Search Results (88)

Axial flow fans are widely used for heat dissipation in electronic devices. Due to its frequent speed-regulation to adapt to the change in heat load, a fan can cause significant electromagnetic radiation interference. In this study, a peak absorption filtering method is proposed to address the radiation interference issue in a high-speed PWM axial flow fan. The mechanism and coupling paths of radiation interference were analyzed, and a radiation interference calculation using finite integration technique by a hybrid field-circuit model and experimental measurement were conducted to identify the winding as the main source of radiation in PWM fan. Considering the limited space inside the fan, an integrated, non-inductive filtering circuit was designed to absorb the peak voltage entering the windings and the filter parameters are determined via circuit simulation. The measurement results indicate that the filtering method can reduce overall electromagnetic interference with a maximum peak reduction of 41.9 dB, without affecting the useful signals. Full article

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

Based on the Daozhen–Wulong Zimuyan tunnel, the distance from the outlet of the air duct to the tunnel face and the diameter of the air duct are studied through an orthogonal experimental design. Aiming at the influence of the position of the air duct of the axial flow fan in the tunnel on the ventilation flow field, the improved TOPSIS theory is adopted for detailed data analysis, and the flow field characteristics are thoroughly checked to identify the optimal working condition configuration. The results show that with the increase in the distance between the air duct and the tunnel face, the local CO concentration will first decrease and then increase, indicating that too large or too small a distance will weaken the effective CO emission ability of the tunnel face, and the distance between the air duct outlet and the tunnel face is the best scheme; by combining the TOPSIS theory, entropy weight method, and analytic hierarchy process, the optimization scheme is obtained. When the distance between the outlet of the air duct and the working face is 15 m, the side wall of the air duct is 4 m away from the air, the diameter of the air duct is 1.8 m, the flow field in the tunnel shows a high degree of stability, the wind speed is significantly increased, and the vortex area that may hinder the air flow is effectively eliminated. The ventilation efficiency is greatly improved and the overall stability of the tunnel is enhanced. Full article

We introduce the solver ARES: Axial-flow pump Radial Equilibrium through Streamlines. The code implements a meanline method, enforcing the conservation of flow momentum and continuity across a set of discrete streamlines in the axial-flow pump’s meridional channel. Real flow effects are modeled with empirical correlations, including off-design deviation and losses due to profile shape, secondary flows, tip leakage, and the end-wall boundary layer (EWBL). Inspired by aeronautical fan and compressor methods, this implementation is specifically tailored for the analysis of the Outboard Dynamic-inlet Waterjet (ODW), the latest aero-engine-derived innovation in marine engineering. To ensure the reliable application of ARES for the systematic designs of ODW pumps, the present investigation focuses on prediction accuracy. Global and local statistics are compared between numerical estimates and available measurements of three test cases: two single rotors and a rotor–stator waterjet configuration. At mass flow rates near the design point, hydraulic efficiency is predicted within $1\%$ discrepancy to tests. Differently, as the flow coefficient increases, the loss prediction accuracy degrades, incrementing the error for off-design estimates. Spanwise velocity and pressure distributions exhibit good alignment with experiments near midspan, especially at the rotor exit, while end-wall boundary layer complex dynamics are hardly recovered by the present implementation. Full article

Axial flow fans, used for heat dissipation in electronic equipment, may generate significant electromagnetic interference during PWM speed regulation. Due to its multiple radiation sources and relatively smaller size compared to the equipment, the radiation prediction model for equipment-level EMC analysis often involves a huge number of grids, which leads to computational difficulties and inefficiencies, and thus an equivalent modeling method for the electromagnetic radiation of PWM fan is presented. First, a detailed field-circuit coupling model of the radiation from winding and driving circuits is established using the time-domain finite-integral method with non-uniform grids. Then, a near-field hexahedron is defined to surround the fan, and the electromagnetic field of all its surfaces is derived based on the Huygens principle and calculated. Finally, the hexahedron encapsulating all radiation sources within the fan can be used in a higher level simulation as replicable and reusable equivalent sources. The proposed method is validated by a numerical example and actual measurements and applied to predict the radiation emissions within an electronic enclosure. The results show that the equivalent model can reduce 81.4% computation time and maintain good consistency in comparison to the detailed field-circuit coupling model. Full article

