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Acquisition of unsteady pressure using remote scanners can provide practical advantages over making the same measurements directly using flush-mounted pressure transducers. However, pneumatic distortion of the signal is introduced by the tubing between the sensing module and surface port. This typically limits the usefulness of such measurements to averaged, steady data only, restricting the application of pressure scanners for unsteady pressure measurements in wind-tunnel and flight-testing applications. In this work, unsteady pressure on the surface of a 1.75%-scale model of the NASA Space Launch System Block 1B Cargo vehicle was remotely measured using an electronic scanning pressure module at the NASA Langley Research Center 14-by 22-Foot Subsonic Tunnel. Subsequent reconstruction using an empirically tuned, Wiener-filtered inverse transfer function produced excellent agreement compared to nearby surface-mounted transducers within a usable bandwidth of approximately 500 Hz. Interactions between the launch vehicle and the support tower produced strong oscillations that were absent in the vehicle-alone configuration, and it is likely that the wake interaction leads to a resonant flow response when the launch tower is immediately downstream of the vehicle. [ABSTRACT FROM AUTHOR]

This document describes the reasoning and trade studies used to evaluate tools for constructing the aerodynamic lineload databases for the liftoff and transition phases of flight for the Space Launch System. Three computational fluid dynamics codes (USM3D, FUN3D, and Kestrel) were investigated with various turbulence models as well as detached eddy simulation variants for the launch vehicle in free air and in proximity to the tower. Decisions were made mostly based on results from brief developmental studies performed in response to specific, unforeseen challenges that were encountered in the analysis of a given configuration. The need to develop databases in a timely manner, as well as to accurately capture the expected leeward-wake flowfield characteristics, led to the selection of the Kestrel flow solver with its delayed detached eddy simulation method, the Spalart-Allmaras turbulence model, and the adaptive mesh refinement capability in the off-body Cartesian grid region. [ABSTRACT FROM AUTHOR]

Typical wind tunnel testing involves a series of configuration changes (to the angles of control surfaces) to simulate the lift and resistance characteristics of control surfaces in different flight conditions. It is very time-consuming and labor-intensive to manually change the angles of control surfaces, especially in the large continuous reflux wind tunnel. Thus, there is a demand for a morphing system design within the wind tunnel model that can deflect the control surfaces remotely and automatically. The basic design flow and characteristics of different actuator techniques for the morphing systems were summarized in this paper, including electromechanical actuator, pneumatic actuator, shape memory material actuator and piezoelectric actuator. In the case study, the accuracy of the control surface angle and aerodynamic performance of the ultrasonic-driven automatic control surface system reached the level of traditional fixed control surface systems, while its efficiency was much higher than that of the traditional fixed control surface systems. [ABSTRACT FROM AUTHOR]

Recent studies have shown that semi-aeroelastic hinge devices can enable larger aircraft wingspans. Such a device would be folded on the ground to meet airport width restrictions, locked during cruise for optimal aerodynamic performance, and released during maneuvers to alleviate flight loads. In contrast, this paper uses a wind tunnel experiment to study the aeroelastic behavior of floating wingtip fuel tanks. This device consists of a freely floating wingtip with an additional mass attached in the form of a liquid-filled fuel tank. The static aeroelastic results show that altering the fuel tank's filling level and position allows the wingtip to float at an optimal angle for aerodynamic efficiency across various angles of attack and fuel masses. Additionally, this paper shows that, with careful selection of the mass distribution of the wingtip, dynamic load alleviation comparable to the semi-aeroelastic hinge concept can be achieved during turbulence and one-minus-cosine encounters. Furthermore, the effect of fluid motion is shown to reduce incremental loads during random turbulence encounters by up to 10%; however, it has a negligible impact on the response to one-minus-cosine encounters. Such results are also confirmed by a numerical model incorporating a simple reduced-order fluid sloshing model. [ABSTRACT FROM AUTHOR]

Typical wind tunnel testing involves a series of configuration changes (to the angles of control surfaces) to simulate the lift and resistance characteristics of control surfaces in different flight conditions. It is very time-consuming and labor-intensive to manually change the angles of control surfaces, especially in the large continuous reflux wind tunnel. Thus, there is a demand for a morphing system design within the wind tunnel model that can deflect the control surfaces remotely and automatically. The basic design flow and characteristics of different actuator techniques for the morphing systems were summarized in this paper, including electromechanical actuator, pneumatic actuator, shape memory material actuator and piezoelectric actuator. In the case study, the accuracy of the control surface angle and aerodynamic performance of the ultrasonic-driven automatic control surface system reached the level of traditional fixed control surface systems, while its efficiency was much higher than that of the traditional fixed control surface systems.

