PIV Measurements of the Effects of Geometric Scale on Electronics Cooling Axial Fan Flow

2007 ◽  
Author(s):  
Ronan Grimes ◽  
David Quin ◽  
Edmond Walsh ◽  
Jeff Punch
Keyword(s):  
Velocity Distribution ◽  
Axial Flow ◽  
Electronics Cooling ◽  
Thermal Design ◽  
Small Scale ◽  
Axial Fan ◽  
Flow Angle ◽  
Piv Measurements ◽  
Cooling Fan ◽  
Macro Scale

The emergence of highly functional portable electronic systems in recent times means that passive dissipation of heat in these devices may not be an option in the near future. Micro fan technology is currently being developed to address this emerging need. Past investigations by the current authors indicate that the reduction of scale of conventional electronics cooling fan design to the mini scale does not excessively impair the bulk pressure flow performance of the fan. However, the detailed velocity distribution at the outlet of mini scale axial flow fans is unknown, and so effective thermal design in systems which use mini scale fans may be difficult, as the designer does not know the path taken by the flow emerging from the fan. To address this issue, this paper presents PIV measurements performed at the outlet of a series of geometrically similar axial flow fans, whose diameters range from 120 to 6mm, and whose design is based on that of a commercially available macro scale electronics cooling fan. The measurements show that as fan scale is reduced, there is a significant change in the fan outlet velocity distribution, and a large increase in the outlet radial flow angle. As a result, a designer using a small scale axial flow fan must be aware that the region downstream of the fan, where one would normally expect high velocity flow, will in fact be uncooled. Therefore, components should be mounted radially downstream of the fan, where highest air velocities are shown to exist.

Advances in Fan Modeling: Using Multiple Reference Frame (MRF) Approach on Blowers

2011 ◽  
Author(s):  
Gokul Shankaran ◽  
M. Baris Dogruoz
Keyword(s):  
Reference Frame ◽  
Axial Flow ◽  
Flow Region ◽  
Pressure Head ◽  
Thermal Design ◽  
Axial Fan ◽  
Acceptable Error ◽  
Error Margin ◽  
Lumped Models ◽  
Multiple Reference

Forced convection air-cooled electronic systems utilize fans to sustain air flow through the enclosure. These fans are typically axial flow fans, radial impellers, and centrifugal blowers. When computing flow fields in electronic enclosures, axial fans have traditionally been abstracted as lumped fan models which may or may not be able to capture the necessary details. Under certain conditions, such lumped models may also capture some flow characteristics in the case of impellers and centrifugal blowers. These lumped models comprise a significantly simplified fan geometry, i.e. usually a planar (2-D) rectangular or circular surface with/without an inner (hub) concentric no-flow region for an axial fan or a rectangular prism/cylinder with a planar inlet for blowers/impellers, and a “pressure head-flow rate” (P-Q) curve, which may be supplied by the fan vendor or experimentally derived by the thermal designer. Irrespective of the source, the P-Q curve is obtained from laboratory experiments that conform to the test codes published by societies such as ASME and AMCA. Convenience and accuracy of lumped fan models are dependent on the specific application, cooling method and also the acceptable error margin. The acceptable error margin of the thermal design has shrunk significantly in the last decade. This has caused an interest in more accurate and robust fan modeling techniques such as Multiple Reference Frame (MRF) model which has already been commonly and successfully used in many different industries for a while. In this paper, an attempt was made to provide a validation of the MRF fan modeling applied to different types of fans. The computational fluid dynamics (CFD) model of an AMCA standard wind tunnel was used for each of the fans investigated. The P-Q curve obtained from the MRF model is benchmarked against the corresponding experimentally derived P-Q curve. Benefits and limitations of the MRF model are also discussed.

