Search

The methods incorporated in an aerodynamic analysis tool are introduced to support aircraft conceptual designs, where a boundary layer ingestion (BLI) propulsion system is deployed. In order to integrate the BLI model to a generic tool for aircraft designs, two methods of approximating boundary layer profiles along the airframe/fuselage have been examined. For an airfoil-shaped wing/body configuration, the airfoil analysis program XFOIL is used and, alternatively, the flat plate boundary layer theory may be adopted. With the boundary layer characteristics approximated from these methods, the fan performance in terms of pressure ratio and efficiency is corrected considering the inflow distortion incurred by the boundary layer ingested, based on a simplified parallel compressor method. Given the corrected fan pressure ratio and efficiency, an equivalent velocity bookkeeping method is used for predicting the BLI fan performance in terms of power requirement and thrust generation. A validation against the boundary layer approximation is also presented in comparison with the RANS-based CFD simulations for a blended wing body (BWB) aircraft.

A novel wire mesh consisting of very fine wires and pores is numerically investigated for the purpose of noise reduction. To develop a numerical model for this wire mesh, a set of experimental flow-field data has been deployed for the model validation. The experimental data were measured with only 22% of the wind-tunnel cross section covered by the wire mesh, taking into account the vortex shedding from both sides of the wire-mesh fairing. It is found that existing wire-mesh models using a damping-type source term proportional to the square of flow velocity do not perform well in modeling this novel wire mesh. To tackle this issue, an improvement is proposed by additionally introducing a linear term to account for the permeability of the wire mesh, based on another set of experiments with the wind-tunnel cross section fully covered by the wire mesh. The proposed model is then validated against the experimental data, demonstrating its capability in modeling the wire mesh. Subsequently, the model is applied to a tandem cylinder configuration. Results show that a wide but short-span wire mesh significantly reduces the dominant tone of tandem cylinders, noise at higher frequencies, as well as the overall sound pressure levels.

Purpose In the European project AFLoNext, active flow control (AFC) measures were adopted in the wing tip extension leading edge to suppress flow separation. It is expected that the designed wing tip extension may improve aerodynamic efficiency by about 2 per cent in terms of fuel consumption and emissions. As the leading edge of the wing tip is not protected with high-lift device, flow separation occurs earlier than over the inboard wing in the take-off/landing configuration. The aim of this study is the adoption of AFC to delay wing tip stall and to improve lift-to-drag ratio. Design/methodology/approach Several actuator locations and AFC strategies were tested with computational fluid dynamics. The first approach was “standard” one with physical modeling of the actuators, and the second one was focused on the volume forcing method. The actuators location and the forcing plane close to separation line of the reference configuration were chose to enhance the flow with steady and pulsed jet blowing. Dependence of the lift-to-drag benefit with respect to injected mass flow is investigated. Findings The mechanism of flow separation onset is identified as the interaction of slat-end and wing tip vortices. These vortices moving toward each other with increasing angle of attack (AoA) interact and cause the flow separation. AFC is applied to control the slat-end vortex and the inboard movement of the wing tip vortex to suppress their interaction. The separation onset has been postponed by about 2° of AoA; the value of ift-to-drag (L/D) was improved up to 22 per cent for the most beneficial cases. Practical implications The AFC using the steady or pulsed blowing (PB) was proved to be an effective tool for delaying the flow separation. Although better values of L/D have been reached using steady blowing, it is also shown that PB case with a duty cycle of 0.5 needs only one half of the mass flow. Originality/value Two approaches of different levels of complexity are studied and compared. The first is based on physical modeling of actuator cavities, while the second relies on volume forcing method which does not require detailed actuator modeling. Both approaches give consistent results.

