Effect of Geometric Parameters on Simplex Atomizer Performance

Abstract

A computational analysis of flow in simplex fuel atomizers using the arbitrary-Lagrangian-Eulerian method is presented. It is well established that the geometry of an atomizer plays an important role in governing its performance. We have investigated the effect on atomizer performance of four geometric parameters, namely, inlet slot angle, spin chamber convergence angle, trumpet angle, and trumpet length. For a constant mass flow rate through the atomizer, the atomizer performance is monitored in terms of dimensionless film thickness, spray cone half-angle, and discharge coefficient. Results indicate that increase in inlet slot angle results in lower film thickness and discharge coefficient and higher spray cone angle. The spin chamber converge angle has an opposite effect on performance parameters, with film thickness and discharge coefficient increasing and the spray cone angle decreasing with increasing convergence angle. For a fixed trumpet length, the trumpet angle has very little influence on discharge coefficient. However, the film thickness decreases, and spray cone angle increases with increasing trumpet angle. For a fixed trumpet angle, the discharge coefficient is insensitive to trumpet length. Both the spray cone angle and the film thickness are found to decrease with trumpet length. Analytical solutions are developed to determine the atomizer performance considering inviscid flow through the atomizer. The qualitative trends in the variation of film thickness at the atomizer exit, spray cone angle, and discharge coefficient predicted by inviscid flow analysis are seen to agree well with computational results. NomenclatureA a = air core area at orifice exit A o = orifice area A p = total swirl slot area A t = the trumpet end area A ta = air core area at the trumpet end C d = discharge coefficient,ṁ/A o (2 p/ρ) 0.5 D s = spin chamber diameter d o = orifice diameter d t = trumpet diameter at atomizer exit f = body force K = atomizer constant, A p /(D s d o ) K t = A p /(πr t r s ) K 1 = A p /(πr o r s ) L s = spin chamber length l o = orifice length l t = trumpet length p = static pressure Q = volume flow rate = radial distance from axis to inlet slot r o = orifice radius, d o /2 r s = spin chamber radius, D s /2 r t = d t /2 S(t) = surface enclosing control volume V (t) t = film thickness at exit t * = dimensionless film thickness, t/(d o /2) U = average total velocity at the end of orifice U = arbitrary velocity vector for the control volume V (t) u = axial-velocity component u = velocity vector u o= average axial velocity at the end of orifice u oa = axial velocity at the liquid-air interface at the end of orificē u t = average axial velocity at the end of trumpet u ta = axial velocity at the liquid-air interface at the end of trumpet V (t) = control volume w = tangential velocity component w i = average tangential velocity at the inlet w o = average tangential velocity at the end of orifice w oa = tangential velocity at the liquid-air interface at the end of orificē w t = average tangential velocity ...

Quasi-cylindrical approximation to the swirling flow in an atomizer chamber

“…The size of the recirculation region and the direction of circulation of the liquid depend on the inlet conditions. Thus, this direction is opposite in the simulations of Jeng et al (1998), Yule & Chinn (2000) and Xue et al (2004), in which the liquid is injected with a radial velocity component, and in those of Nouri-Borujerdi & Kebriaee (2012), in which it is injected with an axial velocity component. Nevertheless, such large differences do not seem to have a large effect on the characteristic of the atomizer, probably because the velocity components of the recirculating flow in an axial section of the chamber are small compared to the azimuthal velocity in other regions of the chamber and to the velocity around the orifice.…”

“…Comparisons were made with predictions of irrotational theories and correlations derived by Rizk & Lefebvre (1985). In two follow-up works, Sakman et al (2000) and Xue et al (2004) numerically explored and rationalized the dependence of the atomizer characteristics on geometrical parameters not accounted for by irrotational models. The effects of various geometrical parameters and of the Reynolds number on the size of the air core and other characteristics of the atomizer have also been investigated by Haider, Dash & Som (2003) and Nouri-Borujerdi & Kebriaee (2012), while Steinthorsson & Lee (2000), Hansen et al (2002), , and von Lavante, have carried out three-dimensional and non-stationary flow computations.…”

Trends in Comprehensive Modeling of Spray Formation

“…Giffen and Muraszew [31] conducted measurements with a number of swirl atomizers which showed that their inviscid theory predicted the trends in the dependence of atomizer constant on performance parameters reasonably well. More recently, Xue et al [34] carried out inviscid analysis for newer atomizer geometries that include a trumpet and have inlet angle (β) that may vary from 0 to 90 degrees. The qualitative behavior of film thickness, spray cone angle, and discharge coefficient predicted by their analysis agrees well with detailed computational simulations [34,35,36].…”

“…Detailed comparison of experimental measurements/empirical correlations [46,47,48] and computational results was carried out which showed excellent agreement. The validated computational code was then used to investigate the effects of atomizer geometry under two flow regimes -constant mass flow rate through the atomizer [34,36,45,49] and constant pressure drop across the atomizer [35].…”

Influence of Design Parameters of the Swirl Nozzle on Its Spray Characteristics

“…Based on the results of 9 test cases with different design parameters, it is found that the best location of tangential slot is at the radial location of 1/2 or 3/4 cone's radius, while its tilt angle is 20°. 。 对于离心式喷嘴内部结构的研究，国外学者 XUE 等 [12] 利用数值方法研究 90°到 180°的喷嘴内部 锥形室锥角，发现其对雾化锥角 [13] 的影响较小，但 会改变液体薄膜的厚度；关于燃用重油的两相流喷 嘴，FERREIRA 等 [14] 通过试验探究了影响其喷射效 果的重要设计参数；SAKAMEN [15] 通过任意拉格朗 日一欧拉方法探究喷嘴旋流室、出口的长径比等各 个参数之间的关系对雾化效果的影响；国内在该方 面的研究相对较晚，但发展迅速。王国辉等 [16] 采用 流体体积函数法模拟了一种旋流式喷嘴内部的气液 流动，并结合试验，发现改变喷嘴内部结构可以使 出口速度发生变化，而雾化锥角的变化只取决于旋 流器螺旋升角和旋流槽数量；张永良 [17] 利用试验和 数值计算，探讨了某些关键参数对传统离心式喷嘴 雾化效果的影响，而且表明利用流体体积函数法对 喷嘴雾化锥角的模拟与试验值有差异，需要对其进 行修正，但雾化锥角变化规律一致；吴高杨等 [18] 通 过试验和数值模拟研究了螺旋离心式喷嘴的雾化效 果，结果表明喷注压降和背压对液膜的一、二次破 碎有很大影响，而且背压对液膜锥角的影响明显小 于喷注压降；何志霞等 [19] …”