The present paper studies whirl flutter stability of the TiltRotor Aeroelastic Stability Testbed (TRAST) using the comprehensive analysis code Rotorcraft Comprehensive Analysis System (RCAS). The TRAST wing and pylon are systematically developed in RCAS as beams based on a NASTRAN model starting with a spar and more sophisticated models are incrementally built up by adding components one at a time. Natural frequencies are compared with those of the NASTRAN model at each step. The elastic wing-pylon beam model is then combined with an elastic gimbaled rotor model, and whirl flutter analysis is carried out. Comparisons are made between uniform inflow and dynamic inflow for aeroelastic stability. Increased flutter speed with dynamic inflow is observed against uniform inflow. Wing and pylon aerodynamics are also added to the model, and their effects on aeroelastic stability are examined. A few key design parameters [pitch spring stiffness, rotor rotational speed, and pitch-flap coupling (δ3)] are varied, and their effects on whirl flutter speed are examined. In particular for TRAST, the pitch spring stiffness and pitch-flap coupling have an important influence on whirl flutter speed. [ABSTRACT FROM AUTHOR]

Although there have been many proposed methods to model unsteady aerodynamic effects in the stall and poststall region, little work has been done to directly assess the impact of unsteady aerodynamic models on stability and control characteristics. In this paper, the state-space method for unsteady aerodynamic modeling is combined with bifurcation analysis to examine the sensitivity of stall and poststall behavior to the choice of aerodynamic modeling method: quasi-steady or unsteady. It is found that quasi-steady modeling can adequately capture the dynamics of the chosen example of a T-tailed transport aircraft with negligible wing-tail coupling. The study is then expanded to investigate a hypothetical situation with highly unsteady aerodynamic characteristics resembling a delta wing configuration--achieved by increasing the time delay constants in the unsteady model. This results in an aircraft with significantly lower flying qualities as indicated by bifurcation analysis. These findings highlight the need to implement unsteady aerodynamic modeling techniques in high-performance aircraft with significant vortex-related unsteady aerodynamics in order to sufficiently capture their stall and poststall dynamics. [ABSTRACT FROM AUTHOR]

Transitory control and regulation of the aerodynamic loads on a static and dynamically pitching VR-12 airfoil is investigated in wind tunnel experiments. Actuation is enabled by a spanwise array of integrated combustion-based actuators that are triggered intermittently relative to the airfoil's motion, producing high-impulse actuation jets on characteristic time scales that are an order of magnitude shorter than the airfoil's convective time scale. Poststall transitory actuation leads to a momentary reattachment of the flow over the airfoil, and the effects of sequencing of actuation pulses on the aerodynamic characteristics of the airfoil are assessed using time-resolved measurements of the lift force and pitching moment coupled with particle image velocimetry that is acquired phased-locked to the airfoil motion. The present investigations show that the aerodynamic loading can be significantly altered by a number of actuation programs using strategically timed bursts during the pitch cycle. While actuation during the upstroke primarily affects the formation, evolution, and advection of the dynamic stall vortex, actuation during the downstroke accelerates flow reattachment. Superposition of such actuation programs can lead to enhancement of cycle lift and pitch stability, and reduced cycle hysteresis. [ABSTRACT FROM AUTHOR]

Supersonic and hypersonic vehicles experience significant aerothermal loads from the exterior flowfield and/or their propulsion system. Thus, reliable prediction of aerothermal heating is important for the design of such vehicles. However, even modest temperature changes can lead to buckling of mechanically constraint lightweight structures. This deformation changes the flowfield, which can lead to locally amplified heating, which in turn increases deformation and temperature even further. Thus, fluid-structure coupled modeling of such problems is crucial for the reliable prediction of the resulting temperatures. To investigate these phenomena numerically, we conducted a three-dimensional thermomechanical simulation of fluid-structure interaction (FSI) for thermal buckling. It is necessary to use a thermomechanically coupled model because the temperature and deformation distributions across the panel are highly nonlinear and dependent on both the flowfield and the state of the structure. Due to the high temperatures (>1400 K) in the metallic panel and the constrains, which allow no uniform expansion, the stresses exceed the yield stress, and plasticity occurs. A strong two-way coupled FSI simulation was set up and split into a thermal solid, a mechanical solid, and a fluid computation. The simulated temperature and displacement distribution were compared to experiments conducted in the arc-heated wind tunnel L3K at the German Aerospace Center (DLR). We obtained good agreement between the simulation and experimental results. The observed deformation of the structure was found to locally increase the wall heat flux by up to 40%. [ABSTRACT FROM AUTHOR]

