Numerical simulations of wake structure generated by rotating blades using a time marching, free vortex blob method

1999 ◽  
Vol 18 (1) ◽  
pp. 147-159 ◽  
Author(s):  
Duck Joo Lee ◽  
Seon Uk Na
Keyword(s):  
Numerical Simulations ◽  
Wake Structure ◽  
Free Vortex ◽  
Rotating Blades ◽  
Time Marching

scholarly journals Investigation of the Flow Field in the Vicinity of an Axial Flow Fan During Low Flow Rates

2014 ◽  
Author(s):  
Francois G. Louw ◽  
Theodor W. von Backström ◽  
Sybrand J. van der Spuy
Keyword(s):  
Flow Field ◽  
Numerical Simulations ◽  
Flow Rate ◽  
Axial Flow ◽  
Operating Conditions ◽  
Design Flow ◽  
Low Flow ◽  
Axial Flow Fan ◽  
Free Vortex ◽  
Flow Rates

Large axial flow fans are used in forced draft air cooled heat exchangers (ACHEs). Previous studies have shown that adverse operating conditions cause certain sectors of the fan, or the fan as a whole to operate at very low flow rates, thereby reducing the cooling effectiveness of the ACHE. The present study is directed towards the experimental and numerical analyses of the flow in the vicinity of an axial flow fan during low flow rates. This is done to obtain the global flow structure up and downstream of the fan. A near-free-vortex fan, designed for specific application in ACHEs, is used for the investigation. Experimental fan testing was conducted in a British Standard 848, type A fan test facility, to obtain the fan characteristic. Both steady-state and time-dependent numerical simulations were performed, depending on the operating condition of the fan, using the Realizable k-ε turbulence model. Good agreement is found between the numerically and experimentally obtained fan characteristic data. Using data from the numerical simulations, the time and circumferentially averaged flow field is presented. At the design flow rate the downstream fan jet mainly moves in the axial and tangential direction, as expected for a free-vortex design criteria, with a small amount of radial flow that can be observed. As the flow rate through the fan is decreased, it is evident that the down-stream fan jet gradually shifts more diagonally outwards, and the region where reverse flow occur between the fan jet and the fan rotational axis increases. At very low flow rates the flow close to the tip reverses through the fan, producing a small recirculation zone as well as swirl at certain locations upstream of the fan.

scholarly journals Aeroacoustic Analysis of the Tonal Noise of a Large-Scale Radial Blower

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Aurélien Marsan ◽  
Stéphane Moreau
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Navier Stokes ◽  
Noise Generation ◽  
Tonal Noise ◽  
Radiated Noise ◽  
Rotating Blades ◽  
Reynolds Averaged Navier Stokes ◽  
Generation Mechanisms ◽  
Made In

Large-scale radial blowers are widely used in factories and are one of the main sources of noise. The present study aims at identifying the noise generation mechanisms in such a radial blower in order to suggest simple modifications that could be made in order to reduce the noise. The flow in a representative large-scale radial blower is investigated thanks to unsteady Reynolds-averaged Navier–Stokes (URANS) numerical simulations. The radiated noise is calculated, thanks to an in-house propagation code based on the Ffowcs Williams Hawkings' (FWH) analogy, SherFWH. The results highlight the main noise generation mechanisms, in particular the interaction between the rotating blades and the tongue, and the interaction between the rotating blades and the trapdoors located on the volute sidewall. Some modifications of the geometry are suggested.

Wake structure analysis of wind turbines based on a free vortex wake model

2016 ◽  
Author(s):  
Bo-Feng Xu ◽  
Li Chen ◽  
Zhen-Zhou Zhao ◽  
Yue Yuan ◽  
Tong-Guang Wang
Keyword(s):  
Structure Analysis ◽  
Wind Turbines ◽  
Vortex Wake ◽  
Wake Structure ◽  
Free Vortex ◽  
Wake Model

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

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