Engineering Commons^™

Piv Measurements Of Open-Channel Turbulent Flow Under Unconstrained Conditions, James K. Arthur

Faculty Journal Articles

Many open-channel turbulent flow studies have been focused on highly constrained conditions. Thus, it is rather conventional to note such flows as being fully developed, fully turbulent, and unaffected by sidewalls and free surface disturbances. However, many real-life flow phenomena in natural water bodies and artificially installed drain channels are not as ideal. This work is aimed at studying some of these unconstrained conditions. This is achieved by using particle image velocimetry measurements of a developing turbulent open-channel flow over a smooth wall. The tested flow effects are low values of the Reynolds number based on the momentum thickness Re …

Jet Noise Reduction: A Fresh Start, Christopher K. Tam, Fang Q. Hu

Mathematics & Statistics Faculty Publications

Attempts to reduce jet noise began some 70 years ago. In the literature, there have been many publications written on this topic. By now, it is common knowledge that jet noise consists of a number of components. They possess different spectral and radiation characteristics and are generated by different mechanisms. It appears then that one may aim at the suppression of the noise of a single component instead of trying to reduce jet noise overall. The objective of the present project is to reduce large turbulence structures noise. It is the most dominant noise component radiating in the downstream direction. …

Development Of An Unmanned Aerial Vehicle For The Measurement Of Turbulence In The Atmospheric Boundary Layer, Brandon M. Witte, Robert F. Singler, Sean C. C. Bailey

Mechanical Engineering Faculty Publications

This paper describes the components and usage of an unmanned aerial vehicle developed for measuring turbulence in the atmospheric boundary layer. A method of computing the time-dependent wind speed from a moving velocity sensor data is provided. The physical system built to implement this method using a five-hole probe velocity sensor is described along with the approach used to combine data from the different on-board sensors to allow for extraction of the wind speed as a function of time and position. The approach is demonstrated using data from three flights of two unmanned aerial vehicles (UAVs) measuring the lower atmospheric …

Direct Numerical Simulation Of Turbulent Katabatic Slope Flows With An Immersed-Boundary Method, Clancy Umphrey, Ray Deleon, Inanc Senocak

Mechanical and Biomedical Engineering Faculty Publications and Presentations

We investigate a Cartesian-mesh immersed-boundary formulation within an incompressible flow solver to simulate laminar and turbulent katabatic slope flows. As a proof-of-concept study, we consider four different immersed-boundary reconstruction schemes for imposing a Neumann-type boundary condition on the buoyancy field. Prandtl’s laminar solution is used to demonstrate the second-order accuracy of the numerical solutions globally. Direct numerical simulation of a turbulent katabatic flow is then performed to investigate the applicability of the proposed schemes in the turbulent regime by analyzing both first- and second-order statistics of turbulence. First-order statistics show that turbulent katabatic flow simulations are noticeably sensitive to the …

Turbulence Analysis For The Improvement Of Internal Combustion Engine Efficiency, James R. Macdonald, Claudia Fajardo-Hansford

Research and Creative Activities Poster Day

Developing a complete understanding of the structure and behavior of the near-wall region (NWR) in reciprocating, internal combustion (IC) engines and of its interaction with the core flow is needed to support the implementation of advanced combustion and operating strategies to improve engine efficiency. The NWR in IC engines is fundamentally different from the canonical steady-state turbulent boundary layers (BL), which have been extensively researched. Motivated by this need, this poster presents results from the analysis of two-component velocity data measured with particle image velocimetry near the head of a single-cylinder, optical engine. The interaction between the NWR and the …

An Experimental Investigation Of Wing-Tip Vortex Decay In Turbulence, Hai G. Ghimire, Sean C. C. Bailey

Mechanical Engineering Faculty Publications

Particle image velocimetry measurements were conducted for a wing-tip vortex decaying in free-stream turbulence. The vortex exhibited stochastic collapse with free-stream turbulence present, with the breakdown initiating earlier for higher levels of turbulence. An increased rate of decay of the vortex tangential velocity was also observed, increasing with increasing free-stream turbulence. The decay of the vortex tangential velocity without the free-stream turbulence was well represented by viscous diffusion, resulting in an increase in the core radius and decrease in the peak tangential velocity. With the addition of free-stream turbulence, the rate of decay of the peak tangential velocity of the …