In the present study, a novel concave bump for impinging-shock control in two-dimensional supersonic flows is investigated. An analytical method for preliminary bump design based on a generalized shape of a shock-canceling bump has been developed and verified numerically. An extensive proof-of-concept study was performed at a freestream Mach number ranging from 2.5 to 5.0 for shock-generator angles varying from 6 to 12 degrees. It could be demonstrated that a concave bump designed for a given flow-deflection angle is capable of significantly reducing the size of the separation bubble as well as the total pressure losses throughout the Mach number range investigated. The achievable gains depend on the Mach number, the flow-deflection angle, and the relative impingement position of the incident shock front on the bump. The highest values of separation-length reduction (up to 100%), momentum thickness reduction (up to 31%), and pressure recovery factor increase (up to 33%) were obtained at the optimum shock impingement position for the largest deflection angle studied. The concave bump is less effective, and in some cases even disadvantageous, when the incident shock wave does not optimally strike the bump crest. [ABSTRACT FROM AUTHOR]

Non-transferred low-power arcjet wind tunnels with pure argon working gas are widely used as inexpensive laboratory plasma sources to simulate a weakly ionized supersonic flow around an atmospheric entry vehicle. Many experiments using argon arcjet wind tunnels have been conducted, but their numerical modeling is not yet complete. We develop an axisymmetric Navier-Stokes model with thermochemical nonequilibrium and arc discharge that simulates the entire flow field in a steady-operating argon arcjet wind tunnel, which consists of the inside of the arcjet and its arc plume entering a rarefied vacuum chamber. The computational method we develop makes it possible to reproduce the arc column behavior far from thermochemical equilibrium in the low-voltage discharge mode typical of argon arcjets. Furthermore, the results reveal that the plasma characteristic of being far from thermal equilibrium, which is particular to argon, causes the arcjet to operate in the low-voltage mode and its arc plume to be completely thermochemically frozen. Moreover, the arc plume has electroconductive non-uniformity with an electrically insulating boundary in the radial direction. Our computed values for the shock standoff distance in front of a blunt body and the drag exerted on it agree with measured values. As a result, the self-consistent computational model in this study is useful in investigating thermochemical nonequilibrium plasma flows in argon arcjet wind tunnels. [ABSTRACT FROM AUTHOR]

The topologies of membrane and shell structures are not covered by existing wind load Standards and wind tunnel testing should be used to obtain representative wind loads for these structures. However, accurate scale-models of these organically shaped and often open thin structures are complex, time-consuming and expensive to build. To stimulate experimental research on wind load distributions over these structures, this paper illustrates a prototyping methodology for double curved thin shell wind tunnel models with integrated pressure sensors. The production process is illustrated for a hyperbolic paraboloid roof structure. The obtained wind load distributions are validated with literature for a flat roof and canopy that is made according to the same methodology and for two hyperbolic paraboloid roofs. Results indicate that, compared to conventional wind tunnel models, these thin shell wind tunnel models yield more realistic wind pressure distributions over very thin canopy structures. Finally, Cp-distributions are shown for the hyperbolic paraboloid canopy with the high corner under attack. The production of glass-fibre reinforced composites in a CNC-milled mould is convenient and accurate and facilitates the production of wind tunnel models to be used for wind load measurements on organically shaped thin canopy structures. • Wind tunnel models of scaled canopies with integrated pressure taps are prototyped. • Simultaneous pressure measurement on both sides of thin canopies is achieved. • Cp-distributions are drafted for two hyperbolic paraboloids with different curvature. • The low thickness results in more relevant Cp-values close to the upwind edges. [ABSTRACT FROM AUTHOR]

