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A CFD simulation methodology for the inclusion of the post-impact trajectories of splashing/bouncing Supercooled Large Droplets (SLDs) and film detachment is introduced and validated. Several scenarios are tested to demonstrate how different parameters affect the simulations. Including re-injecting droplet flows due to splashing/bouncing and film detachment has a significant effect on the accuracy of the validations shown in the article. Validation results demonstrate very good agreement with the experimental data. This approach is then applied to a full-scale twin-engine turboprop to compute water impingement on the wings and the empennage.

This paper details the process involved in the numerical optimisation of a helicopter engine inlet electrothermal ice protection system. Although the process was developed using a production aircraft, it is demonstrated here using a generic intake and flight conditions, due to confidentiality of the actual design. The process includes adherence to the overall system design objectives (maximum power demand), including tolerances required to account for an industrial system (aircraft voltage variation, manufacturing tolerances). The numerical optimisation was performed using a combination of 2D and 3D methods to define the required heated area, power density, locations and settings for temperature control sensors. The use of 2D design tools allows a rapid iteration process to be performed, leading to the possibility of a higher level of optimisation within the allowable time-frame compared to the use of full 3D methods.

This paper presents the basic test data obtained from tests of a cabin air distribution system in a simulated Space Station Man-Tended Capability (MTC) configuration and correlations of some of this data with the results from analytical modeling of the test setup flow conditions. The MTC configuration simulated in the test setup includes: Lab-A, the Node, the Cupola, and the Pressurized Module Adaptor (PMA). The test data and analytical data presented are confined to those for the Lab module. The cabin air distribution system controls the flow of air in the open space of a Space Station module. In order to meet crew comfort criteria the local velocities for this cabin air are required to be distributed within a specified range with upper and lower limits.

This paper presents the results of a study in which the free rolling behavior of a F-16 tire was numerically modeled. The tire contact patch normal and shear stresses as well as the displacement distributions were obtained from a three dimensional finite element computer program used at the Wright-Patterson Air Force Base, Ohio. It is shown how the predicted deflections are in reasonable agreement with the rated load vs. deformation characteristics, while predicting the effective rolling radius using a theoretical solution. A significant development of this work is the formulation and execution of a finite difference algorithm to evaluate the contact patch slip velocity distribution by methodically manipulating the above computer program results. Slip velocities are then utilized in assessing the rate of slip energy generation at the contact patch, which directly contributes to tire wear. Finally, it is shown how even a low brake slip ratio can increase the contact patch slip energy.

Sealant is applied between joined aircraft parts in the final stage of the assembly, before installation of permanent fasteners. In this paper a novel approach for aircraft assembly simulation is suggested, which allows to resolve the transient interaction between parts and sealant in the course of airframe assembly process. The simulation incorporates such phenomena as compliance of parts, contact interaction between them and fluidity of sealant with presence of free surface. The approach based on fluid-structure interaction techniques consists of two basic steps: at the first one the pressure of sealant is found after corresponding fluid dynamics problem is solved and at the second the displacements of parts and sealant are calculated through the solving of contact problem. Iterations between structural and fluid dynamics solvers are performed to achieve convergence. The developed approach is demonstrated on example of joining of two test aircraft panels.

A 3D CFD methodology is presented to simulate ice build-up on propeller blades exposed to known icing conditions in flight, with automatic blade pitch variation at constant RPM to maintain the desired thrust. One blade of a six-blade propeller and a 70-passenger twin-engine turboprop are analyzed as stand-alone components in a multi-shot quasi-steady icing simulation. The thrust that must be generated by the propellers is obtained from the drag computed on the aircraft. The flight conditions are typical for a 70-passenger twin-engine turboprop in a holding pattern in Appendix C icing conditions: 190 kts at an altitude of 6,000 ft. The rotation rate remains constant at 850 rpm, a typical operating condition for this flight envelope.

A numerical approach based on a finite element method has been developed to simulate the two-dimensional blade-vortex interaction in viscous flows. In the scheme, the incompressible Navier-Stokes equations in the vorticity-stream form are used. When the passing vortex is approaching the airfoil from upstream, two different models for the vortex are used. Firstly, the vortex is modeled as an ivicsid vortex convecting at the speed of the local fluid, and the total flow is the superposition of the vortex-induced flow and the viscous flow. Secondly, when the vortex is close to the airfoil, it is distributed in a weighted manner at the nodes of the element where it is located, and then the total flow is governed by the Navier-Stokes equations. Some numerical results are presented, and the potential of the present work is discussed.

