Experimental investigation of stall inception of a low speed contra rotating axial flow fan under circumferential distorted flow condition

2017 ◽  
Vol 70 ◽  
pp. 534-548 ◽  
Author(s):  
Tegegn Dejene Toge ◽  
A.M. Pradeep
Keyword(s):  
Experimental Investigation ◽  
Flow Condition ◽  
Axial Flow ◽  
Axial Flow Fan ◽  
Stall Inception ◽  
Low Speed

scholarly journals Experimental Investigation of Stall Inception Mechanisms of Low Speed Contra Rotating Axial Flow Fan Stage

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
Tegegn Dejene Toge ◽  
A. M. Pradeep
Keyword(s):  
Mass Flow ◽  
Wavelet Transforms ◽  
Axial Flow ◽  
Short Length ◽  
Length Scale ◽  
Pressure Data ◽  
Flow Conditions ◽  
Axial Flow Fan ◽  
Stall Inception ◽  
Low Speed

The present paper is an attempt in understanding the stall inception mechanism in a low speed, contra rotating axial flow fan stage, using wavelet transforms. The rotors used in this study have relatively large tip gap (about 3% of the blade span) and aspect ratio of 3. The study was carried out near stall and at stall mass flow conditions for different speed ratios of rotor-2 to rotor-1. Unsteady pressure data from the casing wall mounted sensors are used to understand the stall inception mechanism. The wavelet transform clearly indicates that stall inception occurs mainly through long length scale disturbances for both rotors. It also reveals that short length disturbances occur simultaneously or intermittently in the case of rotor-1. The analysis shows the presence of a strong modal disturbance with 25–80% of the rotor frequency in the case of rotor-1 at the stall mass flow for all the speed combinations studied. The most interesting thing observed in the present study is that the frequency amplitude of the disturbance level is very small for both rotors.

Spike and Modal Stall Inception Patterns in a Variable-pitch Axial-flow Fan

2003 ◽  
Vol 2003.2 (0) ◽  
pp. 27-28
Author(s):  
Takahiro NISHIOKA ◽  
Shuuji KURODA ◽  
Tadashi KOZU
Keyword(s):  
Axial Flow ◽  
Axial Flow Fan ◽  
Variable Pitch ◽  
Stall Inception

Effects of Compact Radial-Vaned Air Separators on Stalling Characteristics of an Axial-Flow Fan

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Nobuyuki Yamaguchi ◽  
Masayuki Ogata ◽  
Yohei Kato
Keyword(s):  
Axial Length ◽  
Critical Size ◽  
Axial Flow ◽  
Leading Edge ◽  
Flat Plates ◽  
Axial Flow Fan ◽  
Low Speed ◽  
Geometrical Dimensions ◽  
Stall Prevention ◽  
Inlet Opening

The stall-prevention effect of air separators incorporating radial vanes in place of the existing axial vanes was investigated on a low-speed, single-stage, lightly loaded axial-flow fan for effective and compact air separators of a simplified structure. From the survey, paying attention to several geometrical dimensions of the device, the following conclusions are obtained: (1) Simplified radial vanes made of flat plates could show strong stall-prevention effect comparable to those of the curved-vane type one. The most favorable ones showed no stall up to the fan shut-off conditions. (2) Radial heights of the recirculation passage within the air separator showed significant influences on the stall improvement. It should be larger than some critical size experimentally given in the study. (3) The axial length of the device should be larger than some critical size given experimentally in the study. Too much reduced axial length could give rise to an abrupt loss in the effect. (4) The optimum axial locations of the rotor-tip blade leading edge within the device inlet opening were found to lie near the center of the width of the inlet opening from both aspects of stall improvement and fan efficiency.

scholarly journals A Model to Predict Stall Inception of Transonic Axial Flow Fan/Compressors

2011 ◽  
Vol 24 (6) ◽  
pp. 687-700 ◽  
Author(s):  
Xiaofeng SUN ◽  
Dakun SUN ◽  
Weiwei YU
Keyword(s):  
Axial Flow ◽  
Axial Flow Fan ◽  
Stall Inception

Stall Inception, Evolution and Control in a Low Speed Axial Fan With Variable Pitch in Motion

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Stefano Bianchi ◽  
Alessandro Corsini ◽  
Luca Mazzucco ◽  
Lucilla Monteleone ◽  
Anthony G. Sheard
Keyword(s):  
Pressure Fluctuations ◽  
Axial Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Variable Pitch ◽  
Stall Inception ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall ◽  
Stagger Angle

Obtaining the right pitch in turbomachinery blading is crucial to efficient and successful operations. Engineers adjust the rotor’s pitch angle to control the production or absorption of power. Even for low speed fans this is a promising tool. This paper focuses on the inception and the evolution of the flow instabilities in the tip region which drive the stall onset in low speed axial fans. The authors conducted an experimental study to investigate the inception patterns of rotating stall evolution at different rotor blade stagger-angle settings with the aim of speculating on stable operating margin. The authors drove the fan to stall at the design stagger-angle setting and then operated the variable pitch mechanism in order to recover the unstable operation. They measured pressure fluctuations in the tip region of the low-speed axial-flow fan fitted with a variable pitch in motion mechanism, with flush mounted probes. The authors studied the flow mechanisms for spike and modal stall inceptions in this low-speed axial-flow fan which showed relatively small tip clearance. The authors cross-correlated the pressure fluctuations and analyzed the cross-spectra in order to clarify blade pitch, end wall flow, and tip-leakage flow influences on stall inception during the transient at the rotor blades’ different stagger-angle settings. The authors observed a rotating instability near the maximum pressure-rise point at both design and low stagger-angle settings. The stall inception patterns were a spike type at the design stagger-angle setting as a result of the interaction between the incoming flow, tip-leakage flow and end wall backflow.

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.

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