scholarly journals A semi-empirical model for predicting the frequency of profile vortex shedding relevant to low-speed axial fan blade sections

2019 ◽  
Author(s):  
Esztella Balla ◽  
Janos Vad
Keyword(s):  
Vortex Shedding ◽  
Empirical Model ◽  
Axial Fan ◽  
Low Speed ◽  
Fan Blade ◽  
Semi Empirical

scholarly journals Profile vortex shedding from low-speed axial fan rotor blades: a modelling overview

2021 ◽  
pp. 095765092110268
Author(s):  
Gábor Daku ◽  
János Vad
Keyword(s):  
Vortex Shedding ◽  
Empirical Model ◽  
Rotor Blades ◽  
Evaluation Methodology ◽  
Future Research ◽  
Axial Fan ◽  
Low Speed ◽  
Simplifying Assumptions ◽  
Set Up ◽  
Semi Empirical

This paper presents an overview of the characteristics potentially influencing the profile vortex shedding (PVS) phenomenon being relevant in noise and vibration of low-speed axial fan rotor blades. Dimensional analysis has been applied to explore the essential dimensionless quantities in a systematic and comprehensive manner. On this basis, limitations have been established, and simplifying assumptions have been set up in terms of PVS investigation. Groups of dimensionless characteristics playing a role in the semi-empirical model for predicting the PVS frequency were identified. The available semi-empirical model and its unique features related to the measurement evaluation methodology and Reynolds number dependence have been outlined. The presented comprehensive analysis provides guidelines from the perspective of transferability of the literature data on PVS from steady, isolated blade profile models to low-speed axial fan rotors. It also results in the formulation of objectives of future research related to PVS.

scholarly journals Experiment-Based Preliminary Design Guidelines for Consideration of Profile Vortex Shedding From Low-Speed Axial Fan Blades

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Gábor Daku ◽  
János Vad
Keyword(s):  
Vortex Shedding ◽  
Design Guidelines ◽  
Preliminary Design ◽  
Axial Fan ◽  
Noise Emission ◽  
Blade Vibration ◽  
Low Speed ◽  
Blunt Trailing Edge ◽  
Axial Fans ◽  
Semi Empirical

Abstract This paper presents hot-wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for the consideration of profile VS in preliminary design of axial fans in the moderation of VS-induced blade vibration and noise emission.

scholarly journals Experiment-Based Preliminary Design Guidelines for Consideration of Profile Vortex Shedding From Low-Speed Axial Fan Blades

2020 ◽  
Author(s):  
Gábor Daku ◽  
János Vad
Keyword(s):  
Vortex Shedding ◽  
Design Guidelines ◽  
Preliminary Design ◽  
Axial Fan ◽  
Noise Emission ◽  
Blade Vibration ◽  
Low Speed ◽  
Blunt Trailing Edge ◽  
Axial Fans ◽  
Semi Empirical

Abstract The paper presents hot wire measurements in a wind tunnel, close downstream of basic models of blade sections being representative for low-speed, low-Reynolds-number axial fans, in order to explore the signatures of vortex shedding (VS) from the blade profiles. Using the Rankine-type vortex approach, an analytical model was developed on the velocity fluctuation represented by the vortex streets, as an aid in evaluating the experimental data. The signatures of profile VS were distinguished from blunt-trailing-edge VS based on Strouhal numbers obtained from the measurements in a case-specific manner. Utilizing the experimental results, the semi-empirical model available in the literature for predicting the frequency of profile VS was extended to low-speed axial fan applications. On this basis, quantitative guidelines were developed for consideration of profile VS in preliminary design of axial fans in moderation of VS-induced blade vibration and noise emission.

scholarly journals Preliminary Design Guidelines for Considering the Vibration and Noise of Low-Speed Axial Fans Due to Profile Vortex Shedding

2022 ◽  
Vol 7 (1) ◽  
pp. 2
Author(s):  
Gábor Daku ◽  
János Vad
Keyword(s):  
Vortex Shedding ◽  
Design Method ◽  
Axial Flow ◽  
Design Guidelines ◽  
Worst Case ◽  
Low Speed ◽  
Increased Risk ◽  
Axial Fans ◽  
Fan Blade ◽  
Set Up

This paper presents a critical overview on worst-case design scenarios for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in twofold approaches of blade mechanics and aerodynamics. For these purposes, the frequency of the first bending mode of a plate of arbitrary circular camber is expressed by modeling the fan blade as a cantilever beam. Furthermore, an iterative blade design method is developed for checking the risky scenarios for which spanwise and spatially coherent shed vortices, stimulating pronounced vibration and noise, may occur. Coupling these two approaches, cases for vortex-induced blade resonance are set up. Opposing this basis, design guidelines are elaborated upon for avoiding such resonance. Based on the approach presented herein, guidelines are also developed for moderating the annoyance due to the vortex shedding noise.

