(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

The drag force F on a car depends upon its speed V, length L, the density ρ of the air

and the dynamic viscosity of the air µ . Show that this statement regarding five

physical quantities can be re-written in terms of two independent non-dimensional

groups. Preferably using the method of sequential elimination of dimensions, find two

appropriate non-dimensional groups

I have got my two non- dimensional groups as (Dρ/µ^2) and (ρVL/µ)

FOR THE SECOND PART (BELOW) I AM UNSURE ON HOW TO ACHIEVE THE AIRSPEED IN THE TUNNEL

A car being developed for the Le Mans 24 Hour Endurance Race is to have a top speed

of 230 mph assuming an air density of 1.2kg/m^3 and dynamic viscosity of 1.9 x 10^-5

Pa.s. Tests carried out on a 1/4-scale model car in a pressurized and cooled wind tunnel

in which the air density is 5kg/m^3 and the dynamic viscosity is 1.1 x 10^-5

Pa.s give a drag force of 469 N. What must be the airspeed in the wind tunnel for dynamic similarity (at top speed for the full-size car)? Calculate the drag force on the full size car

and the power needed to run at top speed.

2. Relevant equations

3. The attempt at a solution

for part a i have the two non dimensional groups shown above and for part (b) I have worked out the drag force using the equation

Df= (ρm/ρf)* (μf/μm)^2 * Dm

(f= full scale, m= model)

It would be of great help if someone could help me understand how to calculate the windspeed and power needed?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Fluid mechanics- Dimensional analysis

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**