TY - JOUR A1 - Biedermann, Till M. A1 - Hintzen, Nils A1 - Kameier, Frank T1 - Aeroacoustic Interactions of Blade Skew and Leading Edge Serrations Applied to Low-Pressure Axial Fans JF - Journal of Engineering for Gas Turbines and Power N2 - Leading edge serrations are well known for their ability to reduce turbulence-induced noise of single aerofoils while also providing aerodynamic advantages under certain operating conditions. Continuatively, applying leading edge serrations to rotating machinery such as axial fans proved the validity to generally transfer the obtained aeroacoustic benefits of single aerofoils. However, for the rotating applications the noise reduction potential highly depends on the point of operation. The current work aims at assessing the aeroacoustic effects of serrated leading edges under the increased geometrical complexity of the fan blades through blade skew. Therefore, the question is whether combining two potentially effective noise-reducing treatments through blade skew and leading edge serrations results in leveraging or obstructing effects. By varying the skew angle from 0 deg to 38 deg, four different prototypes of the fan impeller are tested experimentally in a test rig according to ISO 5136 and ISO 5801. All configurations are tested with original blades of straight leading edges plus five sets of serrations each, parameterised by the serration amplitude and the serrations wavelength. The intensity of the incoming turbulence ranges from 2.6% to 12.1%. The results obtained show the skewed blades to improve both the aerodynamic performance and the noise radiation after exceeding an initial skew angle, complemented by a significant onset of stall. Moreover, no contraindication between blade skew and serrated leading edges is encountered, showing the potential to further extend the noise reduction capabilities by combining effects of blade skew and leading edge treatment. Y1 - 2022 U6 - https://doi.org/10.1115/1.4055637 SN - 0742-4795 VL - 144 IS - 12 PB - ASME International ER - TY - JOUR A1 - Biedermann, Till M. A1 - Reich, M. A1 - Paschereit, C. O. T1 - Multi-Objective Modeling of Leading-Edge Serrations Applied to Low-Pressure Axial Fans JF - Journal of Engineering for Gas Turbines and Power N2 - A novel modeling strategy is proposed which allows high-accuracy predictions of aerodynamic and aeroacoustic target values for a low-pressure axial fan, equipped with serrated leading edges. Inspired by machine learning processes, the sampling of the experimental space is realized by use of a Latin hypercube design plus a factorial design, providing highly diverse information on the analyzed system. The effects of four influencing parameters (IP) are tested, characterizing the inflow conditions as well as the serration geometry. A total of 65 target values in the time and frequency domains are defined and can be approximated with high accuracy by individual artificial neural networks. Furthermore, the validation of the model against fully independent test points within the experimental space yields a remarkable fit, even for the spectral distribution in 1/3-octave bands, proving the ability of the model to generalize. A metaheuristic multi-objective optimization approach provides two-dimensional Pareto optimal solutions for selected pairs of target values. This is particularly important for reconciling opposing trends, such as the noise reduction capability and aerodynamic performance. The chosen optimization strategy also allows for a customized design of serrated leading edges, tailored to the specific operating conditions of the axial fan. KW - Acoustics KW - Artificial neural networks KW - Blades KW - Design KW - Fans KW - Flow (Dynamics) KW - Modeling KW - Noise control KW - Optimization KW - Pareto optimization KW - Pressure KW - Turbulence KW - Noise (Sound) KW - Rotors KW - Signals KW - Wavelength Y1 - 2020 U6 - https://doi.org/10.1115/1.4048599 SN - 0742-4795 VL - 142 IS - 11 PB - ASME International ER - TY - CHAP A1 - Felker, Alexander A1 - Biedermann, Till M. A1 - Kameier, Frank T1 - Low-Noise Design of Axial Fans Through Optimized Spanwise Application of Leading Edge Serrations T2 - ASME Turbo Expo 2023, Vol. 6: Education; Electric Power; Energy