Development of an Ultra-Quiet Fan for Computer Cooling Applications

2014 ◽  
Author(s):  
Zhenyu Wang ◽  
Hui Hu
Keyword(s):  
Flow Field ◽  
Noise Reduction ◽  
Sound Pressure ◽  
Field Measurements ◽  
Vortex Structures ◽  
Tip Clearance ◽  
Axial Fan ◽  
Fan Noise ◽  
Piv Measurements ◽  
Cooling Fan

We report the progress made in our recent study to develop an ultra-quiet axial fan for computer cooling applications. By using a commercially-available cooling fan as the baseline, a number of acoustically tailored modifications are implemented in order to reduce the noise level of the cooling fan, which includes optimizing the rotator blades and guide vanes according to axial fan design theory, adding an intake cone in the front of the hub to guide the airflow into the axial fan smoothly, and reducing the tip clearance to lower the noise generation due to tip vortex structures. A comparison study is conducted to measure the sound pressure level (SPL) of the reformed axial fan in an anechoic chamber, in comparison to that of the prototype fan, in order to assess the effects of the modifications on the fan noise reduction. The measurement results of our preliminary study reveal that, at the same flow rate, the SPL of the reformed fan would be up to 5 dB lower than that of the prototype fan. In addition to measuring the sound pressure levels (SPLs) of the fans, a digital particle image velocimetry (PIV) system is also used to conduct detailed flow field measurements to reveal the changes of the flow characteristics and unsteady vortex structures associated with the modifications. Besides conducting “free-run” PIV measurements to determine the ensemble-averaged statistics of the flow quantities such as mean velocity, Reynolds stress, and turbulence kinetic energy (TKE) distributions at the exit of the axial fan, “phase-locked” PIV measurements are also performed to elucidate further details about evolution of the unsteady vortex structures in fan exhaust in relation to the position of the rotating fan blades. The detailed flow field measurements are correlated with the SPL measurements in order to elucidate underlying physics associated with the fan noise reduction.

The Effect of Reynolds Number on Microfan Performance

2004 ◽  
Author(s):  
David Quin ◽  
Ronan Grimes ◽  
Ed Walsh ◽  
Mark Davies ◽  
Stefan Kunz
Keyword(s):  
Reynolds Number ◽  
Heat Dissipation ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Electronic Systems ◽  
Piv Measurements ◽  
Flow Characterization ◽  
Image Velocimetry ◽  
Macro Scale

Miniaturisation of modern electronics means that future compact electronic systems are likely to be too hot to be held in the users hand. Simultaneous increases in heat dissipation will also require the development of novel compact cooling technologies. In systems such as mobile phones and palmtop computers, macro scale fans cannot be used to overcome this problem, as they are too large. As a solution, the implementation of micro fan technology is proposed. Previous investigators have shown that reduction of the Reynolds number of turbomachinery results in reduced efficiency. To experimentally investigate this predicted phenomenon, a series of geometrically similar axial flow fans have been fabricated. These range in size from the macro to the micro scale with the Reynolds numbers varying linearly with fan dimensions. Through detailed Particle Image Velocimetry (PIV) measurements and pressure flow characterization of these fans, this investigation aims to quantify the reduction in efficiency, which occurs as the Reynolds number is reduced. This paper concludes that the extent to which fan efficiency is reduced by Reynolds number is in surprisingly good agreement with relatively simple predictions developed by the authors in previous investigations. Reduced Reynolds number was also seen to alter the velocity distribution at the fan outlet. This is an important point as it indicates a change in the physics of the flow with reducing scale.

Exit Flow Behavior of Axial Fan Flows With/Without Impingement

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
D. Sui ◽  
S. S. Wang ◽  
J. R. Mao ◽  
T. Kim ◽  
T. J. Lu
Keyword(s):  
Flow Behavior ◽  
Axial Flow ◽  
Electronics Cooling ◽  
Wall Pressure ◽  
Axial Fan ◽  
Stagnation Region ◽  
Flow Recirculation ◽  
Plate Spacing ◽  
Flow Interaction ◽  
Plate Center

The exit flow patterns of an axial flow fan widely used in electronics cooling are experimentally characterized both in free exit and in the presence of a flat impingement plate. The axial fan is rotated with 12.0 V input from a dc power supply, leading to a nominal Reynolds number of Re=9.0×103 based on fan diameter. One shear layer each is found to form between the exit flow from the axial fan and the surrounding fluid at rest, and between the exit flow and the flow along the fan axis. In addition to creating a highest wall pressure region (the primary stagnation region), the presence of the flat plate induces a flow recirculation zone (the secondary stagnation region) at the plate center. When the fan exit-to-plate spacing normalized by fan diameter (H/D) equals to about 0.6, the wall pressure is minimized in the secondary stagnation region due to the maximized “recirculation” as a result of intensified flow interaction. Within the range considered (0.2≤H/D≤2.0) and with the case of H/D∼0.6 serving as a reference, the flow interaction tends to be suppressed by the proximity of the plate at H/D=0.2 and weakened due to the momentum dissipation at H/D∼2.0.