© 2018 A grey area mitigation method is proposed for hybrid RANS-LES modeling. The proposed methodology is evaluated using a hybrid RANS-LES method based on a Low-Reynolds-Number k−ω model applied to channel flow, boundary layer flow and a spatially developing mixing layer flow. Emphasis is put on the use of commutation terms at the RANS-LES interfaces in the transport equations for the turbulent kinetic energy, the specific dissipation rate and the momentum equation in order to rapidly reduce the turbulent viscosity across a RANS-to-LES interface and to stimulate the development of resolved turbulent fluctuations. The proposed methodologies are applied at both wall-normal (and inlet) and wall-parallel RANS-LES interfaces. The proposed methodology gives a rapid reduction of the turbulent viscosity at the wall-normal RANS-LES interface from its RANS level to its LES level. Moreover, the proposed methodology contributes to a substantially more rapid establishment of the turbulence-resolving LES flow downstream of the wall-normal RANS-LES interface than if no grey-area mitigation method is applied. However, the proposed methodology has a weaker effect at wall-parallel RANS-LES interfaces, due to a stronger entrainment of LES contents into the near-wall RANS region, than at the wall-normal RANS-LES interfaces. Good agreement with experimental data is obtained with the proposed interface method for the evaluated flow cases. The most obvious grey area mitigation effect is given in the simulated mixing layer flow. Turbulent velocity fluctuations are efficiently established with the commutation term in the momentum equation at the RANS-LES interface in this flow as well as a rapid reduction of the turbulent viscosity due to the commutation terms in the k and ω equations, which gives an almost negligible delay in the development of the resolved turbulence.

International audience; Within the European project AFLoNext, one of the technological streams is dedicated to the investigation of active flow control (AFC) to increase the robustness of the wing tip design at takeoff conditions, whilst allowing the optimization of aerodynamic efficiency in cruise. AFC is used to delay the wing tip stall, which is caused by vortex breakdown, thus improving the lift to drag ratio and allowing a steeper climb gradient during second segment climb when the landing gear is retracted. The numerical parametric studies of AFC aerodynamic sizing were shared between the involved partners on the basis of actuator location (in the leading edge region or on the upper surface) and actuator types (steady blowing, synthetic jets, pulsed jets). Most of the numerical results have been obtained for steady blowing through continuous or segmented slots. The specific effect of the unsteady means of actuation on the flow topology was also identified. The aim of this study was to take into account industrial requirements defined by Airbus and geometric constraints of AFC actuators arising from the project partners involved in the development of AFC hardware. Some comparisons between the partners’ results are presented, allowing preliminary conclusions to be drawn. The most effective and efficient device turned out to be pulsed blowing through segmented slots located at the leading edge separation line.

With the aim to mitigate the grey area at the RANS-LES interface, the effect of commutation terms is investigated. Simulations of fully developed channel flow and spatially developing boundary layer flow are presented using the commutation terms at the RANS-LES interfaces. The commutation terms are added as source terms in the k, \(\omega \) and momentum equations of a zonal RANS-LES model. It is concluded that as an inlet in embedded LES of the developing boundary layer flow, the use of the proposed commutation terms are needed for the LES simulated flow to accurately predict the skin friction. However, it is demonstrated for flows where the RANS-LES interface aligns with the mean flow direction that the effect of the proposed interface methodology is weak.

The results presented at the Second AIAA High-Lift Prediction Workshop, using the flow-solver Edge, are summarized for the DLR, German Aerospace Center F11 model. A comparative study of the results, using three turbulence models, is carried out, including the Spalart–Allmaras model, an explicit algebraic Reynolds-stress model, and a curvature correction to the explicit algebraic Reynolds-stress model. The comparisons include a grid-convergence study on a simplified model without slat- and flap-track fairings, and polar calculations including the fairings. The grid-convergence study shows relatively small differences due to different grid resolution and turbulence models, but the differences are larger than those obtained in the first workshop for the NASA trap wing. The prediction has fairly large discrepancies from experimental measurements at low Reynolds numbers for which the computations were carried out assuming fully turbulent flow. The explicit algebraic Reynolds-stress model (with or without curva...

Three surface integral approaches of the acoustic analogies are studied to predict the noise from three conceptual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings (FW-H) method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to construct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill's stress tensors on the noise prediction are then evaluated by comparing the results of the Curle method with the other two methods.

Results carried out for the 4th AIAA Drag Prediction Workshop with the flow solver Edge are summarized. Simulations have been carried out for wing–body–tail configurations with three horizontal tail incidences and for one tail-off configuration. The computations consist of a grid-refinement study and a downwash study with polar calculations to explore the trimmed condition and delta effects. An investigation of the sensitivity to the grid and turbulence model is carried out from calculations on two sets of unstructured grids with three turbulence models, including the explicit algebraic Reynolds stress model, the k-ω SST model, and the Spalart–Allmaras model. The grid-refinement study, for which the flow is attached, shows rather small differences due to different grids and models. The major difference is obtained from the turbulence models where about 10 drag counts between the highest and lowest drag values are predicted, respectively, by the explicit algebraic Reynolds stress model and the Spalart–Allm...

