Esteban Valencia

Methodology to assess the performance of an aircraft concept with distributed propulsion and boundary layer ingestion using a parametric approach

The performance benefits of boundary layer ingestion in aircraft with distributed propulsion have been extensively studied in the past. These studies have indicated that propulsion system integration issues such as distortion and intake pressure losses could mitigate the expected benefits. This paper introduces and develops a methodology that enables the assessment of different propulsion system designs, which are optimized to be less sensitive to the effects of the aforementioned issues. The study models the propulsor array and main engine performance at design point using a parametric approach, and further at component level, the study focuses on identifying optimum propulsor configurations, in terms of propulsor pressure ratio and BL capture sheet height. At a system level, the study assesses the effects of splitting the thrust between the propulsor array and main engines. The figure of merit used in the optimization is the TSFC. The suitability of the concepts is further assessed using performance predictions for HTS electrical motors. For the purpose of this study, the NASA N3-X aircraft concept is selected as baseline configuration, where the different propulsion designs are tested. As the study focuses on performance assessment of the propulsion system, sizing implication issues and aircraft performance installations effects have not been included in the analysis. The results from the parametric analysis corroborated previous studies regarding the high sensitivity of the propulsion system performance to intake losses and BL inlet conditions. As the study found low-power consumption configurations at these operating conditions, this may be considered as a major issue. The system analysis from the study indicated that splitting the thrust between propulsors and main engines results in improved system efficiency with beneficial effects in fuel savings. When a 2% increase in intake pressure losses and a similar reduction in fan efficiency were assumed due to boundary layer ingestion, the study found an optimum configuration with 65% of thrust delivered by the propulsor array. To summarize, the present work built on past research further contributes to the field through the inclusion of the thrust split as a key variable in the propulsion system design. The thrust split, when introduced, enabled reduction of the detrimental effects of intake losses on the overall system performance. Additionally, as it reduces the power required for the propulsor array, it is expected to reduce the operating power of HTS and cooling systems and therefore improve the effectiveness of the concept.

Design point analysis of the turbofan-driven turboelectric distributed propulsion system with boundary layer ingestion:

The performance benefits of boundary layer ingestion in the case of air vehicles powered by distributed propulsors have been documented and explored extensively by previous study. However, the increased inlet flow distortion and the system total weight would dramatically reduce the expected benefits. In this paper, a novel turboelectric distributed propulsion module on the N3-X airframe has been developed. It includes two direct-shaft-driven turbofans (each drives a free power turbine) and a propulsors array, and therefore both the direct-shaft-driven turbofan and the propulsors unit produce thrust. Secondly, a parametric and quasi two-dimensional study at component and at system level is carried out so that the effects of these two aerodynamic issues over the system performance can be assessed. The figure of merit in this study is the thrust-specific fuel consumption and the system parameters examined are: the thrust split between propulsors and engines, the capture height and the direct-shaft-driven turbofan parameters. Preliminary results found optimum configurations at around 60–90% thrust split ratio, when installation effects were neglected. The final value depends on the propulsor intake pressure loss and the bypass ratio of the propulsion system.

Sediment Erosion Prediction for a Francis Turbine Based on Liquid-Solid Flow Simulation Using Modified PANS

A challenge in the prediction of the sediment erosion is the proper estimation of the motion and velocity of the solid particles, where Reynolds average Navier-Stokes (RANS) methods show limited resolution to determine the motion of solid phase affected by flow fluctuations. The present study adopts a modified partially averaged-Navier Stokes (PANS) method to analyse the sediment erosion prediction for Francis turbines. Numerical simulations were carried out to obtain liquid-solid two-phase flow information in entire flow passage of a Francis turbine using Eulerian-Lagrangrian approach. The hydraulic performance such as efficiency and discharge of the turbine achieved experimentally, are used to validate the present simulation method. The results show that the modified PANS model can improve the prediction accuracy and the smallest unresolved-to-total ratio of turbulence kinetic energy, fk, decided with the consideration of the difference between local average grid size and smallest grid size shows a slight accuracy improvement. Based on the two-phase flow field, sediment erosion was predicted in stay vane, guide vane and runner using a semi-empirical equation obtained from an erosion experiment of liquid-solid flow. It is noted that higher physical resolution captured by the turbulence model causes a diminution of the sediment erosion predicted. Further, the numerical simulation reveals that sediment erosion in stay vane is lower than guide vane and runner, whereas the highest values of the erosion intensity occurs in the runner. The sediment erosion due to fine solid particles in the turbine is mainly resulted from cutting. However, high sediment erosion due to deformation is also produced at the leading edges of stay vane and guide vane.

Numerical simulation of cavitation erosion on a NACA0015 hydrofoil based on bubble collapse strength

The prediction of erosion under unsteady cavitation is crucial to prevent damage in hydraulic machinery. The present investigation deals with the numerical simulation of erosive partial cavitation around a NACA0015 hydrofoil. The study presents the calculation of the bubble collapse strength, Sb, based on the bubble potential energy to identify the surface areas with highest risk of damage. The results are obtained with a numerical scheme assuming homogeneous mixture flow, implicit LES and Zwart cavitation model. The 3D unsteady flow simulation has been solved using OpenFOAM. Python language and OpenFOAM calculator (foamCalcEx) have been used to obtain and represent Sb. The obtained results clearly show the instants of erosive bubble collapse and the affected surface areas.