Influence of an Upstream Obstacle on the Flow Characteristics of Axial-Flow Fans

2014 ◽  
Author(s):  
Shinsaku Nakamura ◽  
Masayuki Takahashi ◽  
Kotaro Sato ◽  
Kazuhiko Yokota
Keyword(s):  
Reverse Flow ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Operating Conditions ◽  
Generation Mechanism ◽  
Flow Instabilities ◽  
Positive Slope ◽  
Axial Flow Fan ◽  
Cell Structures ◽  
Performance Curves

System environments vary for axial-flow fans, which are often used under unsuitable operating conditions. In the recent high density design of such equipment, obstacles are being more frequently distributed upstream of the fan to determine a smaller fan size. In this study, an attempt is made to clarify the influence of an obstacle on the flow characteristics of axial-flow fans. In our experiment, blockage disks with various diameters were placed upstream of a typical cooling axial-flow fan. The performance curves of the axial-flow fan with the blockage disks were measured. In addition, the flow instabilities and their cell structures were investigated under typical conditions. The main objectives of the present study are as follows: (1) to evaluate the performance degradation when obstacles are placed upstream of the test fan, (2) to elucidate the causes of a positive slope and reverse flow, and (3) to clarify the generation mechanism of flow instabilities when the blockage disks, which have a larger diameter than the test fan, are used.

Total Unsteadiness Downstream of an Axial Flow Fan With Variable Pitch Blades

2001 ◽  
Vol 124 (1) ◽  
pp. 280-283 ◽  
Author(s):  
Sandra Velarde-Sua´rez ◽  
Rafael Ballesteros-Tajadura ◽  
Carlos Santolaria-Morros ◽  
Eduardo Blanco-Marigorta
Keyword(s):  
Axial Flow ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Major Influence ◽  
Axial Flow Fan ◽  
Variable Pitch ◽  
Fan Performance ◽  
Performance Curves ◽  
Unsteady Operation ◽  
Variable Operating Conditions

Variable pitch axial flow fans are widely used in industrial applications to satisfy variable operating conditions. The change of the blade pitch leads to a different rotor geometry and has a major influence on the unsteady operation of the machine. In this work, an experimental research on an axial flow fan with variable pitch blades has been carried out. First of all, the fan performance curves has been obtained. Then the flow field has been measured at ten radial locations both at the inlet and exit rotor plane using hot wire anemometry. Velocity components and total unsteadiness were determined and analyzed in order to characterize the influence of pitch blade and operating conditions on the flow structure.

Unsteady Flow Analysis of the Stator-Rotor Interaction in an Axial Flow Fan

2003 ◽  
Author(s):  
J. Ferna´ndez Oro ◽  
K. Argu¨elles Di´az ◽  
C. Santolaria Morros ◽  
R. Ballesteros Tajadura
Keyword(s):  
Unsteady Flow ◽  
Flow Analysis ◽  
Flow Characteristics ◽  
Axial Flow ◽  
3D Models ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Axial Flow Fan ◽  
Rotating Blade ◽  
Flow Phenomena

In the usual operation of turbomachinery, some unsteady flow phenomena appear due to the non uniformity of the flow inside the rotor, when observed in the fixed reference frame. These phenomena are often related to the unsteady character of the pressure and velocity fields, which produce oscillating forces on the blades, superimposed to the steady force. These oscillating forces are the main mechanism of noise generation, which appear even at a constant rotational speed and at flow rates where the performance curves are stable. In axial turbomachines, the interaction is due to relative motion between the static and rotating blade rows. Considering the case of a fixed blade row (stator) placed upstream of the rotor, the non uniform flow leaving those blades (usually referred as IGV blades) is observed as an unsteady flow by the rotor blades. The effect of this interaction is the generation of unsteady forces on the rotor blades, which generate vibrations (risk of fatigue failure) and noise, and non-uniformity and unsteadiness of the pressure field, that propagates as an acoustic wave. The first part of this work is a brief description of a URANS numerical modeling of the unsteady flow characteristics of a one-stage subsonic axial flow fan with a reaction degree greater than 1. The focus is placed on the statorrotor interaction performance. Both 2D and 3D models of the fan, with 13 IGV’s and 9 rotor blades, were developed and an unsteady simulation was achieved to carry out the main characteristics of the flow inside the turbomachine. Once the actuating forces are determined, the influence of the radial position, the operating conditions and the distance of the fixed and the rotating blade rows is also analyzed. The final part of the paper is focused over the identification, through the definition of deterministic stresses — related to the characteristic blade-passage frequency of every row — that provoke the interaction between fixed and rotating blade rows and its evolution through time. The object is to obtain, in a stress tensor form, the contribution of the velocity field, that is changing because of the sucessive relative positions between blade rows, to the pressure distribution over the blade surfaces in the interior of the stage. Finally, a map of deterministic stresses and even, deterministic kinetic energy, can be obtained to show the influence of the blade rows in the interaction, unsteady phenomena.

