Doctor of Philosophy (PhD)
Mechanical and Industrial Engineering
Jets in crossflow (JICF) have applications ranging from oil spill to film cooling of turbine blades. Hence, an understanding of the flow physics is important. The majority of the research has been conducted for low velocity ratios between jet and crossflow with round jets. JICF is demonstrated to behave differently for high velocity ratios and different jet shapes. Circular and rectangular jets are commonly used in aircraft applications. Current study focuses on high velocity ratio JICF issuing from both circular and rectangular exit.
For simulating JICF, an in house code “Chem3D” is used with Large Eddy Simulation (LES) to model turbulence. Initially, a circular jet is simulated and validated. A rectangular jet with the same mass flow rate is simulated for comparison. Dynamic mode decomposition (DMD) is used for modal study of these jets. An inlet turbulence generation algorithm, Synthetic Eddy Method (SEM), is implemented to simulate incoming jets with different turbulence levels. The SEM algorithm is used to study pipe flow and validation with experiment was obtained.
Rectangular JICF exhibits axis switching which is consistent with observations in literature for a rectangular jet without crossflow. Results from different aspect ratio of rectangular jets (0.5, 2.0, and 3.0) are compared. For rectangular JICF with short edge facing the crossflow, axis switching happens earlier if the aspect ratio is decreased. For the same aspect ratio, if the long edge is facing the crossflow, axis switching is delayed. Effect of geometry is seen in trajectory, turbulence and shear layers of the JICF. Overall, rectangular JICF is shown to exhibit dominance of higher frequencies in the shear layer. However, the effect on turbulence is higher for circular JICF.
Additionally, circular and rectangular JICF with different turbulent kinetic energy of jet is simulated. Analysis reveals earlier breakdown of near field shear layer vortices as the turbulence kinetic energy of jet increases. Effect on the trajectory, turbulence and dynamics of the JICF is observed. In rectangular JICF, axis switching is enhanced by the increase of turbulence levels of the jet. This enhancement is related to wall normal vortices which increase with turbulence of the jet.
Pokharel, Pranaya, "Large Eddy Simulations of Vertical Jets in Crossflow" (2018). LSU Doctoral Dissertations. 4747.