Experimental and Numerical Study on a Straight Exhaust Pipe

Abstract

In this study, radiated noise is investigated by experimental and numerical methods for a straight exhaust pipe of diameter 23mm that replaces the original exhaust pipe of a motorcycle of EZ 125cc provided by Kwang Yang Motor Co. In experiment, temperature, pressure and flow speed of the exhausted gas have been measured for different engine speeds ranging from 3000-5000rpm without loading. Sound pressure levels (SPL) at a distance of 0.5m from the exhaust pipe exit for different inclination angles (0 ~ 90) were recorded and compared with the result of simulation. In numerical simulation, a high-resolution 5th-order Euler solver was used and conducted on a parallel computation system with a cluster of 4 personal computers with dual processors. It is found that the back-and-forth reflection of expansion waves inside the pipe due to the shock wave diffraction around the pipe exit is the mechanism of radiating sound waves from the exhaust pipe. The numerical result shows the exhausted-gas flow with complicated vortex rings and its associated acoustic field. The acoustic field indicates that there are three sound lobes with different directivities for the engine speed of 4000rpm.

Spatio-temporal variation of water requirement and meteorological impact factors of maize Shaanxi, China

“…The water requirement of maize at the fertility stage is the sum of daily water requirements, and the sowing time and duration of each fertility stage differ in different climatic zones, so the water requirement of the crop at different fertility stages also has significant differences. The division of maize growth time nodes in this paper was obtained from experimental studies by others and has been confirmed to be feasible (Liang et al, 2011;Li et al, 2015;Qin et al, 2016;Cheng et al, 2018).…”

“…In this paper, maize fertility is divided into four stages according to the characteristics of maize growth: seedling stage, jointing stage, male stage and maturity stage. The time points of each fertility stage are based on experiments and studies conducted by other scholars (Liang et al, 2011;Li et al, 2015;Qin et al, 2016;Cheng et al, 2018) and are shown in Table 1. The Guanzhong Plain is suitable for growing summer maize due to the advantages of soil and climate, so its planting time is quite different from other areas.…”

“…Crop coefficients: The piecewise single value average method recommended by FAO-56 in 1998 was adopted to calculate the crop coefficient, which should be revised according to the actual local situation when used. The value of the modified maize coefficient was referred to the studies of Liang (2011), Kang (1990), Liu (2009), Lu et al (2019), and the revised values of crop coefficients are shown in Table 2.…”