Transition to Turbulence - Revision history

Ian at 20:04, 15 May 2019

2019-05-15T20:04:58Z

Julialiu18: /* Real-world applications 2 */

2019-03-24T20:45:08Z

‎Real-world applications 2

Julialiu18: /* Real-world applications 2 */

2019-03-24T20:41:31Z

‎Real-world applications 2

Julialiu18: /* Real-world applications 2 */

2019-03-24T20:35:51Z

‎Real-world applications 2

Julialiu18: /* Real-world applications 2 */

2019-03-24T20:33:02Z

‎Real-world applications 2

Julialiu18: /* Real-world applications 2 */

2019-03-24T20:31:45Z

‎Real-world applications 2

Julialiu18: /* Real-world applications 2 */

2019-03-24T20:30:03Z

‎Real-world applications 2

Julialiu18: /* Viscosity */

2019-03-23T13:14:00Z

‎Viscosity

Julialiu18: /* Viscosity */

2019-03-23T13:13:15Z

‎Viscosity

Julialiu18: /* Viscosity */

2019-03-23T13:02:20Z

‎Viscosity

← Older revision		Revision as of 20:04, 15 May 2019
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	[[File:Water Vort VelMagVectors.0134.png\|none\|800px\|Early-timestep vorticity map of a numerical model of water flowing past a cylinder, showing an instability developing in the wake of the cylinder.]]		[[File:Water Vort VelMagVectors.0134.png\|none\|800px\|Early-timestep vorticity map of a numerical model of water flowing past a cylinder, showing an instability developing in the wake of the cylinder.]]

		+
		+	Here is a satellite loop of a von Karman Vortex Street developing in the wake of Guadalupe Island off the coast of Baja California, Mexico. (source: twitter user [https://twitter.com/weatherdak/status/1128453166725353473 @weatherdak])
		+
		+	[[File:GuadalupeVonKarman.mp4\|none\|1000px]]

	= Overview =		= Overview =

@@ Line 296: / Line 296: @@
-Below are velocity, shear rate, vorticity, Reynolds number, and pressure plots generated in COMSOL for the same fluid flowing around a teardrop-shaped object instead of the cylinder. Compare these to the plots shown above for the cylindrical impediment. You may still notice signs of oscillating flow resulting from the disturbance, but flow is MUCH more laminar. Can you explain why this might be in terms of pressure and vorticity?
+Below are velocity, shear rate, vorticity, Reynolds number, and pressure plots generated in COMSOL for the same fluid flowing around a teardrop-shaped object instead of the cylinder. Compare these to the plots shown above for the cylindrical impediment. You may still notice signs of oscillating flow resulting from the disturbance, but flow is ''much'' more laminar. Can you explain why this might be?
 [[File:fairing_water_velocity.gif]]
@@ Line 314: / Line 314: @@
 [[File:fairing_water_pressure.gif]]
-This also looks vastly different from the pressure plot for the cylinder model. How does the teardrop shape influence the pressure and vorticity?
+This also looks vastly different from the pressure plot for the cylinder model. It's amazing how such a simple design can result in a major shift in flow around the object.

@@ Line 296: / Line 296: @@
-Below are velocity, shear rate, vorticity, Reynolds number, and pressure plots generated in COMSOL for the same fluid flowing around a teardrop-shaped object instead of the cylinder. Compare these to the plots shown above for the cylindrical impediment. Take note of how the velocity vectors differ through time! You can still notice signs of oscillating flow resulting from the disturbance, but flow is MUCH more laminar. Can you explain why this might be in terms of pressure and vorticity?
+Below are velocity, shear rate, vorticity, Reynolds number, and pressure plots generated in COMSOL for the same fluid flowing around a teardrop-shaped object instead of the cylinder. Compare these to the plots shown above for the cylindrical impediment. You may still notice signs of oscillating flow resulting from the disturbance, but flow is MUCH more laminar. Can you explain why this might be in terms of pressure and vorticity?
 [[File:fairing_water_velocity.gif]]
 [[File:fairing_water_shear.gif]]
 [[File:fairing_water_vorticity.gif]]
 [[File:fairing_water_reynolds.gif]]
 [[File:fairing_water_pressure.gif]]
 Now, let's take a look at this behavior in a fluid with two orders of magnitude less viscosity than water: air.

@@ Line 295: / Line 295: @@
 [[File:ADCPfairing_operation.JPG|Fairing sheath in action. Note teardrop shape, meant to reduce pressure instability behind survey mount pole.]]
-Here are velocity, shear rate, vorticity, Reynolds number, and pressure plots generated in COMSOL for the same fluid flowing around a teardrop-shaped object instead of the cylinder. Compare these to the plots shown above for the cylindrical impediment. Take note of how the velocity vectors differ through time! Flow is much more laminar. Can you explain why this might be in terms of pressure and vorticity?
 [[File:fairing_water_velocity.gif]]

@@ Line 299: / Line 299: @@
 [[File:fairing_water_velocity.gif]]
-[[File:fairing_water_shear.gif]
+[[File:fairing_water_shear.gif]]
 [[File:fairing_water_vorticity.gif]]

@@ Line 75: / Line 75: @@
 ==== Viscosity ====
-[[File:Shearthinthick.png|thumb|400px|Viscous regimes. Newtonian fluids exhibit a linear relationship between stress and strain rate. This means that deformation occurs proportional to the forces acting on the fluid. (Image from https://neutrium.net/fluid_flow/viscosity/]]
+[[File:Shearthinthick.png|thumb|400px|Viscous regimes. Newtonian fluids exhibit a linear relationship between stress and strain rate. This means that deformation occurs proportional to the forces acting on the fluid. (Image from https://neutrium.net/fluid_flow/viscosity/)]]
 Keeping those real-world examples in mind, we can brainstorm about the differences in those fluid systems that might affect the flow pattern. There are differences in the fluid properties between the molasses, toothpaste, and atmospheric air. Once of the main differences, which we examine in depth in this module, is their difference in viscosity. "Viscosity" is a term you might be familiar with in terms of describing a fluid. The technical definition of [https://en.wikipedia.org/wiki/Viscosity viscosity] is a fluid's capability of resisting deformation. Molasses and toothpaste are more viscous than water, which means that their flow is more difficult to deform or disturb. Meanwhile, air has a much lower viscosity and is quite easily deformed! We deform air every time we move. Therefore, if everything else is held constant, increasing viscosity decreases the Reynolds number which means that fluid flow becomes more laminar. If we decrease viscosity, fluid flow will begin to transition towards turbulence.