How much wind force does a moving vehicle generate?

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Discussion Overview

The discussion centers around calculating the wind force generated by a moving vehicle, particularly focusing on how much wind or energy is produced when a car travels at various speeds. Participants explore concepts related to drag forces, energy transfer, and the implications of these calculations in practical scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants inquire about the calculation of wind force generated by moving vehicles, suggesting that it may relate to wind resistance and drag forces, including pressure drag and friction drag.
  • One participant proposes that the resistance force from wind can be determined by subtracting the force required to overcome rolling friction from the total force needed to maintain constant velocity.
  • Another participant suggests that measuring the energy generated by a car traveling at a specific speed is complex and questions how to define the area for measurement.
  • Some participants express skepticism about the practicality of harvesting energy from the wind generated by vehicles, noting that it is not easily captured.
  • There is a discussion about the difference between drag forces acting on a vehicle and the larger air mass displaced by the vehicle's motion.
  • One participant mentions that energy imparted to the air comes from the fuel used to propel the car, emphasizing that there is no free energy available from the air pushed aside.
  • Another participant references the concept of slipstreaming and its effects on energy efficiency in cycling and driving contexts.
  • Links to external resources are shared, including information on drag coefficients and energy losses in vehicles.

Areas of Agreement / Disagreement

Participants express a range of views on the feasibility and implications of calculating wind force and energy generation from moving vehicles. There is no consensus on the practicality of harvesting this energy or the methods for calculation, indicating ongoing debate and uncertainty.

Contextual Notes

Participants highlight limitations in defining measurement areas and the complexity of energy calculations, as well as the dependence on various assumptions regarding drag and energy transfer.

Q-man
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Does anyone know how to calculate how much force (or wind) a moving vehicle generate?
I am trying to figure out how much wind does a moving car (or any vehicle) generate when traveling at certain speed.
 
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Q-man said:
Does anyone know how to calculate how much force (or wind) a moving vehicle generate?
I am trying to figure out how much wind does a moving car (or any vehicle) generate when traveling at certain speed.
Are you talking about how much wind resistance a car has to overcome?? In that case there are two types of drag forces: Pressure drag and friction drag. The formulae for these are available in every fluid mechanics text.
 
Hi Benny_91,
Thank you for responding to my posting. I want to measure how much energy is generated when a car is travels at at a certain speed (e.g. sixty miles per hour).
Imagine when you're standing on the side of the road, when a car travels at sixty miles per hour passing by and you feel the energy (wind) from the car passing by. I want to measure or calculate that energy or how much wind when a car is traveling at a certain speed.
thanks in advance for helping.
 
Q-man said:
Hi Benny_91,
Thank you for responding to my posting. I want to measure how much energy is generated when a car is travels at at a certain speed (e.g. sixty miles per hour).
Imagine when you're standing on the side of the road, when a car travels at sixty miles per hour passing by and you feel the energy (wind) from the car passing by. I want to measure or calculate that energy or how much wind when a car is traveling at a certain speed.
thanks in advance for helping.
The force required by the car to travel at a constant velocity minus the force required to overcome rolling friction at the wheels will give the resistance force offered by the wind. This force multiplied by the constant velocity of the car will give the energy generated or energy transferred to the air per second. This energy mostly appears as heat or kinetic energy.
 
Q-man said:
Hi Benny_91,
Thank you for responding to my posting. I want to measure how much energy is generated when a car is travels at at a certain speed (e.g. sixty miles per hour).
Imagine when you're standing on the side of the road, when a car travels at sixty miles per hour passing by and you feel the energy (wind) from the car passing by. I want to measure or calculate that energy or how much wind when a car is traveling at a certain speed.
thanks in advance for helping.
I think what you are looking for will be hard to define, how will you determine the area to measure ? but using the same math as when calculating windmill energy is what I think you will need.
 
Q-man said:
Imagine when you're standing on the side of the road, when a car travels at sixty miles per hour passing by and you feel the energy (wind) from the car passing by. I want to measure or calculate that energy or how much wind when a car is traveling at a certain speed.
Why do you want to calculate this? It is not energy that is easily harvested.
 
berkeman said:
Why do you want to calculate this? It is not energy that is easily harvested.
perhaps he/she is just interested in the calculation?
 
lychette said:
perhaps he/she is just interested in the calculation?
That certainly could be, but we sometimes get folks here wanting to figure out how much energy they can recover by putting a fan/windmill on a car...
 
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  • #10
berkeman said:
That certainly could be, but we sometimes get folks here wanting to figure out how much energy they can recover by putting a fan/windmill on a car...
OK...I wonder what they wanted
 
  • #11
This link has a breakdown showing where the energy goes...

http://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.html

Only about 2.5% into drag.
 
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  • #12
Is there not a difference, as to drag from air staying in contact with the skin surface of a moving object ? and the buffeting of the large air mass that has been pushed aside by said object ?
 
  • #13
What do you mean by "difference"?

Any energy imparted to the air by the motion of the car must ultimately come from the fuel used to propel the car. Where else could it come from?
 
  • #14
PS The air "pushed aside" by the car doesn't stay pushed aside. There is no vacuum behind the car.

If you tried to harness the energy in the air pushed aside you might be able to capture more than the 2.5% I referred to BUT this would come at the expense of increasing the drag and energy wasted by the car. There is never any free lunch.
 
  • #15
I can see where most might assume a harvest from the car, I took it to be a harvest on solid ground as the car moved past. :smile:
 
  • #16
Either way the energy still comes from the car.
 
  • #17
berkeman said:
That certainly could be, but we sometimes get folks here wanting to figure out how much energy they can recover by putting a fan/windmill on a car...
Or on the side of the road.
 
  • #18
CWatters said:
If you tried to harness the energy in the air pushed aside you might be able to capture more than the 2.5% I referred to BUT this would come at the expense of increasing the drag and energy wasted by the car. There is never any free lunch.
It's the same with slipstreaming behind another vehicle. The 'pull' you get comes from the muscles of the poor guy, cycling in front. Skeins of geese have the strongest flyers near the front and they are also donating energy to those behind. The leader could always be going faster and cheaper without hangers on.
I must say, the concept of 'harvesting' energy is continually being brought up by people as if it's the answer to all our energy needs. If there is wasted energy in any process, the best solution by far is usually just to make that process more efficient. The only example that I can think of where this doesn't apply is in Combined Heat and Power systems, in which the Efficiency of the generation system is limited by thermodynamic constraints. In that case, the basic Efficiency is truly disastrous and getting a bit of home heating out of it just ameliorates the situation a bit.
 

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