Response Dynamics of Recirculation Structures in Coaxial Nonpremixed Swirl-Stabilized Flames Subjected to Acoustic Forcing

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Uyi Idahosa ◽  
R. Santhosh ◽  
Ankur Miglani ◽  
Saptarshi Basu
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Fluid Dynamic ◽  
High Energy ◽  
Reacting Flow ◽  
Flow State ◽  
Response Dynamics ◽  
Jet Flame ◽  
Flame Response ◽  
Acoustic Forcing

This paper reports the time-mean and phase-locked response of nonreacting as well as reacting flow field in a coaxial swirling jet/flame (nonpremixed). Two distinct swirl intensities plus two different central pipe flow rates at each swirl setting are investigated. The maximum response is observed at the 105 Hz mode in the range of excitation frequencies (0–315 Hz). The flow/flame exhibited minimal response beyond 300 Hz. It is seen that the aspect ratio change of inner recirculation zone (IRZ) under nonreacting conditions (at responsive modes) manifests as a corresponding increase in the time-mean flame aspect ratio. This is corroborated by ∼25% decrease in the IRZ transverse width in both flame and cold flow states. In addition, 105 Hz excited states are found to shed high energy regions (eddies) asymmetrically when compared to dormant 315 Hz pulsing frequency. The kinetic energy (KE) of the flow field is subsequently reduced due to acoustic excitation and a corresponding increase (∼O (1)) in fluctuation intensity is witnessed. The lower swirl intensity case is found to be more responsive than the high swirl case as in the former flow state the resistance offered by IRZ to incoming acoustic perturbations is lower due to inherently low inertia. Next, the phase-locked analysis of flow and flame structure is employed to further investigate the phase dependence of flow/flame response. It is found that the asymmetric shifting of IRZ mainly results at 270 deg acoustic forcing. The 90 deg phase angle forcing is observed to convect the IRZ farther downstream in both swirl cases as compared to other phase angles. The present work aims primarily at providing a fluid dynamic view point to the observed nonpremixed flame response without considering the confinement effects.

Numerical Research on Flow Field for Petroleum Tar Cutting Pump

2013 ◽  
Author(s):  
Jing-ning Hu ◽  
Jing Wang ◽  
Rengui Gu ◽  
Ying-ying Tian ◽  
Qun Ye
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Tilt Angle ◽  
Fluid Dynamic ◽  
Reference Value ◽  
Flow State ◽  
Solid Concentration ◽  
Two Phase ◽  
Revolution Speed ◽  
Small Flow

In order to study the flow state and distribution of the solid particle in the flow field of petroleum tar cutting pump, the Computational Fluid Dynamic method was used to conduct the numerical simulation of liquid-solid two-phase flow based on Euler-Euler multiphase flow model and standard turbulence equation. The influence of flow rate, revolution speed and tilt angle of stator slot on streamline and distribution of solid concentration were analyzed. The result shows:strong swirl exists in inlet segment in small flow rate, but flow rate has little influence on the solid concentration, so it has no obvious influence on the cutting and grinding efficiency.Grinding efficiency could be improved by increasing revolution speed, but the requirement for the equipment would be higher, so the revolution speed should be determined reasonably. Reducing the tilt angle of stator slot is favor for improving the grinding and cutting efficiency, so it could provide some reference value for the optimal design.

Effects of Outlet Boundary Conditions on the Reacting Flow Field in a Swirl-Stabilized Burner at Dry and Humid Conditions

2012 ◽  
Author(s):  
Steffen Terhaar ◽  
Bernhard C. Bobusch ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Measurement Techniques ◽  
Theoretical Explanation ◽  
Clear Correlation ◽  
Reacting Flow ◽  
Flow State ◽  
Swirl Number ◽  
Emission Analysis ◽  
Exit Boundary

