Contenuto scaricabileScarica il pdf
Hot wire anemometry : hardware, software, design and application
The purpose of this project was to design and build a laboratory apparatus which would permit the measurement of velocity profiles in boundary layer flow. Boundary layer flow is one particular type of external flow (as opposed to an internal flow) that goes over solid surfaces. As the fluid flows over the solid boundary, a thin region is created next to the solid surface where viscous actions and turbulent effects are important and sharp velocity gradients exist due to the no-slip boundary condition at the surface. This region of the flow is called boundary layer flow. Flow outside the boundary layer is considered inviscid in which the viscous effects are negligible and the flow approaches the ideal flow behavior. A typical boundary layer has three different regions in its time history: laminar, transition, and turbulent. The laminar region is characterized when the Reynolds number is below 500,000.00, turbulent is over 1,000,000, and in between is when the boundary layer goes through a transition in which any disturbances to the flow cannot be dampened out by the action of viscous forces so that laminar behavior can be maintained. The disturbances grow in magnitude and develop into distinctive vortex patterns that eventually break down to form a fully turbulent boundary layer at Reynolds numbers greater than 1,000,000. It is in the boundary layer that most mass transfer, momentum transfer, and heat transfer occur. Understanding all these transport phenomenon requires a thorough understanding of the boundary layer flow characteristics and behavior. In order to study the effects of boundary layer flow we will first become familiar with the IFA 100 hot-wire anemometer and data acquisition software so that test measurements can be acquired. Secondly, a controlled environment with a variable fluid flow will be designed and then built to facilitate the acquisition of velocity and thermal boundary layer measurements. Finally, we will create Fluid Dynamics and Heat transfer laboratory experiments utilizing hot wire anemometry, to help students gain a better understanding of hydrodynamic and thermal boundary layer flows.