A Variational Multiscale Method for Particle Dispersion Modeling in the Atmosphere

A LES model is proposed to predict the dispersion of particles in the atmosphere in the context of Chemical,Biological,Radiological and Nuclear(CBRN)applications.The code relies on the Finite Element Method(FEM)for both the fluid and the dispersed solid phases.Starting from the Navier-Stokes equations and a general description of the FEM strategy,the Streamline Upwind Petrov-Galerkin(SUPG)method is formulated putting some emphasis on the related assembly matrix and stabilization coefficients.Then,the Variational Multiscale Method(VMS)is presented together with a detailed illustration of its algorithm and hierarchy of computational steps.It is demonstrated that the VMS can be considered as a more general version of the SUPG method.The final part of the work is used to assess the reliability of the implemented predictor/multicorrector solution strategy.

Impact of Clocking on the Aero-Thermodynamics of a Second Stator tested in a One and a Half Stage HP Turbine

This paper focuses on the experimental investigation of the time-averaged and time-accurate aero- thermodynamics of a second stator tested in a 1.5 stage high-pressure turbine. The effect of clocking on aerodynamic and heat transfer are investigated. Tests are performed under engine representative conditions in the VKI compression tube CT3. The test program includes four different clocking positions, i.e. relative pitch-wise positions between the fh-st and the second stator. Probes located upstream and downstream of the second stator provide the thermodynamic conditions of the flow field. On the second stator airfoil, measurements are taken around the blade profile at 15, 50 and 85% span with pressure sensors and thin-film gauges. Both time-averaged and time-resolved aspects of the flow field are addressed. Regarding the time-averaged results, clocking effects are mainly observed within the leading edge region of the second stator, the largest effects being observed at 15% span. The surface static pressure distribution is changed locally, hence affecting the overall airfoil performance. For one clocking position, the thermal load of the airfoil is noticeably reduced. Pressure fluctuations are attributed to the passage of the up- stream transonic rotor and its associated pressure gradients. The pattern of these fluctuations changes noticeably as a function of docking. The time-resolved variations of heat flux and static pressure are analyzed together showing that the major effect is due to a potential interaction. The time-resolved pressure distribution integrated along the second stator surface yields the unsteady forces on the vane. The magnitude of the unsteady force is very dependent on the clocking position.

Conservative Residual Distribution Method for Viscous Double Cone Flows in Thermochemical Nonequilibrium

Amulti-dimensionally upwind conservative ResidualDistribution algorithm for simulating viscous axisymmetric hypersonic flows in thermo-chemical nonequilibrium on unstructured grids is presented and validated in the case of the complex flowfield over a double cone configuration.The resulting numerical discretization combines a state-of-the-art nonlinear quasi-monotone second order blended scheme for distributing the convective residual and a standard Galerkin formulation for the diffusive residual.The physical source terms are upwinded together with the convective fluxes.Numerical results show an excellent agreement with experimental measurements and available literature.

A Similitude Method and the Corresponding Blade Design of a Low-Speed Large-Scale Axial Compressor Rotor

A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper.The first step of this method is the derivation of similarity criteria for tip clearance flow,on the basis of an inviscid model of tip clearance flow.The aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor rotor.According to the aerodynamic and geometric parameters of the target compressor rotor,a large-scale low-speed rotor blade is designed with an inverse blade design program.In order to validate the similitude method,the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate points.It is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed model.These results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.

Experimental and Numerical Investigation of the Flow in Rotating Diverging Channels

This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the Coriolis forces on the flow in radial rotating channels. Operating conditions correspond to the flow in radial impellers for micro gasturbine applications. A comparison of detailed flow measurements with CFD resuits indicates that Navier Stokes solvers with standard k-ω and SST turbulence models predict the flow surprisingly well and that no extra corrections for Coriolis forces are required at these operating conditions

Conjugate Heat Transfer Characterization in Cooling Channels

Cooling technology of gas turbine blades,primarily ensured via internal forced convection,is aimed towards withdrawing thermal energy from the airfoil.To promote heat exchange,the walls of internal cooling passages are lined with repeated geometrical flow disturbance elements and surface non-uniformities.Raising the heat transfer at the expense of increased pressure loss;the goal is to obtain the highest possible cooling effectiveness at the lowest possible pressure drop penalty.The cooling channel heat transfer problem involves convection in the fluid domain and conduction in the solid.This coupled behavior is known as conjugate heat transfer.This experimental study models the effects of conduction coupling on convective heat transfer by applying iso-heat-flux boundary condition at the external side of a scaled serpentine passage.Investigations involve local temperature measurements performed by Infrared Thermography over flat and ribbed slab configurations.Nusselt number distributions along the wetted surface are obtained by means of heat flux distributions,computed from an energy balance within the metal domain.For the flat plate experiments,the effect of conjugate boundary condition on heat transfer is estimated to be in the order of 3%.In the ribbed channel case,the normalized Nusselt number distributions are compared with the basic flow features.Contrasting the findings with other conjugate and convective iso-heat-flux literature,a high degree of overall correlation is evident.

Experimental Characterization of the Supersonic Transitional Wake Downstream of a Single Roughness Element

An experimental campaign was carried out to investigate the characteristics of the transitional supersonic wake downstream of a single roughness element. Two Mach numbers were tested, 1.6 and 2.3, and two roughness heights, 0.1 mm and 1 mm. Unsteady and steady wall temperature measurements were taken along and across the roughness wake. The spatial trends of adiabatic wall temperature and heat flux, and the spectral time evolution of temperature were documented in this paper. The initial wall temperature was varied during the temperature measurements, and the resulting steady and unsteady effects on the roughness wake were investigated. The streamwise trends of heat-flux and adiabatic-wall temperature confirmed the transitional nature of the roughness wake. Spectral analysis showed that roughness height and initial wall temperature had the same type of effect on the wake wall-temperature fluctuations. The effect of roughness height was more sensible at Mach 2.3, and that of the initial wall temperature was more evident with the smallest roughness also tested at Mach 2.3.

Solving PDEs with a Hybrid Radial Basis Function:Power-Generalized Multiquadric Kernel

Radial Basis Function(RBF)kernels are key functional forms for advanced solutions of higher-order partial differential equations(PDEs).In the present study,a hybrid kernel was developed for meshless solutions of PDEs widely seen in several engineering problems.This kernel,Power-Generalized Multiquadric-Power-GMQ,was built up by vanishing the dependence of e,which is significant since its selection induces severe problems regarding numerical instabilities and convergence issues.Another drawback of e-dependency is that the optimal e value does not exist in perpetuity.We present the Power-GMQ kernel which combines the advantages of Radial Power and Generalized Multiquadric RBFs in a generic formulation.Power-GMQ RBF was tested in higher-order PDEs with particular boundary conditions and different domains.RBF-Finite Difference(RBF-FD)discretization was also implemented to investigate the characteristics of the proposed RBF.Numerical results revealed that our proposed kernel makes similar or better estimations as against to the Gaussian and Multiquadric kernels with a mild increase in computational cost.Gauss-QR method may achieve better accuracy in some cases with considerably higher computational cost.By using Power-GMQ RBF,the dependency of solution on e was also substantially relaxed and consistent error behavior were obtained regardless of the selected e accompanied.