The present paper emphasizes on the characteristics of the wake flowfield emanating from a helicopter fuselage and rotor head, including cyclic and collective pitch motion. Predicting the convection of the coherent vortical flow structures generated by the fuselage as well as the rotor head is a difficult goal by the application of numerical methods. Furthermore, the accurate determination of the wake flowfield requires the detailed knowledge of the origin of the associated coherent structures. Therefore, numerical and experimental investigations have been conducted on a twin-engine light utility helicopter. The wind-tunnel model includes a fuselage and a rotating five-bladed rotor head. To obtain the wake flowfield, stereoscopic particle image velocimetry is applied. The numerical investigations are performed with a commercial flow solver. The flow solver is based on the unsteady Reynolds-averaged Navier-Stokes equations. Turbulence modeling is performed with the scale-adaptive simulation model. The motion of the rotor head is covered by the moving and deforming mesh methods. The wake-flow velocity distribution obtained by the experimental data and the numerical results shows a good agreement and allows a detailed analysis of the dominant vortical flow structures propagating downstream. [ABSTRACT FROM AUTHOR]

Wind-Driven Rain (WDR) is one of the major moisture sources that cause building envelope failures. The quantity and spatial distribution of WDR are important considerations for durable building envelope designs and are essential boundary conditions for hygrothermal modelling. Within a comprehensive research program of quantifying WDR exposure of buildings and the effectiveness of overhang on reducing WDR wetting, a six-storey building located in Vancouver, Canada was instrumented for field WDR measurements. One of the challenges in field WDR measurements is the validity of on-site wind measurements. The accurate measurements of on-site wind conditions are essential for correlating WDR on façade with on-site weather conditions and for generating the spatial distribution correction factor required in the semi-empirical WDR models. This paper focuses on discussing the procedure necessary for proper on-site wind measurements for quantifying WDR on façade based on field and wind-tunnel measurements. The proper procedure to calculate the spatial distribution correction factor, namely wall factor according to ISO standard, and its impact on the accuracy of the ISO model is also discussed. The accuracy of ISO model can be significantly improved by using more detailed wall factors calculated based on high-resolution on-site wind and rain measurements. [ABSTRACT FROM AUTHOR]

Scalar dispersion from ground-level sources in arrays of buildings is investigated using wind-tunnel measurements and large-eddy simulation (LES). An array of uniform-height buildings of equal dimensions and an array with an additional single tall building (wind tunnel) or a periodically repeated tall building (LES) are considered. The buildings in the array are aligned and form long streets. The sensitivity of the dispersion pattern to small changes in wind direction is demonstrated. Vertical scalar fluxes are decomposed into the advective and turbulent parts and the influences of wind direction and of the presence of the tall building on the scalar flux components are evaluated. In the uniform-height array turbulent scalar fluxes are dominant, whereas the tall building produces an increase of the magnitude of advective scalar fluxes that yields the largest component. The presence of the tall building causes either an increase or a decrease to the total vertical scalar flux depending on the position of the source with respect to the tall building. The results of the simulations can be used to develop parametrizations for street-canyon dispersion models and enhance their capabilities in areas with tall buildings. [ABSTRACT FROM AUTHOR]

For more than fifty years, atmospheric dispersion predictions based on the joint use of a Gaussian plume model and wind tunnel experiments have been applied in both Japan and the U.K. for the evaluation of public radiation exposure in nuclear safety analysis. The effective source height used in the Gaussian model is determined from ground-level concentration data obtained by a wind tunnel experiment using a scaled terrain and site model. In the present paper, the concentrations calculated by this method are compared with data observed over complex terrain in the field, under a number of meteorological conditions. Good agreement was confirmed in near-neutral and unstable stabilities. However, it was found to be necessary to reduce the effective source height by 50% in order to achieve a conservative estimation of the field observations in a stable atmosphere. [ABSTRACT FROM AUTHOR]

An aerospace vehicle traveling through the atmosphere is subject to triboelectrically induced electrostatic charge build-up caused by dust and ice crystal impingement. Electrostatic discharges between an antenna housing and the exterior of the vehicle may interfere with system operation. Paschen's Law, derived for stationary, charged surfaces, fails to account for the loss of electron-ion pairs with high gas velocity between the electrodes. The purpose of this work is to develop a version of Paschen's Law that takes into account the flow of ambient gas past electrode surfaces. The basic hypothesis of this work is that the number of electron-ion pairs created per unit distance between electrode surfaces is mitigated by the electron-ion pairs removed per unit distance by the flow of gas. The revised theoretical model must be a function of the mean velocity, v xm , of the ambient gas and reduce to Paschen's law when the gas mean velocity, v xm = 0. This model has been evaluated by wind tunnel experimentation. Initial data of the baseline wind tunnel experiments show results consistent with the hypothesis. Based on the results of this work, it is hoped that the safety of aerospace vehicles will be enhanced with a redefinition of electrostatic launch commit criteria. It is also possible that new products, such as anti-static coatings, may be formulated from this data. [ABSTRACT FROM AUTHOR]