Storage; Fans and Blowers N2 - Recent studies have shown that leading edge serrations can effectively reduce broadband noise in axial fans and expand their operational range. However, additional aerodynamic losses have to be considered alongside the benefits of improved acoustic performance. The majority of studies focused on applying leading edge serrations along the entire span of the rotor blades regardless of local differences in radial inflow angles, deflection effects, and blade loading. In this regard, local and spanwise varying applications of leading edge serrations are considered crucial to reconciling maximum aeroacoustic and aerodynamic performance. In making these applications, a fan blade span is divided into five sub-segments. Each segment can then be equipped with either an acoustic or aerodynamic optimum as well as a baseline straight leading edge. Through testing at three different inflow turbulence levels along the full characteristic curve, an extensive statistical experimental design is executed. Ultimately, a simplified statistical model is derived. The model provides information on the optimum spanwise shape of a serration design. The results indicate significant effects of the local spanwise selection of varying serration designs. Discrepancies between aerodynamic and aeroacoustic optimum solutions can be satisfactorily resolved where, primarily, a significant extension of the working area is observed. Moreover, an extended potential in the delay of stall entry and the associated improvement of total pressure as well as a significant reduction of aeroacoustic signature is found. The underlying mechanisms are attributed to the compartmentalization effects of the serrations which restrict separation phenomena to local cells of finite spanwise extension. Furthermore, the spanwise geometrical parametrization of the serration segments correlates well with radial blade loading as well as respective flow conditions. By taking the radial distribution of aerodynamic quantities into account, an individual design of locally applied leading edge serrations can be integrated into the fan design process, enabling improved balancing between aeroacoustic benefits while maximizing aerodynamic performance. KW - fan noise, axial fan design, aeroacoustics, leading edge serrations, experimental Y1 - 2023 SN - 978-0-7918-8699-1 U6 - https://doi.org/10.1115/GT2023-102629 PB - American Society of Mechanical Engineers ER - TY - JOUR A1 - Al-Sadawi, Laith A. A1 - Mohammed, Ali F. A1 - Biedermann, Till M. A1 - Yusaf, Talal T1 - The influence of a divergent slot on the near-wake region of a circular cylinder JF - International Journal of Thermofluids N2 - Controlling flow around a circular cylinder is essential for reducing drag, alleviating lift fluctuations, and enhancing aerodynamic efficiency in various engineering applications. In the present work, the effect of localized passive air-jet injection at different azimuthal angles on the near-wake region of circular cylinder was numerically investigated at subcritical Reynolds numbers Re = 3900 and 20,000 using ANSYS-FLUENT commercial software. The slot angle was varied from 70° to 130° with an increment of 10°. To insure the reliability of the current numerical model, the simulation results were validated with available experimental and numerical literature. The results revealed that the slot can significantly affect the flow structure in the near-wake region and pressure distribution around the cylinder at slot angles 100° ≤ θs ≤ 130°. It was found that the optimum slot angle was 130° at which a good pressure recovery on the rear surface of the cylinder was achieved. Moreover, turbulent kinetic energy in the very near-wake region showed a substantial decrease of 40 % compared to the BL case at lower tested Reynolds number, as well as an 11 % reduction in the extent of the recirculation region. The drag analysis showed that the drag can be reduced by 26 % when the slot inclined at 130°. It can be concluded that the position of the slot induced jet plays a vital role on the flow structure, pressure distribution, and drag coefficient. Additional experimental studies are required to further explore the impact of the slot on the wake