Simone Salvadori

Whispering Gallery Mode Aptasensors for Detection of Blood Proteins

Whispering gallery mode resonators (WGMR), as silica microspheres, have been recently proposed as an efficient tool for the realisation of optical biosensors. In this work we present a functionalization procedure based on the DNA-aptamer sequence immobilization on WGMR, able to recognize specifically thrombin or VEGF protein, preserving a high Q factor. The protein binding was optically characterized in terms of specificity in buffer solution or in 10% diluted human serum. Simulation of the protein flow was found in good agreement with experimental data. The aptasensor was also chemically regenerated and tested again, demonstrating the reusability of our system.

Uncertainty Quantification: A Stochastic Method for Heat Transfer Prediction Using LES

In Computational Fluid Dynamics (CFD) is possible to identify namely two uncertainties: epistemic, related to the turbulence model, and aleatoric, representing the randomunknown conditions such as the boundary values and or geometrical variations. In the field of epistemic uncertainty, Large Eddy Simulation (LES and DES) is the state of the art in terms of turbulence closures to predict the heat transfer in internal channels. The problem concerning the stochastic variations and how to include these effects in the LES studies is still open. In this paper, for the first time in literature, a stochastic approach is proposed to include these variations in LES. By using a classical Uncertainty Quantification approach, the Probabilistic Collocation Method is coupled to Numerical Large Eddy Simulation (NLES) in a duct with pin fins. The Reynolds number has been chosen as a stochastic variable with a normal distribution. It is representative of the uncertainties associated to the operating conditions, i.e. velocity and density, and geometrical variations such as the pin fin diameter. This work shows that by assuming a Gaussian distribution for the value of Reynolds number of +/-25%, is possible to define the probability to achieve a specified heat loading under stochastic conditions, which can affect the component life by more than 100%. The same method, applied to a steady RANS, generates a different level of uncertainty. This procedure proves that the uncertainties related to the unknown conditions, aleatoric, and those related to the physical model, epistemic, are strongly interconnected. This result has directed consequences in the Uncertainty Quantification science and not only in the gas turbine world. Copyright

Geometrical Uncertainty and Film Cooling: Fillet Radii

This study presents an investigation of the impact of filleted edges variations on heat transfer. In real gas turbines, sharp edges are an approximation, because of manufacturing tolerances and/or geometrical modifications occurring during operation. The value of fillet radius is not exactly known a priori. It can be assumed that a specific radius occurs with a probability following a probabilistic distribution. For this reason, the effect of variation of the filleted edge on internal channel of a film cooling configuration has been studied numerically using an in house solver. The hole exit is fan-shaped and the feeding duct axis and the main stream are perpendicular to each other. A response surface has been generated varying the internal Mach number of coolant and the pressure ratio range between coolant and main gas. Four fillets radii for the internal duct have been analysed, r/D=0.0-5%. A Gaussian distribution for the fillet radius has been assumed. Using the over mentioned distributions it is possible to obtain the probabilistic functions of the corresponding discharge coefficient, C d, and adiabatic effectiveness, h. The overall variation of C d and h can be more than 10% the value without fillet. Furthermore the differences on Cd due to the uncertainties on fillet radius are bigger than those obtained modifying the exit duct shape (i.e. from cylindrical to fanshaped). This paper shows that the effect of variation of fillet radii must be included in numerical simulations. This has direct consequences on LES and DNS simulations, which normally include sharp corners or mean radii. A probabilistic approach must be included in the analysis of the results and the equivalent fillet radius assumed instead.

Uncertainty quantification in computational fluid dynamics and aircraft engines

Introduction to jet engine reliability and safety.- Impact of manufacturing deviations on jet engine life and performance.- Introduction to Uncertainty Quantification in Computational Fluid Dynamics: Monte Carlo Simulation and Polynomial Chaos Expansions.- The matrix of knowledge in CFD: deterministic simulations, turbulence closures, uncertainty quantification and black swans.- Robust design and optimization under uncertainty.- Future directions.

Conjugate Heat Transfer Analysis of a Film Cooled High-Pressure Turbine Vane Under Realistic Combustor Exit Flow Conditions

In this paper conjugate heat transfer analysis of the cooled vane of the MT1 research high-pressure stage is presented. Inlet boundary conditions (including non-uniform total temperature, non-uniform total pressure, swirl, turbulence intensity and turbulence length scale) are obtained considering the exit flow field of a reactive annular combustor simulator. The combustor model has been designed in order to reproduce data available in literature about exit profiles of real combustion chambers and other combustor simulators. Steady simulations are performed on a hybrid unstructured grid obtained from a grid dependence study. The transitional kT-kL-ω model by Walters and Cokljat is used as turbulent closure. Thermal fields obtained from CHT analysis of the vane considering two different clocking positions with respect to the combustor are compared. Results, including film cooling parameters and High-Pressure Vane aerodynamics, are also compared with a uniform inlet case showing the crucial importance of considering realistic boundary conditions for thermal analysis of turbine components.Copyright

Optical fibre nanotips fabricated by a dynamic chemical etching for sensing applications

Nanoprobe tips are key components in many applications such as scanning probe microscopes, nanoscale imaging, nanofabrication and sensing. This paper describes a dynamic chemical etching method for the fabrication of optical nanoprobes. The tips are produced by mechanically rotating and dipping a silica optical fibre in a chemical etching solution (aqueous hydrofluoric acid) covered with a protection layer. Using different dynamic regimes of the mechanical movements during the chemical etching process, it is possible to vary the cone angle, the shape, and the roughness of the nanoprobes. It is found that the tip profiles are determined by the nonlinear dynamic evolution of the meniscus of the etchant near the fibre. Computational fluid dynamic simulations have been performed, showing that different flow regimes correspond to different shear forces acting on the forming nanotip, in agreement with experimental results. With this method, a high yield of reproducible nanotips can be obtained, thus overcoming ...

