CFD - Based Investigation of Effects of Obstruction in Front of Small Axial Cooling Fan and Deterioration of Supply Flow Rate

2021 ◽  
Author(s):  
Tetsushi Fukuda ◽  
Yukio Masuda ◽  
Takashi Fukue ◽  
Yasuhiro Sugimoto ◽  
Tomoyuki Hatakeyama ◽  
...  
Keyword(s):  
Flow Pattern ◽  
Flow Rate ◽  
Pressure Rise ◽  
Leading Edge ◽  
Rotating Stall ◽  
High Density ◽  
Electronic Equipment ◽  
Fan Performance ◽  
Cooling Fan ◽  
High Density Packaging

Abstract This study describes the deterioration of a small axial fan’s supply flow rate in high-density packaging electronic equipment. A cooling fan flow rate can be predicted by its P-Q curve, which shows a relationship between a pressure rise at a fan (ΔP) and a supply flow rate (Q). However, in high-density packaging electronic equipment, the fan performance is affected by the mounting components around the fans, and the accurate prediction of the supply flow rate becomes difficult. This paper tried to do flow visualization around a small axial cooling fan’s impellers when the obstruction was mounted in front of the fan through CFD analysis. A relationship between the supply flow rate by the fan and the flow pattern around the impellers was investigated while changing the distance between the test fan and the obstruction. Through this study, the following results can be obtained. The fan’s flow is stable in the rotating stall region and the higher flow rate operating points regardless of whether or without the obstruction. At the lower flow rate conditions, the formation of a complex unsteady flow is reproduced. As the flow rate decreases, the flow’s separation point becomes closer to the leading edge of the impeller. In the case of obstruction, the change of the flow pattern causes a larger attack angle. As a result, fan performance is degraded.

Study on P-Q Curves of Cooling Fans for Thermal Design of Electronic Equipment (Effects of Opening Position of Obstructions Near a Fan)

2011 ◽  
Author(s):  
Takashi Fukue ◽  
Masaru Ishizuka ◽  
Tomoyuki Hatakeyama ◽  
Shinji Nakagawa ◽  
Katsuhiro Koizumi
Keyword(s):  
Flow Rate ◽  
Perforated Plate ◽  
Pressure Rise ◽  
High Density ◽  
Thermal Design ◽  
Electronic Equipment ◽  
Flow Passage ◽  
Fan Performance ◽  
Cooling Fan ◽  
Cooling Fans

This study describes an operation pressure and supplies flow rate of an axial cooling fan installed in high-density packaging electronic equipment. Fan performance is generally defined by their P-Q curve, specifically, a relationship between fan pressure rise (ΔP) and flow rate (Q). A compact cooling fan often operates in a high-density mounting device, which may decrease the fan performance. In this study, we focus on an obstruction near a fan, which is electronic components such as PCBs, capacitors and heat sinks, as one of a factor which decreases fan performance. We installed a perforated plate which simulated the above components near a fan and measured the P-Q curve. To investigate a relationship between a fan performance decrease and an opening position near the fan, a part of the perforated plate was closed. Closed position was changed and explored an opening condition which caused the dominant fan performance decrease. From experiments, it was found that the fan performance was decreased when flow passage in front of a fan was blocked by an obstruction. Especially, when flow passage in front of a fan hub was blocked, a dominantly reduction of fan pressure was caused. An obstruction rear a fan has no effect on a fan performance curve itself. In addition, opening conditions in front of a fan tip had a little influence on a fan pressure characteristic when there was no obstruction in front of a hub.

An Experimental Study of Stall Suppression and Associated Changes to the Flow Structures in the Tip Region of an Axial Low Speed Fan Rotor by Axial Casing Grooves

2017 ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Subhra Shankha Koley ◽  
Nick Doeller ◽  
Joseph Katz
Keyword(s):  
Flow Rate ◽  
Large Scale ◽  
Pressure Rise ◽  
Leading Edge ◽  
Suction Side ◽  
Rotating Stall ◽  
Flow Structures ◽  
Flow Angle ◽  
Low Speed ◽  
Flow Characterization

