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The use of straighteners in the inlet duct of centrifugal fans is suggested for eliminating any inlet distortion. An experimental investigation was performed to study the effect of inlet straighteners on the performance characteristics of centrifugal fans. Two types of straighteners were used, circular tubes and zigzag cross section, with different...
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The use of straighteners in the inlet duct of centrifugal fans is suggested for eliminating any inlet distortion. An experimental investigation was performed to study the effect of inlet straighteners on the performance characteristics of centrifugal fans. Two types of straighteners were used, circular tubes and zigzag cross section, with different...
Citations
... Due to the nature of their use, these devices should be characterized by operational efficiency, which is measured by the generated flow parameters [4,5]. Flow parameters, including the amount of air injected into the interior of a building, will depend on the device's power [6,7], rotor size [8] (including the presence of a flow straightener on its surface [9]), rotor blade geometry [10,11] or mechanisms for changing it [12,13], and positioning parameters, such as the distance from the door opening and the rotor's angle of inclination. There are numerous scientific studies 2 of 19 in the literature aimed at evaluating the parameters that influence operational efficiency. ...
Determining the appropriate position of a positive pressure ventilator, where it exhibits the highest efficiency (measured by the achieved volumetric flow rate), can influence the success of rescue operations conducted by fire protection units. The aim of this article is to evaluate the possibility of using LES (Large Eddy Simulation) analyses to verify the positioning parameters of positive pressure ventilators in numerical simulation conditions, without the need for time-consuming experiments. The article presents a comparative analysis of full-scale experimental studies (conducted on a test setup to assess the velocity profile of the air jet in open flow) and CFD numerical analyses. The analysis confirmed the convergence of the flow rate parameter entering the surface of the door opening model installed on the test setup. Depending on the distance of the ventilator position (1–7 m), a convergence degree ranging from 1.6% to 3.8% was achieved for the volumetric flow rate. This publication demonstrates that the LES model is a suitable tool for effectively determining the working positions of positive pressure ventilators, as defined in real working conditions (open flow). The analysis may serve as a helpful tool for manufacturers of mobile ventilators, who can use the method for the technological testing of their units without conducting time-consuming experiments.
... However, due to the mechanical structure of squirrel-cage fans, the flow direction undergoes an axial-to-radial transition when the airflow enters the moving blade from the inlet channel. This transition results in a separated flow at the fan's inlet, causing a strong inhomogeneity in the airflow when it enters the impeller, which is commonly referred to as inlet distortion [4,5]. ...
In order to improve the inlet distortion of the squirrel-cage fan, this study proposes a parametric design method for the bionic structure of the inlet nozzle generatrix, which is spliced by multiple sinusoidal curves, based on the bionic structure of the humpback whale flipper leading-edge nodule. The geometric shape of the bionic generatrix is controlled by three parameters: the number of segments n, the amplitude ratio Tm, and the amplitude of the last curve An. These parameters are optimized through orthogonal tests and numerical simulations, with the aim of improving the fan’s aerodynamic efficiency. Based on the selected solution, a comparative analysis is conducted to examine the impact of cylindrical, conical, and bionic inlet nozzles on inlet distortion and flow evolution within the centrifugal fan. Numerical calculations demonstrate that the fan’s maximum total efficiency, with a bionic inlet nozzle designed in a rational manner, is 5.46% higher than that of the original fan and is 2.01% higher than that of the fan with a conical inlet nozzle. The proposed bionic structure can create a buffer zone at the fan’s inlet, thereby reducing the region of high vorticity caused by the separated flow. Consequently, this improvement leads to enhanced uniformity at the impeller’s inlet. Furthermore, the design method proposed in this study for the inlet nozzle’s bionic structure effectively regulates the airflow angle near the impeller shroud, thereby enhancing the fan’s inlet distortion and improving its overall aerodynamic performance.
... This difference leads to higher outlet flow velocities and Reynolds numbers in larger centrifugal fans, contributing to notable flow separation at the blade trailing edges-a critical aspect of understanding fan dynamics. Furthermore, conventional fans typically feature an inlet straightener, which not only enhances aerodynamic performance [12] but also helps in noise reduction, emphasizing the dual functionality of this component in optimizing fan operation. In the context of miniature fans, where blade height is minimal and the Mach number of the flow does not exceed 0.1, it is feasible to disregard monopole and quadrupole noise sources. ...
