Squirrel Cage Fan Research Articles

C17 シロッコファンのケーシング内部流動と性能評価(C1 流体工学(空気機械))

C17 シロッコファンのケーシング内部流動と性能評価(C1 流体工学(空気機械))

Reduction of the aerodynamic tonal noise of a forward-curved centrifugal fan by modification of the volute tongue geometry

In this work, an experimental study about the influence of some geometric features on the aeroacoustic behaviour of a squirrel-cage fan, used in automotive air conditioning units, has been carried out. The study focused on the effect of both the shape and the position of the volute tongue on the noise generated by the fan. Different geometric configurations were tested in order to compare the results. First of all, the performance curves were measured in a standardized test facility. Then, the acoustic behaviour of the fan was characterized by means of acoustic pressure measurements near the fan inlet. The comparison of the test results indicated a great dependence of both the shape and the position of the volute tongue and the noise generation. In particular, some geometric configurations of the volute tongue were able to reduce the fan noise generation without reducing the fan operating range.

Performance and laser Doppler anemometry experimental investigation of squirrel cage fans with half-cone rotors

Squirrel cage fans with non-cylindrical rotors, shaped as frustums of right circular cones, are compared with a similar fan but with a cylindrical rotor. Performance measurements for cone angles ranging from -10° to +10° showed that for positive angles, which means that a larger diameter at the rotor inlet decreases towards the back plate, it was possible to have higher fan efficiencies for a similar head. Alternatively, at negative cone angles, the head coefficient could be superior for a similar efficiency. The optimum angles were different for each case. These statements are true for the working part of the performance curves, which is located to the right of the maximum head coefficient. The velocity profiles at selected circumferential positions at the rotor exit showed that the flow did not spread evenly round the rotor when fan geometry was changed or the fan was throttled. If air flowed out of the rotor at a position closer to the fan exit, this flow then travelled a shorter distance inside the volute. A smaller loss and, therefore, a higher efficiency ensued. This pattern was true for both cylindrical and conical rotors and, therefore, the better efficiency for the positive half-cone rotor was a result of the way the rotor and volute combination guided the flow. The negative cone rotor had a higher head as the rotor diameter was larger where the flow passed through the blades.

A study of slip factor and velocity components at the rotor exit of forward-curved squirrel cage fans, using laser Doppler anemometry

Velocity profiles outside the rotor of four squirrel cage fans are measured in order to calculate their local slip factors. They show that the fluid exit angle from the rotor and the blade outlet angle of such fans are very different. Inlet configuration and volute spread angle both affected the direction of the flow out of the rotor and hence the slip factor. The general understanding in centrifugal turbomachines is that more energy transfer per unit mass is equivalent to a larger tangential component of velocity and therefore a larger slip factor. In squirrel cage fans a small slip factor results from a large radial velocity component out of the rotor. This gives a larger volumetric flowrate with no sensible head loss. The advantages of a large incidence angle and a large deviation mean that flow adherence to the blades is not always a prime design criterion in such fans.

Inlet induced flow in squirrel-cage fans

Energy conversion in squirrel-cage fans is sensitive to the inlet geometry. It occurs at the inlet where a separation zone which occupies a major volume in the rotor and the volute starts. In this research, different inlets of inward and outward types were tested on two fans. First, the inlet diamenter and position were matched with the rotor, which improved the fan characteristic curves. The results of the experiments were sensitive to the width of the blade retaining ring (shroud). Later the tangential and radial components of the velocity out of the rotor were measured. The resulting velocity profiles across the scroll width showed that outward inlets produce a more uniform velocity angle inside the volute than inward inlets did. This was not because of a more aerodynamic flow through the rotor blades by was due to a better match between the inlet and the volute. The axial energy transfer resulted in tangential velocities larger than the rotor velocity, at axial positions across the volute where there was no flow out of the rotor.