region. Specifically, investigating the combined effect of 70° and 130° slot angles could provide deeper insights, potentially leading to a more significant influence on the wake region KW - Passive flow control Slot-induced jet Divergent slot Wake control Drag coefficient Y1 - 2024 U6 - https://doi.org/10.1016/j.ijft.2024.100985 SN - 2666-2027 VL - 24 PB - Elsevier BV ER - TY - JOUR A1 - Biedermann, Till M. A1 - Czeckay, Pasquale A1 - Geyer, Thomas F. A1 - Kameier, Frank A1 - Paschereit, Christian O. T1 - Effect of Inflow Conditions on the Noise Reduction Through Leading Edge Serrations JF - AIAA Journal Y1 - 2019 U6 - https://doi.org/10.2514/1.J057831 SN - 0001-1452 VL - 57 IS - 9 SP - 4104 EP - 4109 PB - American Institute of Aeronautics and Astronautics (AIAA) ER - TY - CHAP A1 - Biedermann, Till M. A1 - Czeckay, Pasquale A1 - Geyer, Thomas F. A1 - Kameier, Frank A1 - Paschereit, Christian O. T1 - Noise Source Identification of Aerofoils Subjected to Leading Edge Serrations using Phased Array Beamforming T2 - 2018 AIAA/CEAS Aeroacoustics Conference Y1 - 2018 U6 - https://doi.org/10.2514/6.2018-3794 PB - American Institute of Aeronautics and Astronautics CY - Reston, Virginia ER - TY - CHAP A1 - Biedermann, Till M. A1 - Hintzen, Nils A1 - Kameier, Frank A1 - Chong, Tze Pei A1 - Paschereit, Christian O. T1 - On the Transfer of Leading Edge Serrations from Isolated Aerofoil to Ducted Low-Pressure Fan Application T2 - 2018 AIAA/CEAS Aeroacoustics Conference Y1 - 2018 U6 - https://doi.org/10.2514/6.2018-2956 PB - American Institute of Aeronautics and Astronautics CY - Reston, Virginia ER - TY - CHAP A1 - Biedermann, Till M. A1 - Kameier, F. A1 - Paschereit, C. O. T1 - Optimised Test Rig for Measurements of Aerodynamic and Aeroacoustic Performance of Leading Edge Serrations in Low-Speed Fan Application T2 - Volume 1: Aircraft Engine; Fans and Blowers; Marine N2 - With the aim of analysing the efficiency of leading edge serrations under realistic conditions, an experimental rig was developed where a ducted low-speed fan is installed that allows to gather data of both, aerodynamic and aeroacoustic nature. Turbulent inflow conditions were generated via biplane-square grids, resulting in turbulence intensities of different magnitude and of high isotropic character that were quantified by use of hotwire measurements. The fan blades were designed according to the NACA65(12)-10 profile with interchangeable features and an independently adjustable angle of attack. Altogether, five different parameters can be analysed, namely the serration amplitude and wavelength, the angle of attack, the inflow turbulence and the rotational speed. In addition, the blade design allows for a variation of the blade skew, sweep and dihedral as well. The presented work focusses on validating and optimising the test rig as well as a detailed quantification of the turbulent inflow conditions. Furthermore, first aerodynamic and aeroacoustic results of fan blades with straight leading edges are compared to those of serrated leading edges. The aerodynamic performance was found to be mainly affected by the serrations as a function of the serration amplitude. Aeroacoustically, a clear sensitivity towards different incoming turbulence intensities and serration parameters was detected, showing significant broadband noise reduction below 2 kHz with an overall noise reduction of ΔOASPL = 3.4 dB at maximum serration amplitudes and minimum wavelengths. Y1 - 2018 U6 - https://doi.org/10.1115/GT2018-75369 PB - American Society of Mechanical Engineers ER - TY - JOUR A1 - Biedermann, Till M. A1 - Scholz, Max A1 - Chong, Tze Pei T1 - Aeroacoustic assessment of porous blade treatment applied to centrifugal fans JF - International Journal of Aeroacoustics N2 - Heavy-duty centrifugal fans account for a significant share of energy consumption in the process and manufacturing industries. As a result, these machines are under increasing pressure to operate at maximum efficiency to reduce costs, pollutants and noise: only combined optimization is considered competitive for future generations of fans. Preliminary studies have shown that applying structured porosity to aerofoil rear parts can lead to a reduction in self noise and trailing edge