NASA Low-Speed Centrifugal Compressor for Fundamental Research

A centrifugal compressor facility being built by the NASA Lewis Research Center is described; its purpose is to obtain benchmark experimental data for internal flow code verification and modeling. The facility will be heavily instrumented with standard pressure and temperature probes and have provisions for flow visualization and laser Doppler velocimetry. The facility will accommodate rotational speeds to 2400 rpm and will be rated at pressures to 1.25 atm. The initial compressor stage for testing is geometrically and dynamically representative of modern high-performance stages with the exception of Mach number levels. Design exit tip speed for the initial stage is 500 ft/sec with a pressure ratio of 1.17. The rotor exit backsweep is 55 deg from radial

OPTIMIZATION TO INCREASE ENERGY EFFICIENCY OF A SIROCCO CENTRIFUGAL FAN USING COMPUTATIONAL FLUID DYNAMICS (CFD)

This paper presents a numerical and experimental study on the aerodynamic performance of Sirocco centrifugal fans seeking an increase in energy efficiency. Numerical simulations are performed by the Finite-Volume Method commercial code ANSYS Fluent. Characteristics such as flow rate at the outlet, consumed power and sound pressure levels emitted by centrifugal fans with the original model of 16 blades and the optimized models of 16 and 14 blades are compared. Numerical calculations are performed by the continuity equation, the Reynolds Averaged Navier- Stokes (RANS) equations and the k-ω SST turbulence model. The quality of the mesh is evaluated for three different mesh densities. Results demonstrate that it was possible to obtain an increase of flow rate up to 22.7%, and reductions in the noise levels without increasing the consumption of the electric motor

Tonal Noise of Voluteless Centrifugal Fan Generated by Turbulence Stemming from Upstream Inlet Gap

Volutes for radial-flow turbomachines (e.g., centrifugal fans and pumps) are spiral funnel-shaped casings that house rotors. Their function is to guide the flow from rotors to outlets and maintain constant flow speeds. Under specific conditions, however, volutes are removed (termed voluteless) to reduce flow losses and noise. In this paper, a generic voluteless centrifugal fan is investigated for the tonal noise generation at an off-design operation point. In contrast to typical tonal noise sources induced by the fan blades, we find out that another predominant source is the turbulence stemming from the clearance gap between the fan front shroud and the inlet duct. The turbulence evolves along with the front shroud and is swept downstream to interact with the top side of the blade leading edge. An obvious additional tone is observed at\ua0273 Hz other than the blade passing frequency (BPF0) and relevant harmonic frequencies. By coarsening the mesh resolution near the inlet gap and front shroud in the simulations, we artificially deactivate the gap turbulence. Consequently, the tone at\ua0273 Hz disappears completely. The finding indicates that the interaction between the gap turbulence and blades accounts for the tone. As the gap turbulence exists near the front shroud, this rotating wall introduces rotational momentum into the turbulence due to skin friction. Hence, this tonal interaction frequency is smaller than\ua0BPF0 with a decrement of the fan rotation frequency. To the authors\u27 knowledge, this is the first time that voluteless centrifugal fans are studied for the gap-turbulence noise generation

