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

Balla, Esztella; Vad, János

doi:10.29008/etc2019-311

Cited by 5 publications

(13 citation statements)

References 18 publications

(64 reference statements)

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“…b) Relative roughness (Ψ3 = k/c). As will be demonstrated later, the coefficient CD plays a substantial role in the semi-empirical model for PVS frequency prediction [32,37]. The effect of relative roughness is discussed herein via its influence on CD.…”

Section: ) Results and Discussionmentioning

confidence: 99%

“…As demonstrated in Eq. ( 14), and emphasized already in the Introduction, the benefit of such Strouhal number is that, according to the measurement experiences [14][15]32], it can be regarded as constant.…”

Section: ) Semi-empirical Model For Predicting the Pvs Frequencymentioning

confidence: 94%

“…In the case of low-speed axial fan blades, the relative thickness is usually less than 10 to 15 %, which corresponds to a lower limit of Rec,low ≈ 50 000 [32,[37][38], as considered in what follows. The upper limit depends on the critical Reynolds number triggering the natural laminar-to-turbulent transition.…”

Section: D) Blade Solidity (ψ6 = C/s)mentioning

confidence: 99%

“…The role of CD was already indicated in the "Relative roughness" subsection. As detailed in [21,32,37,41], the following relationship is valid between CD and Θ, the momentum thickness of the blade wake. Using this relationship, the wake thickness is implicitly included in the empirical modelling of b/c with the use of CD.…”

Section: ) Semi-empirical Model For Predicting the Pvs Frequencymentioning

confidence: 99%

See 3 more Smart Citations

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

Daku

Vad

2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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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.

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Section: ) Results and Discussionmentioning

confidence: 99%

Section: ) Semi-empirical Model For Predicting the Pvs Frequencymentioning

confidence: 94%

Section: D) Blade Solidity (ψ6 = C/s)mentioning

confidence: 99%

Section: ) Semi-empirical Model For Predicting the Pvs Frequencymentioning

confidence: 99%

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

Daku

Vad

2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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“…In [17] a NACA 0018 airfoil was investigated, and the results showed that, below Re C = 70000 (when the separated LBL fails to reattach) the f VS (Re C ) curve has 10 times lower slope, than in case Re C = 100000. Based on the above, the LBL VS is a complicated phenomenon, however, in the literature some semi-empirical formulas [6,18,19] can be found to predict the frequency of the LBL VS, which formulas are useful in the preliminary design of axial flow fans.…”

Section: Introduction and Objectivesmentioning

confidence: 99%

Computational Aeroacoustic Investigation of Airfoil Cascades

Lendvai

Benedek

2020

Period. Polytech. Mech. Eng.

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At moderate Reynolds numbers and angles of attack, the Laminar Boundary Layer (LBL) becomes unstable on the surface of airfoils, and causes periodic vortex shedding, which means undesired tonal peaks in the spectrum of the emitted aeroacoustic noise along with increased vibration and decreased aerodynamic performance. In the past, numerous research campaigns focused on the LBL vortex shedding, including measurements and numerical simulations as well. The results of these investigation showed that, the formation of the LBL instability related to the presence of the laminar separation bubble. It was also shown that, the spectrum of the emitted noise has a multitonal behavior, and the scaling of the mean frequency with the free stream velocity has a ladder structure. Based on these results, the LBL instability is a complex phenomenon; however, in the preliminary design of axial flow turbomachines the prediction of the frequency of the vortex shedding is essential, therefore the use of semi-empirical formulas is usual to achieve this goal. The previous researches mostly focused on separated airfoils, however, in case of turbomachines, the blades form a cascade, which can significantly affect the aerodynamic of the airfoils, i.e. it can affect the behavior of the LBL instability as well. According to this, in the present paper the LBL instability of NACA 0012 cascades are investigated, using 2D computational fluid mechanics and aeroacoustics simulations. The investigation involves the variation of the angle of attack, the chord based Reynolds-number and the spacing. The results are compared to the semi-empirical Brooks-Pope-Marcolini model.

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

Daku

Vad

2021

Journal of Turbomachinery

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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 semiempirical 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.

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

Cited by 5 publications

References 18 publications

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

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

Computational Aeroacoustic Investigation of Airfoil Cascades

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

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