A real-time modeling and control architecture for coupled shear layer von Kármán instabilities on a wing section wake is developed. Previous wind tunnel experiments highlighted that these wake instabilities give rise to limit cycles on both local and resulting airloads. The two-state Van der Pol system is employed to model the self-sustained oscillations exhibited by the actual flow. Schemes featuring either one or two coupled Van der Pol oscillators in parallel are taken under consideration. Open-loop and closed-loop control laws to manipulate and reduce the self-sustained oscillations are extensively studied. An adaptive control scheme is developed to optimize the performance of the controller, according to the flow conditions. For the open-loop control scheme, the consistency with experimental tests performed on a wind tunnel model is shown. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to use a computational technique to simulate the flow in a two-dimensional (2D) wind tunnel where the effect of the solid walls facing the model has been addressed using a porous geometry so that interference arriving at the solid walls are duly damped and a flow suction procedure has been adopted at the side wall to minimize the span-wise effect of the growing side wall boundary layer.Design/methodology/approach A CFD procedure based on discretization of the Navier–Stokes equations has been used to model the flow in a rectangular volume with appropriate treatment for solid walls of the confined volume in which the model is placed. The rectangular volume was configured by stacking O-Grid sections in a span-wise direction using geometric growth from the wall. A porous wall condition has been adapted to counter the wall interference signatures and a separate suction procedure has been implemented for reducing the side wall boundary layer effects.Findings It has been shown that through such corrective measures, the flow in a wind tunnel can be adequately simulated using computational modeling. Computed results were compared against experimental measurements obtained from IAR (Institute for Aerospace, Canada) and NAL (National Aeronautical Laboratory, Japan) to show that indeed appropriate corrective means may be adapted to reduce the interference effects.Research limitations/implications The solutions seemed to converge a lot better using relatively coarser grids which placed the shock locations closer to the experimental values. The finer grids were more stiff to converge and resulted in reversed flow with the two equation k-w model in the region where the intention was to draw out the fluid to thin down the boundary layer. The one equation Spalart–Allmaras model gave better result when porosity and wall suction routines were implemented.Practical implications This method could be used by industry to point check the results against certain demanding flow conditions and then used for more routine parametric studies at other conditions. The method would prove to be efficient and economical during early design stages of a configuration.Originality/value The method makes use of an O-grid to represent the confined test section and its dual treatment of wall interference and blockage effects through simultaneous application of porosity and boundary layer suction is believed to be quite original. [ABSTRACT FROM AUTHOR]

The present study was devoted to the development and application of a remote microphone technique for aeroacoustic measurements in large aerodynamic wind tunnels. In this technique, the microphone and its connecting line to the sensing port are fitted within an aerodynamically streamlined fairing. A model-based calibration method was applied to account for the phase lag and dissipation within the microphone connecting line. The proposed system permits to carry out acoustic measurements when the wind tunnel surface cannot be altered, since the fairing can be simply glued on the wall. The fairing is streamlined to minimize flow disturbances as well as the risk of separation which would otherwise contaminate the wind tunnel flow quality and acoustic measurements. It was furthermore hoped that the acceleration of the flow over the fairing surface might reduce the turbulence fluctuations and thereby increase the signal-to-noise ratio of the acoustic measurements. Those aerodynamic effects were investigated with a set of hot-wire measurements performed in the subsonic L2B small wind tunnel of von Karman Institute (VKI). The mean velocity and the turbulence intensity profile were analyzed in the presence of different inflow turbulence characteristics at 5, 10 and 15 m/s freestream velocity. The effect of incident turbulence on the acoustic measurement was investigated applying the calibration procedure and comparing the measurements with a wall-mounted reference microphone signal in similar flow conditions. The results indicate that the wished beneficial effects of the flow acceleration are not significant. As an application, this technique is used to measure the noise emitted from the contra-rotating fans of the large L1 subsonic wind tunnel of the von Karman Institute, where the microphone fairing is placed inside the diffuser and thus subjected to a thick turbulent boundary layer. The results indicate that in spite of the mitigated turbulence-reduction performance of the fairing, it provides a measurement solution that is suitable for large wind tunnels provided the signals are compensated using the measured dynamic calibration. While it should be stressed that the calibration procedure itself is not new, the originality of the present paper stands in the proposed fairing design, and in the aerodynamic/acoustic investigation of its effect on the flow. [ABSTRACT FROM AUTHOR]

