan performance and noise level it is important to decrease the effect of leakage at the tip clearance. The authors investigated the performance of the straight-through type of labyrinth seal which operates in an extremely low static pressure difference with a large clearance. It was hoped that by sealing this clearance with the labyrinth seal the performance would be improved. It was verified that the labyrinth seal satisfied almost the same performance as that predicted by the previous theory. This theory was established by experimental studies in the condition of quite high static pressure difference when the labyrinth is stationary. However, it was later discovered that the leakage rate decreased significantly even though there was far lower ring speed in comparison to past research results where the ring rotated. This phenomenon is conspicuous in a lower differential pressure. However, the cause of this phenomenon has not been determined.

A study of radiator cooling fan with labyrinth seal

The performance of a conventional axial flow fan and other fans, which have various types of rings fixed at the blade tips of the same fan, were compared. Then, the effects of these rings were investigated in detail. The fans displayed higher performance with a fixed ring. The authors also showed that a labyrinth seal is able to seal the tip clearance between the ring and the fan shroud of the fan with a fixed ring, especially when the fan operates in a low static pressure difference. As a result, the fan with a fixed ring and the labyrinth seal prevented the effect of the tip clearance, and achieved higher fan performance and lower fan noise than the conventional fan in any practical tip clearances.

107 リング付低圧軸流ファン用直通形ラビリンスシールの特性

The low-pressure axial flow fans with an outer ring, used for cooling automobile radiators, have a significantly large tip clearance between the ring tip and the fan shroud. It has been known that the turbulence of reverse flow, or leakage flow, which occurs at the tip clearance, greatly affects the performance and noise level. In order to improve the performance and noise level, the authors studied about the labyrinth seal which was used at the clearance. As a result, we discovered that it was possible to predict the performance by conventional theory when the labyrinth was stationary, and that the leakage rate decreased significantly even though the ring speed was much less than that of past research when the ring was rotated.

Performance of Straight-Through Type Labyrinth Seal for a Low-Pressure Axial Flow Fan with an Outer Ring

The low-pressure axial flow fans with an outer ring, used for cooling automobile radiators, have a significantly large tip clearance between the ring tip and the fan shroud. It has been found that the turbulent reverse flow, which occurs at the tip clearance, greatly affects the fan performance and noise level. Therefore, in order to improve the fan performance and noise level it is important to decrease the effect of leakage at the tip clearance. The authors investigated the performance of the straight-through type of labyrinth seal which operates in an extremely low static pressure difference with a large clearance. It was hoped that by sealing this clearance with the labyrinth seal the performance would be improved. It was verified that the labyrinth seal satisfied almost the same performance as that predicted by the previous theory. This theory was established by experimental studies in the condition of quite high static pressure difference when the labyrinth is stationary. However, it was later discovered that the leakage rate decreased significantly even though there was far lower ring speed in comparison to past research results where the ring rotated. This phenomenon is conspicuous in a lower differential pressure. However, the cause of this phenomenon has not been determined.

An Aerodynamic Shroud for Automotive Cooling Fans

Results from an experimental investigation of an aerodynamic fan shroud are reported. The device was motivated by the relatively large (2.5 cm) tip clearance required in automotive cooling fans which are mounted to the engine. The shroud consists of a pressurized plenum and a Coanda attachment surface to deliver a jet of high momentum air into the tip clearance region. Both the performance and the efficiency for the initial system design were enhanced at higher flow rates, and degraded at lower flow rates. A small tuft was used to observe qualitative flow features in the near wake and tip clearance region of the fan. This information was used to create a modified design. The new geometry was tested and found to provide improved performance characteristics for a wider range of flow rate conditions.

