Tunnel Facility Research Articles

Experimental characterization of the flowfield and cavitation physics of a tip-loaded hydrofoil

This paper reports an experimental study of tip vortex flowfield and cavitation inception of a tip-loaded hydrofoil. Vortex strength, wandering, and turbulence statistics are characterized using stereo particle image velocimetry (SPIV) in a water tunnel facility, at a chord Reynolds number of 1.3×106. Cavitation physics are characterized using high-speed videography and dual-hydrophone acoustic cavitation measurements. The loading of the rectangular planform hydrofoil has a maximum at 65% span, 56% greater than that at the root, i.e., the hydrofoil loading is representative of non-elliptically loaded open propellers. Acoustic cavitation inception is quantified and is observed to precede visual cavitation onset using unaided and high-speed imaging. Measurements reported here show that vorticity fluctuations are nearly of the same magnitude as the ensemble vorticity. Instantaneous measurements of vorticity at the trailing edge, 12-chord downstream, and one-chord downstream positions are reported. Their peak magnitudes are located adjacent to the ensemble vortex center and are between four and five times the ensemble mean. The fluctuating vorticity measurements, taken in conjunction with high-speed video observations, provide insight into the hydrodynamic conditions responsible for intermittent cavitation events. The reported measurements elucidate instantaneous and mean turbulence physics associated with vortex cavitation and can provide a validation basis for numerical simulations.

Effect of wind barriers on the aeroelastic instabilities of a hinged-deck cross-section cable-stayed bridge

The main idea of a hinged-deck cross-section cable-stayed bridge appears with the need of increasing the capacity of a simple bridge by adding to lateral extension decks to the main deck. An experimental wind tunnel campaign to analyse the aeroelastic behaviour of a hinged-deck cross-section cable-stayed bridge has been performed. The bridge cross-section under study is formed by three parts: a central deck and two lateral extension decks joined to the central one using hinges and supported by their respective cable systems. The experimental model used is a reduced 6 degrees of freedom (DOFs) model for the elastic problem, which has previously proved to give good results concerning the bridge behaviour. The number of DOFs induces a new complexity in the oscillating motion of the bridge deck, compared to classical single deck 2 DOFs configurations.In this work, the aeroelastic tests performed at the UPM/IDR ACLA-16 wind tunnel facility to address the effect of wind barriers on the aeroelastic characteristics of the bridge section are reported. Nominal barriers are considered and compared with the case with no barriers. The effect of barrier porosity (wind barriers of the central deck and lateral decks) is also analysed. Stability ranges are reported in terms of reduced wind speed. The results show the large influence of the barriers in controlling the aeroelastic characteristics of the bridge. In some configurations, a large increase in bridge stability has been found due to the relevant effect of the barriers in changing the flow around the bridge.

The Ford Rolling Road Wind Tunnel Facility

<div class="section abstract"><div class="htmlview paragraph">The Ford Motor Company Rolling Road Wind Tunnel (RRWT) is a state-of-the-art aerodynamic wind tunnel test facility in Allen Park, Michigan. The RRWT has operated since January 2022 and is designed for passenger and motorsport vehicle development. The test facility includes an office area, three secure customer vehicle preparation bays, a garage area, a vehicle frontal area measurement system, and a full-scale ¾ open jet wind tunnel. The wind tunnel features an interchangeable single belt and 5-belt Moving Ground Plane (MGP) system with an integrated 6-component balance, a two-position nozzle, boundary layer removal systems, and two independent flow traverse systems. Each flow traverse has a large horizontal box beam and vertical Z-strut that can position the flow traverse accurately within the test volume. The individual traverse systems can also operate in tandem and have the capability to perform stereo PIV measurements and scale model vehicle testing, including vehicle passing or drafting simulations. The MGP can be quickly changed between single belt and 5-belt operations, requiring only a single eight-hour shift to transition between the two configurations. The efficient wind tunnel airline is capable of airspeeds up to 250 km/h in the large 26.4 m<sup>2</sup> nozzle configuration and 322 km/h in the small 18.6 m<sup>2</sup> nozzle configuration using a 12-blade, 8 m diameter fan with a 5.4 MW motor. The wind tunnel’s flow quality and aerodynamic performance compare well with similar facilities in the automotive industry. Ford Motor Company is currently correlating aerodynamic measurement data from the RRWT with other similar facilities, using 60 vehicles across multiple product lines.</div></div>

