scholarly journals Explicit analytic prediction for hydrogen–oxygen ignition times at temperatures below crossover

2012 ◽  
Vol 159 (2) ◽  
pp. 748-752 ◽  
Author(s):  
Pierre Boivin ◽  
Antonio L. Sánchez ◽  
Forman A. Williams
Keyword(s):  
Analytic Prediction ◽  
Ignition Times

Non-universal scaling transition of momentum cascade in wall turbulence

2019 ◽  
Vol 871 ◽  
Author(s):  
Xi Chen ◽  
Fazle Hussain ◽  
Zhen-Su She
Keyword(s):  
Wall Turbulence ◽  
Normal Velocity ◽  
Large Set ◽  
Flow State ◽  
Energy Cascades ◽  
Full Coupling ◽  
Turbulent Momentum ◽  
Analytic Prediction ◽  
Prevailing View ◽  
Near Wall

As a counterpart of energy cascade, turbulent momentum cascade (TMC) in the wall-normal direction is important for understanding wall turbulence. Here, we report an analytic prediction of non-universal Reynolds number ($Re_{\unicode[STIX]{x1D70F}}$) scaling transition of the maximum TMC located at $y_{p}$. We show that in viscous units,$y_{p}^{+}$(and$1+\overline{u^{\prime }v^{\prime }}_{p}^{+}$) displays a scaling transition from$Re_{\unicode[STIX]{x1D70F}}^{3/7}$($Re_{\unicode[STIX]{x1D70F}}^{-6/7}$) to$Re_{\unicode[STIX]{x1D70F}}^{3/5}$($Re_{\unicode[STIX]{x1D70F}}^{-3/5}$) in turbulent boundary layer, in sharp contrast to that from$Re_{\unicode[STIX]{x1D70F}}^{1/3}$($Re_{\unicode[STIX]{x1D70F}}^{-2/3}$) to$Re_{\unicode[STIX]{x1D70F}}^{1/2}$($Re_{\unicode[STIX]{x1D70F}}^{-1/2}$) in a channel/pipe, countering the prevailing view of a single universal near-wall scaling. This scaling transition reflects different near-wall motions in the buffer layer for small$Re_{\unicode[STIX]{x1D70F}}$and log layer for large $Re_{\unicode[STIX]{x1D70F}}$, with the non-universality being ascribed to the presence/absence of mean wall-normal velocity $V$. Our predictions are validated by a large set of data, and a probable flow state with a full coupling between momentum and energy cascades beyond a critical$Re_{\unicode[STIX]{x1D70F}}$is envisaged.

Combustion of torrefied pellets of furniture work dusts as blends with lignite

2020 ◽  
pp. 1-21
Author(s):  
Melek Yilgin ◽  
Bedriye Hos ◽  
Dursun Pehlivan
Keyword(s):  
Natural Convection ◽  
Initial Temperature ◽  
Volatile Matter ◽  
Nitrogen Atmosphere ◽  
Moisture Contents ◽  
Vertical Furnace ◽  
Carbon Combustion ◽  
Ignition Times

Abstract In this study, torrefaction of pellets formed from furniture work dusts collected as a part of space cleaning actions in the industry have been examined. Burning behaviour of torrefied dusts and lignite blends was studied. Torrefaction experiments were done under nitrogen atmosphere for one hour at temperatures of 220, 260 and 300°C which corresponded to light, mild and severe torrefaction, respectively. Combustion of blend pellets prepared by adding lignite in specific ratios to powders of torrefied pellets was carried out at 700°C initial temperature using a vertical furnace system through which air was flowing in natural convection. Ignition times of blend pellets were affected from volatile matter and moisture contents. Volatile matter combustion rates were lower than those of raw waste and accordingly, combustion times were higher. However, no relation between volatile matter combustion rates and times was observed. Blending raw or torrefied furniture work dusts with lignite have significantly influenced volatile matter and carbon combustion periods. There was no relation between carbon combustion rates and times. It was concluded that blend pellets of mild or severe torrefaction products of furniture work dusts and lignite behaved similarly to lignite during combustion.

The Effect of Orifice Angle and Cavity Dimension on Rectangular Synthetic Jet Actuators

2011 ◽  
Author(s):  
Pooya Kabiri ◽  
Douglas G. Bohl ◽  
Goodarz Ahmadi
Keyword(s):  
Particle Image ◽  
Vortical Structure ◽  
Active Flow Control ◽  
Cross Flow ◽  
Synthetic Jet ◽  
Synthetic Jet Actuators ◽  
Image Velocimetry ◽  
Jet Actuators ◽  
Active Flow ◽  
Analytic Prediction

In the last decade, a great deal of interest has been focused on the application of synthetic jet actuators (SJA) for active flow control. SJAs delay separation by injecting vortex pairs into the cross flow and energizing the turbulent boundary layer. The goal of this study was to investigate the effects of the orifice angle on the performance of axisymmetric SJAs. The SJAs used in this experiment were composed of a piezoelectric (PZT) membrane, cavities and orifices. SJA’s with either a straight (90°) or angled (60°) orifices were characterized using hot-wire anemometry and Particle Image Velocimetry (PIV). It was found that the structure of the jet flow changed depending on the angle of the orifice with differences in the resulting vortical structure observed. The peak jet speed was found to be higher for the straight orifice than for the angled orifice contradicting the analytic prediction based on cavity dimension.

Analytic Prediction of Surface Pressures over a Hemisphere-Cylinder at Incidence

2003 ◽  
Vol 40 (4) ◽  
pp. 645-652 ◽  
Author(s):  
Lance W. Traub ◽  
Othon Rediniotis
Keyword(s):  
Analytic Prediction
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