Combusting Jets Issued From Rectangular Nozzles of High and Low Aspect Ratios With Co-Flowing Air

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Rong Fung Huang ◽  
Reuben Mwanza Kivindu ◽  
Ching Min Hsu
Keyword(s):  
Diffusion Flame ◽  
Thermal Structure ◽  
Reynolds Numbers ◽  
Jet Flames ◽  
Combustion Performance ◽  
Side Channels ◽  
Aspect Ratios ◽  
Fine Wire ◽  
Fuel Jet ◽  
Flame Behavior

The flame behavior and the thermal structure of gaseous fuel jets issued from rectangular nozzles of high and low aspect ratios with co-flowing air were experimentally studied. Two rectangular nozzles with aspect ratios AR = 36 and 3.27 and with side channels for co-flowing air were examined. Flame behaviors were studied by photography techniques. Flame temperatures were measured using a fine-wire thermocouple. The AR = 36 burner exhibited three characteristic flame modes: attached flame, transitional flame, and lifted flame. The AR = 3.27 burner presented three characteristic flame modes: diffusion flame, transitional flame, and triple-layered flame. High AR jets promoted entrainment and mixing in the region around the flame base, whereas low AR jets enhanced mixing in the regions along the flame edges. At low co-flows, at Rec < 1200, the low AR burner flames were shorter, but at Rec > 1200, the high AR burner flames became shorter and wider. At Rec > 950, the high AR burner recorded higher flame temperatures, compared to the low AR burner by over 100 °C. At high fuel jet Reynolds numbers and moderate co-flow, high AR burner flames presented better combustion performances when compared to low AR jet flames. The good combustion performance of the high AR jet flames was due to enhanced entrainment and mixing, which were induced by flame lifting. However, at low Rec and high co-flow, the low AR jet flames exhibited desirable flame characteristics due to improved entrainment and turbulence at the jet interfaces.

Effects of Pulsation Intensities on Flame Characteristics of a Small Backward-Inclined Jet Flame in Crossflow

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Ching Min Hsu ◽  
Farha Khan ◽  
Dickson Bwana Mosiria
Keyword(s):  
Low Temperatures ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Reynolds Numbers ◽  
Mode I ◽  
Gas Analyzer ◽  
Jet Flames ◽  
Jet Flame ◽  
Fine Wire ◽  
Characteristic Modes

Abstract The effects of pulsation intensities on the flame characteristics of a 10 deg-backward-inclined jet flame in the crossflow were investigated in a wind tunnel. The jet and the crossflow Reynolds numbers were 1527 and 2165, respectively. The jet-to-crossflow momentum flux ratio was 0.10. A loudspeaker was used to acoustically excite the jet flame. The excitation Strouhal number was 0.73, while the jet pulsation intensities varied from 0 to 1.26. The flame behaviors were studied through photography techniques. The flame temperatures were measured using a fine-wire R-type thermocouple. The combustion-induced emissions were probed by a commercial multi-gas analyzer. The jet flames were categorized into five characteristic modes with increasing pulsation intensities. Mode I was characterized by a yellowish down-washed recirculation flame, a blue neck flame, and a yellow tail flame. Modes II and III featured a split yellow tail flame, a yellowish recirculation flame, and a blue neck flame. Mode IV was characterized by a blue down-washed recirculation flame and neck flame, as well as a split yellow tail flame. Mode V was identified by a single yellow tail flame and the absence of the down-washed recirculation flame. When the jet flames were excited beyond mode I, the combustion-induced pollutants of carbon monoxide and nitric oxide were significantly reduced. However, the excited jet flame in mode V displayed low temperatures in the near-tube region.