During the design and testing process of swirl-stabilized combustors, it is often impractical to maintain identical outlet boundary conditions. Furthermore, it is a common practice to intentionally change the acoustic boundary conditions of the outlet in order to suppress thermoacoustic instabilities. In the presented work the susceptibility of the reacting flow field to down-stream perturbations is assessed by the application of an area contraction at the outlet. Since combustion and fuel composition are shown to be important parameters for the influence of the boundary conditions on the flow field, highly steam diluted flames are investigated in addition to dry flames, at different equivalence ratios and degrees of swirl. The applied measurement techniques include Particle Image Velocimetry, Laser Doppler Velocimetry, and emission analysis. The results reveal a clear correlation of the susceptibility of the flow field to downstream perturbations to both, the inlet swirl number and the amount of dilatation caused by the flame. The concept of an effective swirl number down-stream of the flame is applied to the results and is proven to be the dominating parameter. A theoretical explanation for the influence of this parameter is provided by the usage of the well known theory of subcritical and supercritical swirling flows, where perturbations can propagate upstream solely in subcritical flows via standing waves. Knowledge of the flow state is of particular importance for the evaluation of combustion tests with differing exit boundary conditions and the results emphasize the need for realistic exit boundary conditions for numerical simulations.

Effects of Outlet Boundary Conditions on the Reacting Flow Field in a Swirl-Stabilized Burner at Dry and Humid Conditions

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Steffen Terhaar ◽  
Bernhard C. Bobusch ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Measurement Techniques ◽  
Theoretical Explanation ◽  
Clear Correlation ◽  
Reacting Flow ◽  
Flow State ◽  
Swirl Number ◽  
Emission Analysis ◽  
Exit Boundary

During the design and testing process of swirl-stabilized combustors, it is often impractical to maintain identical outlet boundary conditions. Furthermore, it is a common practice to intentionally change the acoustic boundary conditions of the outlet in order to suppress thermoacoustic instabilities. In the presented work the susceptibility of the reacting flow field to downstream perturbations is assessed by the application of an area contraction at the outlet. Since combustion and fuel composition are shown to be important parameters for the influence of the boundary conditions on the flow field, highly steam diluted flames are investigated in addition to dry flames at different equivalence ratios and degrees of swirl. The applied measurement techniques include particle image velocimetry, laser doppler velocimetry, and emission analysis. The results reveal a clear correlation of the susceptibility of the flow field to downstream perturbations to both the inlet swirl number and the amount of dilatation caused by the flame. The concept of an effective swirl number downstream of the flame is applied to the results and is proven to be the dominating parameter. A theoretical explanation for the influence of this parameter is provided by the usage of the well known theory of subcritical and supercritical swirling flows, where perturbations can propagate upstream solely in subcritical flows via standing waves. Knowledge of the flow state is of particular importance for the evaluation of combustion tests with differing exit boundary conditions and the results emphasize the need for realistic exit boundary conditions for numerical simulations.

Analysis of Gas Dynamics in a Rotating Disk Cavity

2011 ◽  
Vol 86 ◽  
pp. 893-897
Author(s):  
Yang Liu ◽  
Yong Hong Zhang ◽  
Guo Ding Chen ◽  
Ran Wan
Keyword(s):  
Flow Field ◽  
Gas Flow ◽  
Radial Direction ◽  
Fluid Dynamic ◽  
Tangential Velocity ◽  
Rotating Disk ◽  
Flow State ◽  
The Impact ◽  
Gas Medium ◽  
Gas Flow Field

A fundamental study has been performed to analysis the fluid dynamic characteristics of the gas medium in a rotating disk cavity through the commercial software CFX11.0. This paper aims to discuss the impact of the speed of rotating disk, axial and radial size and parietal lubricant film velocity and other factors on the gas flow state in cavity. Several conclusions have been obtained: the speed of rotating disk has a great impact on velocity distribution of gas flow field; the dimensionless tangential velocity of the gas medium decreases along the radial direction, and with the speed increasing, it shows a certain regularity; Dimensionless radial velocity decreases along the radial direction, and the speed of rotating disk nearly has no influence on this; The shear stress distribution along the radial direction and the distribution of tangential velocity have similar regularity; the impact of disk cavity height on the distribution of the tangential velocity along radial direction in the gas flow field is much more obvious than the impact of disk cavity width.

