scholarly journals A Numerical Research on Vortex Street Flow Oscillation in the Double Flapper Nozzle Servo Valve

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 721 ◽  
Author(s):  
Liang Lu ◽  
Shirang Long ◽  
Kangwu Zhu
Keyword(s):  
Vortex Street ◽  
Oscillating Flow ◽  
Main Stage ◽  
Flow Oscillation ◽  
Servo Valve ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy ◽  
Turbulent Modeling ◽  
Grid Independence

The oscillating flow field of the double nozzle flapper servo valve pre-stage is numerically analyzed through Large Eddy Simulation (LES) turbulent modeling with the previous grid independence verification. The vortex street flow phenomenon can be observed when the flow passes through the nozzle flapper channel, the vortex alternating in each side produces the periodical flow oscillation. The structural and flow parameter effects on the oscillating flow are emphasized, and it could be determined that the pressure on the flapper is nearly proportional to the flow velocity and inversely proportional to the actual distance between the flapper and the nozzle. On the other hand, the main frequency of oscillation decreases with the velocity and increases with the distance between the nozzle flapper. The main stage movement is further considered with a User Defined Function (UDF), and it could be determined that the influences of the structural and flow parameters on the flow oscillation are rarely changed, but the main frequencies drop, generally.

scholarly journals Prediction of flow and dispersion in cross–ventilated buildings

2019 ◽  
Vol 128 ◽  
pp. 05002
Author(s):  
Ali Cemal Benim ◽  
Michael Diederich ◽  
Ali Nahavandi
Keyword(s):  
Computational Analysis ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Turbulence Structure ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Grid Independence

The present paper presents a detailed computational analysis of flow and dispersion in a generic isolated single–zone buildings. First, a grid generation strategy is discussed, that is inspired by a previous computational analysis and a grid independence study. Different turbulence models are appliedincluding two-equation turbulence models, the differential Reynolds Stress Model, Detached Eddy Simulation and Zonal Large Eddy Simulation. The mean velocity and concentration fields are calculated and compared with the measurements. A satisfactory agreement with the experiments is not observed by any of the modelling approaches, indicating the highly demanding flow and turbulence structure of the problem.

Large Eddy Simulation Study of Flow Dynamics in a Multiswirler Model Combustor at Elevated Pressure and High Temperature

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Weijie Liu ◽  
Qian Yang ◽  
Ranran Xue ◽  
Huiru Wang
Keyword(s):  
High Temperature ◽  
Large Eddy Simulation ◽  
Elevated Pressure ◽  
Dominant Frequency ◽  
Flow Dynamics ◽  
Main Stage ◽  
Eddy Simulation ◽  
Precessing Vortex Core ◽  
Flow Interaction ◽  
Large Eddy

Large eddy simulation (LES) of nonreacting turbulent flow in a multiswirler model combustor is carried out at elevated pressure and high temperature. Flow interaction between the main stage and the pilot stage is discussed based on the time-averaged and instantaneous flowfield. Flow dynamics in the multiswirling flow are analyzed using a phase-averaged method. Proper orthogonal decomposition (POD) is used to extract dominant flow features in the multiswirling flow. Numerical results show that the main stage and the pilot stage flows interact with each other generating a complex flowfield. Flow interaction can be divided into three regions: converging region, merging region, and combined region. A precessing vortex core (PVC) is successfully captured in the pilot stage. PVC rotates with a first dominant frequency of 2756 Hz inducing asymmetric azimuthal flow instabilities in the pilot stage. POD analyses for the velocity fields also show dominant high-frequency modes (mode 1 and mode 2) in the pilot stage. However, the dominant energetic flow is damped rapidly downstream of the pilot stage such that it has a little effect on the main stage flow.

Three-dimensional study of separated flow over a square cylinder by large eddy simulation

2005 ◽  
Vol 219 (3) ◽  
pp. 225-234 ◽  
Author(s):  
M Farhadi ◽  
M Rahnama
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Mean Flow ◽  
Central Difference ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy

Large eddy simulation of flow over a square cylinder in a channel is performed at Reynolds numbers of 22 000 and 21 400. The selective structure function (SSF) modelling of the subgrid-scale stress terms is used and the convective terms are discretized using quadratic upstream interpolation for convective kinematics (QUICK) and central difference (CD) schemes. A series of time-averaged velocities, turbulent stresses, and some global flow parameters such as lift and drag coefficients and their fluctuations are computed and compared with experimental data. The suitability of SSF model has been shown by comparing the computed mean flow velocities and turbulent quantities with experiments. Results show negligible variation in the flow parameters for the two Reynolds numbers used in the present computations. It was observed that both QUICK and CD schemes are capable of obtaining results close to those of the experiments with some minor differences.

