Fire-induced temperature distribution beneath ceiling and air entrainment coefficient characteristics in a tunnel with point extraction system

The NOx emissions of low NOx premix combustors are not only determined by the burner design, but also by the multi burner interaction and the related distribution of air and fuel flows to the individual burners. Often the factors that have a positive impact on NOx emission have a negative impact on the flame stability, so the main challenge is to find an optimum point with the lowest achievable NOx while maintaining good flame stability. The hottest flame zones are where most of the NOx is formed. Avoiding such zones in the combustor (by homogenization of the flame temperature) reduces NOx emissions significantly. Improving the flame stability and the combustion control allows the combustor to operate at a lower average flame temperature and NOx emissions. ALSTOM developed a combustion optimization package for the GT13E2. The optimization package development focused on three major issues: • Flame stability; • Homogenization of flame temperature distribution in the combustor; • Combustion control logic. The solution introduced consists of: • The reduction of cooling air entrainment in the primary flame zone for improved flame stability; • The optical measurement of the individual burner flame temperatures and their homogenization by burner tuning valves; • Closed loop control logic to control the combustion dependent on the pulsation signal. This paper shows how fundamental combustion research methods were applied to derive effective optimization measures. The flame temperature measurement technique will be presented along with results of the measurement and their application in homogenization of the combustor temperature distribution in an engine equipped with measures to improve flame stabilization. The main results achieved are: • Widening of the main burner group operation range; • Improved use of the low NOx operation range; • NOx reduction at the combustor pulsation limit and hence, large margins to the European emission limit (50 mg/m3 @ 15%O2).

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Influence of Primary and Secondary Flow Interaction on the Near Flow Field Mixing in an Enclosed Space

Fluids Engineering ◽

10.1115/imece2006-16335 ◽

2006 ◽

Author(s):

Ijaz M. Khan ◽

Tony Gilbert ◽

Mostafa Barigou

Keyword(s):

Temperature Distribution ◽

Flow Field ◽

Air Entrainment ◽

Streamwise Velocity ◽

Nozzle Geometry ◽

Turbulence Characteristics ◽

Mass Entrainment ◽

Diffusion Characteristics ◽

Velocity Decay ◽

Enclosed Space

This paper presents the influence of an induction diffuser ports on a turbulent jet and its effect on the axial mean streamwise velocity decay, mass entrainment, turbulence characteristics and the temperature distribution in the near flow field of an enclosed numerical space. Convergence of the steady state simulations is achieved by RNG kappa-epsilon turbulence model. Comparisons of the axial mean streamwise velocity decay, turbulence characteristics and the temperature distribution in an enclosed space are reported for JETs (Jet Environmental Techniques) nozzle, and another similar simulation was conducted for an induction diffuser box with open ports at specific positions to evaluate its performance. The numerical analysis was validated by prototype experiments using the JETs nozzle geometry in a test room 11 m in length, 5.5 m wide and 2.5 m high. The measurement of the streamwise velocity and temperature distribution was measured inside the room on a grid with the help of a hotwire anemometer and digital thermometer, respectively. From the analysis of the data, it was found that the near flow field air entrainment and diffusion characteristics of the jet were significantly influenced by the air induction diffuser.

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Induced aeration flow over stepped spillways: mean pressures, air entrainment and flow behavior

RBRH ◽

10.1590/2318-0331.262120210098 ◽

2021 ◽

Vol 26 ◽

Author(s):

Carolina K. Novakoski ◽

Rute Ferla ◽

Priscila dos Santos Priebe ◽

Aline Saupe Abreu ◽

Marcelo G. Marques ◽

...

Keyword(s):

Flow Behavior ◽

Air Entrainment ◽

Stepped Spillway ◽

Air Concentration ◽

Stepped Spillways ◽

Jet Impact ◽

Entrainment Coefficient ◽

The Mean ◽

Inception Point ◽

Channel Bottom

ABSTRACT Stepped spillways can dissipate a great amount of energy during the flow passage over the chute, however these structures have limited operation due to the risk of cavitation damage. The induced aeration may protect the concrete chute through the air concentration near the channel bottom. Furthermore, some research studies have indicated that the presence of air in flows may reduce the mean pressures. The present research aims to analyze mean pressures, air entrainment coefficient and flow behavior over a stepped spillway with aeration induced by two different deflectors, comparing the results to natural aeration flow. Despite the jet impact influence, the induced aeration does not change significantly the mean pressures compared to natural aeration flow. The air entrainment coefficient, as well as the jet impact position, is higher for the deflector with the longer extension and, although air bubbles can be seen throughout the extension of the chute due to the air entrainment through the inferior flow surface, the induced aeration did not anticipate the boundary layer inception point position.

