Fluid flow around a wind turbine blade -- help please

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Homework Help Overview

The discussion revolves around estimating the Reynolds number for fluid flow around a wind turbine blade, specifically with a blade length of 0.66m. Participants are exploring the necessary parameters and definitions related to the Reynolds number in the context of wind turbine operation.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the definition of the Reynolds number and its significance in fluid dynamics. There are inquiries about the known parameters such as fluid density and viscosity, as well as the characteristic length of the blade. Some participants suggest estimating typical fluid velocities and question the original poster's understanding of the problem.

Discussion Status

The discussion is active, with participants providing guidance on how to approach the estimation of the Reynolds number. There are multiple interpretations of the problem, particularly regarding the typical fluid velocity and the implications of the given blade length.

Contextual Notes

Participants note the lack of complete information regarding fluid velocity and express uncertainty about the typical values that should be used for calculations. There is also mention of the offshore context of the wind turbine, which may influence the expected wind speeds.

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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 got to submit the assignment in a week, I am desperate for help here.
lenght of the blade.png
 
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It says estimate. Have you seen the blades turning?
 
It might help if you started out by providing for us some indication of your understanding of the definition of the Reynolds number.
 
Gordianus said:
It says estimate. Have you seen the blades turning?

I haven't. That is all the information I got which I find strange
 
Chestermiller said:
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)
 
Hdez said:
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?
 
Chestermiller said:
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.
 
Chestermiller said:
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.
 
Hdez said:
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
Chestermiller said:
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
Hdez said:
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
Chestermiller said:
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
Hdez said:
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
Chestermiller said:
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
Hdez said:
The wind turbine is supposed to be an offshore wind turbine
Hdez said:
Apparently, my teacher has just told me I have to use the typical fluid velocity, that I have no idea what it is
Hdez said:
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
What is the speed of typical winds on a moderately windy day? What about in a moderate tropical storm?
 
  • #17
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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