Loading...
Please wait, while we are loading the content...
Similar Documents
One-dimensional Turbulence Modelling of a Lifted Methane/air Jet Flame in a Vitiated Coflow
| Content Provider | Semantic Scholar |
|---|---|
| Author | Starick, Tommy |
| Copyright Year | 2019 |
| Abstract | The present preliminary numerical study investigates a lifted methane/air jet flame in a vitiated coflow by means of the map-based, stochastic One-Dimensional Turbulence (ODT) model. In the considered configuration, a jet flame issues from a central nozzle into a vitiated coflow of hot combustion products from an array of lean H2/air flames. Centreline profiles for mixture fraction, temperature and mass fraction of O2 and OH obtained from ODT simulations with a planar and cylindrical formulation are shown and compared to measurements from Cabra et al. (2005). Additionally, two-dimensional renderings of the jet flame and scatter plots of temperature versus mixture fraction and OH mass fraction versus mixture fraction are provided. Although the application of ODT for reactive flows in jet configurations is not novel, the chosen lifted jet flame in a vitiated coflow represents a challenge for the model. The accurate representation of the subtle interactions of the hot coflow products with the cold unburnt jet flow are crucial for the reaction and autoignition of the jet (Cabra et al., 2005). Considering the reduced order of the model and the taken assumptions, the achieved results reasonably match with the measurement data. INTRODUCTION & ODT FORMULATION Clear understanding of flame extinction and stabilisation has a central importance and is usually addressed by simplified jet flames. Vitiated coflow burners allow detailed insights and investigations of the underlying extinction and flame stabilisation dynamics for lifted jet flames in an environment of hot combustion products. The simple configuration of a jet flame in a coaxial flow of hot combustion products exhibits similar characteristics for chemical kinetics, heat transfer and molecular transport as recirculation burners, while avoiding their complex recirculating fluid mechanics (Cabra et al., 2002). In this work, we address the study of the dynamics of a lifted methane/air jet flame in a vitiated coflow of hot combustion products from an array of lean H2/air flames by means of the One-Dimensional Turbulence (ODT) model. For this purpose, we use both a planar and a cylindrical temporal ODT formulation. This section describes only the cylindrical temporal formulation as in Lignell et al. (2018). The description of the planar formulation can be found in Lignell et al. (2013). The ODT model was formulated by A. Kerstein (Kerstein, 1999). It is an efficient approach for turbulent flow simulations, resolving all time and length scales along a notional line of sight crossing the turbulent flow field. The key advantage of ODT in comparison to filtered simulation approaches such as Reynolds-Averaged Navier-Stokes (RANS) or Large Eddy Simulations (LESs) is that it incorporates molecular processes (like chemical reactions and diffusive transport) without introducing additional approximations or modelling assumptions. The effects of 3-D turbulence are incorporated in ODT directly by modelling the characteristics of the turbulent transport on the fluid properties along the simulated 1-D domain. This is implemented by means of stochastic 1-D eddy events. An eddy event perturbs any of the property fields by the application of a triplet map. A triplet map takes a line segment [r0,r0 + l] with a randomly sampled eddy location r0 and size l, shrinks it to a third of its original length, and then places three copies on the original domain. The middle copy is reversed, which ensures the continuity of advected fields and leads to a steepening of local property gradients (Lignell et al., 2018). These eddy events are sampled in time as a marked Poisson process using presumed Probability Density Functions (PDFs) for eddy locations r0 and sizes l. On average, this process is able to replicate the statistics of turbulent flows by oversampling the number of events modelling the turbulent transport, and maintaining a target mean accep- |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.tsfp-conference.org/proceedings/2019/278.pdf |
| Alternate Webpage(s) | https://ignite.byu.edu/public/Starick_2019_conference.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
