Computational & Theoretical Multiphysics Laboratory

The nucleate boiling process is essential to achieve extreme heat flux in heat exchangers and cooling systems. We have proposed using active vortex generation to manipulate the boiling process dynamics. We have simulated the response of the boiling process in a heat exchanger channel to an oscillating flexible/rigid/hybrid plates and found out the extent of thermal enhancement and effects on dynamics of the vapor bubble. Our preliminary results show that surprisingly, a specific type of active vortex generators may enhance the thermal heat transfer by 500%-1000% much more than other proposed techniques. Considering the impact of active vortex generators compared to the crossflow-only case, we found out that by using a flexible insert, one can reach a 200%-250% increase in the coefficient of performance. The initial results suggest a promising technique to have a paradigm-shift heat transfer enhancement methodology especially for boiling heat transfer in microchannels using minimally invasive piezoelectric or magnetic vortex generators. Further studies will increase our understanding of the critical features of this process, also gives the suitable parameter regimes for experimental studies and practical applications. This may lead to an economical thermal management procedure using a passive system for the real-world applications.

When a shock wave comes into contact with a boundary layer flow, the large adverse pressure gradient associated with the shock wave can cause the flow to separate from the surface. When this happens, a recirculation bubble forms close to the wall, and significantly alters the stability and dynamics of the flow. This shock typically bends as it encounters lower Mach numbers inside the boundary layer and ultimately breaks up into a compression fan and a reflected shock develops. We are doing research on SWBLI with flexible structure focusing on structural load minimization and flow control. Panel dynamics can help us to find a potential use of an aeroelastically tailored flexible panel as a means of passive flow control. Cavity pressure underneath the panel can also create forced panel oscillations which may reduce separation in the interaction zone.

The canonical problem of flow-induced flutter of a thin flexible plate is revisited, with an emphasis on the thermally induced buoyancy effects on the dynamics and thermal characterization of the system. An immersed boundary method is used to simulate mixed convection of a heated 2D inextensible and flexible thin plate. The bending stiffness, Richardson number, and Reynolds number are chosen as the characteristic parameters of the system. The dynamic and thermal responses of the plate are examined over a wide range of the characteristic parameters, and it is shown that the stability boundary growth rate of the flapping dynamics dramatically increases after a particular threshold Richardson number due to the mode switching behavior. The appearance of higher oscillatory modes and a shift in the nodes of the dominant oscillatory mode are found to also be correlated to the observed higher Nusselt numbers.

Wind induced stresses are the major mechanical cause of failure in trees. Our aim is to prevent tree failures from happening due to harsh hurricane–like conditions; helping the department of environment plant trees that have the right reconfiguration ability to withstand such conditions. Trees generally break at a point where they experience maximum stress. Through simulations analytical reasoning, we have seen that the prediction of the fracture risk and pattern of a tree is a function of their reconfiguration capabilities and how they mitigate large wind-induced stresses. Also, the probability of a tree breaking at any point depends on both the cross-section changes in the branching nodes and the level of tree flexibility. It has been noted that at an optimal branching, the stress experienced on a tree is uniform, thereby causing no weak link on the tree. This, in turn, doesn’t make the tree break during harsh conditions since there is no overstress throughout the cross-section of the tree. Prevention of tree failure will lead to a reduced power outage during storms.

A computational model is used to study the effect of wave-induced motion on the aerodynamics of compliant offshore wind turbines. The wake response of two promising offshore platform concepts, Spar buoy and Barge type turbines were studied in details and their aerodynamic, power and wake characteristics were compared with a stationary wind turbine case. Results obtained from this study indicates that surprisingly the wake response of the oscillating wind turbine recovers faster compared to the stationary turbine, with a 50%wake recovery in a distance that is 33% shorter than the static counterpart.

Aeroelastic effect plays an important role in various research topics including aero vehicle stability, renewable energy extraction, and animal locomotion. Active and passive control methods have been proposed to control the flutter phenomenon of the airfoil. For example, the EET high-lift flexible wing with actively bending flaps provides an active actuator that can modify the flow around the airfoil. Through the use of a high-fidelity fluid-structure interaction algorithm we can investigate the effect on the aeroelastic motion of the EET airfoil over a wide range of parameters. Preliminary results show that the active flap is capable of regulating the oscillation period of the airfoil. The simulations can provide physical insight behind the highly nonlinear motion, and eventually derive the control law to regulate the oscillation.

Cryogenic fluids are one of the critical components of current and future space exploration, and a better understanding of cryogenic flow is necessary for safe and efficient transport and storage of cryogenic fluids. This project aims to develop and employ novel modeling and analysis tools for capturing the flow physics and thermodynamics of cryogenic flows in storage vessels in both normal and microgravity conditions. The flow and thermal interaction of cryogenic systems with three phases of the flow, gas, and solid boundaries can generate a rich spectrum of phenomena. To accurately model the system while keeping the running time much lower than the conventional CFD approaches, the block-structured adaptive mesh refinement (AMR) is using. This project's main innovation is the development of an AMR-based computational tool based on the integration of the continuum multiphase-phase model of the cryogenic and the multi-node model of the system. The approach provides high-fidelity modeling of the complex coupled dynamics while maintaining the computational efficiency of nodal models.