Numerical Mechanics Applications International (Belgium)

The prediction of the onset of cavitation to allow investigations of the flow in off-design conditions during design is unavoidable for a variety of applications. Numerical modeling of the cavitation phenomena is however computationally challenging due to the nature of the phenomena. High density ratios, steep pressure gradients, the presence of multiple phase including phase change and hence to occurrence of real gas thermophysical behavior would cause a computational effort unmanageable during design. Today’s models are therefore greatly simplified representations of the reality. Conservation equations are usually solved using a mixture approach with flow properties being a volume fraction weighted average of two incompressible fluids thus neglecting real gas effects. The source term from the phase exchange however usually poses significant stability problems. In this article we will therefore present an approach for cavitation modeling using high-order polynomial real-gas state equations to accurately predict the properties of water at any state. Computational performance is improved by the use of structured tabulation using high order interpolation methods. The numerical results are then compared against measurement data and conventional cavitation model results.

Simultaneous operational and geometrical uncertainties are quantified on a 1.5-stage axial compressor (stator-rotor-stator) with leakage flows. The compressor geometry and operational conditions are provided by Safran Aero Boosters. Uncertainties include the mass flow rates of the leakage flows, the tip gap size of the rotor, and the correlated profiles for the main inflow conditions. In total nine uncertainties are propagated by the nonintrusive probabilistic collocation method available within FINE/Design3D. Uncertainties are quantified for the nominal design point as well as for two off-design operating points, close to stall and choke conditions, respectively. The non-deterministic response is analyzed and discussed in detail. It is shown that a sensitivity study, by means of scaled sensitivity derivatives, allows identifying the most influential uncertainties in the operation of this 1.5-stage compressor.

Abstract Modern HP turbine stages consist of highly loaded aerofoils, including transonic and even supersonic flow regions. In terms of stators a normal shock wave in the passage throat chokes the flow, stabilizing the flow conditions at the operating point. In addition to these flow phenomena, the strong acceleration along the early suction side leads to a relaminarisation of the flow, which in turn has a strong impact on the size of the shock induced separation bubble. Finally, the injection of film coolant via rows of cooling holes further influences the boundary layer state. As heat transfer and film cooling effectiveness are of crucial importance in high pressure turbines, an in-depth understanding of transition mechanisms is needed for a competitive design. The main objective was to study transition location effects (from natural transition to fully turbulent) on separation size, shock structure and unsteadiness. The transition interaction with cooling flow was a real challenge for the TFAST project. This research delivered new knowledge, which is crucial for further improvement of HP turbine stages. As transition control devices AJVG and disturbance strip were used.

A one-pot, two-step method for the preparation of degradable PEG is here presented. The full process addresses the requirements imposed by green chemistry and involves the use of a single and nontoxic non-eutectic mixture of organocatalysts. The strategy relies on the polycondensation of PEG800 after its functionalization by bio-derived 5-membered γ-butyrolactone.

The application of uncertainty quantification (UQ) techniques in the daily engineering practice requires a toolchain that can be used intuitively by a wide range of design engineers. Ideally, this toolchain does not require detailed knowledge of the underlying UQ methods and is highly automated to ease the design tasks of the engineer using it. Such an automated chain is proposed in FINETM, where the user input is limited to the selection of the input uncertainties and a decision on the needed output. The steps of a fully automated UQ chain from simulation set-up, geometry modification, re-meshing and post-processing are detailed in this chapter.