基于CFD的矩形烟道速度面积法中不同积分方法的对比

Comparison of different integral methods in area velocity method for rectangular stack based on CFD

电厂引风机前后矩形烟道由于场地限制往往不能满足国标要求的直管段长度,导致体积流量测量误差偏大,选取合理的测量方法是提高体积流量测量精度的重要途径。利用计算流体力学(CFD)方法对矩形烟道内部流场进行数值模拟,对比分析在烟道弯管上游0.5~2.3倍当量直径的4个测量截面上应用4种不同积分方法进行体积流量测量的相对误差。发现等面积法仅适合在流场发展充分的区域进行体积流量测量但测量效果较差,而在烟道长度受限流场发展不充分的区域,对数切比雪夫法、对数线性法和高斯-勒让德积分法具有更高的测量精度。当测量位置相同测点数量接近时,对数线性法测量相对误差低至0.3255%,远小于其他积分方法的测量结果。

Due to the space limitation,the rectangular stack before and after the induced draft fan in power plant often can’t meet the straight pipe length required by the national standard,which leads to the large error of volume flow measurement.Selecting a reasonable measurement method is an important way to improve the accuracy of volume flow computational fluid dynamics(CFD)method was used to simulate the flow field in a rectangular stack.The relative errors of four different integral methods for volume flow measurement on four cross-sections with 0.5-2.3 times of the equivalent diameter upstream of the stack bend are compared and analyzed.It is found that EPA method is only suitable for volume flow measurement in the area where the flow field is fully developed,but the effect is poor.In the region where the flow field is not fully developed,Log-Chebyshev method,Log-Linear method and Gauss-Legendre integral method have higher measurement accuracy.When the cross-section is the same and the number of traverse points is close,the relative error of Log-Linear method can be as low as 0.3255%,which is far less than that of other integral methods.