When examining the literature for flow effects on circular cylinders one can find many studies on infinite cylinders and cantilevered cylinders but minimal data related to cylinders with two free ends. The limited data available shows that the cylinder aspect ratio affects the drag and frequency content of flow within the wake however these studies were done at discreet Reynolds numbers. In order to better understand the combined impact of aspect ratio and Reynolds number a series of wind tunnel tests and numerical simulations has been conducted for cylinders with two free ends having aspect ratios of 2-15. Tests were carried out in the subcritical regime with Reynolds numbers ranging 13000-105,000. Tip vortex effects, which vary with aspect ratio, are shown to impact the cylinder surface pressure, drag coefficient, and wake Strouhal numbers though Reynolds number effects are minor for the conditions studied. The results are compared against existing historical data and show the trend of drag coefficient increasing with cylinder aspect ratio.

When examining the literature for flow effects on circular cylinders one can find many studies on infinite cylinders and cantilevered cylinders but minimal data related to cylinders with two free ends. The limited data available shows that the cylinder aspect ratio affects the drag and frequency content of flow within the wake however these studies were done at discreet Reynolds numbers. In order to better understand the combined impact of aspect ratio and Reynolds number a series of wind tunnel tests and numerical simulations has been conducted for cylinders with two free ends having aspect ratios of 2–15. Test were conducted in the subcritical regime with Reynolds numbers ranging 9300–105,000. Tip vortex effects, which vary with aspect ratio, are shown to impact the cylinder surface pressure, drag coefficient and wake Strouhal numbers though Reynolds number effects are minor for the conditions studied. The results are compared against existing historical data and show the trend of drag coefficient increasing with cylinder aspect ratio.

Natural convective heat transfer can be enhanced through either fins or riblets, wall roughness elements, or the injection of bubbles in the flow. Bubble injections in a quiescent (pseudo-turbulent) liquid phase or an already turbulent liquid phase had been shown to enhance the natural convective heat transfer from literature. However, study of the combined effect of bubble size and gas volume fraction rather than individual effect on natural convective heat transfer enhancement for homogeneous bubbly flow is lacking. The present work intends to fill in that data gap through conducting numerical simulations to study the combined effect of bubble size and gas volume fraction on natural convective heat transfer enhancement. The present numerical work employs a validated interphase force models and the Eulerian-Eulerian model. ANSYS FLUENT is used to simulate a bubbly flow in a three-dimensional rectangular channel with a natural convective heat transfer. Bubbles ranging from micro to millimeter diameter with inlet gas volume fraction varied in the range of 0.351-3.725% are injected upward to a quiescent liquid phase in a rectangular channel with a heated left wall and a cooled right wall. The flow regime is homogeneous without bubble coalescence and breakup effect. Validated computational models are employed to study the combined effect of bubble size and gas volume fraction on heat transfer enhancement. A relation between Nusselt number, bubble Reynolds number, Rayleigh number, nondimensional bubble size, and inlet gas volume fraction is constructed using the power regression method.