Characteristics of Flow and Flame Behavior Behind Rifled/Unrifled Nozzles

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Kuo C. San ◽  
Hung J. Hsu
Keyword(s):  
Turbulent Flame ◽  
Flow Characteristics ◽  
Combustion Efficiency ◽  
Flame Height ◽  
Mixing Efficiency ◽  
Jet Flame ◽  
Annular Jet ◽  
Image Velocimetry ◽  
Flame Behavior ◽  
The Relationship

A novel rifled nozzle was installed behind a conventional combustion exhauster to improve combustion efficiency. The rifled nozzles improve the momentum transmission, turbulent strength, and mixing efficiency between the central jet and annular jet. The flow characteristics behind the nozzles (rifled and unrifled) were visualized and detected using the smoke-wire flow visualization, particle image velocimetry, and hot-wire anemometry. The cold flow structures were categorized into four modes—jet flow, single bubble, dual bubble, and turbulent flow. The topological scheme was adopted to analyze and verify these flow modes. The flame structures behind the nozzles (rifled and unrifled) are classified into three modes—jet flame, flickering flame, and turbulent flame—using the direct-photo visualization. The flame height of a 12-rifled nozzle is decreased by about 50% under that of an unrifled nozzle. The flame shedding frequency declines rapidly in the flickering flame mode and the relationship between the Strouhal number (Sr) and annular velocity (ua) is Sr=0.0238+0.13/ua.

Flame Structure and Combustion Capability of Non-Premixed Rifled Nozzles

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Kuo C. San ◽  
Hung J. Hsu ◽  
Shun C. Yen
Keyword(s):  
Flame Structure ◽  
Mixing Efficiency ◽  
Gas Analyzer ◽  
Jet Flame ◽  
Gas Concentration ◽  
Air Jet ◽  
Fuel Jet ◽  
Schlieren Photography ◽  
Flame Behavior ◽  
Jet Velocities

The target of this study is to promote combustion capability using a novel rifled nozzle which was set at the outlet of a conventional (unrifled) combustor. The rifled nozzle was utilized to adjust the flow swirling intensity behind the traditional combustor by changing the number of rifles. The rifle mechanism enhances the turbulence intensity and increases the mixing efficiency between the central-fuel jet and the annular swirled air-jet by modifying the momentum transmission. Specifically, direct photography, Schlieren photography, thermocouples, and a gas analyzer were utilized to document the flame behavior, peak temperature, temperature distribution, combustion capability, and gas-concentration distribution. The experimental results confirm that increasing the number of rifles and the annular swirling air-jet velocity (ua) improves the combustion capability. Five characteristic flame modes—jet-flame, flickering-flame, recirculated-flame, ring-flame and lifted-flame—were obtained using various annular air-jet and central fuel-jet velocities. The total combustion capability (Qtot) increases with the number of rifles and with increasing ua. The Qtot of a 12-rifled nozzle (swirling number (S) = 0.5119) is about 33% higher than that of an unrifled nozzle. In addition, the high swirling intensity induces the low nitric oxide (NO) concentration, and the maximum concentration of NO behind the 12-rifled nozzle (S = 0.5119) is 49% lower than that behind the unrifled nozzle.

The Influence of Pressure on Flame-Flow Characteristics of a Reacting Jet in Crossflow

2021 ◽  
pp. 1-30
Author(s):  
Michelle Otero ◽  
Tommy Genova ◽  
Bernhard Stiehl ◽  
Anthony Morales ◽  
Scott Martin ◽  
...  
Keyword(s):  
Ignition Delay Time ◽  
Particle Image ◽  
Flow Characteristics ◽  
Elevated Pressure ◽  
Jet In Crossflow ◽  
Air Jet ◽  
Jet Trajectory ◽  
Image Velocimetry ◽  
Lift Off ◽  
Flame Behavior