An embedded large-eddy-simulation modeling approach is explored and verified using the partially averaged Navier-Stokes model as a platform. With the same base model, the turbulence-resolving large-eddy simulation region is embedded by setting the partially averaged Navier-Stokes model coefficient to f(k) < 1 as distinguished from its neighboring Reynolds-averaged Navier-Stokes region, where f(k) = 1 is specified. The embedded large-eddy simulation approach is verified in computations of a turbulent channel flow and a turbulent flow over a hump. Emphasis is placed on the impact of turbulent conditions at the Reynolds-averaged Navier-Stokes/large-eddy simulation interface using anisotropic velocity fluctuations generated from synthetic turbulence. The effect of the spanwise size of the computational domain is investigated. It is shown that the embedded large-eddy-simulation method based on the partially averaged Navier-Stokes modeling approach is computationally feasible and able to provide reasonable turbulence-resolving predictions in the embedded large-eddy simulation region. The wall-adapting local eddy-viscosity model is also evaluated for the hump flow and it is found that its performance is worse than that of the the low-Reynolds-number partially averaged Navier-Stokes model when the results are compared with experiments.

Results of numerical simulations are presented for flow past a stationary circular cylinder at low Reynolds numbers (Re=50-200). The simulations were carried out using a finite-volume code employing a fractional step method with second-order accuracy in both space and time. A sensitivity study on numerical parameters concerning the domain size, grid independence and time step resolution was carried out in detail for Re=100. Global time-averaged results on force coefficients, non-dimensional velocities and pressures, including their corresponding r.m.s. values, as well as various quantities related to the separation and vortex shedding characteristics are presented. A non-monotonous streamwise velocity recovery in the intermediate wake is observed for Re > 50, a phenomenon that has been grossly overlooked in the past. There are two plateaus along the wake centerline, in particular for Re=200. The first, which is the most distinct, ranges from about x=9 to x=16 at a wake deficit velocity of 0.38, x being counted in diameters behind the cylinder axis; the second one appears from x=25 to x=28 at a wake deficit velocity of 0.54. This phenomenon seems to be related to an associated change-over in the orientation of the von Karman vortices and the merging trends, especially for Re=200 beyond x=25, as observed from instantaneous vorticity fields. Three-dimensional simulations using spanwise lengths of 10 and 12 (diameters) were carried out at Re=200. After a long initial phase with regular three-dimensional mode A flow features increasing very slowly in amplitude, the flow went into a state with distinct pulsating forces acting on the cylinder, the pulsations being seemingly randomly localized across the cylinder span. In this second, much more chaotic, flow state, the time-averaged results were in agreement with previous experiments and with parts of previous numerical studies.

A low Reynolds number (LRN) formulation based on the Partially Averaged Navier-Stokes (PANS) modelling method is presented, which incorporates improved asymptotic representation in near-wall turbulence modelling. The effect of near-wall viscous damping can thus be better accounted for in simulations of wall-bounded turbulent flows. The proposed LRN PANS model uses an LRN k-epsilon model as the base model and introduces directly its model functions into the PANS formulation. As a result, the inappropriate wall-limiting behavior inherent in the original PANS model is corrected. An interesting feature of the PANS model is that the turbulent Prandtl numbers in the k and epsilon equations are modified compared to the base model. It is found that this modification has a significant effect on the modelled turbulence. The proposed LRN PANS model is scrutinized in computations of decaying grid turbulence, turbulent channel flow and periodic hill flow, of which the latter has been computed at two different Reynolds numbers of Re = 10,600 and 37,000. In comparison with available DNS, LES or experimental data, the LRN PANS model produces improved predictions over the standard PANS model, particularly in the near-wall region and for resolved turbulence statistics. Furthermore, the LRN PANS model gives similar or better results - at a reduced CPU time - as compared to the Dynamic Smagorinsky model.