This study employs a combined approach of numerical simulation and experimental methods to investigate the flow and noise characteristics of miniature centrifugal fans used in portable
electronic devices under free inflow conditions. It compares the effects of serrated structures located at the fan inlet and the blade tips on the flow field and aerodynamic noise. The study utilizes Large Eddy Simulation to capture the flow field within the fan accurately and measures the far-field noise spectrum and directivity. By integrating the pressure fluctuations on the fan
blades and upper casing walls in the frequency domain, the research reveals the distribution of dipole sound sources and uses the Q-criterion to visualize the vortex structures inside the
fan. The results uncover the flow and noise characteristics of the miniature centrifugal fan and analyze the impact of the serrated structures on these properties. It was found that tonal noise
is primarily caused by concentrated intake at the inlet of such miniature centrifugal fans. The contribution of the vortex tongue to noise generation is minimal and predominantly contributes
to low-frequency broadband noise. The comparative analysis shows that properly designed serrated structures at the inlet can effectively suppress the generation of BPF tonal noise and that
appropriately designed serrated structures at the blade tops can effectively weaken broadband noise and alter the distribution of broadband pressure fluctuations on particular fan casing walls.
... According to the authors' knowledge, comparable experimental approaches for the investigation of various flow-induced sound generation mechanisms on radial fans are not available in the literature (cf. [29], [30] and [31]). The work of Choi [19], however, points in this direction and can therefore be regarded as a stimulus for the chosen approach. ...
https://authors.elsevier.com/a/1hUfN,5MxpIDt
A low sound pressure level is a crucial quality feature for industrial and non-industrial radial fans. The scientific literature documents numerous mechanisms of flow-induced sound generation that can occur in a radial fan. Nevertheless, not all sound generation mechanisms are considered well-understood today and thus are still dealt with in ongoing research. This work develops an experimental setup to investigate the different mechanisms of flow-induced sound generation in radial fans. The aim is to close the existing gap between available experimental research on axial and radial fans. One critical factor for the experimental investigation of flow-induced sound generation in fans is the control of inflow. Due to the design of radial fans, the fluid flow deflects from the axial supply duct to the radial direction upstream of the impeller, generating a complex flow field with limited control possibilities. Hence, we designed a test rig that improves the control of inflow conditions, aiming to resolve the superposed sound generation mechanisms in acoustic measurements. This paper presents the key features of the test rig and some first experimental results. The investigation of the distinct sound generation mechanisms is left to future work based on the introduced test rig.
... On this basis, Howe [91][92][93] predicted and analyzed the noise reduction value of a flat airfoil with a serrated trailing edge when the angle of attack was 0 • at low turbulence. He assumes that the sawtooth spacing is λ and the height is 2 h, as shown in Figure 24, and the noise reduction is at least 10 log 10 1 + (4h/λ) 2 dB when the sound frequency meets ωh/U 1. ...
... reduction ability [90]. On this basis, Howe [91][92][93] predicted and analyzed the noise reduction value of a flat airfoil with a serrated trailing edge when the angle of attack was 0 at low turbulence. ...
Due to the complexity of the working conditions and the diversity of application scenarios, the normal operation of a fan, whether volute tongue, volute shell surface, or blade, often encounters some unavoidable problems, such as flow separation, wear, vibration, etc.; the aerodynamic noise caused by these problems has a significant impact on the normal operation of the fan. However, despite the use of aerodynamic acoustics to design low-noise fans or the use of sound absorption, sound insulation, and sound dissipation as the main traditional noise control techniques, they are in a state of technical bottleneck. Thus, the search for more efficient methods of noise reduction is looking toward the field of bionics. For this purpose, this paper first analyzes the mechanism of fan noise in the volute tongue and blades, and then, this paper reviews the noise control mechanism and improvement research using the bionic structures in the volute tongue structure, the contact surface of the volute shell, and the leading and trailing edges of the blade in the centrifugal fan. Finally, the current challenges and prospects of bionic structures for aerodynamic noise control of centrifugal fans are discussed.
