Experimental Investigation of Viscoelastic Cavitating and Turbulent Channel Flows Subjected to Different Pressure Gradients
Creators: Azadi, Reza
Publisher: name: University of Alberta Library
Year: 2023

<p>Steam-assisted gravity drainage is a common method for oil production in Alberta, Canada. Production wells are equipped with inflow control devices to improve production efficiency. These devices utilize nozzle-type constrictions to enhance oil production by hindering water and gas breakthroughs. The relatively large pressure drop of the turbulent flow passing the nozzle can lead to chaotic cavitation that deteriorates the production rate and damages the equipment.<br>
In this research, adding minute amounts of polyacrylamide (PAM) drag-reducing additives to the flow was suggested as a viable method to control cavitation and turbulence drag in nozzle flows. A flow facility and an optical setup based on high-speed imaging and microscopic particle image velocimetry (PIV) were developed to scrutinize this hypothesis.<br>
The cavitation process was studied in a converging-diverging nozzle with water and PAM solutions of concentrations from 50 p.p.m. to 400 p.p.m. Rheological measurements demonstrated that solutions were shear-thinning and viscoelastic. Statistical analysis of the instantaneous images showed that polymer additives noticeably relaxed the mean cavitation collapse and growth rate and their fluctuations. A reduction of 65 % was measured in the 400 p.p.m. flow relative to water flow at the highest tested flow rate, where its inception shedding frequency was reduced by 70 %.<br>
The flow’s turbulence was studied using PIV in a channel with a bump resembling the profile of the converging-diverging nozzle used in the cavitation studies. Water, and 200 p.p.m., and 400 p.p.m. PAM flows were examined at three flow rates at regions subjected to zero, favorable and adverse pressure gradients (ZPG, FPG, and APG) and local curvature effects.<br>
A drag reduction (DR) of 30.4 % and 38.6 % were obtained in the fully-developed ZPG 200 p.p.m. and 400 p.p.m. flows at the highest tested flow rate. As the flow rate or the solution concentration increased, the mean velocity profiles approached the ultimate profile, but maximum DR was not achieved. Mean Reynolds shear stress and wall-parallel Reynolds stress were attenuated and enhanced in the PAM solutions.<br>
The accelerating flows were transferred to a fully relaminarized regime, where the turbulent activities were significantly damped relative to a ZPG flow. The velocity profiles were pushed below the logarithmic profile at positions with a stronger FPG or weaker APG. Under FPG, the mean outer-normalized Reynolds shear stress was attenuated compared to ZPG flows. In APG flows, shear stresses showed intensity levels similar to that of a ZPG flow.<br>
Inner-normalized velocity profiles of the accelerating 200 p.p.m. flows deviated from the logarithmic law, depending on the local FPG and curvature strength, and were elevated above the ultimate profile in the accelerating 400 p.p.m. flow at positions with a minimum friction factor. The turbulence production was reduced up to 70 % and 78 % in the accelerating 200 p.p.m flow relative to the ZPG PAM and FPG water flows. Substantial attenuation of the turbulence production in the accelerating 400 p.p.m. flow generated negative Reynolds shear stress zones.<br>
The mean velocity profiles of the decelerating 200 p.p.m. flows deviated above the log-law at positions with small friction factors and collapsed to the ultimate profile where friction was minimum. At the same position and the highest flow rate, the velocity profile of the 400 p.p.m. flow elevated above the ultimate profile.<br>
APG intensified stronger mean Reynolds shear stress in both solutions and attenuated the weaker ones to the extent that negative counter-gradient zones emerged over the boundary layer. The turbulence production was reduced by up to ≈ 58 % in the PAM solutions compared to the water flow. Compared to the APG water flow, the semi-dilute solutions indicated intensified wall-parallel and wall-normal fluctuations.<br>
This study elucidated that adding PAM to the flow can be utilized as an efficient cavitation-controlling method. A novel methodology was presented for quantitative analysis of the cavitation reduction mechanisms from high-speed images. Polymer additives generated significant DR in the fully-developed ZPG PAM solutions. Under pressure gradient and wall curvature effects, flows indicated substantial streamwise dependence. The high spatial resolution and accuracy of the PIV-based flow statistics make the data unique and an important foundation for model development. Another novelty of this research is that, for the first time, the viscoelastic polymer solutions were examined under pressure gradient effects.</p>