Efficient engineering through computer-aided design of experiments

Computer-aided design of experiments (CADOE) is discussed. Work performed using ECHIP software to meet quality and productivity goals for injection molded plastic components is detailed. An example of a fan shroud clearly shows that CADOE provides a powerful and efficient method for solving engineering problems. Although in some cases Taguchi methods may be slightly more accurate, CADOE methods such as ECHIP will usually find a solution to problems with a reduction in time and costs required. The actual time required to run the molding trials for the fan shroud was 3-0.5 h, plus 1 h of running time to confirm the predicted values on a faster molding cycle. >

Effect of Rotor Blade Leading Edge Serrations on Fan Noise

Noise measured from a fan with conventional rotor blading for configurations both with and without a fan shroud plus inlet is compared with similar data for a fan with rotor blade leading edge serrations. Using the conventional fan as a reference, the test data show (1) an increase in high-frequency noise due to the serration pattern for both the shrouded and shroudless configuration, and (2) an increase in low- to middle-frequency range noise for the shroudless configuration. Possible causes for the noise increases are discussed based on results obtained from the configurations tested and on current theories in available literature.

Abridgment of ventilation of revolving field salient-pole alternators

The studies were made experimentally and analytically. In the experimental study, a model of hard wood with a multiple of vent ducts of normal width of 3/8 in. each in the stator, the slots and teeth being of approximately average width was used. A four-pole rotor is distinct from one of a large number of poles; consequently two rotors were built, one of four poles and one of twelve poles, the latter being considered as representative of the greater number. The end-bells and the imitations of the end windings were different for the two numbers of poles. In the test results given, data for only standard fiber wedges are included, but other forms were investigated. The vent fingers extended the full depth of the core, thereby enabling measurement to be made of the volume of air per vent per tooth, a rotating vane anemometer with a suitable funnel attachment being employed. The end-bells were solid, simulating standard construction, and the entrances to the two bells were joined to a common duct, in series with which was a thermal volume meter and an external blower of readily adjustable speed. (See Fig. 6.) Pressures were measured in the inner and in the outer end-bells. The rotor of the model was driven by a d-c. motor. with the power input measured. By this means, windage data were obtained and many of the results are included among other data on the curve sheets. For taking a characteristic pressure volume curve, the first reading was taken with the rotor running at a suitable arbitrary speed, with the external blower stationary and its entrance closed. The pressure was then generated by the poles acting as fans, and by the internal fans. For a number of succeeding readings, cardboard orifices with various size holes were placed over the external blower entrance, until that entrance was wide open. Subsequently, the external blower was started, and readings were taken with it running at a number of speeds. The form of curves thus obtained is shown in Fig. 9, the meaning of the three curves being there indicated. One of the limitations imposed by ventilation tests as usually made on an alternator is that only one point on the inner end-bell pressure — volume curve is obtained — nearly that at D in Fig. 9. The data thereby obtained do not enable the designer to estimate the volumes when conditions out of the ordinary are introduced; these would include, for example, the resistance of external ducts of a cooler, or of the influence of greater or less axial length, or of the effect of change in fan proportions, etc. The effects of these and the influence of the structural changes are treated in the paper. At one or more volumes on the pressure-volume curve, volume distribution curves were taken, and from data thereby obtained the influence of axial length was allowed for in the equations derived. In interpreting the results, it is important to eliminate some independent variables. Thus angular velocity may be eliminated, as the pressure is proportional to the square and the volume to the first power of the speed, the shape of volume distribution curve remaining the same. Ample experimental verification was obtained. Machine dimensions were more uncertain, and after many tests, it appears that for a given value of end-bell pressure and angular velocity, the volume distribution for the shorter machine is substantially the same as for the longer machine with the ends removed. As those tests were many, the number of vents, (or length of machine) is considered in the following list of the 11 structural independent variables: (1) Number of poles; (2) fans; (3) number of vents; (4) wedges in stator; (5) interpolar spaces; (6) fan seals; (7) fan shroud rings; (8) field coil braces; (9) plates in end-bells; (10) round and square pole corners; (11) location of fans, data for Nos. 4, 8, and 11 are not given in this paper, and not all for No. 2. There were several unusual results obtained, such as breaks in some of the pressure volume curves for four poles. Data are given for various fans, and also without fans, for both numbers of poles. For twelve poles centrifugal and axial (or “scoop”) fans were studied. In Appendixes 1 and 2, derivations of the more important equations for resistance and volume distribution are given. Appendix 3 covers a method for allowing for air flow through holes back of the core, for various fans and for external pressure drops. In Appendix 4 the equations for parabolic volume distribution and the method of least squares appear.