The noise-reduction efficiencies of three conceptual designs are explored for a main landing gear (MLG) mounted on a simplified fuselage body with a bay and gear door. The designs are a fairing attached on the strut, compression of the bay space as the gear is deployed, and acoustic liners installed in the interior downstream wall of the bay. The gear door is opened in order to investigate its reflection effect on the noise during the operation. The stochastic noise generation and radiation (SNGR) method coupled with the Reynolds-averaged Navier-Stokes (RANS) equations are used for the noise prediction. This approach has the advantage to speed up the computation of both the fluid flow and noise. The Cartesian immersed boundary method (IBM) that is employed for the RANS solver further shortens the period of the overall assessment process due to fast and automatic mesh generation. The present SNGR method integrates the Lighthill analogy and the boundary element method (BEM). The Lighthill analogy is used for the prediction of the noise produced by a synthetic turbulent field that is constructed with a stochastic model based on the time-averaged turbulence quantities obtained from the RANS solution. The BEM is applied to compute the surface-scattered noise. The current fairing design is found inefficient for the noise reduction. The strategy of reducing the bay depth is not functional as well. However, the liners are effective for absorption of the acoustic pressure on the surfaces. Moreover, the noise reflection effect of the gear door is clarified. Since the horizontally projected area of the door is not negligible, the noise reflected towards the ground is found significant in the high frequency range. The conclusion is that a gear door and the way of arranging it in the gear-deployed stage should be regarded as the important factors of the product design.

Based on hybrid RANS-LES computation of the turbulent flow around a double-flapped wing section, CAA (Computational Aero-Acoustics) analysis was conducted using the Curle, the Kirchhoff and the FW-H acoustic analogy methods. The focus was placed on the flow-induced noise due to the flap side-edges (FSE). It was shown that the FSE has triggered extensive unsteady vortex motions and being the most potent noise-generating source with significant pressure fluctuations on the side-edge surface. In the CAA analysis, two integral surfaces, defined by the iso-surface of vorticity magnitude, were verified when using the Kirchhoff and the FW-H methods. The Kirchhoff method is more sensitive to the location of the integral surface. The analysis using the Curle method indicates that the pressure fluctuations on the surface of the main wing and the first flap have made similar contributions to the far-field noise level, while the second flap contributes slightly less. The Kirchhoff and FW-H methods have predicted overall higher noise levels comparing to the Curle method. In the comparison, the result obtained with a stochastic method based on a RANS solution was also involved. The result has clearly demonstrated that, to capture the most potential noise generation in the presence of flap side edges, turbulence-resolving simulations should be incorporated in hybrid CFD/CAA analysis.

In this paper, the noise reduction efficiency of a flap side-edge fence is revisited and investigated using the stochastic noise generation and radiation (SNGR) method coupled with the Reynolds averaged Navier-Stokes equations (RANS). The configurations are of full scale. The baseline configuration is slotted with double flaps. The fence is attached onto both side edges of the flaps for the purpose of suppressing turbulent vortices induced by the side edge. Furthermore, the efficiency of the SNGR method is assessed as a fast prediction approach for the flap side-edge noise. The noise generation in the SNGR method employs the stochastic model to construct a synthetic turbulent field and takes advantage of the acoustic analogy to formulate the noise sources. The wave equation for the noise radiation is computed by means of the boundary element method (BEM) in frequency space. The BEM takes into account the noise scattered by the surfaces. The fences are found to be efficient for depressing the wake produced by the side edges of the double slotted flaps. Since the energetic vortices contained in the wake are the major contributor of the noise generation, the fence enable an effective noise reduction, particularly in the low frequencies below 200 Hz.

Transonic duct flow with shock/boundary-layer interaction (SBLI) was analyzed using a zonal hybrid RANS-LES approach. The proposed zonal approach simulates the attached boundary layer flow, prior to the SBLI region in RANS mode. At a prescribed streamwise location, upstream of the SBLI region, the model switches to its hybrid RANS-LES mode over a buffer zone in order to avoid possible discontinuities. The corner separation bubbles, induced by the shock at M = 1.4, were mostly simulated in LES mode in order to improve the SBLI flow prediction. In addition to comparisons with experimental data, the zonal approach is compared to simulations using the SA-DDES and SA-IDDES model. The zonal approach predicted a corner separation bubble and a \(\lambda \)-shape shock which is in good agreement with experimental data. Furthermore, the predicted pressure rise across the shock agrees reasonably well with the experiment.