... The multi-wing fan, belonging to centrifugal fans, is widely used in the central air-conditioning industry (Khelladi et al. 2008). In general, researchers try to control the unsteady flow (Kolmogorov 1991;Sipp and Jacquin 2008;Lee et al. 2004;Kolář and Šístek 2015;Lun et al. 2019a) and suppress the aerodynamic noise by modifying the volute tongue of centrifugal fans (Bayomia et al. 2006;Darvish et al. 2015;Mao et al. 2018;Kim et al. 2019;Yang et al. 2019). ...
Multi-wing centrifugal fans are wildly used in the central air-conditioning. The influence of dimensionless clearance of the volute-tongue on aerodynamic performance and noise is studied by numerical simulation and experimental tests in this paper. The complicated internal flow related to unsteady flow in a centrifugal fan with multiple wings is investigated by numerical simulation. Besides, the influence of circumstance on the noise is analyzed. It is testified that the internal flow of centrifugal fans is ameliorated using appropriate volute tongue clearance. Reduced eddy current decreased the local-flow loss near the volute tongue and exit. The experimental results show that the static pressure of model △t/R2=0.12 rose to 7.5 Pa and the aerodynamics noise value reduced to 4 dB compared with that of a reference model. Meanwhile, an obvious reduction of aerodynamics noise by 3.74 dB is obtained for model △t/R2=0.12 installed in the air conditioning unit. The static pressure of centrifugal fan is significantly improved for the model with a cochlear tongue clearance ratio of △t/R2=0.12. It is further demonstrated that the proper dimensionless distance effectively suppresses the aerodynamic noise of forward multi-wing fans.
... They concluded that the uniform flow at the upstream of impeller inlet is helpful for improving cavitation performance of the pump. Bayomi et al. (2006) used unique concept of straighteners in the inlet duct of centrifugal fan for the purpose of elimination of inlet flow distortion, using the experimental analysis. They used two types of straighteners, namely, circular tubes and zigzag cross section, with different lengths. ...
Background
One of the problem areas of fluid flow in the turbomachine is its inlet region, manifested by flow distortions due to the induced fluid swirl accompanied by improper flow incidence onto the impeller. Further, the hub forms one of the main components of many of the turbomachines and it is found that there has not been significant study on geometrical modifications of the same in centrifugal fans for augmented performance. This is partially due to designers trying to reduce the cost of the overall machine.
Objective
There is a scope for detailed parametric study and the present work involves an exploration of flow behavior by parametric variation of hub geometry in terms of both its shape and size.
Methods
Experiments are carried out in order to determine the importance of hub with different size and shapes. The geometric models of hemi-spherical and ellipsoidal hubs are considered for the analyses in the present study.
Results
An optimized ellipsoidal hub configuration is found to yield a relative improvement of about 7.5% for head coefficient and 7.7% increase in relative theoretical efficiency over the hub-less base configuration. Finally, correlations are developed for the optimized hub shape configurations.
Conclusion
It is revealed from experimental analysis that hub plays a vital role in streamlining the flow at the inlet to the centrifugal fan and augments its performance.
... Zachos et al. [17], Vagnoli and Verstraete [18], Shaw et al. [19] and Frohnapfel et al. [20] all conducted numerical simulation on distortion flow characteristics of the intake connected to compressors. Straighteners in the inlet duct were used to eliminate inlet distortion [21], and an experimental investigation was carried out to study the effect of inlet straighteners on centrifugal fans performance. Physical mechanisms which govern the fan response to inflow distortions were identified and how inlet distortion varies at the design flow coefficient was determined [22]. ...
Pressure drop inside the compressor L-inlet duct (CLID) has a great impact on the intake loss, which directly affects the operating cost of the power plant. Generally, every 500Pa inlet pressure drop is equivalent to 0.5% intake loss at standard conditions, which can contribute to higher than 1% of gas turbine power loss in terms of fuel flow. Hence, the pressure drop should be kept as low as possible. Pressure drop that occurs within the CLID mainly depends on the structural parameters, however, no general design guidelines were found in open literature. Moreover, a reasonable intake duct aerodynamic design is the fundamental solution to the problem of compressor inlet distortion. Therefore, in this paper, the fluid dynamics of CLID are revealed by using both the experimental and numerical methods. Then, the effects of typical parameters on the pressure drop and total pressure loss coefficient are investigated. Furthermore, the conceptual design of CLID is proposed on the basis of distortion flow analysis and 1D intake volute design. The results show that larger CLID width (a/D4) and depth (b/D4) result in larger flow separation at the contraction, thereby leading to smaller total pressure drop and total pressure loss coefficient. However, the opposite change occurs at the cone diameter (D0/D4). Besides, the conceptual design of CLID is proposed by indirectly establishing the relationship between the outlet flow angle and inlet structural parameters.