CFD prediction of the reacting flow field inside a subscale scramjetcombustor

1988 ◽  
Author(s):  
T. CHITSOMBOON ◽  
G. NORTHAM ◽  
R. ROGERS ◽  
G. DISKIN
Keyword(s):  
Flow Field ◽  
Reacting Flow

scholarly journals Clogging sensitivity of flow distributors designed for radially elongated hexagonal pillar array columns: a computational modelling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Farideh Haghighi ◽  
Zahra Talebpour ◽  
Amir Sanati-Nezhad
Keyword(s):  
Pressure Drop ◽  
Aspect Ratio ◽  
Contact Zone ◽  
Separation Efficiency ◽  
Fluid Dynamic ◽  
Computational Modelling ◽  
Channel Width ◽  
Fluid Distribution ◽  
Design Parameters ◽  
Pillar Array

AbstractFlow distributor located at the beginning of the micromachined pillar array column (PAC) has significant roles in uniform distribution of flow through separation channels and thus separation efficiency. Chip manufacturing artifacts, contaminated solvents, and complex matrix of samples may contribute to clogging of the microfabricated channels, affect the distribution of the sample, and alter the performance of both natural and engineered systems. An even fluid distribution must be achieved cross-sectionally through careful design of flow distributors and minimizing the sensitivity to clogging in order to reach satisfactory separation efficiency. Given the difficulty to investigate experimentally a high number of clogging conditions and geometries, this work exploits a computational fluid dynamic model to investigate the effect of various design parameters on the performance of flow distributors in equally spreading the flow along the separation channels in the presence of different degrees of clogging. An array of radially elongated hexagonal pillars was selected for the separation channel (column). The design parameters include channel width, distributor width, aspect ratio of the pillars, and number of contact zone rows. The performance of known flow distributors, including bifurcating (BF), radially interconnected (RI), and recently introduced mixed-mode (MMI) in addition to two new distributors designed in this work (MMII and MMIII) were investigated in terms of mean elution time, volumetric variance, asymmetry factors, and pressure drop between the inlet and the monitor line for each design. The results show that except for pressure drop, the channel width and aspect ratio of the pillars has no significant influence on flow distribution pattern in non-clogged distributors. However, the behavior of flow distributors in response to clogging was found to be dependent on width of the channels. Also increasing the distributor width and number of contact zone rows after the first splitting stage showed no improvement in the ability to alleviate the clogging. MMI distributor with the channel width of 3 µm, aspect ratio of the pillars equal to 20, number of exits of 8, and number of contact zones of 3 exhibited the highest stability and minimum sensitivity to different degrees of clogging.

scholarly journals Coupled Fluid–Solid Numerical Simulation for Flow Field Characteristics and Supporting Performance of Flexible Support Cylindrical Gas Film Seal

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 97
Author(s):  
Junfeng Sun ◽  
Meihong Liu ◽  
Zhen Xu ◽  
Taohong Liao ◽  
Xiangping Hu ◽  
...  
Keyword(s):  
Flow Field ◽  
Film Thickness ◽  
Fluid Dynamic ◽  
Structural Characteristics ◽  
Structural Parameters ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
High Rotational Speed ◽  
Flexible Support ◽  
Flow Field Characteristics

A new type of cylindrical gas film seal (CGFS) with a flexible support is proposed according to the working characteristics of the fluid dynamic seal in high-rotational-speed fluid machinery, such as aero-engines and centrifuges. Compared with the CGFS without a flexible support, the CGFS with flexible support presents stronger radial floating characteristics since it absorbs vibration and reduces thermal deformation of the rotor system. Combined with the structural characteristics of a film seal, an analytical model of CGFS with a flexible wave foil is established. Based on the fluid-structure coupling analysis method, the three-dimensional flow field of a straight-groove CGFS model is simulated to study the effects of operating and structural parameters on the steady-state characteristics and the effects of gas film thickness, eccentricity, and the number of wave foils on the equivalent stress of the flexible support. Simulation results show that the film stiffness increases significantly when the depth of groove increases. When the gas film thickness increases, the average equivalent stress of the flexible support first decreases and then stabilizes. Furthermore, the number of wave foils affects the average foils thickness. Therefore, when selecting the number of wave foils, the support stiffness and buffer capacity should be considered simultaneously.

