Tunnel Facility Research Articles

Wind dispersal of seeds of Parthenium hysterophorus L. (Asteraceae) contributes to its steady invasion and spread

AbstractWind dispersal is considered to be a potentially important mode of spread for parthenium weed (Parthenium hysterophorus L.), an invasive Asteraceae herb of worldwide significance. However, empirical evidence of the role of wind dispersal on the seeds (achenes) of parthenium weed in natural landscapes is lacking. The results of a simulation study undertaken at a wind tunnel facility, Australia, indicated that the dispersal distance of parthenium weed achenes is largely determined by wind velocity (109–131% increase in distance where wind velocity is doubled) and plant release height (75–80% increase when release height is doubled). Glasshouse harvested achenes released from 1 m in height could travel up to 2 m under a 2 m s−1 wind velocity, with the majority of achenes reaching more than 1 m. Smaller‐sized achenes travelled 5% further than larger‐sized achenes. The terminal velocity was calculated to be 1.256 ± 0.006 m s−1, indicating a moderate wind dispersal ability for the weed. A complementary field study in Southeast Queensland, Australia, indicated that the cumulative wind velocity and wind direction, instead of the mean wind velocity, determined the direction of dispersal of the achenes. Further post‐dispersal surveys suggested the number of achenes outside of a standing population declined rapidly as distance from the population increased. Most achenes were dispersed less than 2 m from their parent plant, while the maximum distance achieved was less than 5 m under natural conditions in North Queensland. In conclusion, the natural wind dispersal of parthenium weed consists of small, but measurable increments each year, thus contributing to the weed proliferation and spread at the landscape scale level.

Effect of the J-Shaped Wind Turbine Airfoil Opening Ratio and Thickness on the Performance of Symmetrical Airfoils

Abstract In this work, the effect of the inner opening ratio on the J-shaped airfoils aerodynamic performance was studied and documented for symmetrical airfoils. Three different airfoil thicknesses were investigated: small (NACA0008), medium (NACA0015), and large (NACA0024). For each airfoil thickness, effects of three inner opening ratios were analyzed: one-third, one-half, and two-thirds. The performance of each opening ratio was compared with the performance of the solid airfoil “zero opening ratio” for different angles of attack between 5 deg and 20 deg. All designs were simulated using the computational fluid dynamics (CFD) technology against experimental results for solid NACA4412 airfoil in the University of Wisconsin-Milwaukee (UWM) wind tunnel facility and other published experimental data. It was found that large eddy simulation yields accurate solutions with a smaller number of mesh cells compared to the k–ω turbulence model but with much longer computational time. The lift-to-drag ratio for all studied airfoils has a maximum value for solid airfoils compared to those equipped with openings. For airfoils equipped with 00.00% opening ratio “solid,” NACA0015 airfoil has the maximum lift-to-drag ratio. Furthermore, it was found that NACA0008 equipped with a 33.33% opening ratio has the best performance of all studied J-shaped airfoils.

A Fast Thermal 1D Model to Study Aerospace Material Response Behaviors in Uncontrolled Atmospheric Entries.

A preliminary thermal 1D numerical model for studying the demise behavior of stainless steel 316L, silicon carbide (SiC) and carbon fiber reinforced polymer (CFRP) during uncontrolled atmospheric entry is proposed. Test case modeling results are compared to experimental data obtained in the framework of ESA Clean Space initiative: material samples were exposed to different heat flux conditions using the Plasma Wind Tunnel (PWT) facilities at the Institute of Space Systems (IRS) of the University of Stuttgart. This numerical model approximates the heating history of the selected materials by simulating their thermal response and temperature profiles, which have trends similar to the experimental curves that are found. Moreover, when high heat flux conditions are considered, the model simulates the materials’ mass loss due to the ablation process: at the end of the simulation, the difference between the experimental and the modeled results is about 17% for CFRP and 35% for stainless steel. To reduce the model’s uncertainties, the following analysis suggests the need to consider the influence of adequate material thermophysical properties and the physical-chemical processes that affect the samples’ temperature profile and mass loss.

Impact of dust loads in long railway tunnels: In-situ measurements and consequences for tunnel facilities and operation

Reliable information concerning rail tunnel dust emissions dependent on parameters such as train type, train speed, operating conditions, etc. is quite rare. Thus, in order to quantify the effect of heavy metals on the environment, specific data is needed when designing air filtration systems inside the tunnel, or in carrying out environmental assessment studies. Detailed investigations were therefore carried out in a test installation in an Austrian rail tunnel. In order to be able to use these data for the long railway tunnels currently under construction, train-specific emission factors were determined. It was found that emissions from freight trains are up to 6.68 times higher than those from passenger trains. Bulk freight transport in open cars produces the highest emissions, while the short regional passenger trains exhibit the lowest emission levels. Chemical analysis of the samples came up with a mass fraction of 60% related to metals, of which, iron is the dominating component. Based on these findings, maintenance intervals for high quality dust filters were derived.In addition, the knowledge gained on train type-dependent emission factors greatly helps to improve upon the very poor data now used in environmental studies, particularly when determining railway particulate matter emissions.