Numerical simulations of compressible inviscid flows are carried out for the complete configuration of experimental aircraft ‘ASKA’ which adopts the USB technology to increase the amount of lift force. Three different grid systems corresponding to different configurations are generated by a newly developed interactive grid generation method. Euler equations are solved by the second order upwind biased finite volume method. A planar Gauss-Seidel relaxation method is adopted to realize a rapid convergence to steady solutions. Computations are made to see the influences of different arrangements of engine nacelles over the interfered flow fields.

Electro-thermal deicing process was an unsteady heat transfer process including phase change. Based on the investigation of such a process, a code was developed to numerically simulate electro-thermal deicing process. Phase change was performed by an enthalpy method. A staircase approach was used to describe the variable ice thicknesses along the icing surface. The control volume method was adopted to discretize the governing equations. Tri-diagonal matrix method, alternating direction implicit method and block-correction technique were used to solve the discrete equations. Results of temperature distribution in this investigation were compared with experimental results of previous study. Their good agreements indicate the validity of our simulation. The effects of icing conditions, such as ambient temperature, liquid water content (LWC) and flight velocity, etc., were analyzed through a case. Some useful conclusions were achieved.

In helicopter, the icing rotor blades will decrease the effectiveness of the helicopter and endanger the lives of the pilots. The asymmetrical ice break-up and shedding could also lead to severe vibrations of the rotor blade. Ice break-up from the main rotor may strike the fuselage and tail rotor, even worse, find its way into the engine, which may cause serious aircraft accidents. An understanding of the mechanisms responsible for ice shedding process is necessary in order to optimize the helicopter rotor blade design and de-icing system to avoid hazardous ice shedding. In this paper, the ice shedding model is improved by introducing a bilinear cohesive zone model (CZM) to simulate the initiation and propagation of ice/blade interface crack. A maximum stress criterion is used to describe the failure occurred in the ice.

The objective of this paper is to present a numerical simulation method to calculate the gasification of porous particles of different sizes and composition which takes into account morphological changes of the inner pore structure. Different relationships for the evolution of the inner surface dependent on the degree conversion are assessed. In a first approach the gasification mechanism is represented by a one-step reaction. The method operates on the one-dimensional and transient conservation equation for mass and energy for spherical particles with external heat and mass transfer. The solution yields the distribution of temperature, inner surface, porosity, concentration of solid material and gaseous components versus radius and time. One of the main novelties of this approach is that it covers the entire reaction regime between reacting and shrinking core model. Satisfactory agreement is obtained between measured and calculated results.

Ice accretion is a phenomenon in which supercooled water droplets impinge and accrete on a body. In the present study, we focus on a jet engine because it is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe accidents. Although various anti-icing and deicing systems have been developed, such accidents still occur. Therefore, it is important to clarify the phenomenon of ice accretion in a jet engine. However, flight tests for ice accretion are very expensive, and in the wind tunnel it is difficult to reproduce every climate condition where ice accretion occurs. Therefore, it is expected that computational fluid dynamics (CFD), which can estimate ice accretion in various climate conditions, will be a useful way to predict the ice accretion phenomenon. The characteristic phenomena of supercooled large droplets (SLD) are splash and bounce.

A CFD simulation methodology is presented to calculate blockage due to ice crystal icing of the IGV passages of a gas turbine engine. The computational domain consists of six components and includes the nacelle, the full bypass and the air induction section up to the second stage of the low-pressure compressor. The model is of a geared turbofan with a fan that rotates at 4,100 rpm and a low-pressure stage that rotates at 8,000 rpm. The flight conditions are based on a cruising speed of Mach 0.67 in Appendix-D icing conditions with an ice crystal content is 4.24 g/m3. Crystal bouncing, and re-entrainment is considered in the calculations, along with variable relative humidity and crystal melting due to warmer temperatures within the engine core. Total time of icing is set to 20 seconds. The CFD airflow and ice crystal simulations are performed on the full 6-stage domain. The initial icing calculation determines which stage will be chosen for a more comprehensive analysis.