NUMERICAL SIMULATION OF THE EFFECT OF INITIAL NONUNIFORMITY AND FLUCTUATIONS OF FUEL CONCENTRATION ON COMBUSTION STABILITY AND NOX AND CO EMISSION IN A LEAN PREMIXED METHANE/AIR COMBUSTOR

2020 ◽  
Author(s):  
K. Ya. Yakubovskiy ◽  
◽  
A. B. Lebedev ◽  
P. D. Toktaliev ◽  
◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Combustion Stability ◽  
Fuel Concentration ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Low Emission ◽  
Large Eddy ◽  
Co Emission

The effect of initial nonuniformity and fluctuations of fuel concentration on the combustion stability and NOx and CO emission in the model combustion chamber was analyzed with the use of previously developed simple and computationally inexpensive Large Eddy Simulation (LES) methodology for simulation of three-dimensional unsteady turbulent flows with premixed combustion of methane-air mixture in low-emission combustion chamber which geometry is represented by channel with the backward facing step. Typical sizes of the combustion chamber, flow parameters, turbulence level, and method of flame front stabilization are close to those of full-sized industrial combustors.

Large eddy simulation of mean and oscillating flow in a side-dump ramjet combustor

2008 ◽  
Vol 152 (1-2) ◽  
pp. 154-176 ◽  
Author(s):  
A. Roux ◽  
L.Y.M. Gicquel ◽  
Y. Sommerer ◽  
T.J. Poinsot
Keyword(s):  
Large Eddy Simulation ◽  
Oscillating Flow ◽  
Eddy Simulation ◽  
Ramjet Combustor ◽  
Large Eddy

Cooling Performance Comparison of a Low Aspect Ratio Incremental Impingement Pin-Fin Channel Configurations

2017 ◽  
Author(s):  
Susheel Singh ◽  
Sumanta Acharya ◽  
Forrest Ames
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Performance Comparison ◽  
Wake Region ◽  
Pin Fin ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy ◽  
Transfer Behavior ◽  
Effective Use

The effective use of coolant in maintaining gas turbine components below failure limits is becoming increasingly necessary in view of increasing combustor exit temperatures. Incorporating coolant impingement in a pin-finned channel provides an avenue for increased heat transfer. Two types of cooling configuration are modeled and compared: case 1: with the jet impinging in a cut out region behind a pin-fin (thus sheltering the jet from crossflow effects), and case 2: with the jet impinging further downstream along the next row of pin-fin and downstream of the wake region of the upstream pin-fin. In the current work, a Large Eddy Simulation (LES) study is conducted for a Reynolds number of 7500. All other geometrical and flow parameters are kept similar in both the configurations to enable a direct comparison. Since the stagnation point Nusselt number is not affected by the cross-flow in the sheltered configuration, there is enhanced cooling as compared to the configuration in which the jet impinges further downstream and is not protected from the crossflow. In this paper, the flow field, the jet-crossflow interactions and the heat transfer behavior are discussed for both the configurations.

Flow over two tandem wall-mounted cubes using large eddy simulation

2008 ◽  
Vol 222 (8) ◽  
pp. 1465-1475 ◽  
Author(s):  
M Farhadi ◽  
K Sedighi
Keyword(s):  
Large Eddy Simulation ◽  
Eddy Viscosity ◽  
Separation Zone ◽  
Good Correspondence ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy ◽  
Horseshoe Vortices ◽  
Complex Phenomena

Flow over tandem surface-mounted cubes in a channel were investigated numerically using large eddy simulation (LES). The selective structure function model used for the determination of eddy viscosity appears in the subgrid scale stress terms in momentum equations. Flow over this geometry has very complex phenomena such as several horseshoe vortices and recirculation regions. The main objective of this study is identifying the features of flow past two in-line wall-mounted cubes in a channel for Reynolds number 22 000. The LES results obtained are in reasonable agreement with the experiment both qualitatively and quantitatively. The time-averaged streamlines and velocity vectors were compared with the experiment of Martinuzzi and Havel [9], which showed good correspondence. The S/ H length has negligible influence on the turbulence levels in the region upstream and above the first cube in the separation zone. However, in the vortex core downstream of, and above the second cube, elevated levels of turbulence were found for both u′ u′ and v′ v′ especially when the inter-obstacle spacing is increased. A result of this study also includes time-averaged contours of turbulent intensity and some details of flow parameters such as the Strouhal number and drag coefficient.

