Gas diffusion 1. Initial and main segment of transition section Diffusion velocity is uniform when just ejected. Flow along x diffusion bring around medium constantly, making boundary larger, and main velocity of diffusion reduce gradually, part with velocity uo (as in 11-6 AoD cone) called core of diffusion, other part with velocity ower than mo called boundary laver Boundary layer disperse constantly from outlet to around along diffusion line, driving around medium into boundary layer, and expanding to diffusion center till certain distance, boundary expending to axes of diffusion, core region disappeared, only velocity in axes is uo. This section as in fig. 11-1 BoE, called transition section. Take transition section as dividing line outlet section till transition section called initial segment of diffusion. Since transition section called main segment of diffusion
11 1. Initial and main segment of transition section Diffusion velocity is uniform when just ejected . Flow along x , diffusion bring around medium constantly, making boundary larger, and main velocity of diffusion reduce gradually, part with velocity u0 （as in 11—6 AoD cone）called core of diffusion, other part with velocity lower than u0 called boundary layer. Boundary layer disperse constantly from outlet to around along diffusion line, driving around medium into boundary layer, and expanding to diffusion center till certain distance, boundary expending to axes of diffusion, core region disappeared,only velocity in axes is u0 . This section as in fig.11—1 BoE ,called transition section. Take transition section as dividing line, outlet section till transition section called initial segment of diffusion. Since transition section called main segment of diffusion
气流 过流断面(又称转折断面)起始段及主体段 刚喷出的射流速度仍然是均匀的。沿x方向流动,射流不断 代入周围介质,不仅使边界扩张,而且使射流主体的速度逐渐降 低,速度为l的部分(如图其11-6AoD锥体)称为射流核心, 其余部分速度小于4称为边界层。射流边界层从出口开始沿射程 不断地向外扩散,带动周围介质进入边界层,同时向射流中心扩 展,至某一距离处,边界层扩展到射流轴心线,核心区域消失, 有轴心上速度为砌。射流这一断面为图11-1上的BOE,称为过 渡断面或转折断面。以过渡断面分界,出口断面至过渡断面称为 射流起始段。过渡断面以后称为射流主体段
12 一、过流断面（又称转折断面）起始段及主体段 刚喷出的射流速度仍然是均匀的。沿 x 方向流动，射流不断 代入周围介质，不仅使边界扩张，而且使射流主体的速度逐渐降 低，速度为 u0 的部分（如图其11—6 AoD 锥体）称为射流核心， 其余部分速度小于 u0 称为边界层。射流边界层从出口开始沿射程 不断地向外扩散，带动周围介质进入边界层，同时向射流中心扩 展，至某一距离处，边界层扩展到射流轴心线，核心区域消失， 只有轴心上速度为 u0 。射流这一断面为图11—1上的 BoE ,称为过 渡断面或转折断面。以过渡断面分界，出口断面至过渡断面称为 射流起始段。过渡断面以后称为射流主体段
Gas arrosion 2. Coefficient of turbulent flow a and geometrical character Outer boundary layer of diffusion is a beeline, as in fig. 11-1 AB and DE. Ab de prolong to muzzle meeting at point M, this point called culmination. Half of /AMD called pole angle a, as well as called diffusing angle a Bo is radiir of circular diffusion section or half breadth of boundary layer in plane diffusion yb ) It is positive ratio with distance from culmination、Bo=Kx。 oM is x distance calculated from culmination Observing from figure, BoloM=tan a, so tana=-=K=oa(11-1) where K--experiment constant o form coefficient of muzzle, circular muzzle, =3.4 a-coefficient turbulent flow determined by experiment 13