scholarly journals Investigation into the Influence of Division Pier on the Internal Flow and Pulsation in the Outlet Conduit of an Axial-Flow Pump

2021 ◽  
Vol 11 (15) ◽  
pp. 6774
Author(s):  
Fan Yang ◽  
Dongjin Jiang ◽  
Tieli Wang ◽  
Pengcheng Chang ◽  
Chao Liu ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Pressure Pulsation ◽  
Axial Flow ◽  
Hydraulic Loss ◽  
Main Frequency ◽  
Starting Position ◽  
The Difference ◽  
Axial Flow Pump ◽  
Outlet Conduit ◽  
Flow Pump

The outlet conduit is an important construction connecting the outlet of the pump guide vane and the outlet pool; in order to study the hydraulic performance of the straight outlet conduit of the axial-flow pump device, this paper adopts the method of numerical simulation and analyzes the influence of the division pier on the pressure and velocity distribution inside and near the wall of the straight outlet conduit based on three design schemes. Four pressure pulsation measuring points were arranged in the straight outlet conduit, and the low-frequency pulsation characteristic information inside the straight outlet conduit with and without the division pier was extracted by wavelet packet reconstruction. The results show that the addition of a division pier has an effect on the hydraulic loss, near-wall pressure and velocity distribution in the straight outlet conduit. A small high-pressure zone is formed near the wall at the starting position of the division pier, and a large high-speed zone is formed on the left side at the starting position of the division pier. The length of the division pier has no significant effect on the flow distribution of the straight outlet conduit and the pressure and velocity distribution near the wall. Under different working conditions, each monitoring point has the maximum energy in the sub-band (0~31.25 Hz). With the increase of the flow rate, the total pressure energy of the straight outlet conduit decreases gradually. Under each condition, the difference of the energy proportion of the horizontal monitoring points of the straight outlet conduit is small, and the difference of the energy proportion of the two monitoring points at the top and bottom of the outlet channel is relatively large. The energy of the two monitoring points in the straight outlet conduit with a division pier is smaller than that of the two monitoring points in the straight outlet conduit without a division pier. There are differences in the main frequency and the power spectrum corresponding to the main frequency of the monitoring points in the straight outlet conduit, and the reasonable setting of the division pier is conducive to reducing the pressure pulsation of the flow in the straight outlet conduit and is beneficial to the safe and stable operation of the pump device.

EFFECT OF AXIAL CASING GROOVE GEOMETRY ON ROTOR-GROOVE INTERACTIONS IN THE TIP REGION OF A COMPRESSOR

2021 ◽  
pp. 1-54
Author(s):  
Subhra Shankha Koley ◽  
Huang Chen ◽  
Ayush Saraswat ◽  
Joseph Katz
Keyword(s):  
Rotor Blade ◽  
Leading Edge ◽  
Secondary Flows ◽  
Low Flow ◽  
Flow Angle ◽  
Flow Rates ◽  
Piv Measurements ◽  
Tip Leakage ◽  
Large Vortex ◽  
Blade Leading Edge

Abstract This experimental study characterizes the interactions of axial casing grooves with the flow in the tip region of an axial turbomachine. The tests involve grooves with the same inlet overlapping with the rotor blade leading edge, but with different exit directions located upstream. Among them, U grooves, whose circumferential outflow opposes the blade motion, achieve a 60% reduction in stall flowrate, but degrade the efficiency around the best efficiency point (BEP) by 2%. The S grooves, whose outlets are parallel to the blade rotation, improve the stall flowrate by only 36%, but do not degrade the BEP performance. To elucidate the mechanisms involved, stereo-PIV measurements covering the tip region and interior of grooves are performed in a refractive index matched facility. At low flow rates, the inflow into both grooves, which peaks when they are aligned with the blade pressure side, rolls up into a large vortex that lingers within the groove. By design, the outflow from S grooves is circumferentially positive. For the U grooves, fast circumferentially negative outflow peaks at the base of each groove, causing substantial periodic variations in the flow angle near the blade leading edge. At BEP, interactions with both grooves become milder, and most of the tip leakage vortex remains in the passage. Interactions with the S grooves are limited hence they do not degrade the efficiency. In contrast, the inflow into and outflow from the U grooves reverses direction, causing entrainment of secondary flows, which likely contribute to the reduced BEP efficiency.

