Firstly, an improved aero-engine blade casing rubbing model is introduced, in which, the effects of the number of blades and changes in the rotor stator clearance on rubbing forces are considered, the improved rubbing model can simulate rubbing faults for various rubbing conditions, including single-point, multi-point, local-part, and complete-cycle rubbing on the casing and rotor.
Moreover, by establishing the dynamic model of the blade and casing, the dynamic normal rubbing forces are also calculated under the blade-casing rubbing.
The simple Coulomb friction model and the multiple segments linear spring model are used to reveal the nature of the rubbing forces.
Based on this model, the influences of the penetration depth, casing stiffness, friction coefficient, blade physical dimensions (thickness, width and length) on the quasi-static normal rubbing forces are analyzed.
Moreover, the effects of blade types (thin, thick and tapered blades), casing stiffnesses (aluminum and steel casings), penetration depths and rotating speeds on the normal rubbing forces are also evaluated by simulation and experiment.
A matrix of rub tests with blade tip speeds and infeed rates as variables gave rub force and tip wear results.
This yields insights as to the interrelationship between rub force histories, energy levels, rub duration, incidence separation angles, and backward whirl initiation, as well as the overall rotor orbit during successive rubs.
When rub occurs as shown in Figure 2, the radial impact force F N and tangential rub force F T can thus be expressed as [12] F N = 0 for e r < δ e r - δ k s for e r ≥ δ, F T = μ F N (10).
The forces F y and F z are the nonlinear rub forces.
Both components being compliant, time-varying interface characteristics, nonlinearities and uncertainties in the rub forces make this dynamics very complex to model and analyze.