shedding noise in the mid-to-high frequency range. With this in mind, a porous surface cover is applied to a prototype centrifugal fan to evaluate the aeroacoustic potential in a complex rotating machinery. The optimal geometric characteristics of the perforation are derived from experiments with single aerofoils, while the perimeter of the covered area is varied in eight steps. The centrifugal fan specimen is rapid-prototyped and tested at different fan speeds along the complete characteristic curves, while both aerodynamic and aeroacoustic performances are simultaneously recorded. The results obtained show a significant reduction in overall noise level while aerodynamic performance is maintained. Spectral analysis shows that the noise reduction is due to a broadband effect, where the upper and lower cut-off frequencies are determined by the rotational speed and the location of the applied porosity along the blade chord. However, the maximum noise reduction is obtained as a clear function of the minimum distance between the perforation and the trailing edge of the blade, indicating that the underlying working mechanisms are a combination of broadband dissipation effects due to porosity and destructive interference. Y1 - 2024 U6 - https://doi.org/10.1177/1475472X241278645 SN - 1475-472X VL - 23 IS - 7-8 SP - 610 EP - 633 PB - SAGE Publications ER - TY - JOUR A1 - Biedermann, Till M. A1 - Chong, Tze Pei A1 - Kameier, Frank A1 - Paschereit, Christian O. T1 - Statistical–Empirical Modeling of Airfoil Noise Subjected to Leading-Edge Serrations JF - AIAA Journal Y1 - 2017 U6 - https://doi.org/10.2514/1.J055633 SN - 0001-1452 VL - 55 IS - 9 SP - 3128 EP - 3142 PB - American Institute of Aeronautics and Astronautics (AIAA) ER - TY - CHAP A1 - Scholz, Max M. A1 - Biedermann, Till M. A1 - Chong, Tze Pei A1 - Smith, Edward T1 - Statistical Modelling of Aerofoil Self-Noise Subjected to Structured Porous Trailing Edges T2 - 28th AIAA/CEAS Aeroacoustics 2022 Conference N2 - Extensive research efforts in the aeroacoustics community have firmly established the benefits of porous trailing edges to achieve low-noise radiation. However, most studies of porous treatment are based on the use of very complex, open-cell structures to manipulate turbulent flow. Although this implementation has been shown to improve the aeroacoustics performance, the exact physical mechanisms that can be drawn from such a geometry are limited due to their complex topology. This study aims to draw from previous works and to develop an optimised experimental method that utilises a 3D-printed array of rectilinear, structured permeable trailing edges on a NACA-0012 aerofoil based on a Box-Behnken experimental design. The essence of the work is to isolate individual porous parameters, and investigate the interdependencies of these parameters on target values such as the overall sound power level, the Strouhal number of the maximum noise reduction and many other characteristics of the far field. Twenty-eight porous trailing edges were produced based on the initial experimental design. Each is unique with the combination of streamwise and spanwise separation distance between the pores, pore size and porous coverage. The experiment was conducted over various angles of attack and Reynolds numbers. The results show that many of these trailing edges can indeed achieve low-noise radiation, and acceptable prediction accuracies are obtained for all the response variables except the total sound power reduction, ΔOAPWL, and the lower Strouhal limit of the noise reduction. This paper will establish the findings, discuss the results and detail the next stage of the experiment for the improvement of the statistical model. Y1 - 2022 U6 - https://doi.org/10.2514/6.2022-3092 SP - 4869 EP - 4882 PB - American Institute of Aeronautics and Astronautics CY - Reston, Virginia ER - TY - CHAP A1 - Chong, Tze Pei A1 - Biedermann, Till M. A1 - Koster, Oliver A1 - Hasheminejad, Seyed Mohammad T1 - On the Effect of Leading Edge Serrations on Aerofoil Noise Production T2 - 2018 AIAA/CEAS Aeroacoustics Conference Y1 - 2018 U6 - https://doi.org/10.2514/6.2018-3289 PB - American Institute of Aeronautics and Astronautics CY - Reston, Virginia ER - TY - JOUR