Fluid flow around a wind turbine blade -- help please

  • #1
49
0
Homework Statement:
Estimate what the Reynolds number is of the fluid flowing around the table
Relevant Equations:
Reynolds number
I have to estimate the Reynolds number of the fluid flowing around a blade but I only have one detail: the length of the blade is 0.66m.
I have no idea how to do it and I gotta submit the assignment in a week, I am desperate for help here.
lenght of the blade.png
 

Answers and Replies

  • #2
362
64
It says estimate. Have you seen the blades turning?
 
  • #3
21,074
4,648
It might help if you started out by providing for us some indication of your understanding of the definition of the Reynolds number.
 
  • #4
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It says estimate. Have you seen the blades turning?

I haven't. That is all the information I got which I find strange
 
  • #5
49
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It might help if you started out by providing for us some indication of your understanding of the definition of the Reynolds number.
The Reynolds numbers is a parameter that helps obtain a flow pattern estimation in various fluid flow situations
The Reynolds number is mathematically defined as:
yjjj.png

where:
  • is the fluid density (kg/m3)
  • is the flow velocity
  • is a linear dimension
  • is dynamic viscosity (Pa.s)
  • v is kinematic viscosity (m2/s)
 
  • #6
21,074
4,648
The Reynolds numbers is a parameter that helps obtain a flow pattern estimation in various fluid flow situations
The Reynolds number is mathematically defined as:
View attachment 274953
where:
  • is the fluid density (kg/m3)
  • is the flow velocity
  • is a linear dimension
  • is dynamic viscosity (Pa.s)
  • v is kinematic viscosity (m2/s)
Good. I assume you are dealing with air at approximately room temperature conditions. So you know the density and viscosity, right? You also have a characteristic length. Ok so far?
 
  • #7
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Good. I assume you are dealing with air at approximately room temperature conditions. So you know the density and viscosity, right? You also have a characteristic length. Ok so far?

The wind turbine is supposed to be an offshore wind turbine so I am guessing the density of the air= 1,225 kg/m^3 and viscosity of air= 1,789x10^-5 (this is only what I am guessing though, doesn't mean it is right. The only known detail I know as it is visible on the imagen I posted on my post is the wind turbine geometric but I also believe that 660,60mm is too little measurement for a wind turbine blade.
 
  • #8
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Good. I assume you are dealing with air at approximately room temperature conditions. So you know the density and viscosity, right? You also have a characteristic length. Ok so far?
I also got the Area of the blade if it helps.
 
  • #9
21,074
4,648
The wind turbine is supposed to be an offshore wind turbine so I am guessing the density of the air= 1,225 kg/m^3 and viscosity of air= 1,789x10^-5 (this is only what I am guessing though, doesn't mean it is right. The only known detail I know as it is visible on the imagen I posted on my post is the wind turbine geometric but I also believe that 660,60mm is too little measurement for a wind turbine blade.
I’m not so sure that 0.66 m is short for a turbine blade. Why don’t you make a graph of Re vs velocity?
 
  • #10
49
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I’m not so sure that 0.66 m is short for a turbine blade. Why don’t you make a graph of Re vs velocity?
I don't understand you. When it says "Estimate what the Reynolds number is of the fluid flowing around the blade" I am guessing I have to calculate it using a formula.
 
  • #11
21,074
4,648
I don't understand you. When it says "Estimate what the Reynolds number is of the fluid flowing around the blade" I am guessing I have to calculate it using a formula.
You have the formula. Just substitute a selection of values for the velocity and plot a graph.
 
  • #12
49
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You have the formula. Just substitute a selection of values for the velocity and plot a graph.
Apparently, my teacher has just told me I have to use the typical fluid velocity, that I have no idea what it is
 
  • #13
21,074
4,648
Apparently, my teacher has just told me I have to use the typical fluid velocity, that I have no idea what it is
What does your gut tell you about the probable range of velocity values?
 
  • #14
49
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What does your gut tell you about the probable range of velocity values?
My gut? I don't understand the problem and neither I understand what my teacher has said, so I don't think my gut is able to tell me anything.
 
  • #15
berkeman
Mentor
59,467
9,588
The wind turbine is supposed to be an offshore wind turbine
Apparently, my teacher has just told me I have to use the typical fluid velocity, that I have no idea what it is
I don't understand the problem and neither I understand what my teacher has said, so I don't think my gut is able to tell me anything.
What are typical wind speeds for offshore wind installations (Google should be able to find it)? What would a typical speed be for a wind turbine of this size in those wind conditions? Google should be able to help you find ballpark numbers for that as well...
 
  • #16
21,074
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What is the speed of typical winds on a moderately windy day? What about in a moderate tropical storm?
 
  • #17
21,074
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I'm thinking wind speeds of 3-30 m/s, with a typical moderate value being on the order of 10 m/s. Anyway, that's my gut feeling.
 

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