OCR Text |
Show compared with experimental measurements in a buoyant, turbulent jet diffusion flame. The objectives of this work are: (a) to present relevant modeling issues for jet diffusion flames, with special emphasis on turbulence models (b) to examine and quantify the range of applicability of traditional turbulence closure models for modeling buoyant, turbulent jet diffusion flames (c) to evaluate the relative merits of each turbulence model for flare flame modeling applications. Figure 1. Vertical flare flame. Image courtesy of Kaldair. (wwwoffshore-technology.com/contractors /flare/ kaldair) Experimental data Comprehensive experimental data sets for large scale, flare flames under varied ambient conditions (cross winds, direction of gravitational acceleration vector) are largely unavailable. However, fully developed turbulent jets of various types have been shown to follow a self-similar scaling in the jet far field [1-4]. Furthermore, it has been shown that momentum dominated jet flames, when properly nondimensionalized to account for density variations due to heat release, adhere to these same classical scaling laws [5]. These correlations appear to hold over a variety of fuels and operating conditions [5,6]. Thus, by evaluating CFD's ability to predict scaling properties in lab scale flames, w e can gain insight into CFD's ability to predict large scale flare flames. W e thus assume with reasonable confidence that analyses conducted with lab scale jet flames can provide valuable insights into the accuracy of C FD simulations for flare flames. Numerical results are compared with the vertical free turbulent jet diffusion flame data of Meier et al. [7]. The fuel consists of equal parts hydrogen and nitrogen and issues from a round nozzle (d0 = 8 m m ) with a bulk velocity, U0, of 34.8 m/s. The fuel nozzle is surrounded by a coflowing air annulus (OD = 7 0 m m ) with bulk velocity of 0.2 m/s. The jet issues into quiescent air. Fuel and air are at 300 K. The Reynolds number „ VJadQ v is 10,000. The Froude number gd d,=(p./pj2d. is 22,000. Here g is the gravitational acceleration, ds is the effective source Figure 2. Flare flare from horizontal boom on an offshore drilling rig. Image courtesy of Kaldair. (wwwoffshore-technology.com/contractors/flare/ kaldair). |