The effect of heat release on the entrainment in a turbulent mixing layer

2018 ◽  
Vol 844 ◽  
pp. 92-126 ◽  
Author(s):  
Reza Jahanbakhshi ◽  
Cyrus K. Madnia
Keyword(s):  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Mixing Layer ◽  
Reacting Flows ◽  
Mixing Layers ◽  
Turbulent Region ◽  
Entrainment Velocity ◽  
High Level

Direct numerical simulations of a temporally evolving compressible reacting mixing layer have been performed to study the entrainment of the irrotational flow into the turbulent region across the turbulent/non-turbulent interface (TNTI). In order to study the effects of heat release and interaction of the flame with the TNTI on turbulence several cases with different heat release levels, $Q$, and stoichiometric mixture fractions are chosen for the simulations with the highest opted value for $Q$ corresponding to hydrogen combustion in air. The combustion is mimicked by a one-step irreversible global reaction, and infinitely fast chemistry approximation is used to compute the species mass fractions. Entrainment is studied via two mechanisms: nibbling, considered as the vorticity transport across the TNTI, and engulfment, the drawing of the pockets of the outside irrotational fluid into the turbulent region. As the level of heat release increases, the total entrained mass flow rate into the mixing layer decreases. In a reacting mixing layer by increasing the heat release rate, the mass flow rate due to nibbling is shown to decrease mostly due to a reduction of the local entrainment velocity, while the surface area of the TNTI does not change significantly. It is also observed that nibbling is a viscous dominated mechanism in non-reacting flows, whereas it is mostly carried out by inviscid terms in reacting flows with high level of heat release. The contribution of the engulfment to entrainment is small for the non-reacting mixing layers, while mass flow rate due to engulfment can constitute close to 40 % of the total entrainment in reacting cases. This increase is primarily related to a decrease of entrained mass flow rate due to nibbling, while the entrained mass flow rate due to engulfment does not change significantly in reacting cases. It is shown that the total entrained mass flow rate in reacting and non-reacting compressible mixing layers can be estimated from an expression containing the convective Mach number and the density change due to heat release.

Temperature effects on the mass flow rate in the SBI and similar heat-release rate test equipment

2007 ◽  
Vol 31 (1) ◽  
pp. 53-66 ◽  
Author(s):  
Bart J. G. Sette ◽  
Erwin Theuns ◽  
Bart Merci ◽  
Paul Vandevelde
Keyword(s):  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Release Rate ◽  
Release Rate ◽  
Temperature Effects ◽  
Test Equipment ◽  
Rate Test

Numerical and Experimental Study of Fire Whirl Generated in 15 × 15 Square Array Fires Placed in Cross Wind

2008 ◽  
Author(s):  
Kohyu Satoh ◽  
Naian Liu ◽  
Qiong Liu ◽  
K. T. Yang
Keyword(s):  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Release Rate ◽  
Release Rate ◽  
Large City ◽  
Heat Flow Rate ◽  
Fire Whirl ◽  
Square Array

Fire whirls in large city fires and forest fires, which are highly dangerous and destructive, can cause substantial casualties and property damages. It is important to examine under what conditions of weather and geography such merging fires and fire whirls are generated. However, detailed physical characteristics about them are not fully clarified yet. Therefore, we have conducted preliminary studies about merging fires and swirling fires and found that they can enhance the fire spread. If sufficient knowledge can be obtained by relevant experiments and numerical computations, it may be possible to mitigate the damages due to merged fires and fire whirls. The objective of this study is to investigate the swirling conditions of fires in square arrays, applying wind at one corner, in laboratory experiments and also by CFD numerical simulations. Varying the inter-fire distance, heat release rate and mass flow rate by a wind fan, ‘swirling’ or ‘non-swirling’ in the array were judged. It has been found that the fire whirl generation is highly affected by the inter-fire distance in the array, the total heat release rate and also the mass flow rate by a fan. We obtained the conditions of swirling fire generation in 15 × 15 square array for (1) the ratio between the upward mass flow rate vs. applied mass flow rate in the upward swirling plume and (2) a non-dimensional relationship between the heat flow rate in the swirling plume and the applied mass flow rate.