Acoustic Resonance in Heat Exchanger Tube Bundles—Part II: Prediction and Suppression of Resonance

1987 ◽  
Vol 109 (3) ◽  
pp. 282-288 ◽  
Author(s):  
R. D. Blevins ◽  
M. M. Bressler
Keyword(s):  
Experimental Data ◽  
Heat Exchanger ◽  
Vortex Shedding ◽  
Empirical Model ◽  
Acoustic Resonance ◽  
Heat Exchanger Tube ◽  
Tube Bundles ◽  
Semi Empirical ◽  
Exchanger Tube

In the first part of this series, experimental data were presented which suggest that the acoustic resonance in heat exchanger tube bundles is tied to periodic vortex shedding from the tubes. In this paper, a semi-empirical model for predicting the onset of resonance is developed. This model is compared with experimental data and other models from the literature. Methods of suppressing the resonance are developed and experimental data on their effectiveness are presented.

scholarly journals Establishment of a Beamforming Dataset on Basic Models of Low-Speed Axial Fan Blade Sections

2017 ◽  
Vol 61 (2) ◽  
pp. 122 ◽  
Author(s):  
Esztella Balla ◽  
János Vad
Keyword(s):  
Phased Array ◽  
Reynolds Numbers ◽  
Strength Level ◽  
Source Strength ◽  
Axial Fan ◽  
Frequency Bands ◽  
Low Speed ◽  
Noise Characteristics ◽  
Wide Range ◽  
Fan Blade

The paper presents wind tunnel experiments, supplemented with phased array microphone measurements, on 2D basic models of low-speed axial fan blade sections: a flat plate, a cambered plate, and a RAF6-E airfoil. It aims at documenting the establishment of an acoustic beamforming dataset for the three profiles. The phased array microphone measurements offer spatially resolved information on the generated noise. The measurement setup enables the correlation of the streamwise evolution of the blade boundary layer with the associated noise characteristics. The dataset incorporates a wide range of incidence and Reynolds-numbers investigated. The present paper is confined to reporting on experimental results for arbitrarily selected representative incidences, Reynolds numbers, frequency bands, and profiles. The paper outlines a methodology for the evaluation and representation of the beamforming data in the following forms: source strength level based third-octave spectra obtained using background noise subtraction; maps presenting the loci of source strength level maxima; noise source maps for frequency bands of anticipated vortex shedding noise.

scholarly journals Lift and drag force measurements on basic models of low-speed axial fan blade sections

2018 ◽  
Vol 233 (2) ◽  
pp. 165-175 ◽  
Author(s):  
Esztella Balla ◽  
János Vad
Keyword(s):  
Drag Force ◽  
Aerodynamic Force ◽  
Measurement Data ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Force Measurements ◽  
Axial Fan ◽  
Low Speed ◽  
Fan Blade ◽  
Lift And Drag

This paper presents comparative data on the aerodynamic lift and drag of basic model representations of low-speed axial fan blade sections. Three main types of blades are investigated: flat plate, cambered plate and RAF6-E profiled airfoil. Lift and drag force are measured at three different Reynolds numbers (0.6 × 105, 105 and 1.4 × 105) around the threshold value of 105. The measurement data are compared to literature data. The aerodynamic force measurements reveal that, for Reynolds numbers below 105, cambered plate blade sections can be superior to airfoil profiles in terms of aerodynamic efficiency, especially in the high-load range. The effect of leading edge bluntness is also investigated. Leaving the leading edge of cambered plates blunt, tends to be uncritical for low Reynolds numbers at angles of attack between 4° and 10° but is critical at angles between 0° and 4°.

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