A1 - Biedermann, Till M. A1 - Moutamassik, Y. A1 - Kameier, F. T1 - Assessment of the Impeller/Volute Relationship of Centrifugal Fans From an Aerodynamic and Aeroacoustic Perspective JF - Journal of Turbomachinery N2 - Heavy-duty centrifugal fans require high reliability and first-class performance. Besides, extreme conditions and harsh environments are often encountered, such as in the papermaking process, in steel or cement plants or the chemical and petrochemical industry. Therefore, the design of high-performance heavy-duty industrial fans requires robust yet efficient solutions. The previous work indicates a high aerodynamic and aeroacoustic sensitivity concerning the specific position of the volute cutoff (tongue). This effect will be further investigated, not by directly changing the orientation of the cutoff, but by varying the position of the impeller relative to a fixed volute casing. The initial evaluation is done through a numerical study of three influencing parameters, which allow the aerodynamic dependencies to be modeled using low-layer artificial networks. Subsequently, extensive experimental studies were carried out to validate the aerodynamic dependencies and also to incorporate information on the aeroacoustic performance. The obtained results show that the operating point represents the key factor in determining the optimal positioning, with qualitatively comparable dependencies found for both tested fans. From an aeroacoustic point of view, the determined optimal configuration does not necessarily coincide with the observed aerodynamic desires, so careful analysis and a reasonable compromise are required, motivating for a multi-objective optimization process. KW - centrifugal fan, volute optimization, artificial neural networks, aerodynamics, aeroacoustics, computational fluid dynamics (CFD) Y1 - 2023 U6 - https://doi.org/10.1115/1.4062243 SN - 0889-504X VL - 145 IS - 8 PB - ASME International ER - TY - JOUR A1 - Biedermann, Till M. A1 - Czeckay, Pasquale A1 - Hintzen, Nils A1 - Kameier, Frank A1 - Paschereit, C. O. T1 - Applicability of Aeroacoustic Scaling Laws of Leading Edge Serrations for Rotating Applications JF - Acoustics N2 - The dominant aeroacoustic mechanisms of serrated leading edges, subjected to highly turbulent inflow conditions, can be compressed to spanwise decorrelation effects as well as effects of destructive interference. For single aerofoils, the resulting broadband noise reduction is known to follow spectral scaling laws. However, transferring serrated leading edges to rotating machinery, results in noise radiation patterns of significantly increased complexity, impeding to allocate the observed noise reduction to the underlying physical mechanisms. The current study aims at concatenating the scaling laws for stationary aerofoil and rotating-blade application and thus at providing valuable information on the aeroacoustic transferability of leading edge serrations. For the pursued approach, low-pressure axial fans are designed, obtaining identical serrated fan blade geometries than previously analyzed single aerofoils, hence allowing for direct comparison. Highly similar spectral noise reduction patterns are obtained for the broadband noise reduction of the serrated rotors, generally confirming the transferability and showing a scaling with the geometrical parameters of the serrations as well as the inflow conditions. Continuative analysis of the total noise reduction, however, constrains the applicability of the scaling laws to a specific operating range of the rotors and motivates for a devaluation of the scaling coefficients regarding additional rotor-specific effects. Y1 - 2020 U6 - https://doi.org/10.3390/acoustics2030030 SN - 2624-599X VL - 2 IS - 3 SP - 579 EP - 594 PB - MDPI AG ER - TY - CHAP A1 - Biedermann, Till M. A1 - Kameier, F. A1 - Paschereit, C. O. T1 - Successive Aeroacoustic Transfer of Leading Edge Serrations From Single Airfoil to Low-Pressure Fan Application T2 - Volume 1: Aircraft Engine; Fans and Blowers; Marine; Honors and Awards N2 - Leading edge serrations are identified as an effective passive treatment for reducing fan broadband noise due to high turbulent inflow conditions. This paper aim to investigate the