A hybrid LES-RANS modelling approach is proposed. RANS is used in the near wall regions (y ≤ 60), and the turbulence is modelled with a κ-ω model. LES is used in the remaining part of the flow, and the SGS turbulence is modelled with a one-equation κ sgs model. The same continuity and momentum equations are solved throughout the domain, the only difference being that the turbulent viscosity is taken from the κ-ω model in the RANS region, and from the one-equation κ sgs model in the LES region. The new modelling approach is applied to two incompressible flow test cases. They are fully developed flow in a plane channel and the flow over a 2D-hill in a channel

In this paper an improved k−ω turbulence model is proposed, which brings the asymptotic boundary value for ω into accord with direct numerical simulation (DNS) data. In the new ω-equation both a turbulent and a viscous cross-diffusion term are included, justified by an analogy to the Yap-correction and the pressure-diffusion process, respectively. The importance of cross-diffusion terms in removing the freestream sensitivity with respect to ω for free shear flows is shown. The performance of the model is evaluated and compared with DNS and with other turbulence models in a channel flow, a backward-facing step flow and a rib-roughened channel flow with heat transfer. The model requires neither wall-function nor wall-distance information and is fully integrable over the near-wall region.

A non-linear subgrid-scale (SGS) heat flux model is introduced in large eddy simulation for turbulent thermal flows. Unlike the linear isotropic eddy diffusivity model, the proposed model accounts for the SGS heat flux in terms of the large-scale strain-rate tensor and the temperature gradients. This is equivalent to using a tensor diffusivity. The model is to some extent similar to a scale-similarity model subjected to a Taylor expansion for the filtering operation. The formulation leading to the present proposal is discussed. The model is examined in LES for a buoyant flow in an infinite vertical channel with two differentially heated side walls. It is shown that the proposed model reproduces reasonable results as compared with the isotropic SGS diffusivity model and DNS data.

Computational analysis has been conducted on separation control using jet actuators for the flow around NACA0015 airfoil. At an angle of attack of α = 11◦ and a chord-based Reynolds number of about 1 million, the baseline airfoil flow is characterized by a trailingedge flow separation over a range of 30% of the chord length. In the computation with different turbulence models, it was found that the RANS models fail to reproduce the flow scenario of baseline flow, giving generally a much delayed separation onset as compared to the experimental observation. The tested hybrid RANS-LES methods (but DDES), on the other hand, have shown improved performance, in spite of a slightly exaggerated trailing-edge separation bubble. Based on the computations using the IDDES model, the effectiveness of jet actuators in suppressing the trailing-edge flow separation has been explored. In manipulating the baseline flow towards the controlled flow by switching on the jet actuators, the transient process is demonstrated in terms of the evolution of vortex motions and drag. By deploying the jets, the separated flow is reattached in the presence of jet-induced streamwise vortex motions, which inject high-momentum fluids from freestream into the near-wall layer. In response to the jet actuation, large-scale coherent vortex motions are significantly diminished over the airfoil trailing edge and in the wake, where turbulence generation becomes also alleviated.

Laser beam propagation in severe environments such as a jet engine exhaust may influence performance of Airborne Optical Systems such as Missile Early Warning Systems or Directed Infrared Countermeasures. Laser beam propagation in close vicinity of the engine plume causes performance degradation due to beam wander, and beam broadening effects. In this study aero-optical effects are studied based on four CFD simulations of the same engine geometry. The CFD simulations encompasses ReynoldsAveraged Navier-Stokes (RANS), Large Eddy Simulation (LES) and hybrid RANS-LES methods, as well as different spatial resolution for the LES simulations. The CFD simulation results are used to compute estimates on laser beam wander and laser beam profile after passage of the jet.

Hybrid RANS-LES modeling is proposed using a Low-Reynold-Number (LRN) k − ω model. The model is demonstrated in a zonal RANS-LES approach and in an embedded LES approach. The model is calibrated and evaluated using Decaying Homogeneous Isotropic Turbulence (DHIT), turbulent channel flow and turbulent flow over a hump. The effect of different LES length scales on log-layer mismatch and turbulence resolving capability is demonstrated using the proposed model. Interface conditions are proposed in the embedded LES approach in order to reduce the grey area zone in the LES domain downstream of the RANS region. To further improve the development of turbulence resolving flow in the LES region downstream of the interface, anisotropic turbulent velocity fluctuations from synthetic turbulence are added. The hybrid RANS-LES modeling approaches that are presented, using the LRN k − ω based model, show that predictions of turbulence resolving flows are in reasonable agreement with experimental data and DNS data. Moreover, the choice of the LES length scale using the proposed model is shown to be of great importance in reducing the log-layer mismatch.