This paper compares the performance of EARSM, SAS and IDDES turbulence models for the aerodynamic problem of a high-speed train subjected to crosswind. These approaches, as well as the effect of the curvature correction for conventional RANS models (standard k − ε and k − ω SST), are analyzed in terms of aerodynamic force coefficients and pressure distribution at the train surface, time-averaged and instantaneous flow structures, vortices location and viscosity ratio, and computational cost. The turbulence models are also evaluated against wind tunnel experimental data and published numerical results. It has been shown that SAS, which is a turbulence model that is formally a RANS model, can allow the generation of LES content, and so it is found to be a good alternative for LES or DES in this aerodynamic problem. Besides, when a significant save in computational cost is required, EARSM has shown to give reliable results. Consequently, this turbulence model results into a good choice for expensive aerodynamic optimization problems as it balances computational cost and prediction accuracy. [ABSTRACT FROM AUTHOR]

The low-frequency and large-amplitude coupled vibration of the support sting in wind tunnel affects the accuracy of the wind tunnel test's data. An active vibration control system of support sting in wind tunnel is demonstrated using adaptive control method in this paper. Following the establishment of the finite element model, and the extraction of parameter matrix, the original model is reduced to lower-mode model which contains first two pitching modes based on DC gain ranking method. The active control model is proposed based on model reference adaptive control method (RACM) to control the low-frequency vibration of supporting sting in wind tunnel. Research results have justified the effectiveness of the controlled system and provided insight into the practical application of the proposed method. [ABSTRACT FROM AUTHOR]

A review is presented of estimates for the grid resolution requirements for wall-resolved and wall-modeled large-eddy simulation, of flows with an important influence of turbulent boundary layers. The estimates are described within a classification scheme which is formulated based on the grid resolution relative to the length scales of the turbulent boundary layer. The grid resolution estimates are then applied to discuss the computational cost of ship hull hydrodynamics simulations, both in model and in full scale. The hulls of one submarine and one bulk carrier are included in this discussion. Two simulation cases are included in the paper to demonstrate a complete simulation methodology, to illustrate the implications of the grid resolution estimates, and to investigate the resulting predictive accuracy. The first simulation case consists of fully developed turbulent channel flow, for which a comparison is made with direct numerical simulation results. The second simulation case consists of the flow around an axisymmetric body, which is based on a bare-hull version of a generic submarine model, and for which wind tunnel measurement data are available for validation. [ABSTRACT FROM AUTHOR]

In order to check whether the developed airfoil UMY02-T01-26 can improve aerodynamic performance, a multiport device is used to investigate the pressure distribution acting on a single blade surface under inflow conditions. In this experiment, aerodynamic forces are discussed with different Reynolds numbers of Re = 0.5 × 10 5 , 1.0 × 10 5 , 1.5 × 10 5 and 2.0 × 10 5 . Furthermore, for the purpose of clarifying the impact of turbulence intensity, the aerodynamic forces characteristics of HAWT airfoil are estimated in the case of different turbulence intensities generated by static turbulence grids. According to the wind tunnel experimental analysis, it can be known that the blade boundary layer tape has no significant effects on the drag coefficient with or without turbulence grids. For the low turbulence intensity (without grid), the airfoil performance is improved when the boundary layer tape is attached near the leading edge. For the high turbulence intensity (with grid), in the case of the Re = 0.5 × 10 5 , the pressure coefficient presents a steady value from some back positions of x/c = 0.20, where the boundary layer tape is attached on the trailing edge position. [ABSTRACT FROM AUTHOR]

Dispersion of neutral and dense gas over a simplified urban area, comprising four cubes, has been investigated by the means of large-eddy simulations (LES). The results have been compared to wind tunnel experiments and both mean and fluctuating quantities of velocity and concentration are in very good agreement. High-quality inflow profiles are necessary to achieve physically realistic LES results. In this study, profiles matching the atmospheric boundary layer flow in the wind tunnel, are generated by means of a separate precursor simulation. Emission of dense gas dramatically alters the flow in the near source region and introduces an upstream dispersion. The resulting dispersion patterns of neutral and dense gas differ significantly, where the plume in the latter case is wider and shallower. The dense gas is highly affected by the cube array, which seems to act as a barrier, effectively deflecting the plume. This leads to higher concentrations outside of the array than inside. On the contrary, the neutral gas plume has a Gaussian-type shape, with highest concentrations along the centreline. It is found that the dense gas reduces the vertical and spanwise turbulent momentum transport and, as a consequence, the turbulence kinetic energy. The reduction coincides with the area where the gradient Richardson number exceeds its critical value, i.e. where the flow may be characterized as stably stratified. Interestingly, this region does not correspond to where the concentration of dense gas is the highest (close to the ground), as this is also where the largest velocity gradients are to be found. Instead there is a layer in the middle of the dense gas cloud where buoyancy is dynamically dominant. [ABSTRACT FROM AUTHOR]

