IntermediateTopic 69 of 105Thermodynamics & Fluids
Similitude and model testing
Scale models match Reynolds, Froude or Mach numbers.
In depth
Models represent prototypes if geometric, kinematic and dynamic similarity hold; match the key dimensionless group: Re for pipes and aerodynamics, Froude for free surfaces, Mach for compressible flow. Distorted models and scale effects arise when not all can match.
Key points
- Scale factors
- Wind tunnels and towing tanks
- Compensate with correction
ExampleA 1:50 ship model is tested at the same Froude number.
Model testing lets engineers predict full-size performance from a scaled version, which is standard for ships, aircraft and hydraulic structures.
What is Similitude and model testing?
Scale models match Reynolds, Froude or Mach numbers.
Why is it important to understand similitude and model testing?
Model testing lets engineers predict full-size performance from a scaled version, which is standard for ships, aircraft and hydraulic structures.
What is dynamic similarity?
Models and prototypes have matching dimensionless numbers, such as Reynolds for viscous flows and Froude for free-surface flows.
Why can't you match all the numbers at once?
Scaling is often limited because matching one number may mismatch another, so compromises or corrections are needed.
How is Similitude and model testing used in practice?
Typical applications include testing a scale model of a ship hull in a towing tank using Froude scaling, predicting the airflow around a full-size car from a wind tunnel model and scaling the hydraulic performance of a spillway from a physical model.
What should I learn before Similitude and model testing?
Study "Dimensional analysis in fluids" first (topic 68 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Similitude and model testing?
Scale factors. Wind tunnels and towing tanks. Compensate with correction.
Can you give an example of Similitude and model testing?
A 1:50 ship model is tested at the same Froude number.
What comes after Similitude and model testing?
The next topic is "Boundary layer", which builds directly on this one.
How difficult is Similitude and model testing?
It is classed as Intermediate in Thermodynamics & Fluids (topic 69 of 105). It is an intermediate topic. Work through the beginner topics in Thermodynamics & Fluids first.