Steady velocity measurements in the stern wake of submarine hull form at high angles of incidence

Velocity distribution in the stern region over a generic submarine hull form (SUBOFF) at high angles of incidence was investigated through steady velocity measurements in the Wind Tunnel Facility at Naval Science & Technological Laboratory, India. Velocity measurements were performed for a range of angles of incidence in angle of attack (+8° to - 40°) and drift (0°–28°) on 1.372 m model at Reynolds number 1.7 × 106. The present study for high angles of incidence is to depict a submarine motion during extreme manoeuvers in case of emergency situations. The particulars of the SUBOFF model, experimental facility and measurement technique, test results for axial, tangential and radial velocity measurements, non-uniformity and circumferential mean velocity, derived quantities for vorticity and circulation are highlighted in the paper. The velocity measurements data generated from the above studies will greatly complement the current research on turbulent flows over submerged bodies both computationally and experimentally.

Overall Resilient Evaluation of Surrounding Rock of In-Service High-Speed Railway Tunnel Based on Information Fusion-Improved Fuzzy Matter-Element

Once the high-speed railway tunnel is put into use, its resilience will determine the possibility of permanent safety of the tunnel due to the closure of the structural space of the high-speed railway tunnel in service. Resilience theory is introduced into a risk analysis of operating high-speed rail tunnels to improve the ability to respond to risks in operating high-speed rail tunnels and to relieve the aging phenomenon caused by changes in the tunnel with time. First, an evaluation framework for the safety resilience of existing high-speed railway tunnels is constructed. Starting from the attributes of resilience such as resistance, adaptability, and resilience, and considering the characteristics of high-speed railway tunnels, protective measures, emergency management measures, and other factors, we fit the risk factors and probability of accident type of the high-speed railway tunnel and establish a tunnel safety resilience evaluation index system with 10 indexes. Secondly, the method of information fusion is used to combine subjective weighting and objective weighting. Then, the comprehensive weight of the evaluation index is obtained based on the principle of minimum discriminant information. Thirdly, the system resilience evaluation model based on the TOPSIS improved fuzzy matter-element is constructed to determine the classification criteria of resilience. On this basis, based on the temporal and spatial variability of the ductile tunnel, the concepts of ductile transition and ductile attenuation are introduced and the tunnel toughness optimization model is established to suppress the attenuation situation, enhance the transition ability, and then improve the system resilience level. On this basis, an optimal lifting scheme is obtained. Finally, taking Ai-Min tunnel of Ha-Mu high-speed railway as the engineering background, the flexibility of the resilience system is calculated, and the resilience grade (3) of the rock system surrounding the tunnel is obtained. Combined with the numerical model, improvement measures for specific tunnel facilities are proposed. The results show that the Ai-Min tunnel system has a general ability to resist external intrusion and prevent disasters, and the resilience level is general. It should focus on improving the resilience level of the transition index. The resilience evaluation results of the evaluation model are consistent with the actual situation of the project.

Computational and Experimental Study of Nonequilibrium Flow in Plasma Wind Tunnel

The present work examines the thermochemical nonequilibrium flow in the freestream and shock layer of the Plasma Wind Tunnel Facility using experiments and computations. Computational studies were performed using the open-source solver , which was validated using the NASA Interaction Heating Facility case. Two chemical reaction models were used to compute the nonequilibrium state of air, composed of six species (, , NO, N, O, Ar). Optical emission spectroscopy was employed to experimentally capture the first positive system emission from the freestream and molecular CN vibration bands emissions in the shock region. The Boltzmann plot method was employed to estimate the vibrational temperatures from the measured spectra. The measured vibrational temperatures in the freestream for two different transitions of agree with one another, which shows that the vibrational modes obey the Boltzmann distribution for the conditions considered in this study. The vibrational temperatures computed using in the nozzle freestream and the shock layer for the Plasma Wind Tunnel conditions agree with the values obtained from optical emission spectroscopy.

