DNS of Low Reynolds Number Aerodynamics in the Presence of Free Stream Turbulence

Flow dynamics within gate valves must be understood in order to address issues such as turbulence, pressure loss, flow separation, and cavitation. This study examines flow behavior within standard and modified gate valves using experimental and computational fluid dynamics (CFD) methods. Water flow within a gate valve, from 25% to full opening, is simulated to analyze velocity, pressure, and turbulence behaviors. With 25% opening, abrupt velocity accelerations in the valve throat initiate extreme pressure losses and intense turbulent flow due to flow separation. These outcomes serve to underscore the need for efficient valve geometries to induce stability in flow as well as suppress energy losses. Comparison between the standard and modified gate valves at 25%, 40%, and 55% openings highlights the advantages of the modified design. The standard valve exhibits high turbulence, high recirculation areas, and high dissipation of energy, particularly at low openings. Conversely, the modified valve cuts down on turbulence, promotes uniform flow, and reduces pressure losses. By removing vortex generation and velocity oscillations, it obtains more stable flow, which increases system efficiency. Further inspection of a 55% open gate valve with different fluids, for instance, water and SAW15W-40 oil, shows the impact of viscosity on fluid flow. Water specifies a smooth velocity profile and low pressure drops, while oil experiences higher resistance, pressure gradients, and shear forces. The new design addresses these differences well, with reduced potential for cavitation and enhanced performance. All these optimizations enhance operating efficiency in applications ranging from oil and gas to water distribution and chemical processing.

Introduction. In many technical applications, such as thermal energy systems, chemical processing, power production, and HVAC, efficient heat transfer (HT) is essential. Research on improving HT performance in circular pipes is still crucial, especially when it comes to changes that cause thermal boundary layers to be disrupted and turbulence to grow. Purpose of the work: The purpose of this work is to thoroughly examine how convective heat transfer can be improved in circular pipes with purposefully roughened surfaces. It focuses on how surface roughness, flow pulsations, Reynolds number (Re), and heat flow rate (Q) affect thermal performance. Methods of investigation. A combination of experimental and numerical methods is employed to assess the thermo-fluid dynamics inside the pipe. Lab-scale experiments and computational fluid dynamics (CFD) simulations are used to investigate temperature distribution, velocity and pressure fields, turbulent kinetic energy (TKE), vorticity, eddy viscosity, local heat transfer coefficient (h), and Nusselt number (Nu). Additionally, sinusoidal pulsations are introduced at the inlet and the outlet, with regular oscillations in frequency (f) and amplitude (A), over a turbulent flow range (6,753 ≤ Re ≤ 31,000). Results and discussion. The results show that surface roughness enhances HT by significantly increasing turbulence and disrupting the thermal boundary layer. TKE becomes a significant factor when there is a strong correlation between higher HT coefficients and rising turbulence intensity. HT performance is further improved by introducing flow pulsations; downstream pulsation increases Nu by 20–22% and upstream pulsing by 16–19%. The outcomes demonstrate how effectively controlled flow pulsations and surface roughness combine to optimize heat transfer. This collaborative approach holds great potential for compact and highly efficient thermal system designs in industrial environments.