Unstart phenomena induced by mass addition and heat release in a model scramjet

2016 ◽  
Vol 797 ◽  
pp. 604-629 ◽  
Author(s):  
S. Im ◽  
D. Baccarella ◽  
B. McGann ◽  
Q. Liu ◽  
L. Wermer ◽  
...  
Keyword(s):  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
High Speed ◽  
Free Stream ◽  
Mass Loading ◽  
High Enthalpy ◽  
Hypersonic Wind Tunnel ◽  
Flow Features

The unstart phenomena in a model scramjet with a free stream Mach number of 4.5 were investigated at an arc-heated hypersonic wind tunnel. High-speed schlieren imaging and high resonance frequency pressure measurements were used to capture the flow features during the unstart process. Three unstart conditions were tested: (i) a low-enthalpy free stream with mass loading, (ii) a high-enthalpy free stream with mass loading and (iii) a high-enthalpy free stream with mass loading and heat release. It was revealed that the unstart threshold and the time from the onset to the completion of unstart depended strongly on the mass loading rate and the heat exchange. The negative heat addition (cooling) significantly increased the threshold of mass flow rate triggering unstart. The decrement of the mass flow rate threshold for unstart was observed in the presence of heat release by combustion. The observed transient and quasi-steady behaviours of the unstart shockwave system and the jet motion were similar in all of the test conditions. On the other hand, at the lip of inlet model, the unstart shockwave under the cold free stream condition exhibited a relatively steady behaviour while severe oscillatory flow motions of the jet and the unstart shockwave were observed in the combustion-driven unstart process. The different unstarted flow behaviours between the three flow conditions were explained using a simplified one-dimensional flow choking analysis and use of the Korkegi criterion.

scholarly journals The Effects of Non-uniform Distribution of Oxidizer Flow on High-Frequency Combustion Instability

2019 ◽  
Vol 257 ◽  
pp. 01005
Author(s):  
Peng Chen ◽  
Wansheng Nie ◽  
Kangkang Guo ◽  
Xing Sun ◽  
Yu Liu ◽  
...  
Keyword(s):  
Heat Release ◽  
Combustion Chamber ◽  
Uniform Distribution ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Rocket Engine ◽  
Combustion Instability ◽  
Oscillation Amplitude ◽  
Pressure Oscillation

The numerical calculation of three-dimensional unsteady combustion for the combustion chamber of LOX/kerosene high pressure staged combustion rocket engine was carried out. By changing the offset ratio of oxygen mass flow rate in the edge area of the injector face, computational studies were conducted to investigate the effects of non-uniform distribution of oxidizer flow on combustion instability for a liquid-propellant rocket engine. The calculation results show that the offset ratio of oxygen mass flow rate changes the distribution of heat release in the combustion chamber. Within a certain range of offset ratio, the non-uniform distribution degree of oxidizer flow enhances the coupling between the pressure and heat release. As a result, it leads to an increase in the pressure oscillation amplitude in the combustion chamber. However, if the offset ratio is too large, the oxygen-fuel ratio will be too small in some regions, which will reduce coupling between the pressure and heat release and increase the damping of combustion instability.

The Effect of Sauter Mean Diameter Fluctuations on the Heat Release Rate in a Lean-Burn Aero-Engine Combustor

2019 ◽  
Author(s):  
Nicholas C. W. Treleaven ◽  
Andrew Garmory ◽  
Gary J. Page
Keyword(s):  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Release Rate ◽  
Release Rate ◽  
Sauter Mean Diameter ◽  
Lean Burn ◽  
Thermoacoustic Instability ◽  
Mean Diameter

Abstract It has been shown that the fluctuations of pressure caused by a thermoacoustic instability can affect the mass flow rate of air and atomisation of the liquid fuel inside a gas turbine. Tests with premixed flames have confirmed that the fluctuations of the mass flow rate of air can affect the heat release rate through purely aerodynamic phenomenon but little work has been done to test the sensitivity of the heat release rate to changes in the fuel atomisation process. In this study, a lean-burn combustor geometry is supplied with a fuel spray fluctuation of SMD (Sauter mean diameter) of 20% with respect to the mean value and the heat release rate predicted using Large Eddy Simulation (LES) with combustion predicted using a presumed probability density function (PPDF), flamelet generated manifolds (FGM) method. Previous work has shown that at atmospheric conditions the SMD may fluctuate by up to 16% percent and at low frequencies may be reasonably well predicted by using a correlation based on the instantaneous velocity and mass flow rate of air close to the air-blast atomiser. Analysis of the flow fields highlights a complicated spray, flame and wall interaction as being responsible for this observed fluctuation of heat release rate. The heat release rate predicted by the LES shows a 20% fluctuation which implies that even small fluctuations of SMD will significantly contribute to thermoacoustic instabilities.