The effects of axial casing grooves on the performance and flow structures in the tip region of an axial low speed fan rotor have been studied experimentally in the JHU refractive index-matched liquid facility. The four-per-passage semicircular grooves are skewed by 45° in the positive circumferential direction, and have a diameter of 65% of the rotor blade axial chord length. A third of the groove overlaps with the blade front, and the rest extends upstream. These grooves have a dramatic effect on the machine performance, reducing the stall flow rate by 40% compared to the same machine with a smooth endwall. However, they reduce the pressure rise at high flow rates. The flow characterization consists of qualitative visualizations of vortical structures using cavitation, as well as stereo-PIV (SPIV) measurements in several meridional and (z,θ) planes covering the tip region and interior of the casing grooves. The experiments are performed at a flow rate corresponding to pre-stall conditions for the untreated machine. They show that the flow into the downstream sides of the grooves and the outflow from their upstream sides vary periodically. The inflow peaks when the downstream end is aligned with the pressure side (PS) of the blade, and decreases, but does not vanish, when this end is located near the suction side (SS). These periodic variations have three primary effects: First, substantial fractions of the leakage flow and the tip leakage vortex (TLV) are entrained periodically into the groove. Consequently, in contrast to the untreated flow, The TLV remnants remain confined to the vicinity of the entrance to the groove, and the TLV strength diminishes starting from the mid-chord. Second, the grooves prevent the formation of large scale backflow vortices (BFVs), which are associated with the TLV, propagate from one blade passage to the next, and play a key role in the onset of rotating stall in the untreated fan. Third, the flow exiting from the grooves causes periodic variations of about 10° in the relative flow angle around the blade leading edge, presumably affecting the blade loading. The distributions of turbulent kinetic energy provide statistical evidence that in contrast to the untreated casing, very little turbulence originating from a previous TLV, including the BFVs, propagates from the PS to the SS of the blade. Hence, the TLV-related turbulence remain confined to the entrance to groove. Elevated, but lower turbulence is also generated as the outflow from the groove jets into the passage.

A Model for Stall and Surge in Low-Speed Contra-Rotating Fans

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Mohammad Javad Shahriyari ◽  
Hossein Khaleghi ◽  
Martin Heinrich
Keyword(s):  
Rotational Speed ◽  
Current Model ◽  
Characteristic Curve ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Negative Slope ◽  
Initial Slope ◽  
Speed Ratio ◽  
Low Speed ◽  
Fan Performance

This paper reports on a theory for poststall transients in contra-rotating fans, which is developed from the basic Moore–Greitzer theory. A second-order hysteresis term is assumed for the fan pressure rise, which gives the theory more capabilities in predicting the fan instabilities. The effect of the rotational speed ratio of the two counter rotating rotors on the fan performance during the occurrence of surge and rotating stall are studied (the rotational speed of the front rotor is assumed to be kept constant whereas the speed of the rear rotor is variable). One of the new capabilities of the current model is the possibility of investigating the effect of the initial slope on the fan characteristic. Results reveal that unlike the conventional fans and compressors, in the current contra-rotating fan stall cannot be initiated from the negative slope portion of the fan pressure rise characteristic curve. One of the important advantages of the developed model is that it enables investigation of the effect of the rate of throttling on the instabilities. Results show that more the rotational speed of the rear rotor, the more robust to surge (caused by throttling) the fan is.

Axial Fan Performance With Blade-Base Clearance

1983 ◽  
Author(s):  
T. Wright
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Axial Fan ◽  
Fan Performance

A study to evaluate the influence of increasing the clearance between blade and hub on a controllable pitch axial fan (CPAF) is presented. Fan performance was measured over a range of increasing clearance for several settings of blade pitch angles. The resulting variations of pressure rise, flow rate and efficiency have been correlated as functions of established clearance parameters with good results. The study shows that large base clearances may result in reductions in efficiency and flow rate of 5 percent or greater in a typical CPAF configuration.