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Study on air entrainment coefficient of one-dimensional horizontal movement stage of tunnel fire smoke in top central exhaust

Tunnelling and Underground Space Technology ◽

10.1016/j.tust.2016.07.010 ◽

2016 ◽

Vol 60 ◽

pp. 1-9 ◽

Cited By ~ 17

Author(s):

Xuepeng Jiang ◽

Meijia Liu ◽

Jie Wang ◽

Kaiyuan Li

Keyword(s):

Air Entrainment ◽

Horizontal Movement ◽

One Dimensional ◽

Tunnel Fire ◽

Fire Smoke ◽

Entrainment Coefficient

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Stepped spillways with aerators: hydrodynamic pressures and air entrainment

RBRH ◽

10.1590/2318-0331.262120200110 ◽

2021 ◽

Vol 26 ◽

Author(s):

Rute Ferla ◽

Carolina Kuhn Novakoski ◽

Priscila dos Santos Priebe ◽

Mauricio Dai Prá ◽

Marcelo Giulian Marques ◽

...

Keyword(s):

Experimental Study ◽

Physical Model ◽

Air Entrainment ◽

Specific Flow ◽

Flow Rates ◽

Stepped Spillways ◽

Entrainment Coefficient ◽

Flow Through ◽

New Equation ◽

Stepped Chute

ABSTRACT The possibility of damage due to the phenomenon of cavitation leads the design of stepped spillways considering maximum specific discharges of 15 to 30 m2/s, a limit considerably lower than that practiced on smooth chutes. Aerators promote the insertion of air in the flow, allowing for the increase of specific flow rates. This work analyzes the pressures on the vertical faces of the steps and the air entrainment coefficient in the flow, through an experimental study in a physical model with a stepped chute angle of 53.13o, considering the installation of aerators in different places of the channel. Comparing the tested conditions with the natural aeration, it is concluded that the installation of the aerator does not change the magnitude of the minimum extreme hydrodynamic pressures, but anticipates the beginning of the flow aeration. A new equation is proposed to estimate the air entrainment coefficient, as well as a methodology for forecasting extreme pressures on the vertical faces of the steps, both valid in the range 3.0 ≤ Fr ≤ 6.0.

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Performance and Design of a Stepped Spillway Aerator

Water ◽

10.3390/w14020153 ◽

2022 ◽

Vol 14 (2) ◽

pp. 153

Author(s):

Stéphane Terrier ◽

Michael Pfister ◽

Anton J. Schleiss

Keyword(s):

Concentration Distribution ◽

Water Discharge ◽

Air Entrainment ◽

Stepped Spillway ◽

Flow Depth ◽

Air Concentration ◽

Stepped Spillways ◽

Jet Impact ◽

Entrainment Coefficient ◽

Pressure Water

Stepped spillways are frequently limited to specific discharges under around 30 m2/s due to concerns about potential cavitation damages. A small air concentration can prevent such damages and the design of bottom aerators is well established for smooth chutes. The purpose of this study is to systematically investigate the performance of a deflector aerator at the beginning of stepped chutes. Six parameters (chute angle, step height, approach flow depth, approach flow Froude number, deflector angle and deflector height) are varied in a physical model. The spatial air concentration distribution downstream of the aerator, the cavity sub-pressure, water discharge and air discharges are measured. The results describe the commonly used air entrainment coefficient, the jet length, as well as the average and bottom air concentration development to design an aerator. The lowest bottom air concentration measured in all tests is higher than the air concentration recommended in literature to protect against cavitation damages. And, unlike smooth chutes, there appears to be no significant air detrainment downstream of the jet impact. One deflector aerator seems therefore sufficient to provide protection of a stepped spillway.

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