Controlling Plane-Jet Flame by a Fluidic Oscillation Technique

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Hsiu F. Yang ◽  
Ching M. Hsu ◽  
Rong F. Huang
Keyword(s):  
Combustion Product ◽  
Thermal Structure ◽  
Jet Impingement ◽  
Co2 Concentration ◽  
Maximum Temperature ◽  
Jet Flame ◽  
Fluidic Oscillator ◽  
Fuel Jet ◽  
Flame Behavior ◽  
Plane Jet

A plane-jet flame was manipulated by passing the fuel jet through a jet-impingement fluidic oscillator. The plane fuel jet bifurcated into two streams of self-sustained pulsating jets in the cavity of the fluidic oscillator and issued out of two slits on the exit plane of the fluidic oscillator. The oscillation of the bifurcated plane fuel jets caused the flame behavior and combustion characteristics to change significantly compared with the corresponding behavior and characteristics of a nonoscillating plane-jet flame. The oscillation frequency, flame behavior, thermal structure, and combustion-product distributions of the fluidic-oscillator flame were experimentally examined and compared with the nonoscillating plane-jet flame. The flame behavior was studied with instantaneous and long-exposure photography. The temperature distributions were measured with a fine-wire thermocouple. The combustion-product concentrations were detected with a gas analyzer. The results showed that the length and width of the fluidic-oscillator flame were reduced by approximately 45% and enlarged by approximately 40%, respectively, compared with the length and width of the nonoscillating plane-jet flame. The transverse temperature profiles of the fluidic-oscillator flame presented a wider spread than did the plane-jet flame. The fluidic-oscillator flame’s maximum temperature was approximately 100 °C higher than that of the plane-jet flame. The fluidic-oscillator flame presented a larger CO2 concentration and a smaller unburned C3H8 concentration than did the plane-jet flame. The experimental results indicated that the combustion in the fluidic-oscillator flame was more complete than that in the plane-jet flame.

Enhancement of Fluid Mixing in a Double T-Shaped Micromixer by Periodic Disturbances of Pressure

2011 ◽  
Vol 339 ◽  
pp. 118-123 ◽  
Author(s):  
Huan Chao Chiu ◽  
Jerry M Chen
Keyword(s):  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Low Reynolds Numbers ◽  
Periodic Disturbances ◽  
Side Channels ◽  
Aspect Ratios ◽  
Cross Section Area ◽  
Section Area ◽  
Channel Aspect Ratio ◽  
Phase Angles

This paper presents numerical simulations of mixing phenomena in a double T-shaped micromixer to which periodic pressure disturbances are added to enhance the mixing efficiency. The fluids were brought in contact at the upper T-junction. The pressure disturbances of various frequencies (0-50 Hz) and phase angles were introduced through the side channels of the lower T-structure. The simulations were carried out for microchannels having the same cross-section area but with different aspect ratios (1.6-10) at low Reynolds numbers (2.9-8.8). It is found that the mixing efficiency rapidly increases with an increase of the oscillation frequency in the lower range (0-8 Hz) to reach a maximum and then decreases in the higher frequency range except for the in-phase disturbance. The mixing is enhanced most significantly as the two pressure disturbances oscillate exactly out of phase. The effects due to channel aspect ratio and inlet velocity are also discussed.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Power Augmentation of a HAWT by Mie-type Tip Vanes, considering Wind Tunnel Flow Visualisation, Blade-Aspect Ratios and Reynolds Number

2003 ◽  
Vol 27 (3) ◽  
pp. 183-194 ◽  
Author(s):  
Yukimaru Shimizu ◽  
Edmond Ismaili ◽  
Yasunari Kamada ◽  
Takao Maeda
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Flow Visualisation ◽  
Velocity Measurements ◽  
Horizontal Axis Wind Turbine ◽  
Aspect Ratios ◽  
Detailed Surface ◽  
Blade Tips

Wind tunnel results are reported concerning the effects of blade aspect ratio and Reynolds number on the performance of a horizontal axis wind turbine (HAWT) with Mie-type1 tip attachments. The flow behaviour around the blade tips and the Mie-type tip vanes is presented. Detailed surface oil film visualization and velocity measurements around the blade tips, with and without Mie vanes, were obtained with the two-dimensional, Laser-Doppler Velocimetry method. Experiments were performed with rotors having blades with different aspect ratio and operating at different Reynolds numbers. The properties of the vortices generated by the Mie vanes and the blade tips were carefully studied. It was found that increased power augmentation by Mie vanes is achieved with blades having smaller aspect ratio and smaller Reynolds number.