isolated effect of serrated applications in a rotating frame, covering the aerodynamic and aeroacoustic performance. With this purpose, a serration design, previously analyzed in the rigid domain, is transferred to the rotating frame, following a successive approach in form of a continuous increase of the fan blade number. This is considered as a feasible way to isolate the serration effects and to provide information on fan blade interaction and possible masking effects. Comparing blades with straight and serrated leading edges by analyzing the spectral noise reduction and the overall level results in deep insights in the underlying noise reduction mechanisms. Furthermore, analysis of phase differences by means of the wall pressure fluctuations leads to the identification of rotating flow phenomena, non-synchronized with the rotor speed. The results obtained indicate an efficient noise reduction by the serrations in the vicinity of the design point. By use of the presented successive approach, noise reduction phenomena observed with the full rotor could be identified to be of either aeroacoustic or aerodynamic nature. A reduced noise is observed for the full rotor case, showing a reduction of blade interaction effects. At reducing flow coefficients, an improved stall margin of the serrated rotor is identified that also affects the aeroacoustic signature. Y1 - 2019 U6 - https://doi.org/10.1115/GT2019-90212 PB - American Society of Mechanical Engineers ER - TY - CHAP A1 - Biedermann, Till M. A1 - Moutamassik, Youssef A1 - Kameier, Frank T1 - Feasibility Study on the Effect of Blade Inclination for Heavy Duty Centrifugal Fans – Aerodynamic Aspects T2 - Volume 1: Aircraft Engine; Fans and Blowers; Marine; Wind Energy; Scholar Lecture N2 - With a special focus on the industrial feasibility and the manufacturability, a recently proposed novel approach to centrifugal impeller blade inclination is adopted and investigated through extensive CFD analysis. The fan blades, originally aligned perpendicular to the impeller backplate, are inclined in either forward or backward direction. For the presented study, an industrially proven fan design is chosen for testing. Compared to the original design, the inclined fan blades possess an increased total blade area and at the same time providing variable inflow angles at the leading edges of the blades. These two factors are expected to alter the fan characteristic curves in providing an increased range of optimum performance while maintaining high aerodynamic efficiency. The results obtained show a clear trend in aerodynamic performance with the degree of inclination, where the characteristic curves rotate at about the design point, allowing local improvements either at overload conditions or part-load conditions of the fan. Moreover, the trends obtained show the tendency to agree well with the rudimentary models published in previous studies, even though it appears to be affected by the fan volute and the point of operation as well. KW - centrifugal fans KW - optimization KW - aerodynamics Y1 - 2021 U6 - https://doi.org/10.1115/GT2021-58505 PB - American Society of Mechanical Engineers ER - TY - CHAP A1 - Al Jubori, Ayad M. A1 - Al-Sadawi, Laith A. A1 - Biedermann, Till M. A1 - Alfarawi, Suliman T1 - Potential and Evolution of Miniatures Compressed Air Energy Storage Plants Based on Impulse Turbine T2 - Volume 10C: Turbomachinery — Design Methods and CFD Modeling for Turbomachinery; Ducts, Noise, and Component Interactions N2 - This paper describes the work carried out to develop an impulse turbine for miniatures compressed air system. This study hypothesizes the question; what is the effect of combining an impulse turbine loss model into a compressed air energy storage system analysis? The miniatures power system has lower mass flow rates which lead to a small turbine size. The miniature impulse turbine has relatively low efficiency and is highly sensitive to operating conditions at a low mass flow rate due to all losses in terms of passage, trailing edge, incidence, and clearance becoming higher amounts compared to the total losses of the percentage foundation. The development of a novel impulse turbine configuration is presented based on one-dimensional