Optimization of Low Noise Blade of Small Axial Fan at Low Reynolds Number

2021 ◽  
Vol 263 (6) ◽  
pp. 236-256
Author(s):  
Peixun Yu ◽  
Junqiang Bai ◽  
Xiao Han
Keyword(s):  
Sound Pressure Level ◽  
Optimization Design ◽  
Sound Pressure ◽  
Computational Cost ◽  
Low Noise ◽  
Pressure Level ◽  
Multidisciplinary Optimization ◽  
Axial Fan ◽  
Aerodynamic Efficiency ◽  
Cooling Fan

A multidisciplinary optimization design to simultaneously enhance the aeroacoustic and aerodynamic performance of an cooling fan is performed. The flow analysis of the cooling fan is conducted by solving three dimensional steady-state RANS equations with shear-stress transport turbulence model. Based on the results of the steady flow, aeroacoustic analysis is performed by using the Hanson and Brooks model. A multi-objective optimization is performed to simultaneously improve the efficiency and reduce the sound pressure level through an improved non-dominated sorting gentic algorithm. A Kriging surrogate model is used to approximate the function value while reducing computational cost. Series of optimum designs on the pareto front yielded increases in efficiency and decreases in the sound pressure level compared to the reference design. Through numerical analysis and experimental test, the aerodynamic efficiency is increased by 5% and the total sound pressure level is reduced by 4dB without loss of air volume for the selected optimized cooling fan. The thining of rotor boundary layer and inward load shift are the main factors to improve aerodynamic efficiency and reduce noise of the cooling fan.

Noise Reduction Analysis of Electronic Device Cooling Fan With Duct and Its Application Under Variable Working Conditions

2021 ◽  
Author(s):  
Zonghan Sun ◽  
Jie Tian ◽  
Grzegorz Liśkiewicz ◽  
Zhaohui Du ◽  
Hua Ouyang
Keyword(s):  
Noise Reduction ◽  
Working Conditions ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Reduction Method ◽  
Axial Flow ◽  
Pressure Level ◽  
Inlet Flow ◽  
Cooling Fan ◽  
Inlet Duct

Abstract A noise reduction method for axial flow fans using a short inlet duct is proposed. The pattern of noise reduction imposed by the short inlet duct on the axial flow cooling fan under variable working conditions was experimentally and numerically examined. A 2-cm inlet duct was found to reduce tonal noise. As the tip Mach number of the fan increased from 0.049 to 0.156, the reduction in the total average sound pressure level at 1 m from the fan increased from 0.8 dB(A) to 4.3 dB(A), and further achieved 4.8 dB(A) when a 1-cm inlet duct was used. The steady computational fluid dynamics (CFD) showed that the inlet duct has little effect on the aerodynamic performance of the fan. The results of the full passage unsteady calculation at the maximum flow rate showed that the duct has a significant influence on the suction vortexes caused by the inlet flow non-uniformity. The suction vortexes move upstream to weaken the interaction with the rotor blades, which significantly reduces the pulsating pressure on the blades. The sound pressure level (SPL) at the blade passing frequency (BPF) contributed by the thrust force was calculated to reduce by 36 dB at a 135° observer angle, reflecting the rectification effect of the duct on the non-uniform inlet flow and the improvement in characteristics of the noise source. The proper orthogonal decomposition (POD) of the static pressure field on the blades verified that the main spatial mode is more uniformly distributed due to the duct, and energy owing to the rotor-inlet interaction decreases. A speed regulation strategy for the cooling fan with short inlet duct is proposed, which provides guidance for the application of this noise reduction method.

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