Search Results (28)

For a two-stage variable-pitch axial fan, a perforation design in first-stage rotor blades was proposed to improve aerodynamic performance and reduce acoustic noise. Utilizing steady-state simulations in Fluent, the internal flow characteristics of the fan before and after perforation were studied, and the changes in noise and vortex structure were examined by the large eddy simulation. Additionally, the perforation diameter with better performance was applied to the second-stage rotor blades and both first- and second-stage rotor blades, and the effects of perforation on blades of different stages were compared. The results show that an appropriate perforation diameter can improve the performance of the fan. Considering the changes in total pressure rise and efficiency, d = 6 mm is the preferable choice. Proper perforation diameter has a significant effect on noise suppression, and the noise-reduction effect is more pronounced in the high-frequency range. Among the models, d = 10 mm shows the best noise-reduction effect. At this perforation diameter, the vortex at the trailing edge of the rotor blades forms a regular ring-like vortex chain, resulting in lower noise levels. Perforation in the first-stage rotor blade can enhance the fan’s performance, while perforation in the second-stage rotor blades leads to a decrease in performance. Additionally, perforation can effectively reduce the noise at each stage. Considering both performance and noise variations, the preferable perforation scheme is simultaneous perforating in the first- and second-stage rotor blades with a perforation diameter of 10 mm. Full article

The implementation of serrated stator blades in axial compressor and fan stages offers significant advantages, such as enhanced performance and reduced noise levels, making it a practical and cost-effective solution. This study explores the impact of serrated blade design on noise reduction under specific engine operating conditions. A small-scale experimental test setup with a turbulence-inducing grid was designed for testing multiple grid sizes in order to identify the most promising configuration which replicates rotor–stator interaction. Numerical simulations and early experimental tests in an anechoic chamber using a four-blade cascade configuration at an airflow speed of 50 m/s revealed a small but notable noise reduction in the 1–6 kHz range for a partially matched grid–blade geometry. Serrated blades demonstrated an overall sound pressure level reduction of 1.5 dB and up to 12 dB in tonal noise, highlighting the potential of cascade configurations to improve acoustic performance in gas turbine applications. Full article

Future UHBR (Ultra-High Bypass-Ratio) engines might cause serious ‘turbine noise storms’ but, at present, turbine noise prediction capability is lacking. The large turning angle of the turbine blade is the first major factor deserving special attention. The RANS (Reynold Averaged Navier–Stokes equation)-informed (here called RI) method and LINSUB (the bound vorticity 2D model LINearized SUBsonic flow in cascade), developed to predict fan broadband noise, coupled with a two-flat-plates (here called TP) assumption for the turbine blade, is applied here, and one autonomous rapid RI-TP model for predicting turbine wake interaction broadband noise has been developed. Firstly, taking the single axial turbine test rig NPU-Turb as the object, both the experimental data and the DDES/AA (delayed Detached Eddy Simulation/Acoustic Analogy) hybrid model have been used to validate the RI-TP model. High consistency in the medium and high frequencies among the three designed and off-designed rotation speeds indicates that the RI-TP model has the ability to predict turbine broadband noise rapidly. And compared with the original RANS-informed method, with one thin-flat-plate assumption on the blade, the RI-TP model can enhance the PWL (sound power level) in almost the whole spectral range below 10 KHz, which, in turn, is closer to the experimental data and the DDES/AA prediction results. The PWL trend with a ‘dividing point’ position is also studied. The spectrum would move up or down if the location is away from true value. In addition, the extraction location for turbulence as an input for the RI-TP model is negligible. In the future, multi-stage characteristics and the blade thickness effect should be further considered when predicting turbine noise. Full article

Axial fans may be equipped with passive flow control devices to enhance rotor efficiency or minimize noise emissions. In this regard, blade designs influenced by biomimicry, such as rotors with sinusoidal leading edges (LEs), have gained popularity in recent years. However, their design is predominantly driven by a trial-and-error approach, with limited systematic studies on the influence of rotor performance. Furthermore, their effectiveness is typically evaluated under controlled conditions that may significantly differ from operations in real installation layouts. In this work, a systematic review of the design process for sinusoidal LE axial fan rotors is provided, aiming to summarize previous design experiences. Then, a modified sinusoidal LE is designed and fitted to a 7.3 m low-speed axial fan for air-cooled condensers (ACCs). These fans operate at environmental conditions, providing a quasi-zero static pressure rise, often with inflow non-uniformities. A series of RANS computations were run to simulate the performance of the baseline fan and that of the sinusoidal leading edge, considering a real installation setup at Stellenbosh University, where the ACC is constrained between buildings and has a channel running on the ground below the fan inlet. The aim is to explore the nonbalanced inflow condition effects in both rotor geometries and to test the effect of the installation layout on fan performance. The results show that the modification to the rotor allows for a more even distribution of flow in the blade-to-blade passages with respect to the baseline geometry. Full article

