Mehdi Vahdati - Imperial College London - Review of Computational Aeroelasticity of Turbomachines

Aeroelasticity is a branch of applied mechanics that studies the interactions between the inertial, elastic and aerodynamic forces while an elastic body is exposed to fluid flow. In other words:

‘How does a solid body react to fluid forces acting on it, and how does the flow change in response?’

Unsteady turbulent high-speed compressible flows often give rise to complex aeroelasticity phenomena by influencing the dynamic behaviour of the structures on which they act. Under certain conditions, the energy transfer from the fluid to the structure can cause excessive vibration levels and structural integrity may be compromised. The problem is particularly severe for gas turbines where virtually all blade rows are susceptible to aeroelasticity effects either by inherent self-induced motion (flutter and buffet) or by response to aerodynamic flow distortions and blade wakes (forced response). Along with foreign object damage (FOD), High-Cycle Fatigue (HCF) vibration of aerofoils from Fluid-Solid Interactions (aeroelastic excitation) is a major concern for the safety and reliability of all turbomachinery.

With demands for reduced greenhouse gas emissions, the need for cleaner more efficient turbine technology has become critical. To achieve significant improvements in fuel efficiency new novel design concepts are required. The new concepts will usually involve higher aerodynamic loading with lighter and more flexible structures, and hence are more prone to aeroelastic issues. Aeroelastic tests are expensive (specially in case of failure) and moreover, provide a limited amount of data in time and space. Hence alternative methods are required. The objective of this lecture is to present aeroelasticity issues and numerical modelling techniques for turbomachinery.

The outline of the lecture is :

1. What is aeroelasticity ?

2. Examples of aeroelastic events

3. Explain aeroelastic phenomena using a 2D airfoil

4. Basic mechanical vibration

5. Prediction methods for aeroelasticity (Rig test, CFD, Data Driven)