13 2. Coefficient of turbulent flow and geometrical character Outer boundary layer of diffusion is a beeline,as in fig.11—1 AB and DE. AB 、 DE prolong to muzzle meeting at point M, this point called culmination.Half of called pole angle ,as well as called diffusing angle 。 Bo is radii R of circular diffusion section （or half breadth of boundary layer in plane diffusion yb ）.It is positive ratio with distance from culmination , Bo ＝Kx 。 oM is x distance calculated from culmination .Observing from figure,Bo/oM =tan , so AMD tan = = K = (11—1) x Kx where K—experiment constant; —form coefficient of muzzle,circular muzzle,＝3.4； —coefficient turbulent flow,determined by experiment
气流 、紊流系数α及几何特征 射流外边界层是一条直线,如图11-1上的AB及DE线。 AB、DE延至喷嘴内交于M点,此点称为极点,∠AMD的 半称为极角α,又称扩散角a。 Bo为圆断面射流截面的半径R(或平面射流边界层的半 宽度yb)。它和从极点起点算的距离成正比,即BO=Kx。 oM是从极点起算的x距离。由图看出,Bo/OM=tana,故 tanaka =K=oa (11-1) 式中K一试验常数; φ喷口形状系数,圆形喷嘴,φ=3.4; α紊流系数,由实验决定,是表示射流流动结构的 特征系数
14 二、紊流系数 及几何特征 射流外边界层是一条直线，如图11—1上的 AB及 DE 线。 AB 、 DE 延至喷嘴内交于 M 点，此点称为极点， 的 一半称为极角 ,又称扩散角 。 Bo为圆断面射流截面的半径 R（或平面射流边界层的半 宽度 yb ）。它和从极点起点算的距离成正比，即 Bo ＝Kx 。 oM 是从极点起算的 x 距离。由图看出，Bo/oM =tan ,故 AMD tan = = K = (11—1) x Kx 式中 K—试验常数； —喷口形状系数，圆形喷嘴， ＝3.4； —紊流系数，由实验决定，是表示射流流动结构的 特征系数
Gas arrosion Coefficient of turbulent flow a relate to turbulent flow intensity in outlet section, More high as intensity, more high as value a, which make diffusion expending angle a increase. Driving around medium more, velocity along diffusion line reducing more fast. a relates to the uniform of velocity distributing in outlet section. Practical value of turbulent flow coefficient and expending angle on different form muzzle. as in table 11-1 Coefficient of turbulent flow table11-1 kinds of muzzle 2d kinds of muzzle a 2a muzzle with shrink outlet 0.066 25020 Wind machine of axis flow 0.07127910′ with metal gridding 0.2478°40′ 0.076 well shrink plane muzzle 0.108 2930 2900 cylindrical pipe 0.08 narrow gap in plane wall. 1183210 Right-angle pipe with 01244930 leading wind plank 0.2068030′ portrait gap of wind way'0155 4120' with grind round outlet From formula (11-1-1), a is conformed, outer boundary line of diffusion boundary layer, diffusion expending forward along certain expending angle a, this is its geometrical character. Applying this character, variety rule of diffusion radii can be obtained along diffusion way in circular section 15
15 Coefficient of turbulent flow relate to turbulent flow intensity in outlet section,More high as intensity,more high as value a , which make diffusion expending angle a increase. Driving around medium more, velocity along diffusion line reducing more fast. a relates to the uniform of velocity distributing in outlet section.Practical value of turbulent flow coefficient and expending angle on different form muzzle.as in table 11—1. Coefficient of turbulent flow table11—1 Wind machine of axis flow with metal gridding well shrink plane muzzle narrow gap in plane wall portrait gap of wind way with grind round outlet kinds of muzzle muzzle with shrink outlet cylindrical pipe Right-angle pipe with leading wind plank 2 kinds of muzzle 2 0.071 0.066 0.08 0.076 0.20 0.12 27 10 25 20 0 0 29 00 0 68 30 44 30 0 0 0.155 0.118 0.108 0.24 41 20 32 10 29 30 78 40 0 0 0 0 From formula（11—1—1）, a is conformed, outer boundary line of diffusion boundary layer, diffusion expending forward along certain expending angle a , this is its geometrical character.Applying this character , variety rule of diffusion radii can be obtained along diffusion way in circular section