Role of large scale flow features on cycle-to-cycle variations of spark-ignited flame-initiation and its transition to turbulent combustion

2019 ◽  
Vol 37 (4) ◽  
pp. 4945-4953 ◽  
Author(s):  
Wei Zeng ◽  
Seunghwan Keum ◽  
Tang-Wei Kuo ◽  
Volker Sick
2021 ◽  
Author(s):  
Georgios Fragkoulidis ◽  
Volkmar Wirth

<p>The large-scale extratropical upper-tropospheric flow tends to organize itself into eastward-propagating Rossby wave packets (RWPs). Investigating the spatiotemporal evolution of RWPs and the underlying physical processes has been beneficial in showcasing the role of the upper-tropospheric flow in temperature and precipitation extremes. The use of recently developed diagnostics of local in space and time wave properties has provided further insight in this regard. Motivated by the above, these diagnostic methods are now being employed to investigate the intraseasonal to decadal variability of key RWP properties such as their amplitude, phase speed, and group velocity in reanalysis datasets. It is shown that these properties exhibit a distinct seasonal and interregional variability, while interesting patterns thereof emerge. Moreover, the interannual and long-term variability in these RWP properties is explored and significant decadal trends for specific regions and seasons are highlighted. Ongoing work aims at further utilizing the presented diagnostics and analyses toward an improved understanding of the extratropical large-scale flow variability from weather to climate time scales.</p>


1996 ◽  
Vol 23 ◽  
pp. 46-51 ◽  
Author(s):  
D. R. MacAyeal ◽  
V. Rommelaere ◽  
P. Huybrechts ◽  
C. L. Hulbe ◽  
J. Determann ◽  
...  

A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution of stress-equilibrium equations for an ice-shelf velocity consistent with present observations. As a demonstration, we compare five independently developed ice-shelf models based on finite-difference and finite-element methods. Our results suggest that there is little difference between finite-element and finite-difference methods in capturing the basic, large-scale flow features of the ice shelf. We additionally show that the fit between model and observed velocity depends strongly on the ice-shelf temperature field, for which there is presently little observational control. The main differences between model results are due to the equations being solved, the boundary conditions at the ice from and the discretization method (finite element vs finite difference).


2007 ◽  
Vol 53 (181) ◽  
pp. 277-288 ◽  
Author(s):  
Erin C. Pettit ◽  
Throstur Thorsteinsson ◽  
H. Paul Jacobson ◽  
Edwin D. Waddington

AbstractPolycrystalline ice near an ice divide typically shows a crystal fabric (crystal preferred orientation) with c axes clustered vertically. We explore the effect of this fabric on the large-scale flow pattern near an ice divide. We incorporate an analytical formulation for anisotropy into a non-linear flow law within a finite-element ice-sheet flow model. With four different depth profiles of crystal fabric, we find that the effect of fabric is significant only when a profile has a minimum cone angle of less than ~25º. For a steady-state divide, the shape and size of the isochrone arch can depend as much on the crystal fabric as it does on the non-linearity of ice flow. A vertically oriented fabric tends to increase the size of the isochrone arch, never to reduce it. Also, non-random fabric has little effect on the ice-divide-flow pattern when ice is modeled as a linear (Newtonian) fluid. Finally, when we use a crystal-fabric profile that closely approximates the measured profile for Siple Dome, West Antarctica, the model predicts concentrated bed-parallel shearing 300 m above the bed.


2012 ◽  
Vol 134 (2) ◽  
Author(s):  
John Axerio-Cilies ◽  
Emin Issakhanian ◽  
Juan Jimenez ◽  
Gianluca Iaccarino

The flowfield around a 60% scale stationary Formula 1 tire in contact with the ground in a closed wind tunnel at a Reynolds number of 500,000 was computationally examined in order to assess the accuracy of different turbulence modeling techniques and confirm the existence of large scale flow features. A simplified and replica tire model that includes all brake components was tested to determine the sensitivity of the wake to cross flow within the tire hub along with the flow blockage caused by the brake assembly. The results of steady and unsteady Reynolds averaged Navier-Stokes (URANS) equations and a large eddy simulation (LES) were compared with the experimental data. The LES closure and the RANS closure that accounted for unsteadiness with low eddy viscosity (unsteady kω-SST) matched closest to the experimental data both in point wise velocity comparisons along with location and intensity of the strong counter-rotating vortex pair dominating the far wake of the tire.


1996 ◽  
Vol 23 ◽  
pp. 46-51 ◽  
Author(s):  
D. R. MacAyeal ◽  
V. Rommelaere ◽  
P. Huybrechts ◽  
C. L. Hulbe ◽  
J. Determann ◽  
...  

