# Aerodynamic Shape Optimization: Design Principles You Must Know

### Key Takeaways

• What aerodynamic shape optimization is.

• The difference between active and passive control of aerodynamic performance.

• The best design tool capabilities for aerodynamic shape optimization.

Aerodynamic shape of the wing is essential for flight

I have always wanted the opportunity to experience flying at the speeds that military jet pilots do. It must be exhilarating to travel at more than 1,500 mph and do nearly vertical climbs. Feats such as these are only possible due to the work of the engineers and developers that design and build advanced aircraft. These designs require an in-depth understanding of aerodynamic shape optimization and the tools used to design them. In this article, we will discuss aerodynamic shape optimization and the types of aerodynamic control systems.

## What Is Aerodynamic Shape Optimization?

According to Newton’s first law of motion, an object in motion will continue to move uniformly in a straight line unless acted upon by a force that is not adequately balanced with a negating force. This law fundamentally defines the purpose of aerodynamic shape optimization.

 Aerodynamic shape optimization is the term used to describe actions taken to maximize the ability of an object to achieve desired performance or motion by changing or altering its shape.

The actions that may be taken to improve an object’s aerodynamic performance begin with design and include the choice of materials, shape, and whether and how the shape will be controlled while the object is in motion.

## Types of Aerodynamic Control Systems

Optimizing aerodynamic control is a fundamental aerodynamics and fluid mechanics design objective, where the goal is typically to minimize pressure drag and/or prevent boundary layer separation due to changes in fluid flow. There are basically two types of control that can be applied: passive and active.

### Passive Flow Control

Passive flow control systems do not require external energy to operate and are often based on geometrical design. For example, the following are common techniques for airfoils.

#### Passive Aerodynamic Control Systems

• Slat or fixed slat
• Drooped nose
• Krueger flap

Extended Krueger flap example

• Trailing Edge
• Flaps
• Single slotted
• Double slotted
• Triple slotted
• Fowler
• Zap
• Split
• Plain

As the list above indicates, there are many passive technique options that can be used for aerodynamic shape optimization.

### Active Flow Control

Active flow control techniques, listed below, utilize actuators, valves, or some other method of mechanically altering the object’s shape to control the effects of airflow.

#### Active Aerodynamic Control Systems

• Blowing
• Suction
• Trailing Edge
• Circulation control
• Suction
• Slipstream
• Thrust vectoring
• Flaps
• Externally blown
• Augmentor
• Jet
• Coandă jet

Example of the Coandă effect

The Coandă effect (shown above) makes use of the fact that a fluid tends to travel in a convex shape, which can be leveraged to create the pressure difference needed to increase lift. Active control techniques, including the Coandă effect, increase the complexity and costs of system development and production. However, in many cases, the additional flight control and improved safety more than justify these issues.

## Designing for Aerodynamic Shape Optimization

Effective operational control for systems subject to fluid flow changes begins with aerodynamic shape optimization design. The process by which this is incorporated into your design should be a systematic paradigm that covers the important principles listed below:

• Research best material properties.
• Surface smoothness/roughness
• Know and incorporate the system’s operational environment parameters.
• Fluid temperature range
• Fluid pressure range
• Noise levels
• Fluid velocity levels
• Select a control option.
• Active and/or passive
• Technique(s)

It is critical that accurate environmental factors--or at least their ranges--be included. Otherwise, accurate system modeling cannot be achieved and the results obtained may not be applicable to actual online operation.

As for modeling the system, which includes the object or its surface such that boundary conditions can be accurately modeled and analyzed, there are also options. For example, free-form deformation may be employed. The use of this method is grounded in classical mathematics and can be quite useful for modeling simple geometrical shapes using simple splines and b-splines and can be extended to 3-D surfaces. This method is more of a graphics or imaging technique. A statistics-based alternative option is parametric modeling. Here, probability distribution theory is the foundation, and models are created based on the probability of the existence or occurrence of points in certain locations.

Regardless of your specific system design, the best solution method will utilize the principles listed above and should include the capability to perform parametric modeling and/or free-form deformation to create accurate boundary layer conditions that can be applied to your system’s aerodynamic shape optimization.