Pri ispitivanju modela u "rafalnom" aerotunelu sa prekidnim dejstvom T-38, na Mahovim brojevima većim od 2, moraju se uzeti u obzir prelazne pojave koje se javljaju na početku i na kraju rada aerotunela. To su stanja kada su model i aerovaga izloženi velikim aerodinamičkim silama i momentima. Ova kombinovana opterećenja mogu oštetiti modele i aerovage, pa bi bilo potrebno unapred znati kolike se vrednosti očekuju za pojedine konfiguracije modela, kako bi se izvršio pravilan izbor aerovage i odgovarajućih materijala za izradu modela. U tu svrhu postoje dijagrami koji pružaju mogućnost procene ovih opterećenja. Dijagrami su dobijeni na osnovu ispitivanja nekoliko različitih modela na Mahovim brojevima većim od 2. U radu su prikazana merenja prelaznih opterećenja na još dva modela, a rezultati su upoređeni sa već postojećim dijagramima. / The T-38 wind tunnel is a blow down, intermittent-run type of wind tunnels. During model testing in the this type of wind tunnels, at Mach numbers higher than 2, transient loads which appear during the starting and stopping of the wind tunnel runs must be taken into consideration. These are the conditions when a model and the wind tunnel balance are exposed to large aerodynamic forces and moments. These combined loads can damage models and wind tunnel balances, and, for this reason, it is very important to determine them in advance for any particular model configuration so that an appropriate wind tunnel balance and materials for model manufacturing can be chosen. For that purpose there are graphs which give possibilities to estimate these loads. The graphs are based on experiments with a number of different models at Mach numbers higher than 2. This paper gives the measurements of transient loads on two more models and the results are compared with the already existing graphs.

Wind-induced operational variability is one of the major challenges for structural health monitoring of slender engineering structures like aircraft wings or wind turbine blades. Damage sensitive features often show an even bigger sensitivity to operational variability. In this study a composite cantilever was subjected to multiple mass configurations, velocities and angles of attack in a controlled wind tunnel environment. A small-scale impact damage was introduced to the specimen and the structural response measurements were repeated. The proposed damage detection methodology is based on automated operational modal analysis. A novel baseline preparation procedure is described that reduces the amount of user interaction to the provision of a single consistency threshold. The procedure starts with an indeterminate number of operational modal analysis identifications from a large number of datasets and returns a complete baseline matrix of natural frequencies and damping ratios that is suitable for subsequent anomaly detection. Mahalanobis distance-based anomaly detection is then applied to successfully detect the damage under varying severities of operational variability and with various degrees of knowledge about the present operational conditions. The damage detection capabilities of the proposed methodology were found to be excellent under varying velocities and angles of attack. Damage detection was less successful under joint mass and wind variability but could be significantly improved through the provision of the currently encountered operational conditions. [ABSTRACT FROM AUTHOR]

SIRANERISK is an operational model for the simulation of the dispersion of unsteady atmospheric releases of pollutant within and above an urban area. SIRANERISK is built on the same principles as the SIRANE model, and couples a street network model for the pollutant transfers within the urban canopy with a Gaussian puff model for the transfers above it. The performance of the model are here analysed by a detailed comparisons with wind-tunnel experiments. These experiments concern the dispersion of steady and unsteady pollutant releases within and above obstacle arrays with varying geometrical configurations, representing different topologies of idealised urban districts. The overall good agreement between numerical and experimental data demonstrates the reliability of SIRANERISK as an operational tool for the assessment of risk analysis and for the management of crises due to the accidental release of harmful airborne pollutants within a built environment. [ABSTRACT FROM AUTHOR]

