Modeling of transient flows in viscoelastic pipe network with partial blockage

In this study, transient flow and partial blockage in polyethylene (PE) pipe network are investigated experimentally and numerically using the method of characteristics in the time domain considering pipe-wall viscoelasticity. The experiments were conducted on a PE pipe network with and without partial blockage. The experimental pressure signals were damped during a short period of time in the blockage-free case. The numerical model was calibrated by the inverse transient analysis (ITA). The hydraulic transient solver calibrated with one Kelvin–Voigt element showed good consistency with the experimental results. Partial blockages with different lengths and sizes were examined at different locations of the pipe network. Results reveal an increase in head loss, pressure signal damping, and phase shift with increase in blockage. In addition, the location and characteristics of blockages with different sizes were determined using the ITA in the pipe network.

Numerical modeling of water hammer in long water transmission pipeline

In the present study, a water transmission pipeline under steady conditions is modeled followed by examining the transient flow created by the failure of pumps in the pipeline. This pipeline is 31 km from the water transmission pipeline of Kerman, Iran. The software analysis results were compared with those of a numerical model for a laboratory test to validate transient flow modeling. While transient flows are created by pump failure, various areas of the water transmission pipelines will be affected by the transient waves produced. Long water transmission pipelines, usually large in diameter and flow rate, will pose problems in the negative pressure phase. The negative pressure causes threatening problems like water column separation and cavitation. The results indicated that using equipment like air valves when the pumps fail alone does not have the appropriate efficiency in eliminating the hazards in the water transmission pipelines. More examination showed that installing equipment like water flow feed and hydropneumatic tanks along the pipeline length in the right places prevents the negative pressure created and the pipeline risk significantly reduces.

Modeling Transient Flows in Heterogeneous Layered Porous Media Using the Space–Time Trefftz Method

In this study, we developed a novel boundary-type meshless approach for dealing with two-dimensional transient flows in heterogeneous layered porous media. The novelty of the proposed method is that we derived the Trefftz space–time basis function for the two-dimensional diffusion equation in layered porous media in the space–time domain. The continuity conditions at the interface of the subdomains were satisfied in terms of the domain decomposition method. Numerical solutions were approximated based on the superposition principle utilizing the space–time basis functions of the governing equation. Using the space–time collocation scheme, the numerical solutions of the problem were solved with boundary and initial data assigned on the space–time boundaries, which combined spatial and temporal discretizations in the space–time manifold. Accordingly, the transient flows through the heterogeneous layered porous media in the space–time domain could be solved without using a time-marching scheme. Numerical examples and a convergence analysis were carried out to validate the accuracy and the stability of the method. The results illustrate that an excellent agreement with the analytical solution was obtained. Additionally, the proposed method was relatively simple because we only needed to deal with the boundary data, even for the problems in the heterogeneous layered porous media. Finally, when compared with the conventional time-marching scheme, highly accurate solutions were obtained and the error accumulation from the time-marching scheme was avoided.

Virologic microparticle fluid mechanics simulation: COVID-19 transmission inside an elevator space

COVID-19 is a serious respiratory disease caused by a devastating coronavirus family (2019-nCoV) that has become a global epidemic. It is an infectious virus transmitted by inhalation or contact with the droplet core produced by infected people when they sneeze, cough, and speak. SARS-COV-2 transmission in the air is possible even in a confined space near the infected person. This study examines air conditioners’ effect on the mixed virus and droplets with aerosol disinfectant and gets throughout the elevator to detect the SARS-COV-2, which helps protect passengers’ lives. This study uses fluent 2019R3 software to simulate the virus transmission to model the transient flows numerically. The analysis found that the ventilation system’s turbulent fields can be an effective method of protecting the space from being saturated by the coronavirus.

Influence of Marine Propeller Geometry on Turbulence Model Selection for CFD Simulations

One of the big challenges yet to be addressed in the numerical simulation of wetted flow over marine propellers is the influence of propellers' geometry on the selection of turbulence models. Since the Reynolds number is a function of the geometrical parameters of the blades, the flow type is controlled by these parameters. The majority of previous studies employed turbulence models that are only appropriate for fully turbulent flows, and consequently, they mostly caused high discrepancy between numerical predictions and corresponding experimental measurements specifically at geometrical parameters generating laminar and transient flows. The present article proposes a complete procedure of computational fluid dynamics simulation for wetted flows over marine propellers using ANSYS FLUENT 16 and employing both transition-sensitive and fully turbulent models for comparison. The K-Kl-ω transition model and the fully turbulent standard K-ε model are suggested for this purpose. The investigation is carried out for two different propellers in geometrical features: the INSEAN E779a model and the Potsdam Propeller Test Case (PPTC) model. The results demonstrate the effectiveness of the K-Kl-ω transition model for the INSEAN E779a propeller rather than the PPTC propeller. This can be interpreted as the narrow-bladed and small-diameter propellers have more likely laminar and transient flows over its blades.