Tip leakage flow interacts with the mainstream, impacting the energy transmission process within the impeller of the fan and causing a significant flow loss. Understanding the flow characteristics within the impeller is a prerequisite and foundation for achieving efficient operation of the fan. Therefore, numerical simulations and experimental methods were employed to obtain the internal flow field of the mining counter-rotating axial flow fan, and the influence of flow rate on the tip leakage flow pattern was mastered. The spatial trajectory of the leakage vortex was quantified, and the distribution characteristics of the backflow were explored. The mechanism of energy loss caused by the leakage flow was revealed. The research findings indicate that when the flow rate exceeds 1.0 Q_BEP (Q_BEP is flow rate at the best efficiency point), the complex flow field near the blade tip is mainly caused by the tip leakage flow. However, the tip leakage flow and the leading edge overflow are the main factors causing disturbances in the flow field within the impeller at small flow rates. At large flow rates, the starting positions of the tip leakage vortex cores for both the front and rear impellers are located near the middle of the blade tip. As the flow rate decreases, the starting position of the vortex core gradually shifts toward the leading edge point, and the vortex structure evolves from an initial circular shape to an elliptical shape. The tip leakage flow and the leading edge overflow are the main cause of the backflow at the impeller inlet. The helical vortices caused by the tip leakage flow and the leading edge overflow, as well as the backflow in the impeller, are the key factors causing energy loss in the tip clearance flow field. Full article

Since fan blades are exposed to fatigue, and in some cases harsh loading conditions, they may exhibit fracture failures due to crack propagation, resulting in significant losses. Previous studies of crack propagation in blades are mainly confined to either simplified blade geometry or loads, resulting in a significant discrepancy between the simulated crack propagation and the real blade propagation behavior, while it is lacking for challenging shapes and loads. A co-simulation approach of FRANC3D and ABAQUS was developed to study the crack propagation of an axial-flow fan blade subjected to centrifugal, aerodynamic, and combined loads. The projected approach is validated with results obtained from analytical calculations and experiments. Meanwhile, making use of benchmarks, the Stress Intensity Factor (SIF) and the prediction of mixed-mode crack growth path are validated. Considering various loads, the crack propagation path response for the fan blade is computed for different growth steps. The results pinpoint that the crack propagation length of the crack tip center is maximum under centrifugal loading. However, the aerodynamic load led to a maximum propagation length of the crack tip endpoints. In addition, the combined force of centrifugal and aerodynamic loads limits the crack from growing. Full article

As one of the most widely used appliances in home and office scenarios over recent decades, electrical fans and their use in built environments have garnered considerable research interest. However, current methods are insufficient to reflect the overall characteristics of different types of fan equipment. This study conducted airflow field tests for six typical electrical fans and human comfort experiments across background temperature conditions of 26 °C, 28 °C, and 30 °C. The airflow test results showed the following: (1) for the mechanical airflow generated by fans, the mean airflow speed (MAS) had a strong negative correlation with turbulence intensity (Tu) and the power spectral index (β), which made Tu and β have a complementary distribution with airflow speed, meaning that areas with a higher airflow speed had lower dynamic characteristics; and (2) the form of the fan mainly affected the flow field distribution in the near-fan area (within 2 m), where tower fans and vaneless fans with elongated outlets had a mainstream airflow area that spread to about 0.2 m in width but 0.6 m in height at a distance of 0.25 m from the fan. The airflow speed distribution shape of axial-flow fans with circular outlets was circular on the test surface at the same position, with a radius of about 0.1–0.2 m. The human comfort experiment revealed that, at 28 °C, in the low-airflow-speed area (v < 1.5 m/s), the increased Tu and power spectral β of the airflow near the head and chest could reduce the thermal sensation vote (TSV). Additionally, this improvement slightly increased as the room temperature rose. When the airflow speed was high, the dynamic characteristics were generally low, and at this time, airflow speed played a leading role in reducing thermal sensation. The results of this paper have certain reference value for the improvement of comfortable dynamic characteristics and functional flow field design in subsequent fan product development. Full article

The main objective of the current study is a detailed (both numerical and experimental) investigation of the highly unsteady and complex swirl flow in a straight conical diffuser (with a total divergence angle of 8.6°) generated by an axial fan impeller. Pressure, and axial and tangential velocity profiles along several cross-sections were measured by original classical probes in two different flow regimes at the inlet: the modified solid body type of moderate swirl and the solid body type of strong swirl and reverse flow; they were additionally confirmed/validated by laser Doppler anemometry measurements. Computational studies of spatial, unsteady, viscous, compressible flows were performed in ANSYS Fluent by large eddy simulation. The fan was neglected, and its effect was replaced by the pressure and velocity profiles assigned along the inlet and outlet boundaries. The two sets of data obtained were compared, and several conclusions were drawn. In general, the relative errors of the pressure profiles (2–5%) were lower than the observed discrepancies in the axial velocity profiles (5–40% for the first and 15–50% for the second flow regime, respectively). The employed reduced numerical model can be considered acceptable since it provides insights into the complexity of the investigated swirl flow. Full article