Axial-flow fans are widely used as cooling fans in the outdoor units of split-type air conditioners. The design of an axial-flow fan blade involves stacking several airfoils that can be differently designed for each spanwise section. However, the complex flow field around the fan blade, including circumferential and axial flows, presents challenges when applying the single airfoil theory. This study proposed a systematic performance-based design method for axial-flow fans using a cascade of airfoils based on the blade strip theory. The theory characterized the complex three-dimensional flow field driven by an axial-flow fan in terms of a two-dimensional cascade of airfoil flows. Computational fluid dynamics based on finite volume methods were used to predict the flow field and aerodynamic sound sources of an existing low-pressure axial-flow fan partially covered by a fan shroud, and the results were validated against experimental measurements. Three radial locations in the spanwise region from the hub to the blade tip that have a significant impact on aerodynamic performance were selected, and the two-dimensional flow field on a cylindrical surface with a constant radius was extracted from the three-dimensional flow field to characterize the performance of an axial fan. Then, the airfoils at the targeted span locations were optimized for a higher flow rate and greater efficiency via two-dimensional simulations using the cascades of the airfoil, and the selected optimized airfoils were applied to existing fan blades. The effectiveness of the proposed performance-based design method for low-pressure axial-flow fans was validated by the results, which showed that the redesigned fan blades with cascades of airfoils performed as predicted, increasing the intended higher flow rate by about 1%, improving power consumption by 8%, and lowering the overall sound pressure level by 1.5 dBA. Full article

A compact off-road machine tends to have a compact engine structure, which may result in small clearances between the main engine, the cooling system, and the radiator. In the design of its cooling system, the heat exchanger, fan, and conveyor are normally chosen based on their fixed operating point. Unfortunately, these machines work in variable conditions and the performance of each component is different when they are working as a whole under the hood. The aim of this work is to optimize the position of these components through a parametric analysis of some variables, using the Computational Fluid Dynamics technique. The air flows are analyzed in order to show the pressure waves created by the air moved by the fan blades, showing how the fluid interacts with the engine. The results show that optimizing this installation can increase the efficiency of the fan by 10% and reduce the noise emitted by 13 dB. These results should sensitize designers to use CFD analyses, not for a single component, but for the entire system. The methodology shown can be applied for the better design of cooling systems, mainly in off-road vehicles that have noise emission problems. Full article

Air-cooled condensers (ACCs) are commonly found in power plants working with concentrated solar power or in steam power plants operated in regions with limited water availability. In ACCs, the flow of air is driven toward the heat exchangers by axial fans that are characterized by large diameters and operate at very high mass flow rates with a near-zero static pressure rise. Given the overall requirements in steam plants, these fans are subjected to inflow distortions, unstable operations, and are characterized by high noise emissions. Previous studies show that leading edge bumps in the tip region of axial fans can effectively reduce the sound pressure levels without affecting the static efficiency. Nevertheless, the effects of this treatment in terms of flow patterns and heat exchange in the whole ACC system were not investigated. In this work, the effect of leading edge bumps on the flow patterns is analyzed. Two RANS simulations were carried out using OpenFOAM on a simplified model of the air-cooled condenser. The fans are simulated using a frozen rotor approach. Turbulence modeling relies on the RNG k-epsilon model. The fan is characterized by a diameter of 7.3 m and a 333 m³/s volumetric flow rate at the design point. The presence of the heat exchanger is modeled using a porous medium. The comparison between the flow fields clearly exerts that the modified blade is responsible for the redistribution of radial velocities in the rotor region. This drastically reduces the losses related to the installation of the fan in a real configuration. Full article