Acoustic Shielding and Scattering Effects of a Propeller Mounted Above a Flat Plate

To reduce the overall noise pollution generated by aircraft, design choices often attempt to incorporate acoustic shielding often using aircraft wings to minimise the noise generated by engines and propellers. By mounting a propeller above a wing, increasing the noise shielding, acoustic scattering effects can be introduced which change the directivity and magnitude of the noise generated. Experiments were carried out to investigate the acoustic shielding and scattering effects of a propeller mounted above a flat plate trailing edge. Two propellers were tested at constant rotational rates of 5000 RPM and 7000 RPM respectively. The tests were conducted within an anechoic wind tunnel facility with loading and far-field noise data collected by microphone arrays at a parametric set of propeller locations relative to the flat plate trailing edge. Analysis of the spectral content of the noise along with the tonal content of the signals are presented. The levels of coherence and cross spectrum phase are considered to give greater insights into the levels of noise attenuation due to shielding and scattering effects. Analysis of the acoustic data shows locations with notable levels of noise attenuation for both the tonal and broadband noise content.

General Analytical Method to Predict the Spatial–Temporal Distribution of Extreme Pressure in High-Speed Railway Tunnels in the Post-Train Stage

Long-duration aerodynamic pressure fluctuation in high-speed railway tunnels in the post-train stage causes fatigue damage to tunnel structures and facilities. It increases the risk of accidents and requires in-depth research. This complex phenomenon is caused by the superposition of multiple pressure waves generated successively when a train enters/leaves a tunnel. In this study, the spatial–temporal distribution of the pressure state (SDPS) model was developed, and general equations describing the transient pressure state distribution were given. Furthermore, a prediction method for extreme pressures in tunnels and a fast calculation program were proposed based on the SDPS model. The proposed model was verified using field measurements. Using the SDPS model, the worst conditions of pressure fluctuations in tunnels were analyzed. The results show that most of the maximum positive and negative pressures are symmetrical around the midpoint of the tunnel axis and appear alternately around it. When the train/wave velocity ratio M ≤ 0.8 and the train/tunnel length ratio ε ≤ 0.8, the dimensionless position of the maximum peak-to-peak pressure region was concentrated in the region of [0.33,0.67] in the tunnel, indicating the location of potential fatigue damage. The proposed model is helpful in building safe and sustainable transportation systems.

Analysis of Wind Effects on Different Shapes of Tall Buildings

The rapid expansion of cities and increasing population means that land is limited and what land is available is shaped in an erratic manner, while its demand is increasing day by day. Therefore, to cope with this increasing demand and to achieve maximum utilization of resources, tall buildings are being built. However, these buildings are extremely vulnerable to lateral loads, particularly wind loads.To ensure the safety of these buildings, wind tunnel studies are used to examine the effects of wind loads. To combat the issue of shortage of wind tunnel facilities in the world, numerical analysis is used instead. Thus, this project aims to analyse the impact of wind effects on high-rise buildings of different shapes with the help of CFD, by making use of ANSYS. The wind effects have been assessed by obtaining the velocity profile and turbulent profile, pressure contours for different faces of the building, and velocity streamlines for the plan and elevation of the building.

Comparative Study on the Effect of Leading Edge Protuberance of Different Shapes on the Aerodynamic Performance of Two Distinct Airfoils