scholarly journals Explicit filtering to obtain grid-spacing-independent and discretization-order-independent large-eddy simulation of compressible single-phase flow

2012 ◽  
Vol 697 ◽  
pp. 399-435 ◽  
Author(s):  
Senthilkumaran Radhakrishnan ◽  
Josette Bellan
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Small Scale ◽  
Spatial Discretization ◽  
Grid Spacing ◽  
Eddy Simulation ◽  
Filter Width ◽  
Spacing Ratio ◽  
Large Eddy ◽  
Grid Independence

AbstractIn large-eddy simulation (LES), it is often assumed that the filter width is equal to the grid spacing. Predictions from such LES are grid-spacing dependent since any subgrid-scale (SGS) model used in the LES equations is dependent on the resolved flow field which itself varies with grid spacing. Moreover, numerical errors affect the flow field, especially the smallest resolved scales. Thus, predictions using this approach are affected by both modelling and numerical choices. However, grid-spacing-independent LES predictions unaffected by numerical choices are necessary to validate LES models through comparison with a trusted template. First, such a template is created here through direct numerical simulation (DNS). Then, simulations are conducted using the conventional LES equations and also LES equations which are here reformulated so that the small-scale-producing nonlinear terms in these equations are explicitly filtered (EF) to remove scales smaller than a fixed filter width; this formulation is called EFLES. First, LES is conducted with four SGS models, then EFLES is performed with two of the SGS models used in LES; the results from all these simulations are compared to those from DNS and from the filtered DNS (FDNS). The conventional LES solution is both grid-spacing and spatial discretization-order dependent, thus showing that both of these numerical aspects affect the flow prediction. The solution from the EFLES equations is grid independent for a high-order spatial discretization on all meshes tested. However, low-order discretizations require a finer mesh to reach grid independence. With an eighth-order discretization, a filter-width to grid-spacing ratio of two is sufficient to reach grid independence, while a filter-width to grid-spacing ratio of four is needed to reach grid independence when a fourth- or a sixth-order discretization is employed. On a grid fine enough to be utilized in a DNS, the EFLES solution exhibits grid independence and does not converge to the DNS solution. The velocity-fluctuation spectra of EFLES follow those of FDNS independent of the grid spacing used, in concert with the original concept of LES. The reasons for the different predictions of conventional LES or EFLES according to the SGS model used, and the different characteristics of the EFLES predictions compared to those from conventional LES are analysed.

Flow Dynamics in a Multiswirler Model Combustor Based on Large Eddy Simulation and Proper Orthogonal Decomposition Analysis

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Weijie Liu ◽  
Huiru Wang ◽  
Qian Yang ◽  
Ranran Xue ◽  
Bing Ge ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Particle Image ◽  
Swirling Flow ◽  
Flow Instability ◽  
Flow Dynamics ◽  
Main Stage ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Proper Orthogonal

Abstract Swirling flow is often employed in gas turbine combustion chambers for the sake of improving flame stability. Swirling flow induces not only recirculation zones but also large coherent structures, which show close relationship with flow dynamics and combustion instability. The flow dynamics including precessing vortex core (PVC) in simple swirlers is extensively studied, while the flow instability characteristics in a multiswirler combustor are not fully reported. In this paper, large eddy simulation (LES) of nonreacting turbulent swirling flow is conducted in a multiswirler burner, which comprises a pilot stage and a main stage. Flow dynamics in the multiswirler combustor are analyzed based on phase-averaged evolution of instantaneous flowfield. LES results are compared with particle image velocimetry (PIV) data in terms of mean and root mean square (RMS) velocities. Proper orthogonal decomposition (POD) is employed to identify the coherent structures in the multiswirling flow. Results show that LES results are in good agreement with particle image velocimetry (PIV) data. Main stage and pilot stage flow interact with each other generating highly turbulent swirling flow. PVC is successfully captured at the boundary of main recirculation zone (MRZ) in the pilot stage with a dominant frequency of 1915 Hz. The PVC leads to periodic azimuthal flow instability. POD analyses for the velocity fields show dominant high-frequency modes (modes 1 and 2) in the pilot stage. However, the dominant energetic flow is damped rapidly downstream of the pilot stage that it has little effect on the main stage flow.

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