Abstract This work experimentally investigates the effects of elevated combustor pressures on the characteristics of a lean premixed reacting methane/air jet injected into a lean vitiated crossflow using a 12.7mm axial jet. Experiments were conducted in an axially staged combustor, which implements a reacting jet in crossflow (RJIC) configuration and operates over a pressure range of 1 to 5 atmospheres. Simultaneous CH* chemiluminescence and Particle Image Velocimetry (PIV) are used to study the flow field and flame behavior. The results show that the reacting jet trajectory exhibits greater penetration with elevated pressure, which is a novel finding compared to available data in the literature. However, the flame lift-off point and ignition delay time both decreased with elevated pressure, which was attributed to decreased vorticity along the flame boundary which corresponds to increased Damköhler numbers (Da). Emissions measurements confirm the NOx increase with pressure as reported in the literature for single stage gas turbine combustors. Concurrently, emission measurements for the staged configuration show the strong NOx benefit of the RJIC system: the data proves a reduction of global outlet emission levels at elevated pressure with the axially staged configuration. The axial emission reduction was attributed to the decreasing lift-off at elevated pressure levels. Hence, the research emphasizes that the flame and emission characteristics are coupled; they are not only dependent on the geometric parameters and momentum flux ratios but are also a function of pressure.

An improved de Laval nozzle experiment

2021 ◽  
pp. 030641902110341
Author(s):  
Nicholas Goodman ◽  
Brian J Leege ◽  
Peter E Johnson
Keyword(s):  
Data Acquisition ◽  
Laval Nozzle ◽  
Flow Characteristics ◽  
Data Acquisition System ◽  
Isentropic Flow ◽  
Hands On ◽  
De Laval Nozzle ◽  
Physical Phenomena ◽  
The Impact ◽  
The Relationship

Exposing students to hands-on experiments has been a common approach to illustrating complex physical phenomena that have been otherwise modelled solely mathematically. Compressible, isentropic flow in a duct is an example of such a phenomenon, and it is often demonstrated via a de Laval nozzle experiment. We have improved an existing converging/diverging nozzle experiment so that students can modify the location of the normal shock that develops in the diverging portion to better understand the relationship between the shock and the pressure. We have also improved the data acquisition system for this experiment and explained how visualisation of the standing shock is now possible. The results of the updated system demonstrate that the accuracy of the isentropic flow characteristics has not been lost. Through pre- and post-laboratory quizzes, we show the impact on student learning as well.

Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels

2006 ◽  
Author(s):  
Renqiang Xiong ◽  
J. N. Chung
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Micro Channel ◽  
Pressure Drops ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Shape And Size

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re<100. Those vortices appear and continue to develop with the Re number when Re> 100-300, and the shape and size of the vortices almost remain constant when Re>1000. The bend loss coefficient Kb was observed to be related with the Re number when Re<100, with the Re number and channel size when Re>100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

Thermal and Fluid Dynamic Structures of a Laboratory-Scale Fixed-Frame Fire-Whirl

2001 ◽  
Author(s):  
Mohamed I. Hassan ◽  
A. Helali ◽  
Kozo Saito
Keyword(s):  
Heat Flux ◽  
Fluid Dynamic ◽  
Azimuthal Velocity ◽  
Video Camera ◽  
Liquid Pool ◽  
Flame Height ◽  
Buoyancy Flow ◽  
Image Velocimetry ◽  
Fire Whirl ◽  
Dynamic Structures

Abstract Fire whirl is one of the most destructive phenomena in mass fires. To study thermal and fluid dynamic structures of a fire whirl in a laboratory, a fire whirl generator consisting of two vertically oriented split-cylinders were placed in an asymmetric position to form a compartment leaving two open slits in each end. A 5-cm diameter liquid pool fire was placed at the center of the compartment floor, the fire generated buoyancy flow moved upwardly, and fresh air entered to the compartment creating swirl motion. The visible flame height of the generated fire whirl was measured by a video camera, 2-D azimuthal velocity profiles at several different heights by particle image velocimetry (PIV), and the average heat flux input to the fuel surface by a Gardon gauge type heat flux meter.

