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This study is concerned with the analyses of heat transfer through an exhaust valve considering the real unsteady effects during the cycle of an internal combustion engine and to identify the factors and parameters affecting the heat transfer. The valve is segmented into several zones to facilitate incorporating the boundary conditions and evaluating the heat transfer coefficient and the adiabatic wall temperature based on the finite element method. The unsteady simulations were carried out using ANSYS-APDL for the proposed thermal model. The effect of lubricating oil and the contact resistance between guide and engine block and the thermal contact between exhaust valve and seat are included, as well as the differential displacement of both the guide and engine block walls due to high working temperature. The averaged values of heat transfer coefficient and adiabatic wall temperature used in the boundary conditions are shown to underestimate the temperature maps. The cyclic boundary conditions required more run time to reach the steady state and allowed better monitoring of the thermal process. The thermal contact resistance has the main contribution in the zone of valve-seat, whereas the resistance of oil film between the guide and stem valve is shown to affect mainly heat transfer coefficient. The obtained maps of temperature reveal the locations of maximum temperatures in the exhaust valve.

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The erosion of an axial fan was investigated, both theoretically and experimentally. A computer program was developed to predict particle trajectories and erosion through turbomachines. It also accounts for different boundary conditions and stage interfaces. The governing equations of the particle motion were solved using Runge-Kutta Fehlberg technique in a given flowfield. The tracking of particles and their locations are based on the finite element interpolation method. The methodology was applied to an axial fan with inlet guide vanes (IGV). The flowfield was solved using the TASCflow code. The number of particles seeded upstream of the IGV was determined from experimentally measured profile concentration, with respect to a random distribution of particle sizes. The erosion of the blades and changes to the chord and tip clearances were also measured. The concentration profiles and velocities of the particle were measured with a laser transit anemometer and used as input to the trajectory code. The fan performance was measured before and after sand ingestion to assess the degradation in performance due to the eroded geometry

Aero-engines operating in dusty environments are subject to ingestion of erodent particles leading to erosion damage of blades and a permanent drop in performance. This work concerns the study of particle dynamics and erosion of the front compression stage of a commercial turbofan. Particle trajectories simulations used a stochastic Lagrangian tracking code that solves the equations of motion separately from the airflow in a stepwise manner, while the tracking of particles in different cells is based on the finite element method. As the locations of impacts and rates of erosion were predicted, the subsequent geometry deteriorations were assessed. The number of particles, sizes, and initial positions were specified conformed to sand particle distribution (MIL-E5007E, 0-1000 micrometers) and concentrations 50–700 mg/m3. The results show that the IGV blade is mainly eroded over the leading edge and near hub and shroud; also the rotor blade has a noticeable erosion of the leading and trailing edges and a rounding of the blade tip corners, whereas in the diffuser, erosion is shown to spread over the blade surfaces in addition to the leading edge and trailing edge.

An experimental investigation was conducted to study the effects of sand ingestion on an axial fan with an upstream guide vane (contra-whirl). The experimental work was divided into two types of testing. Firstly, local injection tests were carried out to generate qualitative erosion patterns in order to validate a trajectory code. Secondly, global sand injection tests were carried out in order to assess the geometry deterioration and the subsequent degradation in the axial fan aerodynamic characteristics. Two types of particle were used; a narrow size bandwidth sand (150 -300 mm) and MIL-E5007E sand (0 -1000 mm). In all sand injection tests the fan operated near design point at a constant speed of rotation.

Centrifugal compressors are required to increase their operating range and efficiency, which are limited at low mass flow rates by the rotating stall and surge. This paper presents a surrogate-based multi-objective optimization of a centrifugal compressor to improve its efficiency and stall margin. Curvatures of the blade, the impeller shroud, and the diffuser hub are selected as optimization parameters since they influence highly both the efficiency and the stall limit. The implemented optimization procedure starts by the construction of a metamodel, which is the radial basis function that uses a database composed of a well-selected set of geometries and their corresponding computational fluid dynamics predicted objectives using the Ansys-CFX 12 code. The NSGA-II optimization algorithm is used afterward to search the Pareto front based on radial basis function approximations. To improve the accuracy of the radial basis function and subsequently the Pareto front, a database refinement is sequentially achieved, using the leave-one-out-cross-validation uncertainty to select infill points. The present procedure is tested on the NASA lowspeed centrifugal compressor, showing its ability to increase both the compressor operating range and efficiency. Furthermore, the flow pattern analysis confirms the suppression of separations that lead to instability in the optimized compressor at the stall point of the baseline design.

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