design and three-dimensional simulations. The impulse turbine in single-stage configuration was designed and analyzed for a range of operating conditions in terms of pressures, temperatures, mass flow rate, and rotational speeds. The simulations results showed that the maximum efficiency and power were 65.93% and 4.019 kW respectively with a mass flow rate of 0.2 kg/s. The energy analysis revealed that the system efficiency was 10.3%. The miniature compressed air energy storage system driven by an impulse turbine can be used to generate electricity for small power applications. Y1 - 2022 U6 - https://doi.org/10.1115/GT2022-82627 PB - American Society of Mechanical Engineers ER - TY - CHAP A1 - Balde, Nina Maimuna A1 - Biedermann, Till M. A1 - Kameier, Frank A1 - Pohlmann, Tobias T1 - Aeroacoustic Scaling of Axial Low-Pressure Fans With Leading Edge Serrations T2 - Volume 6: Education; Electric Power; Energy Storage; Fans and Blowers N2 - Previous as well as ongoing studies have shown that bioinspired modifications of the leading edge of axial fans, so-called leading edge serrations, have beneficial effects on sound radiation in rotating systems such as a broadband noise reduction. The objective of this study is to elaborate on the comparability of two geometrically similar low-pressure axial fans that differ in fan diameters. For this purpose, a fan design based on the geometric characteristics of an existing fan, which had been tested in previous studies, was developed with and without leading edge serrations at a scale of 1:3. Extensive experiments were carried out to gather detailed data on the aerodynamic and aeroacoustic performance of the specimen. Similarity laws and non-dimensional parameters are used to investigate whether a transferability comparison of the aerodynamic and aeroacoustic experimental results of these geometrically similar axial fans is possible. The latter also includes an analysis of the spectral range. The results prove that it is possible to derive a comparability of the aerodynamic parameter of the flow coefficient and thus of the flow rate of the fans. Furthermore, a correlation between the noise reduction potential of the two models can be established through spectral Strouhal number normalization. The proposed aerodynamic and aeroacoustic coherences ensure transferability from the model fan to an upscaled fan and thus allow generalized statements to accurately transfer the aeroacoustic potential of leading edge serrations for different geometrically similar fan applications. Y1 - 2023 U6 - https://doi.org/10.1115/GT2023-103181 PB - American Society of Mechanical Engineers ER - TY - JOUR A1 - Swanepoel, Pieter Coenraad A1 - Biedermann, Till M. A1 - van der Spuy, Sybrand J T1 - Experimental noise reduction (aeroacoustical enhancement) of a large diameter axial flow cooling fan through a reduction in blade tip clearance JF - International Journal of Aeroacoustics N2 - Aerodynamic and aeroacoustic performance experiments were carried out on four- and eight bladed, 1.542 m diameter, axial flow cooling fans, with constant solidity and hub-to-tip ratio. Tests were conducted in an ISO5801, Type A Fan Test facility. The tip gap (TG) was reduced from 4 mm (0.26% fan diameter) to 2 mm (0.13% fan diameter), to 0 mm, for both fan configurations. The noise profile of each fan configuration at the same TG over the whole volumetric flow rate spectrum was compared to each other. The 4 mm (0.26%) TG is used as a baseline to measure the nett increase or decrease in sound levels. Noise emissions decreased as the TG was reduced. It is discovered that the four bladed fan configuration had lower noise emissions than the eight bladed fan configuration at all blade tip clearances at design flow rate. It is concluded that reducing the TG and number of blades, at constant solidity, reduces sound emissions. The 0 mm TG for the four bladed fan produced the greatest reduction in noise emissions. An increase in fan total-to-static performance is observed when reducing the TG for both fan configurations. KW - Axial fan design KW - aeroacoustics KW - blade passing frequency KW - tip clearance noise KW - fan noise Y1 - 2023 U6 - https://doi.org/10.1177/1475472X231183156 SN - 