CFD Study on the Flow Characteristics in Filleted Microchannels

2011 ◽  
Vol 103 ◽  
pp. 268-273
Author(s):  
Hong Jie Yan ◽  
Ping Zhou ◽  
Ze Lin Xu ◽  
Zhuo Chen ◽  
Jing Wen Mo
Keyword(s):  
Pressure Drop ◽  
Aspect Ratio ◽  
Flow Model ◽  
Constant Width ◽  
Flow Characteristics ◽  
Flow Pressure ◽  
Cfd Method ◽  
Poiseuille Number ◽  
The Relationship ◽  
Laminar Flow Model

The flow characteristics of water in filleted microchannels were simulated based on CFD method. The flow pressure drop at different aspect ratioandRenumber were rearranged on the simulating results with laminar flow model. The results indicated that the pressure drop enlarges with the increase of in the case of the constant width of the microchannel. Within the range ofRenumber of interest, Poiseuille number of the flow is constant for differentRe, but decreases with increasing aspect ratio. An equation was fitted to describe the relationship betweenPonumber and aspect ratio, i.e. .

scholarly journals Turbulent Flame Shape Switching at Conditions Relevant for Gas Turbines

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Ivan Langella ◽  
Johannes Heinze ◽  
Thomas Behrendt ◽  
Lena Voigt ◽  
Nedunchezhian Swaminathan ◽  
...  
Keyword(s):  
Turbulent Combustion ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Interaction Model ◽  
Numerical Approach ◽  
Reacting Flow ◽  
Combustion Chambers ◽  
Lean Burn ◽  
Large Eddy ◽  
Flame Behavior

Abstract A numerical investigation is conducted to shed light on the reasons leading to different flame configurations in gas turbine (GT) combustion chambers of aeronautical interest. Large eddy simulations (LES) with a flamelet-based combustion closure are employed for this purpose to simulate the DLR-AT big optical single sector (BOSS) rig fitted with a Rolls-Royce developmental lean burn injector. The reacting flow field downstream this injector is sensitive to the intricate turbulent–combustion interaction and exhibits two different configurations: (i) a penetrating central jet leading to an M-shape lifted flame; or (ii) a diverging jet leading to a V-shaped flame. The LES results are validated using available BOSS rig measurements, and comparisons show the numerical approach used is consistent and works well. The turbulent–combustion interaction model terms and parameters are then varied systematically to assess the flame behavior. The influences observed are discussed from physical and modeling perspectives to develop physical understanding on the flame behavior in practical combustors for both scientific and design purposes.

Precession Effects on the Relationship Between Time-Averaged and Instantaneous Reacting Flow Characteristics

2016 ◽  
Vol 189 (2) ◽  
pp. 248-265 ◽  
Author(s):  
Ianko Chterev ◽  
Gautham Sundararajan ◽  
Ben Emerson ◽  
Jerry Seitzman ◽  
Tim Lieuwen
Keyword(s):  
Flow Characteristics ◽  
Reacting Flow ◽  
The Relationship

Wall Normal Jet Produced by DBD Plasma Actuator With Doughnut-Shaped Electrode

2008 ◽  
Author(s):  
Takehiko Segawa ◽  
Hiro Yoshida ◽  
Shinya Takekawa ◽  
Timothy Jukes ◽  
Kwing-So Choi
Keyword(s):  
Atmospheric Pressure ◽  
Room Temperature ◽  
Particle Image ◽  
Barrier Discharge ◽  
Plasma Actuator ◽  
Dbd Plasma ◽  
Annular Jet ◽  
Image Velocimetry ◽  
Inner Diameter ◽  
Annular Jets

Properties of coaxial annular jets produced by a dielectric barrier discharge (DBD) plasma actuator with a doughnut shaped electrodes were investigated under atmospheric pressure and room temperature. The actuator consists of two circular electrodes sandwiching a thin dielectric layer. By applying 0 – ±3.3 kV between the electrodes at radio frequencies, the plasma jet is formed near the inner edge of the top electrode. The radial jet runs toward the center of the electrode and then impinges at the center to generate a wall normal annular jet. The evolution of the wall normal jet was observed precisely using particle image velocimetry (PIV) system. It was found that characteristic velocities increase in proportion to the bursting frequency and inversely proportional to the inner diameter of the electrode at the surging time of the voltage at 5.0 × 10−6sec.

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