A wind tunnel is needed for a lot of research and model testing in the field of engineering design. Commercial wind tunnels are large and expensive, making them unsuitable for small-scale aerodynamic model testing. This work aims to experimentally investigate the effects of flow, noise, and vibration on constructing and designing a low-speed wind tunnel structure. The flow uniformity in the wind tunnel has been tested by measuring the velocity profiles inside the empty test section with a pitot-static tube at various fan frequencies. The experiment results showed a good flow uniformity of more than 90% across the test section area, and the maximum wind velocity achieved was about 25.1 m/s. Due to the stability of the flow near the exit test section, the vibration measurement revealed that the entrance portion has larger vibration fluctuations than the exit part. Furthermore, as the axial fan frequency increases, the noise level increases. At 40 Hz, the noise level enters the hazardous zone, which has an impact on the person who performs the measurement process. The resonance of the wind tunnel structure is an important measurement test that affects vibration measurement. Full article

To improve the performance of the aerodynamic properties and reduce the aerodynamic noise of an axial flow fan in the outdoor unit of an air conditioner, this study proposed a bionic forked trailing-edge structure inspired by the forked fish caudal fin and implemented by modifying the trailing edge of the prototype fan. The effect of the bionic forked trailing edge on the aerodynamic and aeroacoustic performance was investigated experimentally, and detailed analyses of the blade load and internal vortex structures were performed based on large-eddy simulations (LES). It is shown that the bionic forked trailing edge could effectively adjust the blade load distribution, reduce the pressure difference between the pressure side and suction side near the trailing edge of the blade tip region, and weaken the intensity and influence range of the inlet vortex (IV) and the tip leakage vortex (TLV). The discrete noise caused by the vortices in the rotor tip area was also reduced, particularly at the blade passing frequency (BPF) and its harmonic frequency. The experimental results confirmed the existence of an optimal bionic forked trailing-edge structure, resulting in the maximum power-saving rate γ of 7.5% and the reduction of 0.3 ~ 0.8 dB of aerodynamic noise, with an included angle θ_t of 13.5°. The detailed analysis of the internal vortex structures provides a good reference for the efficiency improvement and noise reduction of axial flow fans. Full article

This paper presents the noise characteristics of axial fans in the process of variable frequency adjustment, so as to clarify the basis of frequency adjustment and high-risk area division for practical purposes. In the aerodynamic performance experiment, 11 kinds of operating conditions (OC) were divided into 3 groups, and the air flow rate and power consumption were measured. At the same time, an aerodynamic noise experiment was carried out, and nine measuring points were selected to test the noise of the air inlet and shell. The data showed that the aerodynamic performance parameters have the characteristics of non-proportional law. The maximum ventilation coefficient of OC2, OC7, OC11 is 3.9%, and its noise always has a negative growth rate. Furthermore, the typical OC were selected from all experiments, and broadband noise and discrete noise analyses were performed. The results indicated that the fan noise of the changes under variable frequency adjustment may come from boundary layer noise and shedding noise. In addition, the fundamental frequency sound pressure level of discrete noise is the highest in the whole frequency band. At the high-speed condition, the contribution of higher harmonics to the fan overall noise increases, but the broadband noise is still the dominant noise. Finally, the noise rating was introduced, and the high-risk noise index was divided for the noise of the air inlet and the shell. It was found that the main noise variation index of typical OC mostly exceeded the high-risk noise index, and the main target frequency band of noise control is 250–4000 Hz. Full article

A novel active turbulence grid of the Institute of Fluid Mechanics at FAU Erlangen-Nuremberg is introduced. The focus of this grid is not on basic investigations of fluid mechanics, as is usually the case with active turbulence grids, but the generation of defined inflow conditions for axial fans. Thus, by means of the active turbulence grid, individual turbulence characteristics in the flow to the fan can be changed; therefore, fundamental interactions between the flow mechanics at the axial fan and the sound radiation can be analyzed. In addition, the replication of the flow fields of heat exchangers by the active turbulence grid is the focus of the investigations. The investigations showed that it is possible to use the active turbulence grid to generate defined inflow conditions for axial fans. It was also possible to reproduce the heat exchanger flow fields both for the mean turbulence values and for the spatial distributions. It was found that the grid induces tonal components due to the drive motors, but also that the inherent noise has no significant influence on the spectrum of the fans under investigation. Based on selected turbulence characteristics, direct correlations were found between the spatial distribution of the turbulence level and sound radiation at the first blade passing frequency of the axial fan. As the variance of the turbulence level increases, the sound radiation of the tonal components becomes more pronounced. The total sound pressure level, however, is mainly determined by the low-frequency broadband sound. A linear relationship between the spatial mean value of the turbulence level and the total sound pressure level was found for the investigated axial fan. Full article