Numerical Investigation of the Influence of Impeller-Diffuser Gap (A- and B-Gaps) on Unsteady Flow in a Centrifugal Pump at Part Flows

2019 ◽  
Author(s):  
Taiki Takamine ◽  
Satoshi Watanabe
Keyword(s):  
Unsteady Flow ◽  
Centrifugal Pump ◽  
Flow Rate ◽  
Internal Flow ◽  
Leading Edge ◽  
High Energy ◽  
Rotating Stall ◽  
Rotor System ◽  
The Other ◽  
High Energy Density

Abstract Because of the high energy density of multi-stage centrifugal pump, it is really important to ensure the reliability of the pumps thus the stability of rotor system in the wide flow rate range. Rotating stall is a well-known unsteady flow phenomenon in which one or several stall cell structures propagate circumferentially in impeller and/or diffuser. Rotating stall alters the peripheral pressure distribution of rotors, and therefore it is often regarded as one of the primary trigger of unstable fluid force acting on the rotor system. One possible factor which could affect the rotating stall is a geometrical relationship between the rotor and the stator. In the present study, unsteady RANS simulations of internal flow in a centrifugal pump are carried out. The pump is the partial model of the final stage of the three-stage centrifugal pump used in our previous study. In order to investigate the effect of the gap between impeller trailing edge and diffuser leading edge on the unsteady flow of the pump, three cases of impeller-diffuser gap is simulated; one is the smaller gap case with original impeller. The other cases are two larger gap cases with only cutting the impeller blades and with cutting the both impeller blades and impeller shroud walls. For all gap cases, the computations are conducted for the nominal flow rate and the low flor rate with 10% of the nominal flow rate. As a result, the rotating stall is observed only in the larger gap case with the cut shroud walls, indicating that the key phenomenon for the stable formation of the stall cell is not only the weakened rotor-stator interaction, but also the other phenomenon attributed to the enlarged gap between the impeller shroud walls and the diffuser walls. In the shroud cut case, a part of the main flow blocked by the stalled region and the secondary flow on the diffuser walls tend to flow into the side gaps more easily than other cases. They might be the important phenomenon associated with the diffuser rotating stall in the enlarged wall gap condition.

Axial Fan Performance With Blade-Base Clearance

1984 ◽  
Vol 106 (4) ◽  
pp. 901-905
Author(s):  
T. Wright
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Axial Fan ◽  
Fan Performance

A study to evaluate the influence of increasing the clearance between blade and hub on a controllable pitch axial fan (CPAF) is presented. Fan performance was measured over a range of increasing clearance for several settings of blade pitch angles. The resulting variations of pressure rise, flow rate, and efficiency have been correlated as functions of established clearance parameters with good results. The study shows that large base clearances may result in reductions in efficiency and flow rate of 5 percent or greater in a typical CPAF configuration.

Fluctuation of Inducer Recirculation Stemming From Diffuser Stall in Centrifugal Turbomachinery Near Surge Condition

2020 ◽  
Author(s):  
Kazuhiro Tsukamoto ◽  
Chisachi Kato
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Time History ◽  
Rotating Stall ◽  
Centrifugal Impeller ◽  
Performance Curve ◽  
Positive Slope ◽  
Lower Flow ◽  
Suction Pipe ◽  
Lower Flow Rate

Abstract This work investigates the unsteady fluctuation of inducer recirculation stemming from the diffuser stall that occurs near the surge condition. Experiments and unsteady numerical simulation were utilized for the investigation. Inducer recirculation is known to occur near the surge occurrence flow rate, where the flow rate has a positive slope of the performance curve and the recirculation extends to the upstream of the impeller inlet when decreasing the flow rate more. However, few papers have investigated the unsteady phenomenon of the recirculation, even though the surge is what causes it. Clarifying the recirculation phenomenon is essential in terms of expanding the operation range to the lower flow rate for centrifugal turbomachinery. This was our motivation for investigating the unsteady oscillation phenomenon of the inducer recirculation. We investigated a single-stage centrifugal blower with the maximum pressure rise ratio of 1.2 and focused on the flow rates near surge occurrence. The blower was equipped with an open type centrifugal impeller, a vane-less diffuser, and a scroll casing. The blower performance and pressure time-history data were obtained by experiments. Unsteady simulations using large eddy simulation (LES) were conducted to investigate the flow field in the blower for each flow rate. The obtained performance curve showed that the positive slope of the pressure rise at the lower flow rate was due to the impeller stall and that the inducer recirculation extending upstream of the suction pipe near the slope of the curve was flat. LES analysis revealed that this inducer recirculation had two typical fluctuation peaks, one at 20% of the rotation frequency and the other at 95%. We also found that the stall cell at the impeller inlet propagated in the circumferential direction and swirled at almost the same frequency as the impeller rotation. In addition, the fluctuation at the diffuser derived from the diffuser rotating stall propagated to the suction pipe.

