Monday, January 14, 2013

Homework: Fluid Flow 1

1. Calculate the Reynolds number, flow speed, or water depth for the following flows using the Reynolds equation.  The density of water is 1000 kg/m3, and it has a viscosity of 0.001 kg/(m*s).  (6 points)

a) Calculate the Reynolds number for a flow with speed = 1 m/s and depth = 1 m.  Is the flow laminar, transitional, or turbulent?

b) Calculate the Reynolds number for a flow with speed = 0.1 m/s and depth = 0.1 m.  Is the flow laminar, transitional, or turbulent?

c) What is the maximum water depth for a laminar flow if the flow speed is 0.01 m/s?

2.  Where in any water flow is there laminar flow even if the flow speed is 0.45 m/s and the depth is 10’s of centimeters?  Why is it laminar?  (Assume that the bed it is flowing over is smooth.  You can watch this video: http://tinyurl.com/7lcc4o for a big hint!) (4 points)

3.  Watch the video at http://youtu.be/TKH1DyV9vNU called Sports Car Aerodynamics: Spoiler Alert!  Using the description of pressure in airflow over cars with spoilers vs. airfoils vs neither, sketch the laminar and turbulent areas of flow over a round sedimentary grain sitting on a flat surface.  Show the areas of low and high pressure and the forces on the grain.   (6 points)

4.  In words, briefly describe the process (Bernouli Effect) that causes grains to be picked up off the bed and entrained in the flow (at least temporarily). This description should be consistent with your sketch in question 3.  (4 points)