ファンから生じる空力騒音の予測と低減に関する計算的研究

Turbomachinery is machinery device in which energy is delivered either to or from fluid that is continuously moving due to action of moving blades. Performance and flow noise are two major indices for evaluation of turbomachinery. In terms of energy transfer, researches on performance of turbomachinery have been conducted since long time ago; and these researches for performance improvement are still ongoing currently. In addition, flow noise produced by turbomachinery came to the fore as turbomachinery has been used in various fields and everyday life closely and frequently. Especially, consumers’ demand on improvement in affective quality has been increased and regulation on noise has been being reinforced due to damages and adverse effects caused by noise. Therefore, development of high performance and low noise turbomachinery is highly required. Meanwhile, experimental methods have been used to develop low noise turbomachinery; however, the experimental methods solely are not sufficient to achieve such aim since measuring in small turbomachinery is challenging. Hence, prediction technique, to which the numerical analysis method that yields complementary effects in combination with the experimental methods is applied, is required. This study was conducted with the aim of applying numerical analysis method for noise reduction in turbomachinery. Therefore, three-dimensional unsteady Navier-Stokes equations were solved to simulate the flow field. Turbulence models used to predict the flow field were SST k–ω model that provides outstanding simulation of separation and adverse pressure gradient in boundary layer and LES model that presents excellence in turbulence intensity modeling, respectively. Computational Aeroacoustics (CAA) used to predict the flow noise in this study was acoustic analogy that is one of the hybrid methods; and the acoustic analogy is the method analyzing unsteady flow field by using Computational Fluid Dynamics (CFD) and then predicting noise by using the information of unsteady flow field obtained from the results of CFD simulation. To conduct acoustic analogy, Lowson equation, which can be used to predict sound pressure for point force that is moving in a free field, was calculated. Despite of disadvantage that influence of an object including scattering, diffraction, and reflection within acoustic field is difficult to be considered, this method that directly reduces noise sources was able to be drawn since the locations of the noise source can be seen by numerical approach. Because predicting the location of the noise source is able to figure out the unsteady flow which causes the noise. As a result, the reduction method of flow-induced noise in this study is to find the way to reduce or remove the unsteady flow generating the noise, based on CAA and CFD. In order to indicate the location of the noise source, “Aeroacoustic source strength, Ast” was defined and compared with the location of the noise source measured by the acoustic camera to which beamforming technology is applied; and they were agreed qualitatively well each other. Due to miniaturization of electronics and maintenance of fan performance, whereas size of fan is getting smaller, the rotational speed of it getting higher. In this study following the current trend, three fans with each other different type were used for adopting numerical method to noise reduction; ⅰ) a small axial fan of rotor’s diameter D = 0.166 m and a rotation speed 2860 rpm with circular shroud, ⅱ) a small axial fan of rotor’s diameter D = 0.076 m and a rotation speed 7000 rpm with square-type shroud used in a rack mount server computer, ⅲ) a small centrifugal fan with rotor’s diameter D = 0.032 m and a rotation speed 10460 rpm used as a cooling fan in portable home electronics such as a small laptop computer. The noise of each type fan was predicted and compared with the measured noise. The predicted noise and measured noise presented agreement in tonal noise of the blade passing frequency (BPF) and its harmonic frequencies and in the broadband noise at low frequency. Although the broadband noise at high frequency was somewhat different due to random broadband noise, the shapes for noise reduction were able to be drawn effectively by predicting the location of the noise sources. Low noise models suggested for noise reduction provided the result of noise reduction from the prediction and specific noise level was used to evaluate the noise reduction considering the changes in fan performance. In case of the axial flow fan with circular shroud, the interaction between the rotating rotor blades and the flow separated from the inlet of the shroud was found to be the major cause of the noise through the analysis on the location of the noise sources and unsteady flow field. Consequently, reduction of the flow noise was predicted by correcting the shape of the shroud inlet. In the small axial flow fan installed in the rack mount server computer, the tonal noise occurring by irregular clearance between the blade tip and the shroud due to the square-shaped shroud was well predicted. In addition, coherence analysis was conducted to identify the relationship between the surface pressure fluctuation due to the flow and the sound pressure predicted from the microphone. As a result, the correlation for each frequency was well presented. For a centrifugal fan that is used as a cooling fan in home electronics such as a portable small laptop computer, the flow structure of the centrifugal fan was simulated by setting the condition to be analogous to the operating condition within the actual product. And then the reduction of the flow noise was predicted by correcting the tip of the impeller blades based on the location of the noise sources. This study aimed to apply the method of numerical analysis to the noise reduction in turbomachinery. For this, the unsteady flow field was analyzed, the result of noise prediction obtained from the flow filed information was compared and validated, and the location of the noise sources and the structure of the flow field causing the noise were understood; hence, the low noise design was able to be drawn effectively and properly. In this study, the reduction of the flow noise was successfully achieved by adopting the method of numerical analysis and the flow noise of the fan that were improved for noise reduction was predicted to be reduced by 0.8 and 3.7 dB, respectively.博士(工学)法政大学 (Hosei University

