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The monitoring point diagram and directivity curve of CRF under different axial spacing. (a) Monitoring point diagram. (b) 310 Hz. (c) 620 Hz. (d) 930 Hz.
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Because of the potential technical advantages, the contra-rotation technology has become a renewed interest in aviation and other applications. Contra-rotation increases efficiency in comparison with the single-rotor design, but this advantage is not fully harnessed. The axial spacing of two-stage contra-rotating blade rows has a significant impact...
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Citations
... Ravelet et al [16] designed three contra-rotating stages with different rotational speed ratios, mean stagger angles of blades and repartitions of blade loads between two rotors to study the global characteristics and the unsteady features of the flow. Luan et al [17] studied the acoustic and vibration effects of the axial spacing based on the experimental analysis and numerical calculation. Ai et al [18] performed experimental studies on the rotational speed matching of two rotors and analyzed its impact on the stable margin and efficient working range. ...
Introduction: In the present paper, experiments for a contra-rotating axial fan have been conducted to investigate the influences of the fan parameters including axial distance, blade number, blade pattern and blade thickness on the performance and noise characteristics under variable rotational speed regulation.
Methods: The characteristic curves and spectrum characteristics of the contra-rotating axial fan with different structural configurations are compared and analyzed. Moreover, the spectrum density of the velocity obtained from the experiment is compared with the classic turbulence models.
Results: The results show the characteristic curves of the shaft power and the sound pressure level (SPL) are nearly identical, which indicates the axial distance and blade number are not sensible factors for the contra-rotating axial fan under variable rotational speed regulation. The blade profiles of the fan have an impact on the characteristic curves of the SPL and the shaft power curves of the fan decrease evidently with increase of the blade thickness, while the shaft power curves are very close with different blade patterns.
Discussion: In general, the blade profiles are sensible factors for the contra-rotating axial fan under variable rotational speed regulation. Through the SPL spectrum analysis of the contra-rotating axial fan with different blade profile, it can be concluded that the blade profile of the rotors has an obvious impact on the broadband noise characteristics under moderate and high frequency range.
... That raises the question of why it is not popular despite its improvement in power efficiency when compared to a conventional single fan setup [3]. Although contra-rotating propellers can offer more power for a given radius compared to a conventional one-fan setup, cancelling out the heeling moment or torque effect produced by one propeller [4,5], and generally improves the efficiency [6], it also brings forth a few disadvantages. Among the disadvantages of the counter-rotating propeller was a noisy from the fan. ...
... The unsteadiness of rotor 1 is caused by the potential disturbance, and the upstream wake leads to the strong unsteadiness of rotor 2. The mean value of sound pressure level decreases by 17.2 dB in total when the axial spacing increased to 1.1 chords from 0.3 chords. With two sets of blades on one shaft and the mechanism to invert the rotating direction for one of the propellers increase the complexity of the whole system [4]. The increased part count also made the system more expensive when compared to a conventional setup. ...
A contra-rotating fan is a mechanism that most used in aviation and marine propulsion system. It has two fan rotors sharing the same driveshaft but spinning in opposite direction by mechanical means. However, its implementation outside of the fields is scarce, possible due to its mechanical difficulty, assembly, and maintenance cost. The objective of this study is to investigate the validity of the advantages brought forth by contra-rotating fans using numerical simulation. The model of the contra-rotating fans was designed by using SolidWorks software and numerical simulation performed by using ANSYS Fluent. The inlet velocity was set at 0 m/s for the control set and 15 m/s for performance evaluation. The results showed that contra-rotating fans performed better in terms of velocity contour and flow streamlines, albeit having lower centreline velocity. From the results obtain, contra-rotating fans are shows to be able to produce a straighter and more focused airflow than a conventional single fan setup.
... Previous studies indicated that the capacity of MCRFs can be modified by optimizing the design of the impeller structures and the angles of installation. (10)(11)(12)(13)(14) Some studies (15)(16)(17)(18)(19) found that optimizing the gap between the impeller tips of rotors may significantly improve the efficiency and stability of operation for an MCRF system. This is because the gap size of R1 may affect the occurrence and development of a turbulence trail in the impeller tip region, and thus the flow conditions in the impellers of R2. ...
... Following this, they studied the relationship between different axial gaps and the unsteady influence on the CRF blade boundary layers [6], finding that, with the increment of the axial gap, the inhibition for separation in the RR boundary layers was weakened, since the rotor-rotor interaction of the CRF was weakened and the blade deformed. However, this had little effect on the radiation noise [7]. Ravelet et al. [8] redistributed the loads of a CRF load by applying three sets of speed ratios. ...