scholarly journals Determination of Zero Dimensional, Apparent Devolatilization Kinetics for Biomass Particles at Suspension Firing Conditions

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 1018
Author(s):  
Anna Espekvist ◽  
Tian Li ◽  
Peter Glarborg ◽  
Terese Løvås ◽  
Peter Arendt Jensen
Keyword(s):  
Aspect Ratio ◽  
Particle Density ◽  
Fluid Dynamic ◽  
Particle Radius ◽  
Biomass Combustion ◽  
Least Squares Regression ◽  
Gas Temperature ◽  
Density Maximum ◽  
Parameter Ranges ◽  
The Impact

As part of the strive for a carbon neutral energy production, biomass combustion has been widely implemented in retrofitted coal burners. Modeling aids substantially in prediction of biomass flame behavior and thus in boiler chamber conditions. In this work, a simple model for devolatilization of biomass at conditions relevant for suspension firing is presented. It employs Arrhenius parameters in a single first order (SFOR) devolatilization reaction, where the effects of kinetics and heat transfer limitations are lumped together. In this way, a biomass particle can be modeled as a zero dimensional, isothermal particle, facilitating computational fluid dynamic calculations of boiler chambers. The zero dimensional model includes the effects of particle aspect ratio, particle density, maximum gas temperature, and particle radius. It is developed using the multivariate data analysis method, partial least squares regression, and is validated against a more rigorous semi-2D devolatilization model. The model has the capability to predict devolatilization time for conditions in the parameter ranges; radius (39–1569 μμm), density (700–1300 kg/m3), gas temperature (1300–1900 K), aspect ratio (1.01–8). Results show that the particle radius and gas phase temperature have a large influence on the devolatilization rate, and the aspect ratio has a comparatively smaller effect, which, however, cannot be neglected. The impact of aspect ratio levels off as it increases. The model is suitable for use as stand alone or as a submodel for biomass particle devolatilization in CFD models.

Nanoparticle Precipitation in a T-Mixer: Coupling Experimental and Numerical Investigations of the Fluid Dynamics With the Solid Formation Processes

2006 ◽  
Author(s):  
Johannes Gradl ◽  
Florian Schwertfirm ◽  
Hans-Christoph Schwarzer ◽  
Hans-Joachim Schmid ◽  
Michael Manhart ◽  
...  
Keyword(s):  
Flow Field ◽  
Fluid Dynamic ◽  
Concentration Field ◽  
Population Balance ◽  
Mixing Process ◽  
Image Velocimetry ◽  
Modeling Material ◽  
Field Information ◽  
Set Up ◽  
3D Information

Mixing and consequently fluid dynamic is a key parameter to tailor the particle size distribution (PSD) in nanoparticle precipitation. Due to fast and intensive mixing a static T-mixer configuration is capable for synthesizing continuously nanoparticles. The flow and concentration field of the applied mixer is investigated experimentally at different flow rates by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF). Due to the PIV measurements the flow field in the mixer was characterized qualitatively and the mixing process itself is quantified by the subsequent LIF-measurements. A special feature of the LIF set up is to detect structures in the flow field, which are smaller than the Batchelor length. Thereby a detailed insight into the mixing process in a static T-Mixer is given. In this study a CFD-based approach using Direct Numerical Simulation (DNS) in combination with the solid formation kinetics solving population balance equations (PBE) is applied, using barium sulfate as modeling material. A Lagrangian Particle Tracking strategy is used to couple the flow field information with a micro mixing model and with the classical theory of nucleation. We found that the DNS-PBE approach including macro and micro mixing, combined with the population balance is capable of predicting the full PSD in nanoparticle precipitation for different operating parameters. Additionally to the resulting PSD, this approach delivers a 3D-information about all running subprocesses in the mixer, i.e. supersaturation built-up or nucleation, which is visualized for different process variables.

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