Squirrel-cage fans are widely applied in air conditioning systems, and their aerodynamic noise mainly related to blade length. The aerodynamic performance and noise spectrum of squirrel-cage fans are synchronously measured in an anechoic wind tunnel. The effect of blade lengths and different geometric configurations on the noise of a squirrel-cage fan is experimentally investigated. This paper focuses on the total sound pressure level and noise spectrum characteristics at different measurement points. Noise distributions of the outlet of the forward squirrel-cage fan exhibited axial-symmetry and large differences for those of vertical direction. In lower fan positions, the noise was greater than that of the top. In particular, it was found that blades were easy to generate higher noise when their length was reduced by 31.7%. The findings suggest that the broadband noise of the squirrel-cage fan should be fully considered for noise reduction. The purpose of this work is to provide a novelty reference for the low-cost modification method of cutting blades. The results show that fans with shorter blades have lower noise and kept an excellent performance. These finding have implications for fan manufacturers. Full article

Digital twins technology (DTT) is an application framework with breakthrough rules. With the deep integration of the virtual information world and physical space, it becomes the basis for realizing intelligent machining production lines, which is of great significance to intelligent processing in industrial manufacturing. This review aims to study the application of DTT and the Metaverse in fluid machinery in the past 5 years by summarizing the application status of pumps and fans in fluid machinery from the perspective of DTT and the Metaverse through the collection, classification, and summary of relevant literature in the past 5 years. The research found that in addition to relatively mature applications in intelligent manufacturing, DTT and Metaverse technologies play a critical role in the development of new pump products and technologies and are widely used in numerical simulation and fault detection in fluid machinery for various pumps and other fields. Among fan-type fluid machinery, twin fans can comprehensively use technologies, such as perception, calculation, modeling, and deep learning, to provide efficient smart solutions for fan operation detection, power generation visualization, production monitoring, and operation monitoring. Still, there are some limitations. For example, real-time and accuracy cannot fully meet the requirements in the mechanical environment with high-precision requirements. However, there are also some solutions that have achieved good results. For instance, it is possible to achieve significant noise reduction and better aerodynamic performance of the axial fan by improving the sawtooth parameters of the fan and rearranging the sawtooth area. However, there are few application cases of the Metaverse in fluid machinery. The cases are limited to operating real equipment from a virtual environment and require the combination of virtual reality and DTT. The application effect still needs further verification. Full article

The effect of blade sweep has been studied numerically with the Lattice Boltzmann Method on a family of low-speed free-vortex axial fans with sweeps of ±45°. Good overall aerodynamic agreement is first demonstrated on all fans at the design condition, particularly in the tip gap. The local larger wall-pressure fluctuations seen in the unswept and backward swept fans compared to the forward case are traced to the stronger tip vortices that remain in the rotational plane or even move upstream. These stronger and faster vortices interacting with the fan blades are then responsible for the larger noise levels observed in the acoustic spectra of these fans, and particularly for large subharmonic humps. Excellent agreement between experimental and numerical noise predictions is finally reported stressing the dominant tip noise. Full article

The localization and quantification of turbomachinery rotating sound sources is an important challenge in the field of aeroacoustics. In order to compensate the motion of a rotating sound source, a rotating beamforming technique is developed and applied in a flow duct, which uses a wall-mounted microphone array placed circularly parallel to the fan, to detect the broadband noise source of the aeroengine fan. A simulation of three discrete rotating sound sources with a non-constant rotational speed is pursued to verify the effectiveness in reconstruction of the correct source positions and quantitative prediction of the source amplitudes. The technique is ulteriorly experimentally implemented at an axial low-speed fan test rig facility. The fan test rig has 19 rotor blades and 18 stator vanes, with a design speed up to 3000 rpm. The method can accurately identify the radial and circumferential positions of the three rotating sound sources in the simulation case, large side-lobes appear near the main-lobe of the sound source due to the geometric influence of the microphone array. A noticeable feature of beamforming images for axial flow fan is that the sound sources appear to be concentrated in the tip region rather than distributed along the span. Full article