1475-472X VL - 22 IS - 3-4 SP - 210 EP - 237 PB - SAGE Publications ER - TY - CHAP A1 - Biedermann, Till A1 - Kammerzelt, Dennis T1 - Relating Cutoff Pressure Distribution and Acoustic Signature of Centrifugal Fans through Experimental Correlation N2 - Potential noise sources of rotating machinery are diverse and complex. This includes the acoustic signature of the impeller itself and the design of the fan casing. This is especially true for centrifugal fans with an asymmetric spiral casing. Here, a nonuniform and unsteady pressure field interacts with the volute cutoff, thus resulting in broadband noise radiation and, under given geometric circumstances, significant tonal noise effects. The current study investigates the relation between the local pressure distribution at the volute cutoff and the acoustic farfield signature of the fan. A low-speed centrifugal fan, placed in an anechoic environment, is equipped with pressure sensors to gather information on the mean pressure distribution and the unsteady wall pressure field at selected spots. Correlating the captured signature with the radiated far-field noise reveals significant common spectral components and helps identify relevant noise sources, affected by the volute cutoff. In the long term, the definition of transfer functions between the near-field wall pressure and the radiated noise into the far-field is expected to enhance the geometric optimisation of the volute cutoff in both experimental and numerical environments. The test rig, in close agreement with ISO 5801, allows for simultaneous capture of the aerodynamic performance, allowing for an analysis of the pressure correlation along the entire characteristic curve. Y1 - 2025 ER - TY - GEN A1 - Biedermann, Till A1 - Vad, János T1 - Aeroacoustic Effects of Fans and Blowers: A Pragmatic Guide for Designers and Engineers BT - Tutorial of Basics TOB-10-01 N2 - A significant percentage of electrical energy consumption is attributable to fans and ventilators of various kinds. They are inextricably linked to our industrial and domestic environment. Low-noise design and development is therefore a key aspect for future systems and machines in urban areas and is a top priority alongside aerodynamic efficiency and mechanical strength. Low noise emissions are required on the one hand to comply with legal guidelines, but on the other hand also to save costs with regard to sound insulation measures on the transmission path (silencers, insulating materials, etc.). This tutorial provides an overview of the sound mechanisms relevant to fans and ventilators and the associated fluid mechanical effects. Practical industrial examples and best practice options as well as their opportunities and obstacles are presented. Y1 - 2025 PB - ASME Turbo Expo & Exhibition 2025, Memphis, USA CY - New York, USA ER - TY - JOUR A1 - Al-Sadawi, L. A1 - Biedermann, Till M. A1 - Fritsche, M. T1 - Passive Control of Vortex Shedding Noise of Circular Cylinders by Passive Air-Jet Blowing JF - Journal of Aerospace Engineering N2 - Passive air-jet blowing is an effective yet simple technique to control flow-induced noise due to vortex shedding of bluff bodies. The current study investigates the effect of the specific slot angles of passive jets in connection with the suppression capabilities of vortex shedding and the byproduct of vortex-induced noise in the wake region of a circular cylinder. Aeroacoustic tests for a baseline case and 10 different slotted cases with slot angles of 80°≤𝜃≤125° are performed for Reynolds numbers 6.6×103≤R≤3.3×104. This is supplemented by numerical computational fluid dynamics (CFD) analyses to identify the underlying aerodynamic mechanisms. The results obtained reveal that using the current passive control method results in a significant reduction of the vortex shedding tonal noise for slot angles of 90°≤𝜃≤125° and high Reynolds numbers. The numerical results showed good agreement with a remarkably reduced kinetic energy for slot-end angles of 115°≤𝜃≤125°. At low Reynolds numbers, however, the identified aeroacoustic benefits tend to cease. Y1 - 2021 U6 - https://doi.org/10.1061/(ASCE)AS.1943-5525.0001301 SN - 0893-1321 VL - 34 IS - 5 PB - American Society of Civil Engineers (ASCE) ER -