A turbulent natural convection flow ( Ra =1.58×10 9 ) in a confined cavity with two differentially heated side walls was numerically investigated by means of large eddy simulation (LES). The mean flow in the cavity is characterized by stable thermal stratification and a relatively low turbulence level. The LES results for the mean flow quantities show good agreement with the experiment. This is particularly the case when the dynamic model is used. Nevertheless, there are some discrepancies in the prediction of turbulence statistics, particularly in the outer region of the near-wall flow where the boundary layer interacts with the recirculating core region. In the viscous/conductive sublayer of the boundary layer close to the heated/cooled vertical walls, the flow tends to form streak-like structures, which do not however emerge in the near-wall flow along the horizontal top and bottom walls. To resolve the flow structure near the vertical walls, sufficient grid resolution is required.

A two-equation turbulence model is proposed in which the turbulent eddy viscosity is not constructed from scale-determining quantities but rather is calculated from a transport equation. To close the equation system while not involving a length scale as in some one-equation models, the turbulent kinetic energy is also solved as a supplemental quantity. The eddy viscosity transport equation is modeled on the basis of an exact form derived from the exact k and " equations. The model allows integration over the near-wall region, requiring neither wall functions as a bridge nor wall distance parameters in the model coefe cients. In contrast to the conventional k‐" model, moreover, natural boundary conditions can be used at the wall for the turbulent transport quantities. It is numerically convenient to use the model for computing complex turbulent e ows. The model is validated against several e ow cases, yielding predictionsin good agreement with experimental and direct numericalsimulation data. Nomenclature C = model constant with various subscripts C f = skin-friction coefe cient fl = damping function H = height of the computational domain h = height of the hill or the step k = turbulent kinetic energy Re = Reynolds number based on freestream velocity Res = Reynolds number based on friction velocity Rt = turbulent Reynolds number, ˜ m t/m

This work deals with the computation of turbulent buoyant convection flows with thermal stratification using the low-Reynoldsnumber (LRN) k-x model. When applying the k-e model to buoyancy-driven cavity flows induced by diAerentially heated side walls, a problem commonly encountered at moderate Rayleigh numbers (Raa 10 10 ‐1 0 12 ) is that the model is not capable of giving gridindependent predictions owing to the transition regime along the vertical walls. It was found that the buoyancy source term for the turbulence kinetic energy, Gk, exhibits strong grid sensitivity, as this term is modelled with the Standard Gradient DiAusion Hypothesis (SGDH). By introducing a damping function into this term, the above grid-dependence problem is eliminated and, additionally, the modelled Gk renders correct asymptotic behavior near the vertical wall. The mechanism held in the k-x model for describing the onset of transition is analyzed. The present approach is simple for practical use and gives reasonable predictions. ” 1999 Elsevier Science Inc. All rights reserved.

The assessment of ventilation performance is discussed. New local indices are developed with the aid of numerical simulations to quantify air diffusion and contaminant dispersion. The local purging effectiveness, Asp, is an index for evaluating the contribution of each inlet in a multi-inlet system. The local specific contaminant-accumulating index, α, can be used to indicate the tolerance of a ventilation flow to contaminants. Asp and α can be derived from transport equations. A method based on age-variation analysis is used to define Asp and the Expected Contaminant Dispersion Index (ECDI). The latter is an index for forecasting contaminant dispersion emitted at a specific location with unknown source strength. These new scales and methods can be used to assess ventilation performance.

This paper deals with the description and determination of the purging flow rate, U p , for ventilation systems or equivalent flow systems. The regional purging flow rate and its use are discussed and proposed. By using the mass conservation principle, U p is embodied in various accessible mathematical expressions in terms of the transfer probability. Some U p -related parameters are described. A Markov chain model is proposed for determining the transfer probability and exploring several useful ventilation indices. An effective CN method is proposed for calculating the interchanging flow rates between various regions. The application of these proposals is demonstrated, and they appear to be promising for analyzing and assessing ventilation performance.