In recent years, few studies focused on adjusting the load distribution of contra-rotating fan (CRF) blades. To improve the overall performance of CRFs, we used a design code to build 32 sets of CRFs to determine the effects of three factors—the front and rear rotor load matching, the load distribution of each rotor and the axial distance between the rotors—on the total pressure rise and efficiency of CRFs using numerical calculations. The relationship between the CRF blades load and velocity components was theoretically analyzed using blade element analysis and the forward problem method. According to the performance curve, it can be concluded that the rear rotor (RR) is the key factor that determines the performance of CRFs. Through analyzing Mach number contours from different perspectives, the relationship between velocity and adjustment load was verified. Furthermore, the flow field characteristics for three specific CRFs were explored at the stall points, design points and choke points to reveal their flow mechanisms. This study provides a reference for the CRF blade design method.
... [17][18][19] With an increase in this axial spacing, the rotor-rotor interactions weaken, while the unsteady features of the two-stage rotor blades tend to be consistent. 20 The performance of an MCRF can also be improved by using an unequal power design for the two rotors, adjusting the blade installation angle, or adjusting the turning and twisting angles. 21 Optimizing the shape of the blades based on aerodynamic, structural, and aeroacoustic criteria could serve as a new multiobjective optimization technique for improving the performance. ...
Existing methods of improving the performance of mine counter‐rotating fans (MCRFs) through speed matching of the rotors have certain drawbacks. This study proposes a variable‐speed method for the two rotors of an MCRF to improve its performance, including the blocking margin, operational safety, high‐efficiency working range (HER), and stability margin. Experimental and numerical methods were used to study the pneumatic performance of the MCRF. The results show that the second rotor (R2) is the critical stage affecting the safety of the motor, HER, and blocking margin. A condition‐adaptive speed matching method was proposed for R2 to avoid overloading the second motor at low‐flow rates and to improve the blocking margin and HER. The first rotor (R1) is the critical stage determining the stability margin of the MCRF. Reducing n1 and increasing n2 at low‐flow rates helped extend the stability margin.
Wheat flour was used in varying proportions ranging between 90% and 40% along with10% to 60% maize flour for the preparation of edible tableware. The best treatment was selected through organoleptic evaluation and textural properties. Among the various combinations, 90 percent wheat flour and 10 percent maize flour was found to be better than other combinations in regards to organoleptic and textural properties. The selected edible tableware was subjected to proximate analysis and observed to have moisture (2.92%), energy (405.98 kcal), protein (13.58 g 100 g-1), fat (3.18 g 100 g-1), carbohydrate (80.76 g 100 g-1), fibre (0.93 g 100 g-1) and total ash (1.56 g 100 g-1). The selected edible tableware was subjected to physico-chemical analysis and observed to have pH (5.28), water absorption index (5.24%), water solubility index (7.76%) and oil absorption capacity (2.20%). The cost of the selected edible tableware was Rs.30.56 per 100 g, which was less than the price of similar products in the market. Biodegradable tableware plays vital role in green marketing for sustainable environment.
In this paper, a three-dimensional calculation model of a two-stage adjustable-blade axial-flow fan is established and verified by grid independence and numerical accuracy. The pressure distribution and sound power level distribution characteristics of the blade surface are explored with variable blade installation angles. Based on the Q-criterion, the study reveals the spatial distribution of the channel and trailing edge shedding and channel vortexes in the flow field. Then, the evolution laws of the fan's aerodynamic noise sound pressure level are also investigated, and its frequency domain characteristics with variable blade installation angles are obtained. The results show that when the rotor blade installation angle is -5{degree sign}, the front-guide vane matches the installation angle of the first-stage impeller. The upper limit of sound power level is the smallest with variable blade installation angles, which is 123.56 dB. Meanwhile, the number and size of vortex structures in the front-guide vane area are the smallest, and the turbulent flow in the flow field is moderate. As the moving blade installation angle is deflected from -10{degree sign} to 10{degree sign}, the total sound pressure level of aerodynamic noise at each component of the fan first decreases and then increases. The minimum value is 121.40 dB and 128.40 dB at the inlet and outlet when the blade installation angle is -5{degree sign}. In addition, the number of eddies periodically shed in the fan flow field is the least. This research can supply technical support for the noise reduction of the two-stage adjustable blade axial fan.
The aviation sector is rapidly evolving with more electric propulsion systems and a variety of new technologies of vertical take-off and landing manned and unmanned aerial vehicles. Community noise impact is one of the main barriers for the wider adoption of these new vehicles. Within the framework of a perception-driven engineering approach, this paper investigates the relationship between sound quality and first order physical parameters in rotor systems to aid design. Three case studies are considered: (i) contra-rotating versus single rotor systems, (ii) varying blade diameter and thrust in both contra-rotating and single rotor systems, and (iii) varying rotor–rotor axial spacing in contra-rotating systems. The outcomes of a listening experiment, where participants assessed a series of sound stimuli with varying design parameters, allow a better understanding of the annoyance induced by rotor noise. Further to this, a psychoacoustic annoyance model optimised for rotor noise has been formulated. The model includes a novel psychoacoustic function to account for the perceptual effect of impulsiveness. The significance of the proposed model lies in the quantification of the effects of psychoacoustic factors, such as loudness as the dominant factor, and also tonality, high frequency content, temporal fluctuations, and impulsiveness on rotor noise annoyance.
