Performed on April 12, 2013
Due date April 19, 2013
Laminar and Turbulent Flow
Table of Contents
In this experiment we used water in a Venturi as this was interpretive of the characteristics of all flowing fluids. The water was conveyed through a conduit in the form of a venturi metre and a copper pipe, however, the general characteristics of fluid flow including the transition from undisturbed laminar flow to disturbed turbulent flow are exhibited by fluid flow in a pipeline transporting liquefied natural gas, a microchannel transporting hydrogen in fuel cell, and the flow of fluid over any solid surface. Thus flow of air over the ground and flow in any pipe, tube, or duct that is completely filled with flowing fluid, all display similar characteristics. (Elger. DF, Williams. CB, Crowe. CT, Roberson, 10th Edition) Sometimes it is hard to put a finger on exactly the type of flow a fluid is moving in, this begs for an expression that numerically describes the flow. The results can be best understood by expressing the flow characteristic in terms of non-dimensionless numbers which measure the ratio of the magnitude of force associated with inertia to the forces arising from fluid viscosity which gives rise to the Reynolds number. If one were to increase a fluid’s inertia - increased mass and acceleration – relative to solid surface and holding other factors constant then Reynolds number would increase (Achela, F, 2013, Lecture Notes) . In the aid of a glass tube we were able to estimate Reynolds number judging on how well the dye mixed in with the flowing water. Also, the loss of flow pressure head along the venturi metre into the copper pipe paved the way to deduce the shear stress the water flow experienced in the long copper pipe. To have this knowledge is especially useful in applications for designing piping systems. Summary
An experiment was carried out to identify different flow types, laminar and turbulent, while also calculating a copper pipe’s frictional forces using an inherent roughness, at the different flow rates. A Reynolds number of approximately 980 were for laminar flow, with a piezometric head height difference of 2mm. The flow was then changed to become turbulent. The achieved Reynolds number was approximately 5000, with a head height of 50mm. Two Reynolds numbers were then chosen to calculate the frictional force/shear stress in the 3m copper pipe. The obtained results differed by 1/10 of the theoretical value. However, the fluctuating head heights create large experimental errors. The turbulent flow yielded a better shear stress. However, the desired h1-h2 could not be achieved as 72mm was the maximum height. If the experiment was carried out again different Reynolds numbers would be chosen. However, the experiment was a success as it highlighted laminar and turbulent flows. Objectives
To obtain the Reynolds number at which the transition from laminar to turbulent flow takes place. And to investigate the shear stresses experienced by laminar and turbulent flow of a fluid in pipes.
Reynolds Number at Transition from Laminar to Turbulent:
1. Started with a steady flow rate in Venturi metre rate steady with die unmixed and relatively straight – laminar. 2. Flow rate turned up gradually until the dye mixed with water flow. Here we measured the head differences (h1-h2) 3. Using Venturi calibration curve (See Figure 1) and Venturi dimensions (See Table 4) Reynolds number was deduced. Shear Stresses in Laminar and Turbulent procedure:
1. Measure water temperature.
2. Reynolds number for laminar and turbulent were estimated to be included in the calculations to deduce an approximate pressure difference in the 3m copper pipe 3. Our...