Simulation of Combustor/NGV Interaction Using Coupled RANS Solvers: Validation and Application to a Realistic Test Case

Numerical techniques are commonly used during both design and analysis processes, mainly considering single components. Technological progress asks for advanced approaches that include real-machine conditions and analyze components interaction, especially considering the combustor/turbine coupling. Modern combustors operate with strong swirl motions in order to obtain an adequate flame stabilization, generating a very complex flow field characterized by high turbulence level. These aspects affect performance of downstream components which are subjected to very aggressive inlet flow conditions: non-uniform total temperature, non-uniform total pressure, swirl and high turbulence intensity. For these reasons coupled analysis of combustor and turbine is necessary to accurately predict aero-thermal aspects that influence performance and reliability of these two components.From a numerical point of view the simulation of a single domain characterized by a reactive flow with very different Mach number regimes (from low-Mach flow in combustion chamber to transonic flow in turbine) is problematic due to the different numerical requirements needed, especially concerning stability and accuracy. These problems could be overcome using coupled methods to simultaneously simulate combustor and turbine in separated domains which are managed by different solvers that communicate with each other.A coupling method for the study of combustor/turbine interaction using the RANS methodology is proposed. In the first part of the paper the method is described and validated. The second part is dedicated to the application of the proposed coupling methodology to a realistic test case consisting of a model annular combustor and the Nozzle Guide Vane (NGV) of the MT1 high-pressure turbine stage. A commercial solver and an in-house code are respectively used for the simulation of combustor and NGV.Results are presented and analyzed highlighting the importance of such type of simulations in understanding aero-thermal phenomena that characterize combustor/vane interaction.Copyright

Hybrid RANS-LES Modeling of a Hot Streak Generator Oriented to the Study of Combustor-Turbine Interaction

Turbine entry conditions are characterized by unsteady and strongly non-uniform velocity and temperature and pressure fields. The uncertainty and the lack of confidence associated to these conditions require the application of wide safety margins during the design of the turbine cooling systems, which are detrimental for the efficiency of the engine. These issues have been further complicated by the adoption of lean-burn technology in modern aeroengines, identified by many manufacturers as the most promising solution for a significant reduction of NOx emission. Such devices are in fact characterized by a very compact design, whereas the strong swirl component generated by the injector is maintained up to the end of the flametube due to the absence of dilution holes, which in conventional combustors provides the required pattern factor.Bearing in mind complexity and costs associated to the experimental investigation of combustor-turbine interaction, CFD has become a key and complementary tool to understand the physical phenomena involved. Due to the well-known limitations of the RANS approach and the increase in computational resources, hybrid RANS-LES models, such as Scale Adaptive Simulation (SAS), are proving to be a viable approach to resolve the main structures of the flow field.This paper reports the main findings of the numerical investigation of a hot streak generator for the study of combustor-turbine interaction. The results were compared to experimental data obtained from a test rig representative of a lean-burn, effusion cooled, annular combustor, developed in the context of the EU project FACTOR. Steady RANS and unsteady SAS runs were carried out in order to assess the improvements related to hybrid models. Additional simulations were performed to investigate the effect of the periodicity assumption and the impact of liner cooling modelling on the exit conditions.Copyright

Methodology for the Residual Axial Thrust Evaluation in Multistage Centrifugal Pumps

Abstract One of the most challenging aspects in horizontal pumps design is the evaluation of the residual axial thrust acting on the rotating shaft. The thrust is affected by pump characteristics and working conditions. Solving this problem is easier for a single stage pump than for multistage pumps, even in partially self-balancing opposite impeller configuration. The challenge is then to individuate a procedure that will provide the residual thrust value with a moderate computational effort, dealing with the industrial requests of accuracy and reduced time consumption. A procedure is proposed, which consists in the numerical simulation of each pump component. For each component, the obtained mass-flow/thrust correlations are coupled by using a momentum balance equation used to calculate the axial thrust as a function of the working conditions. The main topic in multistage pump modeling is the leakage flows characterization by means of accurate numerical analysis. Therefore, the cavity flows behavior is investigated and the flow structures individuated. The numerical investigation of the pump’s components provides also a thorough knowledge of fluid dynamic fields. The proposed procedure is able to predict both the direction and the variation of the thrust in a selected range of flow rates, while the value of the thrust is affected by a non-negligible error generated by “real machine” effects.

Experimental and Numerical Investigation on the Influence of Trailing Edge Bleeding on the Aerodynamics of a NGV Cascade

A series of tests on a specific designed linear nozzle guide vane (NGV) cascade with trailing edge coolant ejection was carried out to investigate the influence of the trailing edge bleeding (TEB) on the loss behaviour of the profile. Wake traverses with a five-hole probe and measurements of the pressure distribution on the profile were taken varying the ejection rate under reference main flow conditions, namely Re2 th = 1.056·10 6 and Ma2 th = 0.8 (Re2 th based on the true chord). Wake total pressure losses and isentropic Mach number distributions on the profile were compared to measurements without coolant ejection, showing a significant influence of the TEB both on the wake development and on the flow in the vane passage. Numerical simulations of the experiments showed good agreement with the measured data and provided a deeper understanding of the flow phenomena, revealing the differences in the development of the wake with and without trailing edge coolant ejection and illustrating the blockage effect of the TEB on the flow in the vane passage.Copyright