Aromatic compounds (ACs) are major components of volatile organic compounds emitted from municipal solid waste (MSW) landfills. The ACs emissions from the working face of a landfill in Beijing were studied from 2014 to 2015 using a modified wind tunnel system. Emission factors (EFs) of fugitive ACs emissions from the working face of the landfill were proposed according to statistical analyses to cope with their uncertainty. And their impacts on air quality were assessed for the first time. Toluene was the dominant AC with an average emission rate of 38.8 ± 43.0 μg m −2 s −1 (at a sweeping velocity of 0.26 m s −1 ). An increasing trend in AC emission rates was observed from 12:00 to 18:00 and then peaked at 21:00 (314.3 μg m −2 s −1 ). The probability density functions (PDFs) of AC emission rates could be classified into three distributions: Gaussian, log-normal, and logistic. EFs of ACs from the working face of the landfill were proposed according to the 95th percentile cumulative emission rates and the wind effects on ACs emissions. The annual ozone formation and secondary organic aerosol formation potential caused by AC emissions from landfills in Beijing were estimated to be 8.86 × 10 5 kg year −1 and 3.46 × 10 4 kg year −1 , respectively. Toluene, m + p -xylene, and 1,3,5-trimethylbenzene were the most significant contributors to air pollution. Although ACs pollutions from landfills accounts for less percentage (∼0.1%) compared with other anthropogenic sources, their fugitive emissions which cannot be controlled efficiently deserve more attention and further investigation. [ABSTRACT FROM AUTHOR]

The simulation performance over complex building clusters of a wind simulation model (Wind Information Field Fast Analysis model, WIFFA) in a micro-scale air pollutant dispersion model system (Urban Microscale Air Pollution dispersion Simulation model, UMAPS) is evaluated using various wind tunnel experimental data including the CEDVAL (Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models) wind tunnel experiment data and the NJU-FZ experiment data (Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data). The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier-Stokes equations, and can produce very high-resolution (1-5 m) wind fields of a complex neighborhood scale urban building canopy (~ 1 km ×1 km) in less than 3 min when run on a personal computer. [ABSTRACT FROM AUTHOR]

Hypervelocity ballistic reference wind tunnel models are of interest to researchers in the field of high-speed aerodynamics, both as the means to validate the measurement chains in wind tunnels, and as test cases for validation of software tools for aerodynamic analysis. Wind tunnel tests of these models and some numeric simulations were performed in the Military Technical Institute in Belgrade. In the analysis of the obtained data, certain issues appeared that urge caution in the use of these models as test cases. It is shown that supersonic starting loads and high dynamic pressures in a wind tunnel can prohibit the use of the slender ‘standard’ support sting, so that some reference data are from tests with various non-standardized stings of larger relative diameters. Besides, the available reference data are actually few and quite old, the only comprehensive, freely available dataset being that from the 1963/64 tests at the Arnold Engineering Development Centre, which seems to be a de-facto reference. However, results for the total axial-force coefficients from those tests differ significantly from results from several other sources, which group well. A need is expressed for a larger database of test results, and a ‘standard’ sting of larger relative diameter is proposed for future tests. [ABSTRACT FROM AUTHOR]

With the rapid increase in China's development, the cities have become immensely more dense putting pressure on design and infrastructure. In the past, most of the China's buildings imitated the foreign architectural styles and had a lack of scientific and meaningful design. These buildings became to be known as the 'the cheap copy buildings'. The primary cause was the shortage of proper technology, such as building wind tunnel test equipment. Therefore, scientific design was not always an option, only reversal or empirical design could be utilized. This meant architects were restricted to construct the same design or imitate foreign buildings. Now that China has access to wind tunnels, building designs can be analysed at a higher level. Forward and scientific designs can be used to improve the buildings' capabilities with low cost. [ABSTRACT FROM AUTHOR]

This paper aims to design a sting support system for a transonic wind tunnel test for a commercial wide-bodied aircraft, which includes a single sting and a blade support. Parameters of the sting support system have been analyzed and three key parameters are selected for optimization. A RANS solver has been developed to investigate the effects of key parameters on the sting support interference. Influences of four incidence angles and five locations of an expanding point on the single sting interference are studied, and also the effects of six vane leading edge sweep angles on the blade support interference are investigated. The optimal key parameters are determined, based on numerical results and structural rigidity. Structural intensity verification of the optimized support system has been performed under the estimated aerodynamic loading by commercial software. Results indicate that a 6° incidence angle and 03 expanding point are the optimal parameters for a single sting and a 50° leading edge sweep angle of the vane is optimal for blade support. The optimized sting system with sufficient safety factors is suitable for commercial wide-bodied aircraft wind tunnel tests, which implies the method in this paper can be used to optimize the sting support system of other vehicles. [ABSTRACT FROM AUTHOR]