MD SHUJAN ALI

One of the most common reported adverse events for intravenous (IV) infusions are infusion site reactions, ranging from redness and pain at the site of infusion to thrombophlebitis. The connection between drug infusion and what drives these adverse events is not well understood. To aid in understanding these phenomena, it is crucial to accurately characterize the evolving hemodynamic environment of the infusion site when developing new intravenous formulations, as too rapid dilution may cause… Show more

One of the most common reported adverse events for intravenous (IV) infusions are infusion site reactions, ranging from redness and pain at the site of infusion to thrombophlebitis. The connection between drug infusion and what drives these adverse events is not well understood. To aid in understanding these phenomena, it is crucial to accurately characterize the evolving hemodynamic environment of the infusion site when developing new intravenous formulations, as too rapid dilution may cause precipitation in the vein, while too little dilution might contribute to phlebitis. In this study, a Large-Eddy Simulation (LES) turbulence modeling inside a Computational Fluid Dynamics (CFD) framework has been used to simulate the flow and mixing characteristics of an infusion entering the bloodstream. This work represents the first such study reporting transient flow fields for intravenous infusions using LES CFD simulations with a realistic non-Newtonian blood model. The output of the CFD model closely resembled the flow and mixing patterns generated in benchtop tests for infusions into a blood analogue and water as the venous fluid across a wide range of flow rates. These models were then investigated further to compare how changes to the fluid rheology model, needle orientation and needle position within the vein resulted in altered mixing regimes at different flow rates. Show less

Head-flow HQ curves for a Fontan cavopulmonary assist device (CPAD) were measured using a blood surrogate in a mock circulatory loop and simulated with various computational fluid dynamics (CFD) models. The tests benchmarked the CFD tools for further enhancement of the CPAD design. Recommended Reynolds-Averaged Navier–Stokes (RANS) CFD approaches for the development of conventional ventricular assist devices (VAD) were found to have shortcomings when applied to the Fontan CPAD, which is… Show more

Head-flow HQ curves for a Fontan cavopulmonary assist device (CPAD) were measured using a blood surrogate in a mock circulatory loop and simulated with various computational fluid dynamics (CFD) models. The tests benchmarked the CFD tools for further enhancement of the CPAD design. Recommended Reynolds-Averaged Navier–Stokes (RANS) CFD approaches for the development of conventional ventricular assist devices (VAD) were found to have shortcomings when applied to the Fontan CPAD, which is designed to neutralize off-condition obstruction risks that could contribute to a major adverse event. The no-obstruction condition is achieved with a von Karman pump, utilizing large clearances and small blade heights, which challenge conventional VAD RANS-based CFD hemodynamic simulations. High-fidelity large eddy simulation (LES) is always recommended; however, this may be cost-inhibitive for optimization studies in commercial settings, thus the reliance on RANS models. This study compares head and power predictions of various RANS turbulence models, employing experimental measurements and LES results as a basis for comparison. Show less

The accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of subsynchronous vibration problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is very sparse. In reality, the impeller, eye-labyrinth seal, and the front shroud heavily influence one another; and… Show more

The accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of subsynchronous vibration problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is very sparse. In reality, the impeller, eye-labyrinth seal, and the front shroud heavily influence one another; and the collective dynamic behavior of the system differs from the sum of the dynamic behavior of isolated components. A computational fluid dynamics (CFD)-based approach is taken to evaluate the dynamic behavior of the system as a whole. The geometry and operating conditions in this work are based on the recent experimental study of Song et al. (2019, “Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement,” ASME J. Eng. Gas Turbines Power, 141(11), p. 111014. 10.1115/1.4044874) on centrifugal compressor. The commercial CFD code cfx 19.0 is used to resolve Reynolds-averaged Navier–Stokes equations to quantify the eye-labyrinth seal and front cavity stiffness, damping, and added mass. The entire compressor stage is modeled to uncover the coupled behavior of the components and assess the stability of the whole system instead of just discrete components. In the current work, three CFD approaches, namely quasi-steady, transient static eccentricity, and transient mesh deformation techniques are studied and benchmarked against analytical and experimental results from the literature. Having established the efficacy of the proposed approach, four types of swirl brakes are proposed and analyzed for stability. The novel swirl brakes create negative swirls at the brake cavities and stabilize both the front shroud and the eye-labyrinth seal simultaneously. Show less

Accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of subsynchronous vibration (SSV) problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is rare. In reality, the impeller, eye-labyrinth seal, and the front shroud heavily influence one another; and the… Show more

Accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of subsynchronous vibration (SSV) problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is rare. In reality, the impeller, eye-labyrinth seal, and the front shroud heavily influence one another; and the collective dynamic behavior of the system differs from the sum of the dynamic behavior of isolated components.
To further investigate, a CFD-based approach is taken to evaluate the dynamic behavior of the system as a whole. The geometry and operating conditions in this work are based on the recent experimental study of Song et al. (2019) on compressor seal and front shroud stiffness values. The compressor impeller is redesigned utilizing turbomachinery design software CFturbo. The commercial CFD code CFX 19.0 is used to resolve Reynolds Averaged Navier-Stokes (RANS) equations to quantify eye labyrinth seal and front cavity stiffness, damping, and added mass, while the whole compressor stage is modeled to uncover the coupled behavior of the components, and assess the stability of the whole system instead of any discrete components. In the current work, three CFD approaches, namely quasi-steady, transient static eccentric, and transient mesh deformation technique are tested, and predictions are made on
stiffness, damping, and virtual mass. Effectiveness of each CFD method is evaluated by comparison with the experimental data. CFD results provide the non-axisymmetric pressure perturbation for the shroud and seal surfaces. Furthermore, rotordynamic coefficients are derived utilizing correlations from the literature, and compared with CFD based and experimental results.