A new concept for squirrel-cage fan inlet

The squirrel-cage fan with a newly introduced outward inlet lip is studied experimentally. Previous research has demonstrated the importance of inlet flow control on the general flow field and vortex generation of such fans. The bell-mouth inlet, which is the common industrial and academic practice, has drawbacks that result in flow separation and turbulence enhancement. The adapted experimental approach is a conceptual study. It is a combination of standard characteristic measurements and detailed laser Doppler anemometry. The measured flow pattern inside the volute demonstrates that the separated flow behind the inlet lip, which for an ordinary inward lip occupies a large part of the rotor blades, disappears. This is promising since removing this separated flow diminishes a major loss-making region in this fan and adds to the effective flow area. It also reduces noise and gives uniform blade loading. The results also show an improvement in performance in comparison with that of a fan with an ordinary inward inlet lip. This modification is industrially feasible with no extra manufacturing cost and therefore can represent a substantial advance over the current practice.

Prediction of Flow Behavior and Performance of Squirrel-Cage Centrifugal Fans Operating at Medium and High Flow Rates

This paper describes a method for predicting flow behavior and performance for centrifugal fans of the squirrel-cage type. The work is directed at improving under standing of the factors affecting performance of these fans. A simulation approach has been adopted. That is, the fan is subdivided into a number of zones (inlet zone, blading zone, volute zone) and the zones are divided into elements. Flow behavior in the zones and elements and interactions between them are modeled using appropriate equations and correlations. The blading correlations make use of new experimental data for high-solidity cascades of bent sheet metal blades, typical of squirrel-cage fans. Predicted fan performance characteristics are in reasonable agreement with experimental results for flow rates at and above the best-efficiency operating point. Although relatively simple, the method recognizes the main flow phenomena and interactions that occur in squirrel-cage fans and it thus represents a substantial advance over what is currently available in the literature. Together with earlier experimental work, development of the method has provided considerable insight into the relative importance of various aspects of flow behavior. The ability to deal with extensive reverse flow through the rotor blading has not yet been incorporated and it is evident that this ability is essential for realistic prediction of flow behavior and performance at below-design flow rates.

Pyroelectric anemometry: Vector and swirl measurements

The characteristics of a vector pyroelectric anemometer that measures the orthogonal components of mass flow are presented. This anemometer consists of three measuring electrodes and two heater elements on a 6 mm × 6 mm chip that form two orthogonal linear anemometers. The characteristics of a single pair of electrodes forming an in-line linear anemometer are in good agreement with recent measurements and theory. A wall-mounted vector pyroelectric anemometer is used to measure the decay of swirl in air flowing through a 45 mm inner diameter, 5 m long flow system. The swirl flow is produced by a 90° out-of-plane double elbow at the flow system inlet. The tube flow generated by a squirrel-cage fan has a Reynolds number of ≈ 24 000, well into the turbulent regime. Measurements are conducted at the wall at a uniform distance along the length of the flow section for both straight and swirl flow. The measured decay length is ≈ 40 pipe diameters, in good agreement with measurements on water.

Pyroelectric anemometry: Vector and swirl measurements

Abstract The characteristics of a vector pyroelectric anemometer that measures the orthogonal components of mass flow are presented. This anemometer consists of three measuring electrodes and two heater elements on a 6 mm × 6 mm chip that form two orthogonal linear anemometers. The characteristics of a single pair of electrodes forming an in-line linear anemometer are in good agreement with recent measurements and theory. A wall-mounted vector pyroelectric anemometer is used to measure the decay of swirl in air flowing through a 45 mm inner diameter, 5 m long flow system. The swirl flow is produced by a 90° out-of-plane double elbow at the flow system inlet. The tube flow generated by a squirrel-cage fan has a Reynolds number of ≈ 24 000, well into the turbulent regime. Measurements are conducted at the wall at a uniform distance along the length of the flow section for both straight and swirl flow. The measured decay length is ≈ 40 pipe diameters, in good agreement with measurements on water.

Flow in a Centrifugal Fan of the Squirrel-Cage Type

This paper presents the results of performance measurements and detailed measurements of the mean flow field at rotor inlet and rotor exit in three squirrel-cage fan configurations. The flow-field measurements were taken with a five-hole probe and yield total pressure, static pressure, and the three components of velocity. Measurements were taken for two casing throat areas and for two different rotors. For each configuration the flow field was measured for flow rates below, near, and above the best-efficiency point. Flow patterns are complex and there is reverse flow through the rotor blading even at the best-efficiency operating condition. Although complex, the main features of flow behavior can be understood. They were common to all three fan configurations.