We have investigated the possibilities of using Computational Fluid Dynamics (CFD) simulations to characterize the impact of refractive index fluctuations in a jet engine plume on Directed InfraRed CounterMeasure (DIRCM) system performance. The jet plume was modelled using both Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) formulations of Navier-Stokes equations. The RANS calculations provided a time-averaged description of the refractive index and the turbulence strength. The more computationally intense LES model provided time resolved data on large scale turbulent eddies within the engine plume. The smaller structures are assumed to be isotropic and are modelled implicitly to reduce the computational demands to levels feasible for current computational hardware. The refractive index data from the CFD calculations was integrated along the optical propagation path to produce phase screens. For RANS data this approach provided time averaged aberrations, whereas for LES data the temporal variation of low spatial frequency aberrations were available for a short time sequence. Modal descriptions of the phase screens were investigated to allow study of temporal variation at longer time scales. Alternatively the structure parameter (Cn2) can be estimated and used to provide order of magnitude approximations for the optical effects. The generated phase screens were used to calculate laser beam system level quality parameters including beam wander, fidelity ratio and power-in-bucket. The paper focuses on method development, but examples of a jet plume simulation showing that the engine plume turbulence has a significant impact on DIRCM system functionality are presented.

Some important aspects of hybrid RANS-LES modelling for a high-lift flow have been discussed on the basis of a number of simulations with different computational settings tabulated in nine cases. By means of comparative studies of these cases grouped in different sets, the effect of the simulation strategies invoked in the computations has been investigated, including local transition (specified around the leading edges of the high-lift elements), hybrid RANS-LES methods, temporal resolution, as well as the extension of computational domain in the spanwise (homogeneous) direction and the grid resolution in this direction. In exploring the effects of these issues, the lessons learned from these computations are also speculated.

Turbulence-resolving computations were conducted for the flow over a rudimentary landing gear (RLG) using the SA-DDES (Delayed Detached Eddy Simulation) model and an algebraic zero-equation hybrid model (HYB0). Linked to flow-induced noise generation, the emphasis of the computations has been placed on the verification of hybrid RANS-LES methods in predicting surface pressure and its fluctuations in comparison with available experimental measurements. A common structured grid was used in the computations with both models and, additionally, a computation was also undertaken using the HYB0 model on an unstructured grid. Both models have shown similar performance with reasonable predictive capabilities of capturing the general flow features. Nonetheless, the discrepancy observed in the prediction of surface pressure fluctuations suggests that the effect of temporal and spatial resolution is significant.

This work introduces the work conducted in the EU JTI project ANOLOCO, which has aimed at an assessment of aerodynamic and aeroacoustic performance of several high-lift configurations of a regional aircraft. The high-lift designs are for a laminar and slat-less wing, including configurations with a double slotted flap, single slotted flap, drooped nose and a Krueger flap. The aerodynamic performance is assessed from steady state RANS calculations up to maximum lift. The aeroacoustic performance is based on hybrid RANS-LES calculations for flow-induced noise generation, and using acoustic analogy methods for far-field noise propagation. Three different analogy methods are evaluated and compared. The assessment shows that the configuration with a Krueger flap gives the best performance. The maximum lift is close to 20% higher than for any other configuration and the noise levels are also reduced, up to 10 dB lower than the configuration with a double slotted flap.

Three surface integral approaches of the acoustic analogies are studied to predict the noise from a three-dimensional, high-lift wing configuration. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings method of the permeable integral surface and the Curle method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specifically from the pressure perturbation on the wall. A new way to construct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex objective – the actual wing with high-lift devices – the integral surface based on the vorticity is constructed to follow the flow structures. The noise from the core flow region is based on the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FWH formulation. The role of each wall component on noise contribution is analyzed using the Curle method. The results of the three methods are then compared.

less contribution to the sound pressure level than the trailing edge ap. This is in agreement with results from a separate computational aero-acoustics analysis. The analysis of combined temporal and spatial correlations, cross correlations, indicate that the largest correlations are seen for zero or very small separation times for many of the considered point pairs. The dominating frequencies of the cross correlation are sorted out through spectral analysis.

Aeroacoustics performance is assessed for three conceptual low-noise and high-lift wings using the surface integral methods of acoustic analogy, including the Kirchhoff method, the Ffowcs Williams and Hawkings method and the Curle method. A new way is proposed to define the integral surface that encloses the core flow region for the first two methods on the basis of the vorticity magnitudes. Both of the first two methods are used to compute the noise generated by the core region of the flow, which is responsible for most of the noise generation. The results obtained by the FWH method support those given by the Kirchhoff method. The Curle analogy approach is adopted to calculate the noise by the boundary layer flow attached on the walls inside the core flow region. Through comparison of the results of the three approaches, the levels of the contribution to the noise by the volume flow and the boundary layers are studied for the configurations. Finally, the mechanism of efficiency on the noise reduction is presented for the three configurations.