The present study introduces a conceptual design of a small axial-flow fan. Both individual and combined effects of blade stagger angle and winglet on the performance of the fan design are investigated in design and off-design operating conditions using a computational flow methodology. A stepwise solution, in which a proper stagger angle adjustment of a specifically generated blade profile is followed by appending a winglet at the tip of the blade with consideration of different geometrical parameters, is proposed to improve the performance characteristics of the fan. The initial model comparison analysis demonstrates that a three-dimensional, Reynolds-averaged Navier–Stokes (RANS) equation-based renormalization group (RNG) k–ε turbulence modeling approach coupled with the multiple reference frame (MRF) technique which adapts multi-block topology generation meshing method successfully resolves the rotating flow around the fan. The results suggest that the use of a proper stagger angle with the winglet considerably increases the fan performance and the fan attains the best total efficiency with an additional stagger angle of +10° and a winglet, which has a curvature radius of 6.77 mm and a twist angle of −7° for the investigated dimensioning range. The present study also underlines the effectiveness of passive flow control mechanisms of the stagger angle and winglets for energy-efficient axial-flow fans. Full article

This study investigates a dual-stage axial-flow fan within a specific power plant context. Numerical simulations encompassing both steady-state and stall conditions were conducted utilizing the Reynolds-averaged Navier–Stokes (RANS) equations coupled with the Realizable k–ε turbulence model. The findings reveal that, under normal operating conditions, there exists a positive correlation between the mass flow rate and outlet pressure with gas density while displaying a negative correlation with dynamic viscosity. Regardless of the changes in air density, the volumetric flow rate at the maximum outlet pressure of the fan remains essentially the same. When a stall occurs, the volumetric flow rate rapidly decreases to a specific value and then decreases slowly. The analysis of the three-dimensional flow field within the first-stage rotor was performed before and after the rotational stall occurrence. Notably, stall inception predominantly manifests at the blade tip. As the flow rate diminishes, the leakage area at the blade tip within a passage expands, directing the trajectory of the leakage vortex toward the leading edge of the blade. Upon reaching a critical flow rate, the backflow induced by the blade tip leakage vortex obstructs the entire passage at the blade tip, progressively evolving into a stall cell, thereby affecting flow within both passages concurrently. Full article

In the mechanized harvesting of Lycium barbarum L. (L. barbarum), there are prominent problems such as low harvesting efficiency, high damage rate, incomplete separation of leaves and delayed transportation. Therefore, an integrated L. barbarum harvester was designed and developed in this study, which has the functions of picking, undertaking, transportation, winnowing and collection. The design requirements and constraints were identified by cultivation agronomy. Through simulation and physical tests, the tarpaulin was determined as the undertaking material. This machine achieved efficient picking with a vibrating picker with a multi-degree-of-freedom picking arm. The two-stage conveyor belts and the intermediate receiving plate were designed for low loss transportation of fruit. The axial flow fan and secondary buffer device were used to realize winnowing and reduce the damage rate. Through the three-factor and three-level orthogonal test, an optimal working parameter combination was determined: the vibration frequency of the picker was 20 Hz, the conveyor speed was 4 m/min, the airflow speed of the fan was 7 m/s. A field test was conducted under these parameters, and the results showed that the harvesting efficiency was about five times that of manual harvesting. The integrated L. barbarum harvester basically met the harvesting requirements and provided a new scheme for mechanized harvesting. Full article

The societal and economic reliance on non-renewable energy sources, primarily fossil fuels, has raised concerns about an imminent energy crisis and climate change. The transition towards renewable energy sources faces challenges, notably in understanding turbine shear forces within wind technology. To address this gap, a novel solution emerges in the form of the ducted horizontal-axis helical wind turbine. This innovative design aims to improve airflow dynamics and mitigate adverse forces. Computational fluid dynamics and experimental assessments were employed to evaluate its performance. The results indicate a promising technology, showcasing the turbine’s potential to harness energy from diverse wind sources. The venturi duct aided in the augmentation of the velocity, thereby increasing the maximum energy content of the wind by 179.16%. In addition, 12.16% of the augmented energy was recovered by the turbine. Notably, the integration of a honeycomb structure demonstrated increased revolutions per minute (RPM) by rectifying the flow and reducing the circular wind, suggesting the impact of circular wind components on turbine performance. The absence of the honeycomb structure allows the turbine to encounter more turbulent wind (circular wind), which is the result of the movement of the fan. Strikingly, the downwash velocity of the turbine was observed to be equal to the incoming velocity, suggesting the absence of an axial induction factor and, consequently, no back force on the system. However, limitations persist in the transient modelling and in determining optimal performance across varying wind speeds due to experimental constraints. Despite these challenges, this turbine marks a significant stride in wind technology, highlighting its adaptability and potential for heightened efficiency, particularly at higher speeds. Further refinement and exploration are imperative for broadening the turbine’s application in renewable energy generation. This research emphasizes the turbine’s capacity to adapt to different wind velocities, signaling a promising avenue for more efficient and sustainable energy production. 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