Application of active flow control technology in an unmanned aerial vehicle

A low speed wind tunnel experimental investigation was conducted to determine the effectiveness of the leading edge pulsed blowing and the trailing edge jet blowing/ Gurney flap on the improvement of aerodynamic performance of an unmanned aerial vehicle at low Reynolds numbers. The wind tunnel tests for the leading edge pulsed jet blowing were conducted at 10%, 30% and 50% location of the chord length from the leading edge at a free stream velocity of 20 m/s. The jet momentum coefficient and the non-dimensional pulser frequency had been varied independently to investigate the effectiveness of the leading edge pulsed blowing. The trailing edge jet blowing tests were conducted at free stream velocity of 20 m/s at different jet momentum coefficients. The leading edge pulsed blowing showed a strong dependency of the actuator effectiveness on the jet momentum and the pulser frequency. The leading edge pulsed blowing had delayed the flow separation over the airfoil from an angle of attack of 17° to 22° with a docile stall for jet emanating at 10% location of the chord length for a jet momentum coefficient of 0.0275. The pulsed blowing at 50% chord location generated higher lift compared to the 10% location of the pulser with an abrupt stall at 19°. There was no evidence of the lift augmentation in the pre-stall angle of attack regime. The experimental results showed that the trailing edge jet flap was capable of generating significant roll moment at realistic jet momentum coefficients. The fluidic actuators were then integrated into the wings of a scale Extra 330 model airplane. The wind tunnel results for the leading edge pulsed blowing on the scale model indicated a delay in the stall of the airplane from an angle of attack of 12° to 21° with a 13% increase in the lift at take-off and landing speed of 17 m/s. The trailing edge jet actuators were also able to augment lift and demonstrate the roll control authority at low angle attacks at a cruising speed of 30 m/s

Inlet Gap Effect on Aerodynamics and Tonal Noise Generation of a Voluteless Centrifugal Fan

In this paper, the gap effects on the aerodynamics and tonal noise generation of voluteless centrifugal fans are studied based on different gap geometries. The study is motivated by the state of the art of this type of fan, for which the tonal noise generation due to the gap turbulence has not been addressed concerning the gap geometry, while a recent study reported that there is tonal noise at the blade passing frequency (BPF) from the gap turbulence. We simulate the configurations using a hybrid method coupling the improved delayed detached eddy simulation (IDDES) with Formulation 1A of Farassat. Our simulation shows regions with high vorticity magnitudes in the channel between two blades near the trailing edges close to the shroud. The turbulence renders a uniform pressure rise. By changing the gap design, the turbulent regions can be reduced. The configurations show a similar trend of the root mean square (RMS) pressure on the blade leading edge (BLE), largest at the shroud, and decays when the distance to the gap increases. The gap designs affect the amplitude of the RMS pressure, which is connected to the BPF. Spectral analysis is performed for the surface pressure fluctuations and the sound pressure upstream of the fan. The surface pressure fluctuations show that, for all cases, the regions with high energy are identical to the locations where the gap turbulence evolves and accounts for the impingement on the BLE. The amplitude of the tonal noise at the BPF differs between the cases

Effect of Forward Sweep on the Performance of an Axial Blower

Effects of changing the blade sweep without redesigning the datum blade sections are studied on the pressure rise, efficiency and 3D flow field of an axial blower. Four forward swept blade configurations (5°, 10°, 15° and 20°) are compared with an unswept blade. RANS and URANS simulations are carried out for the aerodynamic performance analysis and 3D flow field behaviour. Results indicated higher pressure rise and wider stall margin thus improved efficiency with higher forward sweep angles

ターボ機械の最適化と設計知識マイニング

Tohoku University大林 茂課