Keywords: compressor, CFD, eye-labyrinth seal, shroud, rotordynamics, system-level. Show less

Loop heat pipes (LHP) are passive thermal management systems widely used in electronics cooling, military applications, renewable energy, and spacecraft. These two-phase systems employ capillary forces instead of pumps to circulate the coolant. In these devices, the coolant evaporates and condenses in the evaporator and condenser, respectively. The condensed coolant liquid is driven toward the evaporator by capillary action in a wick structure located inside the evaporator. A mechanical pump… Show more

Loop heat pipes (LHP) are passive thermal management systems widely used in electronics cooling, military applications, renewable energy, and spacecraft. These two-phase systems employ capillary forces instead of pumps to circulate the coolant. In these devices, the coolant evaporates and condenses in the evaporator and condenser, respectively. The condensed coolant liquid is driven toward the evaporator by capillary action in a wick structure located inside the evaporator. A mechanical pump can be added to the liquid line of the loop to reach the distributed heat loads and control the temperature to produce an isothermal surface. In this work, the porous wick of an evaporator in a mechanically pumped loop heat pipe was analyzed employing the Computational Fluid Dynamics (CFD) code ANSYS/Fluent. The Volume of Fluid (VOF) model in ANSYS/Fluent is modified using a User Defined Function (UDF) to calculate mass transfer between the liquid and vapor phases at the interface. This research focuses on effect of applied heat flux on the evaporator, liquid mass flow rate at the wick inlet, wick porosity, permeability, and material thermal conductivity, and value of gravitational acceleration on the overall performance of the system. The results illustrate effect of each parameter on overall system performance and flow patterns of two-phase working fluid inside the porous wick. Some design recommendations also are made to fabricate the wick of such a system for any precious thermal management application. Show less

The American Petroleum Institute (API) level 2 rotordynamic stability analysis requires determination of possible destabilization forces on a compressor or pump impeller. Dynamic forces in transient regimes are often excluded although a turbomachine impeller may experience transient operation intentionally or accidentally. The centrifugal pump head, flow direction, rotation and torque can be both positive and negative in transient regimes. For example, in a renewable energy application, pump… Show more

The American Petroleum Institute (API) level 2 rotordynamic stability analysis requires determination of possible destabilization forces on a compressor or pump impeller. Dynamic forces in transient regimes are often excluded although a turbomachine impeller may experience transient operation intentionally or accidentally. The centrifugal pump head, flow direction, rotation and torque can be both positive and negative in transient regimes. For example, in a renewable energy application, pump flow direction and rotation are reversed to generate power from the imposed fluid head. The complete characteristics of a centrifugal pump correspond to all four quadrants (4Q) of operation, to encompass all possible operating conditions. It is required to understand centrifugal pump impeller dynamic forces and rotordynamic responses for all 4Q for design, fault diagnostic, instability analysis, upset conditions (such as water hammer, surge etc.) and for reliable operation of high energy density machines. Centrifugal pump dynamic forces, rotordynamic impedances and flow instabilities of an open impeller are reported for 4Q operating regimes in this paper. A transient Computational Fluid Dynamics (CFD)-based model is implemented which is applicable to nonaxisymmetric turbomachinery components, such as with a volute and/or vaned diffuser. Whirling motion of the impeller is modeled by imposing mesh deformation at the impeller walls. A phase modulated multi-frequency mesh deformation method is imposed for better numerical efficiency. Reynolds Averaged Navier-Stokes (RANS) equations with the Shear Stress Transport (SST) turbulence model along with a transitional bypass turbulence model are employed for the CFD solution. The results show the underlying flow field instability and stall cells responsible for the impedance shapes. Furthermore, the model is employed for determining the dependence of the outputs on specific speed to extract rotordynamic forces more efficiently Show less

Aerodynamic Characteristics is of interest in reducing the power consumption & increasing the speed of the vehicle. By optimizing shape of the vehicle both power consumption can be decreased as well as an increase in speed. Due to limitations in conventional wind tunnel; Computational Fluid Dynamics (CFD) is used to study the aerodynamics characteristics of vehicle. Here Computational Fluid Dynamics has been applied to a car for optimizing its different parameters to achieve a design which is… Show more

Aerodynamic Characteristics is of interest in reducing the power consumption & increasing the speed of the vehicle. By optimizing shape of the vehicle both power consumption can be decreased as well as an increase in speed. Due to limitations in conventional wind tunnel; Computational Fluid Dynamics (CFD) is used to study the aerodynamics characteristics of vehicle. Here Computational Fluid Dynamics has been applied to a car for optimizing its different parameters to achieve a design which is best suited and results in high aerodynamic performance. For this purpose, drag co-efficient parameter was considered. Starting from a basic blunt body design (drag co-efficient of 0.46) to final optimized design (drag co-efficient of 0.37) several design parameters like corner radius, frontal hood-glass radius & slant angles were changed. The final design that was selected for the shape had the drag co-efficient of 0.377531. Show less