A New Test Facility for Advanced Testing of Variable Inlet Guide Vanes

Various experimental and numerical studies of advanced blade configurations for variable inlet guide vanes (VIGVs) were conducted during the past years. Nevertheless, experimental loss characteri-zations of VIGV blade designs vastly focused on the primary profile losses. Secondary flow losses as they occur in a real engine application were often neglected. For this reason, a new wind tunnel facility was erected and commissioned at the Bundeswehr University Munich to enable extensive investigations of application-oriented annular VIGV configurations at typical low subsonic Mach numbers. Five-hole probe field traverses are established by a probe traversing unit in the in-and outflow region of the VIGV. The requirements for a further extension of the applicable measuring techniques by optical methods is moreover provided. Thus, not only profile losses caused by the blades, but also secondary flow losses generated by blade-wall flow interactions and the open blade tips can be resolved in detail.

An experimental study on base pressure behavior during bistability characterisation for a bluff body vehicle close to the ground

The present experimental investigation is concerned with the existence of Bi-stability behaviour at various ground clearances in the wake of Square Back Ahmed Body geometry (SBAB). The experiments were performed at a Reynolds number of 7.2 × 104 in a subsonic open-type wind tunnel facility. The raw readings from the pressure scanner alone were used to predict the existence of bistability character. The bistability behavior in the wake was explored in two different ways (i) The conventional base-pressure contours and pressure gradient plot, and (ii) The wavelet analysis. The minimum ground clearance for the wake to exhibit bistability was found to be 0.468H, much higher than the values determined in the previous experimental works. The discrepancy was due to relatively high turbulence intensity in the test section and experimental setup. We also found that the bi-stability switching rate was found to increase with a decrease in ground clearance. The wavelet analysis helped in determining the existence of long time-scale frequencies associated with the Bi-stability behavior.

탐욕 알고리즘 및 특이치 분해를 이용한 프로펠러 초생 캐비테이션의 위치추정

An accurate evaluation of the inception of propeller cavitation is a prerequisite for the prediction of the underwater radiated noise performance of ships. Current work treats the acoustic localization for incipient cavitation using the compressive sensing (CS) method. Orthogonal matching pursuit (OMP) based on a greedy algorithm is employed to tackle the CS localization problem owing to its low computational cost, making it appropriate for online applications. The application of singular value decomposition (SVD) is also suggested to identify the number of independent sources, which is crucial for initializing the algorithm. The established procedure is verified using experimental data acquired in a cavitation tunnel facility.

CFD analysis of large-scale hydrogen detonation and blast wave overpressure in partially confined spaces

The effect of confinement on the magnitude of overpressure due to a gaseous detonation of a hydrogen-air mixture was studied with the aid of numerical simulations. A simplified combustion reaction kinetic model applied along with computational fluid dynamics (CFD) allowed for the numerical simulation of large-scale detonations of hydrogen-air mixtures. The model was validated against experimental data reported in the literature for the case of a large-scale (300 m3) surface (unconfined space) detonation of a hydrogen-air mixture and the results of a hydrogen-air (confined space) detonation test performed in a 263 m3 tunnel facility. The predicted overpressure and detonation velocity was in agreement with the measurements in both unconfined and confined detonation cases. To verify the effect of confinement on the magnitude of the blast wave overpressure due to detonation of a combustible gas cloud, a series of CFD simulations of hydrogen detonations followed by propagation of a non-reactive blast wave in various geometries were carried out. The results were compared with the correlation applicable for unconfined detonations, which was also found to be applicable for partially confined detonations after the transformation of the distance from explosion centre to spherical blast wave equivalent radius.

Characterization of Supersonic Compressible Fluid Flow Using High-Speed Interferometry.

