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2QV-AF泡沫泵的軸面流動計算
1. 初始軸面流道輪廓確定
設(shè)計離心泵，屬中比轉(zhuǎn)速離心泵，其葉輪軸面流道窄而長,前后蓋板的軸面截線大部分為非平行直線。采用自由曲線生成初始軸面輪廓，如圖1- 100所示。
2. 軸面流動計算
基于沿任意準(zhǔn)正交線的軸面速度梯度方程和流體運(yùn)動的連續(xù)方程的方法,采用準(zhǔn)正交線法迭代計算軸面流線,通過求解軸面速度沿準(zhǔn)正交線的梯度方程[式(1- 108),式中各符號如圖1- 101所示]，求出各質(zhì)點(diǎn)的軸面速度。基于離心泵各流道間流量相等進(jìn)行迭代計算，得出軸面流線與準(zhǔn)正交線的交點(diǎn)坐標(biāo)，最終可確定初始軸面流網(wǎng)。初始確定的軸面流網(wǎng)并不一定能滿足所要求的軸面速度分布規(guī)律因此需要迭代計算，不斷修正軸面流線的位置的形狀，直至滿足要求為止，得到最終軸面流網(wǎng)，如圖1-102所示。
片骨線繪型
基于葉輪內(nèi)葉片無窮多的假設(shè)，計算流面上的葉型骨線應(yīng)與計算所得流線重合。為確定葉型骨線,需確定葉型骨線與軸面流線之間的關(guān)系，采用逐點(diǎn)積分法建立葉片包角與軸面流線長度之間的關(guān)系，得到葉型骨線微分方程,并沿著軸面流線積分，計算出流線上每個計算點(diǎn)所對應(yīng)的包角，即可最終確定葉片骨線，完成葉片繪型。質(zhì)點(diǎn)在軸面中的運(yùn)動如圖1- 103所示。所用葉片骨線方程如下:
4.葉片骨線加厚和頭尾部修圓
為滿足能量傳遞的需要,葉片必須要滿足一定的強(qiáng)度要求，故需對葉片進(jìn)行加厚處理。葉片加厚的方法主要有3種:保角變換平面上的加厚、軸面加厚和回轉(zhuǎn)流面加厚。為減小葉片頭部沖擊損失，需對葉輪葉片頭部進(jìn)行修圓處理。傳統(tǒng)修圓方法為在保角變換平面上進(jìn)行修圓或是流面上進(jìn)行修圓，此處通過四點(diǎn)“貝塞爾”曲線對設(shè)計葉片進(jìn)行頭部修圓，如圖1- 104所示。該方法可根據(jù)不同需求改變頭部修圓形狀.相比傳統(tǒng)設(shè)計方法更為靈活。最終得到葉片模型如圖1-105所示，去掉前蓋板的葉輪如圖1-106所示。
二、內(nèi)流場CFD計算
隨著理論流體力學(xué)和實(shí)驗流體力學(xué)的進(jìn)步,計算機(jī)容量的不斷擴(kuò)大和運(yùn)行速度的迅速提高，使得兩類相對流面方法主要用于流體機(jī)械反問題研究中，對于正問題已很少應(yīng)用。目前流體機(jī)械正問題研究的主要手段是利用計算流體力學(xué)(Computational Fluid Dynamics,簡稱CFD)對其內(nèi)部黏性流動進(jìn)行三維計算和分析。CFD是流體力學(xué)的一個主要研究方向，通過計算機(jī)數(shù)值計算和圖像顯示，是對包含有流體流動和熱傳導(dǎo)等相關(guān)物理現(xiàn)象的系統(tǒng)所做的分析。與理論流體力學(xué)相比，計算流體力學(xué)的突出優(yōu)點(diǎn)是在計算機(jī)條件許可的情況下，可以采用最適合流動物理本質(zhì)的數(shù)學(xué)模型來求解任意復(fù)雜的流動問題;與實(shí)驗研究相比.計算流體力學(xué).
Axial flow calculation of 2QV-AF foam pump
1. Determine the initial axial surface flow channel contour
The design of centrifugal pump is a medium specific speed centrifugal pump. Its impeller axial surface flow channel is narrow and long, and most of the axial plane section lines of the front and rear cover plates are non parallel straight lines. The free-form curve is used to generate the initial axial surface profile, as shown in Fig. 1-100.
2. Calculation of axial flow
Based on the method of the axial velocity gradient equation along any quasi orthogonal line and the continuity equation of fluid motion, the quasi orthogonal method is used to iteratively calculate the axial streamline. The axial velocity of each particle is obtained by solving the gradient equation of the axial velocity along the quasi orthogonal line [equation (1-108), in which the symbols are shown in Fig. 1-101]. Finally, the intersection of the flow line and the flow line can be determined by iteration. The initially determined axial flow network does not necessarily meet the required axial velocity distribution law. Therefore, iterative calculation is needed to constantly modify the shape of the axial streamline position until the requirements are met, and the final axial flow network is obtained, as shown in Fig. 1-102.
Bony line drawing
Based on the assumption that there are infinite blades in the impeller, the blade profile line on the calculated flow surface should coincide with the calculated streamline. In order to determine the blade skeleton line, it is necessary to determine the relationship between blade contour and axial streamline. The relationship between blade wrap angle and axial streamline length is established by point by point integration method, and the differential equation of blade contour is obtained. The blade contour is finally determined by integrating along the axial streamline to calculate the corresponding wrap angle of each calculation point on the flow line. The motion of the particle in the axial plane is shown in Fig. 1-103. The equation of blade bone line is as follows:
4. Blade bone line thickening and head and tail rounding
In order to meet the needs of energy transfer, the blade must meet certain strength requirements, so it is necessary to thicken the blade. There are three main methods of blade thickening: the thickening on conformal transformation plane, the axial surface thickening and the rotary flow surface thickening. In order to reduce the impact loss of blade head, it is necessary to round the blade head. The traditional rounding method is to round on the conformal transformation plane or on the flow surface. Here, the four point "Bessel" curve is used to round the design blade head, as shown in Fig. 1-104. Compared with the traditional design method, this method is more flexible. Finally, the blade model is shown in Fig. 1-105, and the impeller with the front cover removed is shown in Fig. 1-106.
2、 CFD calculation of internal flow field
With the development of theoretical and experimental hydrodynamics, the continuous expansion of computer capacity and the rapid improvement of running speed, the two kinds of relative flow surface methods are mainly used in the study of inverse problems of fluid machinery, and rarely used for forward problems. Computational fluid dynamics (CFD) is one of the most important methods in fluid mechanics. CFD is one of the main research directions of fluid mechanics. Through computer numerical calculation and image display, CFD is the analysis of the system including fluid flow and heat conduction. Compared with the computational fluid mechanics, the computational fluid mechanics model is the most suitable method for the study of fluid mechanics
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