... Similar results were investigated by Galindo et al. [5][6][7], Hou et al. [8], Elkamel [9], Marelli et al. [10] and Serrano [11]. In contrast to Kerres' results, Bayomi [12] stated that map width enhancement is gained by assembling flow straighteners upstream of the compressor, providing a more homogeneous inflow. ...
Compressor surge has been investigated and predicted since the early days of turbomachinery research. Experimental testing of turbomachinery applications is still needed to determine whether stable compressor operation is possible in the expected application regime. Measuring compressor maps and operating ranges on hot gas test stands is common. The test benches are designed and optimized to ensure ideal inflow and outflow conditions as well as low measurement uncertainty. Compressor maps are used to match turbocharger and application. However, a shift in surge limit, caused by the piping system or application, can only be adequately addressed with full engine tests. Ideal measurements use the corresponding piston engine in the charged-air system. This can only take place in the development process, when surge detection is unfavorable from an economic perspective. The surge model for turbochargers presented here is an extension of the Greitzer’s surge model, which considers the effect of inlet throttling. Application components, such as air filters, pipe elbows and flow straighteners, reduce pressure in front of the compressor and flow conditions might differ from those in laboratory testing. Experimental results gathered from the hot gas test stand at TU Darmstadt indicate strong variation in surge limit, influenced by inlet throttling. An extension to the surge model is developed to explain the observed phenomena. The model was validated using extensive experimental variations and matches the experienced surge limit shift. Additional measurements with a piston engine downstream of the turbocharger demonstrated the validity of the surge model. The results also show that surge is a system-dependent phenomenon, influenced by compressor aerodynamics and boundary conditions.
... Although varying the blade's outlet angle does not appear to be very advantageous herein, it certainly shows the potential benefits of such a modification, especially in cases where the fan design is not optimal and demands vigorous enhancements [14]. The transient surface of the models with different outlet angles can be found [15][16][17]. Computational fluid dynamics (CFD) results were implemented to provide insight into revealing flow loss in the internal flow of fan. Thus, the prediction method of CFD is represented to study the internal flow mechanisms in the fan. ...
... In the following section, the three-dimensional equation of fluid dynamics is implemented in fluid flow analysis of the computational domain [15,16]. The incompressible Reynolds Averaged Navier-Stokes (RANS) Turbulence Models are discretized by the finite volume method [16]. ...
... In the following section, the three-dimensional equation of fluid dynamics is implemented in fluid flow analysis of the computational domain [15,16]. The incompressible Reynolds Averaged Navier-Stokes (RANS) Turbulence Models are discretized by the finite volume method [16]. The equation of fluid dynamics is: ...
The effects of single-arc blade profile length on the performance of a forward multiblade fan are investigated in this paper by computational fluid dynamics and experimental measurement. The present work emphasizes that the use of a properly reduced blade inlet angle (β1A) and properly improved blade outlet angle (β2A) is to increase the length blade profile, which suggests a good physical understanding of internal complex flow characteristics and the aerodynamic performance of the fan. Numerical results indicate that the gradient of the absolute velocity among the blades in model-L (reducing the blade inlet angle and improving blade outlet angle) is clearly lower than that of the baseline model and model-S (improving the blade inlet angle and reducing blade outlet angle), where a number of secondary flows arise on the exit surface of baseline model and model-S. However, no secondary flow occurs in model-L, and the flow loss at the exit surface of the volute (scroll-shaped flow patterns) for model-L is obviously lower than that of the baseline model at the design point. The comparison of the test results further shows that to improve the blade profile length is to increase the static pressure and the efficiency of the static pressure, since the improved static pressure of the model-L rises as much as 22.5 Pa and 26.2%, and the improved static pressure efficiency of the model-L rises as much as 5 % at the design flow rates. It is further indicated that increasing the blade working area provides significant physical insight into increasing the static pressure, total pressure, the efficiency of the static pressure and the total pressure efficiency.