This paper presents a very effective interference technique for the sensing and researching of compressible fluid flow in a wind tunnel facility. The developed technique is very sensitive and accurate, yet easy to use under conditions typical for aerodynamic labs, and will be used for the nonintrusive investigation of flutter in blade cascades. The interferometer employs a high-speed camera, fiber optics, and available “of-the-shelf” optics and optomechanics. The construction of the interferometer together with the fiber optics ensures the high compactness and portability of the system. Moreover, single-shot quantitative data processing based on introducing a spatial carrier frequency and Fourier analysis allows for almost real-time quantitative processing. As a validation case, the interferometric system was successfully applied in the research of supersonic compressible fluid discharge from a narrow channel in a wind tunnel. Density distributions were quantitatively analyzed with the spatial resolution of about . The results of the measurement revealed important features of the flow pattern. Moreover, the measurement results were compared with Computational Fluid Dynamics (CFD) simulations with a good agreement.

Experimental investigation of hybrid laminar flow control by a modular flat plate model in the DNW-NWB

To determine the characteristics of new suction concepts for hybrid laminar flow control (HLFC) a modular flat plate wind tunnel model is investigated in the DNW-NWB wind tunnel facility. This approach allows detailed examination of suction characteristics in consideration of realistic boundary layer flow conditions. The following evaluation reveals the effects of joining methods between successive panels and other surface disturbances of porous materials and underlying chambers on HLFC techniques. After successful measurements with and without suction panels, this paper compares experimental results with theoretical and numerical approaches and draws conclusions from N-factor results and boundary layer (BL) measurements.

Modeling In-Flight Ice Accretion Under Uncertain Conditions

In-flight ice accretion under parametric uncertainty is investigated. Three test cases are presented that reproduce experiments carried out at the NASA’s Glenn Icing Research Tunnel facility. A preliminary accuracy assessment, achieved by comparing numerical predictions against experimental observations, confirms the robustness and the predictiveness of the computerized icing model. Besides, sensitivity analyses highlight the variance of the targeted outputs with respect to the different uncertain inputs. In rime icing conditions, a predominant role is played by the uncertainty affecting the airfoil angle of attack, the cloud liquid water content, and the mean volume diameter of droplets. In glaze icing conditions, the sensitivity analysis shows instead that the output variability is due mainly to the ambient temperature uncertainty. Moreover, this paper exposes a challenge inherent in the approximation of the full icing model by means of standard (linear) polynomial chaos regression techniques. The complexity is related to the approximation of the model behavior in domain regions scarcely affected by ice buildup. To mitigate this issue, a nonlinear regression method is proposed and applied.

A New Environmentally Friendly Utilization of Energy Piles into Geotechnical Engineering in Northern China

In the past 30 years, because of built-in advantages, energy saving, pollution control, and sustainability, the energy pile system has had a rapid development around the world. Many scholars did numerous researches on the parameters’ optimization, heat exchange efficiency, and structure-soil response. Also, the researches of evolutional GSHP system using high temperature in deep mine and lager collection surface of tunnel lining were learned. At present, most of researchers are discussing the geothermal collection for the heating or cooling the building, and plenteous and significant research achievements have been obtained. It is a novel attempt to apply energy pile to geotechnical engineering, and good results have been achieved in engineering practice in Northern China. The area of northern China is a typical seasonal frozen region: the high temperature in summer and the cold weather and accumulated snow in winter will result in huge challenge and resource consumption of maintaince on highway tunnel, pavement, and other geotechnical engineering facilities. In this paper, taking example of using the geothermal heat exchanger to melt snow, the novel idea of using energy piles to prevent track in summer and crack in winter of pavement, and guaranteeing the safety of frost crack on tunnel lining were discussed. Also, through simulation research, we propose a buried pipe form with good heat transfer uniformity-spiral buried pipe, which has better engineering applicability. This shows us that the application of energy pile in geotechnical engineering will provide solutions to geotechnical problems, which will have a brilliant future.

Effects of Holes Arrangement on the Superposition Characteristics of Film Cooling Effectiveness

The purpose of the current research is to test and analyze the applicability of the Sellers model in different arrangements and configurations of film cooling holes and then to modify the Sellers model to improve the accuracy of the superposition prediction. The film cooling effectiveness distributions at different blowing ratios are obtained using the infrared thermometry technology. The flat plate experiments are completed in a low-speed closed-loop wind tunnel facility. The mainstream Reynolds number based on the film hole diameter is 6300, and the blowing ratios range from 0.8 to 1.8. The superposition characteristics are described in three different cases: double rows of cylindrical holes in an inline arrangement, double rows of cylindrical holes in a staggered arrangement, and double rows of compound angle holes in an inline arrangement. The results indicate that the Sellers model cannot accurately predict the film cooling effectiveness in certain conditions, which is mainly attributed to the interaction between counter-rotating vortex pairs of the adjacent rows and the increasing momentum of mainstream near the wall surface. For all cases, the corresponding modified superposition prediction methods are given in this paper.