Influence of Rotating Instability on Stall Inception Patterns in a Variable-Pitch Axial-Flow Fan

2006 ◽  
Author(s):  
Takahiro Nishioka ◽  
Shuuji Kuroda ◽  
Tsukasa Nagano ◽  
Hiroshi Hayami
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Pressure Rise ◽  
Leading Edge ◽  
Rotating Stall ◽  
Axial Flow Fan ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Stagger Angle

An experimental study was conducted to investigate the inception patterns of rotating stall at different rotor blade stagger-angle settings with the aim of extending the stable operating range for a variable-pitch axial-flow fan. Pressure and velocity fluctuations were measured for a low-speed axial-flow fan with a relatively large tip clearance. Two stagger-angle settings were tested, the design setting, and a high setting which was 10 degrees greater than the design setting. Rotating instability (RI) was first observed near the peak pressure-rise point at both settings. It propagated in the rotation direction at about 40 to 50% of the rotor rotation speed, and its wavelength was about one rotor-blade pitch. However, the stall-inception patterns differed between the two settings. At the design stagger-angle setting, leading edge separation occurred near the stall-inception point, and this separation induced a strong tip leakage vortex that moved upstream of the rotor. This leakage vortex simultaneously induced a spike and a RI. The conditions for stall inception were consistent with the simple model of the spike-type proposed by Camp and Day. At the high stagger-angle setting, leading edge separation did not occur, and the tip leakage vortex did not move upstream of the rotor. Therefore, a spike did not appear although RI developed at the maximum pressure-rise point. This RI induced a large end-wall blockage that extended into the entire blade passage downstream of the rotor. This large blockage rapidly increased the rotor blade loading and directly induced a long length-scale stall cell before a spike or modal disturbance appeared. The conditions for stall inception were not consistent with the simple models of the spike or modal-type. These findings indicate that the movement of the tip leakage vortex associated with the rotor blade loading affects the development of a spike and RI and that the inception pattern of a rotating stall depends on the stagger-angle setting of the rotor blades.

The Unsteady Pre-Stall Behavior of the Spike-Type Rotating Stall Within an Airfoil Vaned-Diffuser

2018 ◽  
Author(s):  
Jiayi Zhao ◽  
Guang Xi ◽  
Zhiheng Wang ◽  
Yang Zhao
Keyword(s):  
Pressure Rise ◽  
Leading Edge ◽  
Suction Side ◽  
Rotating Stall ◽  
Vaned Diffuser ◽  
Stall Inception ◽  
Impeller Outlet ◽  
Inception Point ◽  
Transient Measurement ◽  
Couple Effect

The spike-type rotating stall (RS) inception inside the vaned-diffuser, which seriously restricts the performance range and brings the problems of blade fatigue, still seems to be a ‘mystery’ since its randomness. The paper intends to explain the mechanisms of this stall inception. To quantitatively assess the critical unsteady behavior to the initiation of RS inception, the transient measurement characterizes the process falling into the RS through the parameter of ‘blade passing irregularity’. The underlying vortex disturbance, related to the growing of the flow complexity and the final spike-type precursor, is further revealed by the full-annulus simulation. The results show the propagation principle of the vortexes from the design to the stall inception point, reflected by the distribution of ‘blade passing irregularity’. The performance change of different sub-components due to the vortex behavior is presented. At the RS limit, the sudden ramp-up of the ‘blade passing irregularity’ near the leading edge (LE), accompanied with the drop of the static pressure rise in the sub-component between the semi-vaneless and throat, corresponds to the spike-type inception in the form of a clockwise vortex connecting the suction side of the diffuser vane and the pressure side of the adjacent vane. Besides, when approaching the spike-type inception point, the couple effect of the growing potential of the diffuser vane and the enhanced vortex disturbance at the impeller outlet degrades the diffuser inlet flow.

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