Research On The Averaging Pitot Tube With Flow Conditioning Wing

Averaging Pitot tube(APT) is a kind of sampling flowmeter with advantages of low pressure loss, simple construction and good reliability. It is widely used in petroleum, metallurgy, chemical industry, light industry, food industry and other flow industry. But its performances are usually influenced seriously by its cross-section and the harsh industry field conditions. So, the paper deals with the APT's cross-section optimization to improve its performances.The main researches of the dissertation are as the following:Three kinds of APT with flow conditioning wing(APTFCW) are designed. Through numerical computation and theoretic analysis,the following problems are discussed: the influence of the APT cross-section to the total pressure and static pressure; the relation between the blockage ratio and the coefficient; the relation of the separating angle, the separating position and the linearity of the APT; the relation between the wake region and the repeatability of the APT. Research shows that the scale of the swirl, after the APTFCW, is larger than that of the other cross-section APTs, and its frequency is lower, the distance between its center and the static pressure hole is larger. So, the swirl's influence to the static pressure is lower and the output difference pressure is more stable. The linearity and repeatability of the APTFCW are better than those of the other cross-section APTs. The fluid velocity is larger than that of other cross-section APT when it flows through the APT, so the static pressure is lower and its difference pressure is larger. At the conditions of straight pipe not enough, the effect of the flow conditioning wing are obvious. So, its accuracy is better than other cross-section APTs. Through numerical computation, the performances of APTs in DN50 pipe are reasearched in quantitative. The linearity of the APTFCWⅡandⅢare 0.45% and 1.54% respectively, better than that of the others. The qualitative and quantitative researches show that the performances of the APTFCWⅡandⅢare better than the others.The method how to simplize three-dimensional entity into two-dimensional model in CFD is researched. Through theoretical anlysis, five two-dimensional models are acquired. Theoretical analysis shows that the model at the position of averaging velocity(MPAV) is the most representative. It could reflect the flow field characters. Numerical computation is done using the five models. It shows that the deviation between the data of numerical computation using the MPAV and the experiment data is least. Thtrough theoretical analysis and numerical computation, the optimal two-dimensional numerical computation model is accquired.Based on numerical computation, the APTFCWⅡ, circle and dianmond cross-section APT are chosed to process prototype of DN50 and DN200. Then, the prototypes are tested in gas flow standard facilities. Experimental researches indicate that the perfoemances of the APTFCW are better than the others. Through experiment, it's proved that the flow conditioning wing works better.Experiments are done to test the performances of the APT when they are installed after the 90°elbow in different type(vertical to the elbow or in the same plane with the elbow) and in different straight pipe length(2D, 4D, 7D, 12D) before the APT. The performances and the adaptability of the three kinds of cross-section APTs are acquired in those conditions. It shows that at the same conditions, the adaptability of the APTFCW is better than the others, because of the effect of the flow conditioning wing. The performances, when the APTFCW are installed vertical to the elbow, are better than those when they are installed in the same plane with the elbow. Through numerical computation, the flow field characters after the 90°elbow is reasearched. The reason why the performances are different when the APT is installed in different type is explained from the point of flow field changing.