A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution of stress-equilibrium equations for an ice-shelf velocity consistent with present observations. As a demonstration, we compare five independently developed ice-shelf models based on finite-difference and finite-element methods. Our results suggest that there is little difference between finite-element and finite-difference methods in capturing the basic, large-scale flow features of the ice shelf. We additionally show that the fit between model and observed velocity depends strongly on the ice-shelf temperature field, for which there is presently little observational control. The main differences between model results are due to the equations being solved, the boundary conditions at the ice from and the discretization method (finite element vs finite difference).


2018 ◽  
Vol 3 (1) ◽  
pp. 243-255 ◽  
Author(s):  
Paul Fleming ◽  
Jennifer Annoni ◽  
Matthew Churchfield ◽  
Luis A. Martinez-Tossas ◽  
Kenny Gruchalla ◽  
...  

Abstract. In this paper, we investigate the role of flow structures generated in wind farm control through yaw misalignment. A pair of counter-rotating vortices is shown to be important in deforming the shape of the wake and in explaining the asymmetry of wake steering in oppositely signed yaw angles. We also demonstrate that vortices generated by an upstream turbine that is performing wake steering can deflect wakes of downstream turbines, even if they are themselves aligned. We encourage the development of improvements to control-oriented engineering models of wind farm control, to include the effects of these large-scale flow structures. Such a new model would improve the predictability of control-oriented models. Further, we demonstrate that the vortex structures created in wake steering can lead to greater impact on power generation than currently modeled in control-oriented models. We propose that wind farm controllers can be made more effective if designed to take advantage of these effects.


Author(s):  
Qinxue Tan ◽  
Jing Ren ◽  
Hongde Jiang

Rotating cavities with axial throughflow are found inside the compressor rotors of turbomachines. The flow pattern and heat transfer in the cavities are known as sophisticated problems. In this paper, the 3D compressible flow field in a rotating cavity is investigated numerically using a steady RANS method, an unsteady RANS method and LES. The numerical results based on the three methods are analyzed in detail and compared with the available experimental data. For the LES method with a subgrid-scale model, the instantaneous flow structure and the heat transfer can be captured very well. For the unsteady RANS method with an appropriate turbulence model, the large-scale flow structure can be revealed acceptably, and the heat transfer solution agrees with the experimental data with a certain error. For the steady RANS method, a reasonable flow structure cannot be obtained, while the distribution of the heat transfer has a same tendency and uncertain error with the experiments. Therefore, it is suggested that the steady RANS method can still be a numerical tool in the quite preliminary design of the rotating cavities, while the LES is more advanced from an academic view. Moreover, the unsteady RANS method is most appropriate for industry. It should be valuable in the detailed design computations for selecting the optimized design.


2006 ◽  
Vol 63 (8) ◽  
pp. 1982-1995 ◽  
Author(s):  
G. Rivière ◽  
A. Joly

Abstract Midlatitude cyclones tend to develop strongly in specific locations relative to the large-scale flow, such as jet-exit zones. Here, the approach developed in Part I that highlights the role of large-scale deformation in constraining the location of such events is continued. The atmospheric flow is decomposed into a high- and low-frequency part separating large and synoptic scales. A new low-frequency diagnostic has been introduced, called effective deformation Δm. It is defined as σ2m − ζ2m, where σm is the low-frequency deformation magnitude and ζm is the low-frequency vorticity. While Part I focused on large-scale conditions inducing an intermediate phase of barotropic growth, the present paper concentrates on other configurations that rather prevent this phase from happening. This large-scale circulation is characterized by the presence of a strong zonal upper-level jet and a lower-level jet that are meridionally quite far from each other over the Atlantic but close to one another in the eastern Atlantic region. As high-frequency disturbances are trapped by the effective deformation of the low-frequency jets, the increasing closeness of the two jets associated with that of the two effective deformation fields computed in the lower and upper levels defines a region called the baroclinic critical region where upper high-frequency disturbances and surface cyclones may strongly interact baroclinically. The increased baroclinic energy collection resulting from this constrained configuration change is outlined. An analysis of the explosive growth of the Christmas wind storms of 1999 and of mid-December 2004 provides different realizations of this configuration and associated mechanism.


2013 ◽  
Author(s):  
Elisabeth J. Ploran ◽  
Ericka Rovira ◽  
James C. Thompson ◽  
Raja Parasuraman

Sign in / Sign up

Export Citation Format

Share Document