Influence of a Downstream-mounted Blockage Disk on Flow Characteristics of Axial-flow Fan

2016 ◽  
Vol 2016 (0) ◽  
pp. S0520302
Author(s):  
Keiichi OCHIAI ◽  
Shohei SHIMIZU ◽  
Masayuki TAKAHASHI ◽  
Kotaro SATO ◽  
Kazuhiko YOKOTA
Keyword(s):  
Flow Characteristics ◽  
Axial Flow ◽  
Axial Flow Fan

scholarly journals Effects of Operating Conditions on the Flow in the Moving Blade Passage of a Single Stage Axial-Flow Fan

1997 ◽  
Vol 3 (4) ◽  
pp. 269-276 ◽  
Author(s):  
Tsutomu Adachi ◽  
Yutaka Yamashita ◽  
Kennichiro Yasuhara ◽  
Tatsuo Kawai
Keyword(s):  
Three Dimensional ◽  
Axial Flow ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Hot Wire ◽  
Axial Flow Fan ◽  
Blade Passage ◽  
Operational Conditions ◽  
Flow Phenomena ◽  
Steady Velocity

Three dimensional steady and unsteady velocity distributions in the axial flow fan were measured using a hot wire probe for various operational conditions, various rotational speeds and various measuring positions. For measuring the velocity distributions in the blade passage, a specially designed and manufactured hot wire traversing apparatus was used. Steady velocity distributions, turning angles, effects of incident to the cascade, flow leakage through the tip clearance and effects of the flow separation show the flow phenomena through the blade passages. Unsteady velocity distributions show time dependent procedures of the wake flowing through the moving blade passage. Considering these results of measurements, the effects of the upstream stationary blade and the effects of Reynolds number on the flow were considered.

scholarly journals Investigation of the Flow Field in the Vicinity of an Axial Flow Fan During Low Flow Rates

2014 ◽  
Author(s):  
Francois G. Louw ◽  
Theodor W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Axial Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Low Flow ◽  
Axial Flow Fan ◽  
Free Vortex ◽  
Flow Rates

Large axial flow fans are used in forced draft air cooled heat exchangers (ACHEs). Previous studies have shown that adverse operating conditions cause certain sectors of the fan, or the fan as a whole to operate at very low flow rates, thereby reducing the cooling effectiveness of the ACHE. The present study is directed towards the experimental and numerical analyses of the flow in the vicinity of an axial flow fan during low flow rates. This is done to obtain the global flow structure up and downstream of the fan. A near-free-vortex fan, designed for specific application in ACHEs, is used for the investigation. Experimental fan testing was conducted in a British Standard 848, type A fan test facility, to obtain the fan characteristic. Both steady-state and time-dependent numerical simulations were performed, depending on the operating condition of the fan, using the Realizable k-ε turbulence model. Good agreement is found between the numerically and experimentally obtained fan characteristic data. Using data from the numerical simulations, the time and circumferentially averaged flow field is presented. At the design flow rate the downstream fan jet mainly moves in the axial and tangential direction, as expected for a free-vortex design criteria, with a small amount of radial flow that can be observed. As the flow rate through the fan is decreased, it is evident that the down-stream fan jet gradually shifts more diagonally outwards, and the region where reverse flow occur between the fan jet and the fan rotational axis increases. At very low flow rates the flow close to the tip reverses through the fan, producing a small recirculation zone as well as swirl at certain locations upstream of the fan.

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