Over the past few years, we have developed a unique approach to simulate aircraft icing numerically; we call this method morphogenetic modelling. Previously, we developed a successful two-dimensional version of the model; the objective of our present research is to show that the morphogenetic modelling approach can be extended to three-dimensional in-flight icing. In this paper, we focus on the simulation of three-dimensional, discrete rime structures forming on the fuselage of a helicopter. The numerical model consists of three components: an airflow solver, a drop trajectory solver, and a morphogenetic ice growth model. The velocity field of the flow is computed using the Euler equations, while the drop trajectories are computed using a Lagrangian approach. Computation of drop impact locations determines the local collision efficiency distribution. The morphogenetic model deals with the processes occurring on the impinging surface.

When conducting experiments in icing wind tunnels (IWTs), a significant question is to what extent the temperature of the water droplets generated by the spray system has converged to the static air temperature when the droplets impinge on the test object. This is a particularly important issue for large droplets, since the cooling rate of droplets decreases sharply with increasing diameter. In this paper, on the one hand, realistic droplet temperature distributions in the measurement section of the Rail Tec Arsenal IWT (located in Vienna) are computed by means of a numerical code which tracks the paths of the droplets from the spraying nozzle to the measurement section and simultaneously calculates their cooling rates. On the other hand, numerical icing simulations are performed to investigate to what extent the deviation of the droplet temperature from static air temperature influences icing and thermal anti-icing processes.

Aerodynamic effects induced from vectoring an exhaust jet are investigated using a well established thin-layer Reynolds averaged Navier-Stokes code. This multiple block code has been modified to allow for the specification of jet properties at a block face. The applicability of the resulting code for thrust vectoring applications is verified by comparing numerically and experimentally determined pressure coefficient distributions for a jet-wing afterbody configuration with a thrust-vectoring 2-D nozzle. Induced effects on the body and nearby wing from thrust vectoring are graphically illustrated.

In this study, computational methods are presented that compute ice accretion on multiple-element airfoils in specified icing conditions. The “Droplerian” numerical simulation method used is based on an Eulerian method for predicting droplet trajectories and the resulting droplet catching efficiency on the surface of the configuration. Flow field and droplet catching efficiency form input for Messinger's model for ice accretion. The droplet trajectory method has been constructed such that the solution of any flow-field simulation (e.g., potential-flow, Euler equations) can be used as input for the finite-volume solution method. On an unstructured grid the spatial distribution of droplet loading and droplet velocity are obtained. From these quantities the droplet catching efficiency is derived. Of special interest in this study are the Supercooled Large Droplets (SLD). The simulation of SLD requires a specific splashing model.

The nonlinear development of stationary crossflow vortices over a 45° swept NLF(2)-0415 airfoil is studied. Previous investigations indicate that the linear stability theories are unable to accurately describe the transitional flow over crossflow-dominated configurations. In recent years the development of nonlinear parabolized stability equations (NPSE) has opened new pathways toward understanding transitional boundary-layer flows. This is because the elegant inclusion of nonlinear and nonparallel effects in the NPSE allows accurate stability analyses to be performed without the difficulties and overhead associated with direct numerical simulations (DNS). Numerical (NPSE) results are presented here and compared with experimental results obtained at the Arizona State University Unsteady Wind Tunnel (ASUUWT) for the same configurations.

Even if the probability of a combustion chamber burn-through is unlikely in modern aeroengines, the behavior of the engine has to be considered in term of airworthiness and safety. The whole 3D flow field inside the bypass duct of two aeroengines, BR710 and BR715 were simulated numerically in the event of a combustion chamber burn-through. The simulations showed the effect of different burn-through hole sizes on the bending of the torch and on the maximum temperature of the bypass duct. Utilizing the latest CFD methods the hypothetical case of an additional failure of the bypass duct structure was also simulated. These simulations also showed that both engines retain their integrity for the various burn-through scenarios.

The aerodynamic/propulsive interaction between a subsonic jet exhausting perpendicularly through a flat plate into a crossflow is investigated numerically using an approximately factored, partially flux-split, implicit solver for the three-dimensional, thin-layer Navier-Stokes equations. This algorithm is applied to flows with a range of jet-to-crossflow velocity ratios between 4 and 8. The computations model the jet trajectory, the contrarotating vortex pair and the wake region near the plate downstream of the jet orifice. Both qualitative and quantitative agreement with the existing experimental database are demonstrated. Flow visualization is instructive for understanding the physics of this flowfield.