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

Toge, Tegegn Dejene; Pradeep, A. M.

doi:10.1155/2015/641601

Cited by 9 publications

(5 citation statements)

References 28 publications

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“…They were able to predict the stall using the transition of the second harmonic signal obtained from the frequency analyses. Tegegn and Pradeep 16 analysed the unsteady casing static pressure measurements using wavelet transforms to understand the stall inception mechanism in a high-aspect ratio contra-rotating fan stage. Stall inception was observed to occur through LLSDs for both rotors.…”

Section: Introductionmentioning

confidence: 99%

Stall inception mechanisms in a contra-rotating fan operating at different speed combinations

Manas

Pradeep

2019

Proceedings of the Institution of Mechanical Engineers, Part A:

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Contra-rotating fan is a concept that can possibly replace the present-day conventional fans due to its several aerodynamic advantages. It has the potential to improve the stability limit and can achieve a higher pressure ratio per stage. One of the advantages of a contra-rotating fan is its capability to operate both the rotors at different speeds. In the present study, experiments are carried out at different speed combinations of the rotors and the stall inception phenomenon is captured using high-response unsteady pressure sensors placed on the casing upstream of the leading edge of rotor-1. The unsteady pressure data are investigated using wavelet and Fourier analysis techniques. It is observed that the mechanism of stall inception is different for different speed combinations. The pre-stall disturbances fall in different frequency ranges for different speed combinations. For the range of speed combinations investigated, the frequency of appearance of stall cells of rotor-1 does not depend on the speed of rotor-2. A higher speed of rotation of rotor-1 leads to a higher frequency of appearance of stall cells and a lower speed of rotation of rotor-1 leads to a lower frequency of appearance of stall cells. For all the speed combinations, there is a range of frequency where no disturbance is observed and this range is termed as the ‘no-disturbance zone’. Disturbances are observed at lower frequencies and at frequencies close to the blade passing frequency. In order to understand the flow physics in detail, computational analysis is carried out for different speed combinations of the rotors. For a higher speed of rotor-2, it is observed that the suction effect of rotor-2 is significant enough to pull the tip-leakage flow towards the axial direction. Thus, the suction effect of rotor-2 plays a significant role in determining the stall of the stage.

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Section: Introductionmentioning

confidence: 99%

Stall inception mechanisms in a contra-rotating fan operating at different speed combinations

Manas

Pradeep

2019

Proceedings of the Institution of Mechanical Engineers, Part A:

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“…This phenomenon is referred to as "stall" caused by an increase in incidence angle due to a decrease in flow rate. When an axial fan enters the stall region during operation, significant energy loss, vibration, and noise are generally caused [37,38]; thus, at least at the designed flow rate, the stall region should be avoided from the viewpoint of saving energy and increasing lifetime for an axial fan. The axial fan of this study was not related to the stall region near the design flow rate.…”

Section: Validation For Numerical Analysismentioning

confidence: 99%

Numerical Investigation of Performance and Flow Characteristics of a Tunnel Ventilation Axial Fan with Thickness Profile Treatments of NACA Airfoil

Kim

Lee²,

Lee

et al. 2020

Energies

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An axial flow fan, which is applied for ventilation in underground spaces such as tunnels, features a medium–large size, and most of the blades go through the casting process in consideration of mass production and cost. In the casting process, post-work related to roughness treatment is essential, and this is a final operation to determine the thickness profile of an airfoil which is designed from the empirical equation. In this study, the effect of the thickness profile of an airfoil on the performance and aerodynamic characteristics of the axial fan was examined through numerical analysis with the commercial code, ANSYS CFX. In order to conduct the sensitivity analysis on the effect of the maximum thickness position for each span on the performance at the design flow rate, the design of experiments (DOE) method was applied with a full factorial design as an additional attempt. The energy loss near the shroud span was confirmed with a quantified value for the tip leakage flow (TLF) rate through the tip clearance, and the trajectory of the TLF was observed on the two-dimensional (2D) coordinates system. The trajectory of the TLF matched well with the tendency of the calculated angle and correlated with the intensity of the turbulence kinetic energy (TKE) distribution. However, a correlation between the TLF rate and TKE could not be established. Meanwhile, the Q-criterion method was applied to specifically initiate the distribution of flow separation and inlet recirculation. The location accompanying the energy loss was mutually confirmed with the axial coordinates. Additionally, the nonuniform blade loading distribution, which was more severe as the maximum thickness position moved toward the leading edge (LE), could be improved significantly as the thickness near the trailing edge (TE) became thinner. The validation for the numerical analysis results was performed through a model-sized experimental test.

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“…3,4 Rotor speed ratio, rotor stagger, axial spacing between the rotors, tip clearance, and solidity are the most important parameters on the performance of contra-rotating fans. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] In the investigation performed by Nouri et al 4 and Mistry and Pradeep, 6 the effect of axial gap between rotors is studied. Results reveal that this parameter does not affect the fan performance considerably.…”

Section: Introductionmentioning

confidence: 99%

“…Flow instabilities in contra-rotating fans have been studied numerically and experimentally by a number of researchers. [7][8][9][10][11][12][13] Dejene Toge and Pradeep 8 studied the stall inception of a low-speed contra-rotating fan, experimentally. It was shown that the rear rotor was critical and limited the fan operability.…”

Section: Introductionmentioning

confidence: 99%

Impact of solidity and speed ratio on the performance of a contra-rotating fan

Shahriyari,

Khaleghi,

Sadoddin

et al. 2023

Proceedings of the Institution of Mechanical Engineers, Part A:

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In this study, the effects of solidity and rotor speed ratio on the performance of a contra-rotating fan are investigated numerically. Simulation results have been validated by experimental tests. The test stand construction and the measurements have been performed according to ISO-5801 standard. In order to investigate the effect of blade solidity, simulations have been conducted with constant blade count of the front rotor and four configurations of the rear rotor (having 6, 8, 12 and 16 blades), and also constant blade count of the rear rotor and three configurations of the front rotor (having 8, 12, and 16 blades). Results suggest that there is an optimum solidity for the rear rotor, which gives maximum pressure rise and efficiency. Furthermore, the effects of the rotor speed ratios have been investigated in this study. It is shown that the speed of the front rotor is more effective on the fan performance, as compared to the rear rotor. Results reveal that the performance drop caused by a 25% reduction in the rear rotor blade count, can be compensated by 5% increase of the front rotor rotational speed. Therefore, a suitable choice of the speed ratio can result in light-weight and high-performance contra-rotating stages.

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

Cited by 9 publications

References 28 publications

Stall inception mechanisms in a contra-rotating fan operating at different speed combinations

Stall inception mechanisms in a contra-rotating fan operating at different speed combinations

Numerical Investigation of Performance and Flow Characteristics of a Tunnel Ventilation Axial Fan with Thickness Profile Treatments of NACA Airfoil

Impact of solidity and speed ratio on the performance of a contra-rotating fan

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