Endwall Heat Transfer and Cooling Performance of a Transonic Turbine Vane With Upstream Injection Flow

Abstract Flow fields near the turbine vane endwall region are very complicated due to the presence of high three-dimensional passage vortices and endwall secondary flows. This makes it challenging for the endwall to be effectively cooled by using traditional endwall cooling methods, such as impingement cooling combined with local film cooling inside the vane passage. One effective endwall cooling scheme: coolant injection flow through discrete holes upstream of the vane leading edge on the endwall, has been considered by many gas turbine companies. The present paper focuses on endwall film cooling effectiveness evaluation with upstream coolant injection through discrete holes. Detailed experimental and numerical studies on endwall heat transfer and cooling performance with coolant injection flow through upstream discrete holes are presented in this paper. High-resolution heat transfer coefficient (HTC) and adiabatic film cooling effectiveness values were measured using a transient infrared thermography technique on an axisymmetric contoured endwall. The endwall tested was a scaled up inner endwall of an industrial transonic turbine vane with double-row discrete cylindrical film cooling holes located 0.39Cx upstream of the vane leading edge. The tests were performed in a transonic linear cascade blowdown wind tunnel facility. Conditions were representative of a land-based power generation turbine with exit Mach number of 0.85 corresponding to exit Reynolds number of 1.5 × 106, based on exit condition and axial chord length. A high turbulence level of 16% with an integral length scale of 3.6%P was generated using inlet turbulence grid to reproduce the typical turbulence conditions in real turbine. Low temperature air was used to simulate the typical coolant-to-mainstream condition by controlling two parameters of the upstream coolant injection flow: mass flowrate to determine the coolant-to-mainstream blowing ratio (BR = 2.5, 3.5), and gas temperature to determine the density ratio (DR = 1.2). To highlight the interactions between the upstream coolant flow and the passage secondary flow combined with the influence on the endwall heat transfer and cooling performance, a comparison of CFD predictions with experimental results was performed by solving steady-state Reynolds-averaged Navier–Stokes (RANS) using the commercial CFD solver ansys fluent V.15. A detailed numerical method validation was performed for four different Reynolds-averaged turbulence models. The realizable κ−ε model was validated to be suitable to obtain reliable numerical solution. The influences of a wide range of coolant-to-mainstream blowing ratios (BR = 1.0, 1.5, 1.9, 2.5, 3.0, 3.5) were numerically studied. Complex interactions between coolant injections and secondary flows in vane passage were presented and discussed. An optimal value of the blowing ratio for the present upstream discrete film hole is also suggested based on the current study. Results indicate that for lower values of BR, the endwall coolant coverage from the upstream double-row discrete holes is strongly controlled by the passage secondary flow, thus the cooling effectiveness is very poor. As the BR increases, the strong secondary flow in vane passage can be suppressed by the coolant injections and begin to be almost eliminated when BR increases to a critical value (BR = 2.5–3.0). Beyond the critical BR, most of the injected coolant begins to lift off from the endwall and penetrate significantly into the mainstream flow, yielding inefficient endwall cooling performance.

Experimental Investigation of Near-Field Aeroacoustic Characteristics of a Pre- and Post-Stall NACA 65-410 Airfoil

The present study reports an experimental investigation of the near-field aeroacoustic characteristics of a cambered NACA 65-410 airfoil. The experiments were performed in an aeroacoustic wind tunnel facility at a moderate chord-based Reynolds number of 4.2×105. Detailed static and dynamic surface pressure information was recorded to reveal the pre- and post-stall dynamics. By varying the angle of attack from 7° to 15°, a stall behavior similar to thin airfoil stall is observed from the evolution of the static and dynamic surface pressure spectra at different chordwise locations. Moreover, while the surface pressure spectra show a monotonic decrease with constant gradients after entering full stall, the pre-stall behavior shows a different trend and partly resembles the attached and stalled flows. Furthermore, the unsteady surface pressure spectra are compared to those obtained from a NACA 0012 airfoil, showing notable differences in the near-field stall dynamics. A scaling formula proposed by a previous study is applied to the present pressure spectra and found to scale well except for measurements close to the leading edge. The present near-field measurements and the streamwise and spanwise length scales can be useful input to the modeling of airfoil separation and stall noise for cambered airfoils.