scholarly journals Numerical Simulation on Effects of Horizontal Natural Opening Area and Heat Release Rate on Temperature Distribution and Vent Flow in Small Compartment

2021 ◽  
Vol 35 (3) ◽  
pp. 23-33
Author(s):  
Min Yeong Park ◽  
Ji Hyun Yang ◽  
Chi Young Lee
Keyword(s):  
Numerical Simulation ◽  
Temperature Distribution ◽  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Release Rate ◽  
Release Rate ◽  
Release Rates ◽  
Small Compartment

In this study, the numerical simulation to investigate the effects of horizontal natural opening areas and heat release rates on temperature distribution and vent flow in a small compartment was performed using a fire dynamics simulator. The reduced scale model of a stage in a real scale theater with horizontal natural opening was selected for this study. The horizontal opening areas were 0.0196, 0.1024, and 0.2025 m2 (1, 5, and 10% of the floor area, respectively), and the heat release rates were 0.46, 1.35, and 2.61 kW. By decreasing the horizontal opening area and increasing the heat release rate, the temperature in the compartment increased. Additionally, by increasing the heat release rate, the average velocity near the center of the opening increased. For the increase in the horizontal opening area from 0.0196 to 0.1024 m2, the velocity near the center of the opening increased. However, when the horizontal opening area increased from 0.1024 to 0.2025 m2, the variation in velocity was not noticeable. Considering the analyses of temperature and velocity distributions of vent flow, the bidirectional flow pattern was observed, where the outflow and inflow occurred at the center and edge of the horizontal opening, respectively. The mass flow rate through the horizontal opening increased with the increase in the horizontal opening area and heat release rate. The previous correlation for mass flow rate under-predicted the present numerical simulation data.

Computational Analysis of a Diesel Engine Autoignition, Combustion, and Emissions Using Injection Rate Shapes

2013 ◽  
Author(s):  
Amit Shrestha ◽  
Ziliang Zheng ◽  
Tamer Badawy ◽  
Naeim A. Henein
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Computational Analysis ◽  
Injection Rate ◽  
Gas Pressure ◽  
Operating Conditions ◽  
Rate Of Heat Release

Injection rate shaping is a method used to control the instantaneous mass flow rate of the fuel during an injection event. The rate at which the fuel is delivered affects the composition of the combustible mixture and its distribution in the combustion chamber, thereby has an impact on the combustion process in the diesel engine. This paper investigates the effects of five different types of injection rate shapes on diesel engine autoignition, combustion, and engine-out emission trends using a three-dimensional computational simulation approach. For this purpose, an n-heptane fuel model is utilized. Initially, a tophat rate-shape, characterized by the constant mass flow rate of the fuel, is assumed to represent the actual injection profile of an actual engine. Then, in order to develop sufficient confidence in the simulation predictions, this assumption together with the calibrated CFD models are validated by reproducing the cylinder gas pressure, the rate of heat release, and engine-out emissions trends for two sets of engine operating conditions. Later, using all the rate shapes the investigation is conducted for one test point considering two different cases of fuel injection: Case 1 - same SOI and duration of injection (DOI), and Case 2 - same combustion phasing and DOI. The results obtained from the computational analysis show that the injection rate shape affects the autoignition, combustion, and emissions of a diesel engine. It is observed that the rate shapes, characterized by high injection rates at the beginning of the injection event, enhance the formation of negative temperature coefficient (NTC) regime. Therefore, the mole fractions of different species are determined during the NTC regime in order to examine the processes relevant to the formation of the NTC regimes for these rate shapes. Further, for the same SOI and DOI case, significant differences in the ignition delays between each rate shapes are observed. The maximum deviation of the ignition delay from the reference tophat is found to be 37%. Furthermore, the paper highlights the differences in the cylinder gas pressure, gas temperature, and rate of heat release due to different fuel delivery rates of different rate shapes. Finally, the comparison of the engine-out emissions for different rate shapes for both the cases of injection are presented and discussed in detail.

The standard unit mass flow rate of gas-liquid mixtures

2020 ◽  
pp. 13-16
Author(s):  
V.N. Petrov ◽  
◽  
V.F. Sopin ◽  
L.A. Akhmetzyanova ◽  
Ya.S. Petrova ◽  
...  
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Liquid Mixtures ◽  
Unit Mass ◽  
Standard Unit

Prediction of Leakage Mass Flow Rate Through Gas Springs

1987 ◽  
Author(s):  
Roberto Bruno Bossio ◽  
Vincenzo Naso ◽  
Marian Cichy ◽  
Boleslaw Pleszewski
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate
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