Investigation on the novel unsteady-liquid thin-walled cutting-edge throttling mechanism incorporated in the rotary valve design for a continuous wave pulse generator

Abstract

The fundamental principle guiding the structural optimization design of the rotary valve in traditional continuous wave mud pulse generators is the steady-liquid thin-walled cutting-edge throttling mechanism (STCTM). However, due to the rotary valve's high-speed rotation, the muddy liquid's flow assumes an unsteady state. Therefore, this theory struggles to provide additional support for the high-speed design of the rotary valve. To address this issue, utilizing Bernoulli's equation as a foundation and considering three key factors: the unsteady flow of drilling mud, the two-stage constriction of fluid as it passes through the rotary valve, and the time-variant flow coefficient, an improved numerical model of the continuous wave pulse differential pressure signal is derived, and unsteady-liquid thin-walled cutting-edge throttling mechanism (UTCTM) of the rotary valve is revealed. Taking the design of a four-blade sector rotary valve port structure as an example, theoretical analysis and CFD experimental research are conducted based on both the STCTM and UTCTM. The results demonstrate that the simulated differential pressure generated by the rotary valve designed based on the UTCTM agrees more closely with the theoretical differential pressure in peak-to-peak value, indicating that the UTCTM better reflects the objective laws associated with continuous wave pulse differential pressure generation. This finding enriches the theoretical foundation for optimizing high-speed mud pulse pulser design and has significant applications in various engineering fields.