Assessment of high enthalpy flow conditions for re-entry aerothermodynamics in the plasma wind tunnel facilities at IRS

This article presents the full operational experimental capabilities of the plasma wind tunnel facilities at the Institute of Space Systems at the University of Stuttgart. The simulation of the aerothermodynamic environment experienced by vehicles entering the atmosphere of Earth is attempted using three different facilities. Utilizing the three different facilities, the recent improvements enable a unique range of flow conditions in relation to other known facilities. Recent performance optimisations are highlighted in this article. Based on the experimental conditions demonstrated a corresponding flight scenario is derived using a ground-to-flight extrapolation approach based on local mass-specific enthalpy, total pressure and boundary layer edge velocity gradient. This shows that the three facilities cover the challenging parts of the aerothermodynamics along the entry trajectory from Low Earth Orbit. Furthermore, the more challenging conditions arising during interplanetary return at altitudes above 70 km are as well covered.

Aerodynamic analysis of aircraft model using indigenously developed wind tunnel facility

This paper presents a design of force balance setup that can measure lift force acting on the aircraft model. The setup was developed indigenously and installed in an open circuit low-speed wind tunnel. It mainly consists of two components viz. a traverse mechanism that can hold the model in the test section at different angles of attack and air speeds and a supporting frame to hold the traverse mechanism over it. The spring balances are used to obtain lift force readings at different angles and air speeds. The experimental and numerical investigations were done in the wide range of Reynolds number (range: 0.55 to 1.12 lakh) and angle of attack (range: -6° to 20°). The results are presented in terms of pressure contours, velocity contours, pressure coefficient and lift coefficient. From the experiments it was found that value of lift coefficient increases with angle of attack and stalling occurs at 18° for all the air speeds. However, in the numerical results the stalling was observed little earlier than 18° angle of attack. The experimental results were compared with CFD results and an average relative error of 18% was observed which may be due to assumption of 2-D airfoil in CFD analysis.

Aerodynamical characteristics of a reduced scale ground vehicle according to yaw angle variations

PurposeThe purpose of this paper is to study pressure measurement correlations, as the location of the pressure sensors should enable to capture variation of the drag force depending on the yaw angle and some geometrical modifications.Design/methodology/approachThe present aerodynamical study, performed on a reduced scale mock-up representing a sport utility vehicle, involves both numerical and experimental investigations. Experiments performed in a wind tunnel facility deal with drag and pressure measurements related to the side wind variation. The pressure sensor locations are deduced from wall streamlines computed from large eddy simulation results on the external surfaces of the mock-up.FindingsAfter validation of the drag coefficient (Cd) values computed with an aerodynamic balance, measurements should only imply pressure tap mounted on the vehicle to perform real driving emission (RDE) tests.Originality/valueRelation presented in this paper between pressure coefficients measured on a side sensor and the drag coefficient data must enable to better quantify the drag force contribution of a ground vehicle in RDE tests.

FLEET velocimetry measurements in the ONR-UTA arc-jet wind tunnel

This manuscript presents and discusses the very first successful application of the Femtosecond Laser Electronic Excitation Tagging (FLEET) velocimetry technique in an arc-jet flow. Specifically, one-dimensional, quantitative, FLEET velocimetry data were obtained in the effort to characterize the 1.6 MW ONR-UTA arc-jet plasma wind tunnel, Leste, housed at the Aerodynamics Research Center of the University of Texas at Arlington. While the FLEET technique has been used in other types of high-speed wind tunnel facilities, application to flows with high background radiation, such as arc-jets, has never been demonstrated before this work. The high background emissions posed concerns on the feasibility of performing FLEET velocimetry measurements. However, this work demonstrates how these concerns were addressed and presents the first successful application of the FLEET technique in arc-jet flows. The FLEET emissions in the arc-jet plume were successfully imaged, and a significant spatio-temporal variation in the tag’s displacement was observed. For the selected operational condition in this study, the average measured gas velocity in the arc-jet plume was 1.78 km/s.

Wind Tunnel Testing of ONERA-M, AGARD-B and HB-2 Standard Models at Off-Design Conditions

Published results for standard wind tunnel models at non-standard test conditions are quite rare and/or may not be available. It has been found that those results are a useful aid in preparations for a number of wind tunnel tests in the Military Technical Institute (VTI) in Belgrade. Test campaigns of standard models at non-standard conditions are performed to serve as an internal database for future wind tunnel tests in such environments. Those tests, that partially overlap the referenced Mach number and/or angle of attack ranges, are conducted in different VTI’s test facilities; different model sizes and support stings were used. The standard models used in static measurements in VTI, ranging from simple missile shapes and re-entry bodies to complicated airplanes, are briefly described and sample non-standard test results are given. The correlation of the test results among models and facilities has been done with references in the available ranges, and, after confirming a good agreement, it is assumed that the results are also valid in the extended ranges of conditions. These results may be useful for researchers in other wind tunnel facilities and for those who handle CFD tools.