Experimental Validation Data For Cfd Of Forced Convection On A Vertical Flat Plate, Jeff R. Harris, Blake W. Lance, Barton L. Smith

Mechanical and Aerospace Engineering Faculty Publications

A CFD validation data set for turbulent forced convection on a vertical plate is presented. The design of the apparatus is based on recent validation literature and provides a means to simultaneously measure boundary conditions and system response quantities. All important inflow quantities for RANS CFD are also measured. Data are acquired at two heating conditions and cover the range 40;000 < Rex < 300;000, 357 < Red2 < 813 and 0:02 < Gr/Re2 < 0:232. The data and uncertainties are contained in files in the supplemental material

There Can Be Turbulence In Microfluidics At Low Reynolds Number, Guiren Wang, F. Yang, Wei Zhao

Faculty Publications

Turbulence is commonly viewed as a type of macroflow, where the Reynolds number (Re) has to be sufficiently high. In microfluidics, when Re is below or on the order of 1 and fast mixing is required, so far only chaotic flow has been reported to enhance mixing based on previous publications since turbulence is believed not to be possible to generate in such a low Re microflow. There is even a lack of velocimeter that can measure turbulence in microchannels. In this work, we report a direct observation of the existence of turbulence in microfluidics with Re on the order …

Numerical Simulation Of Buoyancy-Driven Turbulent Ventilation In Attic Space Under Winter Conditions, Shimin Wang, Zhigang Shen, Linxia Gu

Department of Mechanical and Materials Engineering: Faculty Publications

Attic design and construction have significant impacts on residential buildings’ energy performance. In order to understand how passive ventilation rates affect ridge-vent attic’s performance, a two-dimensional steady-state finite volume model is employed to simulate the buoyancy-driven turbulent ventilation and heat transfer in a triangular attic space of a gable-roof residential building under winter conditions. The modeled attic has a pitch of 5/12 and a passive ventilation system, consisting of continuous ridge and soffit vents. The v2f model is used to analyze the turbulent air flow and natural convection heat transfer inside the attic. The effects of ambient air temperature, vent …

Multidimensional Modeling Of Condensing Two-Phase Ejector Flow, Michael F. Colarossi

Masters Theses 1911 - February 2014

Condensing ejectors utilize the beneficial thermodynamics of condensation to produce an exiting static pressure that can be in excess of either entering static pressure. The phase change process is driven by both turbulent mixing and interphase heat transfer. Semi-empirical models can be used in conjunction with computational fluid dynamics (CFD) to gain some understanding of how condensing ejectors should be designed and operated.

The current work describes the construction of a multidimensional simulation capability built around an Eulerian pseudo-fluid approach. The transport equations for mass and momentum treat the two phases as a continuous mixture. The fluid is treated as …

Drag Reduction In Turbulent Flows Over Micropatterned Superhydrophobic Surfaces, Robert J. Daniello

Masters Theses 1911 - February 2014

Periodic, micropatterned superhydrophobic surfaces, previously noted for their ability to provide drag reduction in the laminar flow regime, have been demonstrated capable of reducing drag in the turbulent flow regime as well. Superhydrophobic surfaces contain micro or nanoscale hydrophobic features which can support a shear-free air-water interface between peaks in the surface topology. Particle image velocimetry and pressure drop measurements were used to observe significant slip velocities, shear stress, and pressure drop reductions corresponding to skin friction drag reductions approaching 50%. At a given Reynolds number, drag reduction was found to increase with increasing feature size and spacing, as in …

Computational And Experimental Investigation Of The Flow Structure And Vortex Dynamics In The Wake Of A Formula 1 Tire, John Axerio, Gianluca Iaccarino, Emin Issakhanian, Chris Elkins, John Eaton

Mechanical Engineering Faculty Works

The flowfield around a 60% scale stationary Formula 1 tire in contact with the ground in a closed wind tunnel was examined experimentally in order to assess the accuracy of different turbulence modeling techniques. The results of steady RANS and Large Eddy Simulation (LES) were compared with PIV data, which was obtained within the same project. The far wake structure behind the wheel was dominated by two strong counter-rotating vortices. The locations of the vortex cores, extracted from the LES and PIV data as well as computed using different RANS models, showed that the LES predictions are closest to the …