Experimental Analysis of Dynamic Interaction Between a Centrifugal Compressor and its Casing

Volume 7C: Structures and Dynamics

Legrand

et al. 2018

In turbomachinery, it is well known that tighter operating clearances improve the efficiency. However, this leads to unwanted potential unilateral and frictional contact occurrences between the rotating (blades) and stationary components (casings) together with attendant thermal excitations. Unilateral contact induces discontinuities in the velocity at impact times, hence the terminology nonsmooth dynamics. Current modeling strategies of rotor-stator interactions are either based on regularizing penalty methods or on explicit time-marching methods derived from Carpenter's forward Lagrange multiplier method. Regularization introduces an artificial time scale in the formulation corresponding to numerical stiffness which is not desirable. Carpenter's scheme has been successfully applied to turbomachinery industrial models in the sole mechanical framework, but faces serious stability issues when dealing with the additional heat equation.This work overcomes the above issues by using the MoreauJean nonsmooth integration scheme within an implicit Â-method. This numerical scheme is based on a mathematically sound description of the contact dynamics by means of measure differential inclusions and enjoys attractive features. The procedure is unconditionally stable opening doors to quick preliminary simulations with time-steps one hundred times larger than with previous algorithms. It can also deal with strongly coupled thermomechanical problems.

“…As for the structure, the external load is separated into external fluxes f 7 . This means that each contact occurrence generates a heat flux proportional to the normal contact force.…”

Section: Description Of the Simplified Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nonsmooth Thermoelastic Simulations of Blade-Casing Contact Interactions

Thorin

Volume 7C: Structures and Dynamics

Legrand

et al. 2018

“…Recent experimental campaigns [4,5] have shown the importance of thermomechanical coupling effects during the interaction. However, very little documentation is available [7,8] and thorough numerical investigations have yet to be undertaken.…”

Section: Introductionmentioning

confidence: 99%

“…It is now recognized that such phenomena have to be accounted for in the design in order to avoid premature maintenance operation and therefore excessive operational costs. Several investigations, both numerical [2,3] and experimental [4,5] are devoted to the modelling and understanding of such events. A detailed summary [6] lists recent studies regarding material, thermal and mechanical aspects of rotor-stator rubbing.…”

Section: Introductionmentioning

confidence: 99%

Thermomechanical Component Mode Synthesis for Blade Casing Interaction Prediction

Volume 7B: Structures and Dynamics

Thouverez

Gibert

et al. 2017

Increasing the efficiency of turbomachines is a major concern as it directly translates into lower environmental impact and improved operational costs. One solution is to reduce the bladecasing operating clearance in order to mitigate aerodynamic losses at the unavoidable cost of increased structural unilateral contact and friction occurrences. In centrifugal compressors, the dynamic behaviour of the structures interacting through unilateral contact and friction is not yet fully understood. In fact, the heat generated during such events may affect the dynamics through thermal stresses.This paper presents a complete thermomechanical modelling strategy of impeller rotor and casing, and of blade-tip/casing contact events. A fully coupled thermomechanical modal synthesis technique is introduced and applied to turbomachinery-related models. The blisk is reduced via a hybrid modal synthesis technique combining the Craig-Bampton method and the characteristic constraint mode method. The casing model is reduced using an axisymmetric harmonic modal synthesis. Both strategies involve thermomechanical modes embedding thermal dilatation effects. The contact modelling algorithm is then introduced. It handles unilateral contact and friction occurrences together with heating effects. This algorithm uses the above mentioned reduced-order models as input data to avoid CPU-intensive simulations.The results show that the thermomechanical behaviour of the structures is well preserved by the reduction strategy proposed. Contact simulations on simple cases show qualitative results in accordance with expectations. Further work is needed in order to validate the strategy based on experimental results. However, this methodology opens the way to extended multiphysics simulations of contact events in turbomachinery.

“…Except for reference [5] in which rotor-stator rub induced thermal expansion effects are studied, thermomechanical coupling is ignored in this context. However, thermomechanical coupling was observed to play a significant role in experimental measurements [6,3]. Indeed, heat is generated by friction and wear phenomena during rub events, leading to material expansion, diffusion and convection which induce strains and affect the contact configuration.…”

mentioning

confidence: 99%

Thermomechanical Model Reduction for Efficient Simulations of Rotor-Stator Contact Interaction

Volume 7C: Structures and Dynamics

Thorin

Thouverez

et al. 2018

Turbomachinery rotor-stator unilateral contact induced interactions play a growing role in lifecycle analysis and thus motivate the use of accurate numerical prediction tools. Recent literature confirmed by ongoing in-house experiments have shown the importance of thermomechanical coupling effects in such interactions. However, most available (possibly reduced-order) models are restricted to the sole mechanical aspects. This work describes a reduction technique of thermomechanical models involving unilateral contact and frictional contact occurrences between rotor and stator components. The proposed methodology is grounded on Guyan and Craig–Bampton methods for the reduction of the structural dynamics in conjunction with Krylov subspace techniques, and specifically the Craig–Hale approach, for the reduction of the thermal equations. The method has the capability to drastically reduce the size of the model while preserving accuracy. It stands as a reliable strategy to perform simulations of thermomechanical models with localized mechanical and thermal loads.