Effect of Surface Roughness on Gaseous Flow Through Microchannels

2000 ◽  
Author(s):  
Stephen E. Turner ◽  
Hongwei Sun ◽  
Mohammad Faghri ◽  
Otto J. Gregory
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Helium Flow ◽  
Local Pressure ◽  
Aspect Ratios ◽  
Corrugated Surfaces ◽  
Flow Through ◽  
Effect Of Surface

Abstract This paper presents an experimental investigation on nitrogen and helium flow through microchannels etched in silicon with hydraulic diameters between 10 and 40 microns, and Reynolds numbers ranging from 0.3 to 600. The objectives of this research are (1) to fabricate microchannels with uniform surface roughness and local pressure measurement; (2) to determine the friction factor within the locally fully developed region of the microchannel; and (3) to evaluate the effect of surface roughness on momentum transfer by comparison with smooth microchannels. The friction factor results are presented as the product of friction factor and Reynolds number plotted against Reynolds number. The following conclusions have been reached in the present investigation: (1) microchannels with uniform corrugated surfaces can be fabricated using standard photolithographic processes; and (2) surface features with low aspect ratios of height to width have little effect on the friction factor for laminar flow in microchannels.

Topology of vortex breakdown in closed polygonal containers

2017 ◽  
Vol 820 ◽  
pp. 263-283 ◽  
Author(s):  
Igor V. Naumov ◽  
Irina Yu. Podolskaya
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Cylindrical Container ◽  
Stagnation Points ◽  
Aspect Ratios ◽  
Particle Visualization ◽  
Cross Section Geometry

The topology of vortex breakdown in the confined flow generated by a rotating lid in a closed container with a polygonal cross-section geometry has been analysed experimentally and numerically for different height/radius aspect ratios $h$ from 0.5 to 3.0. The locations of stagnation points of the breakdown bubble emergence and corresponding Reynolds numbers were determined experimentally and numerically by STAR-CCM+ computational fluid dynamics software for square, pentagonal, hexagonal and octagonal cross-section configurations. The flow pattern and velocity were observed and measured by combining seeding particle visualization and laser Doppler anemometry. The vortex breakdown size and position on the container axis were identified for Reynolds numbers ranging from 500 to 2800 in steady flow conditions. The obtained results were compared with the flow structure in the closed cylindrical container. The results allowed revealing regularities of formation of the vortex breakdown bubble depending on $Re$ and $h$ and the cross-section geometry of the confined container. It was found in a diagram of $Re$ versus $h$ that reducing the number of cross-section angles from eight to four shifts the breakdown bubble location to higher Reynolds numbers and a smaller aspect ratio. The vortex breakdown bubble area for octagonal cross-section was detected to correspond to the one for the cylindrical container but these areas for square and cylindrical containers do not overlap in the entire range of aspect ratio.

Assessment of Stabilization Mechanisms of Confined, Turbulent, Lifted Jet Flames: Effects of Ambient Coflow

2013 ◽  
Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Richard D. Muncey ◽  
Kevin M. Lyons
Keyword(s):  
Turbulent Mixing ◽  
Leading Edge ◽  
Ambient Air ◽  
Turbulent Jet ◽  
Fuel Flow Rate ◽  
Jet Flames ◽  
Combustion Chemistry ◽  
Intermittent Behavior ◽  
Fuel Flow ◽  
Fuel Jet

The aim of this investigation is to determine the effects of confinement on the stabilization of turbulent, lifted methane (CH4) jet flames. A confinement cylinder (stainless steel) separates the coflow from the ambient air and restricts excess room air from being entrained into the combustion chamber, and thus produces varying stabilization patterns. The experiments were executed using fully confined, semi-confined, and unconfined conditions, as well as by varying fuel flow rate and coflow velocity (ambient air flowing in the same direction as the fuel jet). Methane flames experience liftoff and blowout at well-known conditions for unconfined jets, however, it was determined that with semi-confined conditions the flame does not experience blowout. Instead of the conventional unconfined stabilization patterns, an intense, intermittent behavior of the flame was observed. This sporadic behavior of the flame, while under semi-confinement, was determined to be a result from the restricted oxidizer access as well as the asymmetrical boundary layer that forms due to the viewing window. While under full confinement the flame behaved in a similar method as while under no confinement (full ambient air access). The stable nature of the flame while fully confined lacked the expected change in leading edge fluctuations that normally occur in turbulent jet flames. These behaviors address the combustion chemistry (lack of oxygen), turbulent mixing, and heat release that combine to produce the observed phenomena.

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