This study investigated the effect of leading-edge protuberances on the aerodynamic performance of two distinct airfoils with low Reynold’s number (Re): E216 and SG6043. Three protuberance shapes, namely sinusoidal, slot, and triangular, were considered. The amplitudes (A) of protuberances considered were 0.03c, 0.06c, and 0.11c, and the wavelengths (W) were 0.11c, 0.21c, and 0.43c, where c is the chord of the airfoil. The numerical and experimental analyses were performed in the angle of attack (AoA) range of 0° to +20° at and Re of 105. The numerical investigation was performed using the commercial computational fluid dynamics package ANSYS FLUENT. The SST k-ɷ model was used to simulate turbulent flow. The experimental force measurements were conducted using a highly sensitive three-component force balance in a subsonic wind tunnel facility. The flow physics was analyzed using vorticity contours in streamwise and spanwise slices and static pressure distribution contours. The smoke flow visualization technique was used to observe flow streamlines, boundary layer separation, and reattachment over the airfoil surface. The result indicated that the triangular and slot protuberances were the most beneficial for improving poststall lift and reducing skin friction drag. The operating mechanism involved a shift in pressure distribution due to leading-edge alterations and flow energization by secondary flow emanating from the protuberances.

Evaluation of Wind Effects on High-Rise Buildings Using Ansys CFX

Tall building is the growing pattern of cities, these buildings are highly vulnerable to wind loads. Wind load effects on the high-rise building can be found using wind tunnel testing and CFD tools. Wind tunnel facilities are limited all around the world, so CFD tools can be incorporated. In this study, ANSYS CFX is used to investigate the effects of wind on different shapes of high-rise buildings. The results of numerical simulation are compared with the international standards of various countries. Streamline patterns and pressure contours on different faces are discussed in this paper. It is found that building shape and size are having a direct effect on the pressure distribution on various surfaces of the building model. Windward face pressure will always be positive in nature. In this study, the comparison is presented for the variation in the cross-sectional shape of the building model. For this purpose Model C and Model I are having considerable variations and Model X is considered for validation purposes only. It is well established that the results are within the allowable limit. This paper aims to discuss these windgenerated effects in the tall building model.

Fabrication, Testing, and 3D Comprehensive Analysis of Swept-Tip Tiltrotor Blades

This paper covers the design, fabrication, testing, and modeling of a family of Froude-scale tiltrotor blades. They are designed with the objective of gaining a fundamental understanding of the impact of a swept tip on tiltrotor whirl flutter. The goal of this paper is to describe the development of the blades needed for this purpose. The rotor is three bladed with a diameter of 4.75 ft. The blades have a VR-7 profile, chord of 3.15 inches, and linear twist of –37° per span. The swept-tip blades have a sweep of 20° starting at 80% R. The blade properties are loosely based on the XV-15 design. A CATIA and Cubit-based high-fidelity three-dimensional (3D) finite element model is developed. It accurately represents the fabricated blade and is analyzed with X3D. Experiments in a vacuum chamber were carried out to demonstrate the structural integrity of the blades. Measured frequencies and strains were validated with X3D predictions proving the fidelity of the 3D model. Thus, even though the wind tunnel facilities were closed due to COVID-19, hover and forward flight calculations for the blade stress could be performed using the high-fidelity 3D structural model. The results prove the blades have sufficient structural integrity and stress margins to allow for wind tunnel testing.

Characterization of the Anomalous Vibration Response of an Intentionally Mistuned LPT Rotor

The wind tunnel facility at the Centro de Tecnologías Aeronáuticas was used to perform a set of experiments to study the effect of intentional mistuning on the forced response behavior of an aerodynamically unstable low-pressure turbine rotor. The intentional mistuning patterns were implemented by adding a small extra mass to some of the blades. The forced response of the rotor was therefore expected to show two resonance peaks with similar amplitudes, corresponding, respectively, to the vibration frequencies of the blades with and without added mass. However, on the post-processing of the measurements, some anomalous behavior was observed. Near resonance, the system response was synchronous with the forcing, and the frequency sweeps exhibited two resonance peaks, but it was found that the two peaks were clearly different, with the peak at lower frequency showing a much higher vibration amplitude than the high-frequency peak, and with some blades responding at both frequencies with a similar amplitude. In order to give a correct interpretation of the experimental results, a reduced-order model is derived that takes into account only the traveling wave modes coupled by the mistuning. This model, although extremely simple, is capable of reproducing the unexpected behavior of the experiments, and gives a clean explanation of the system response. It is shown that the relative size of the mistuning with respect to the frequency difference of the involved traveling-wave modes is the key parameter for the appearance of this phenomenon.

Experimental study on the characterization of the self-starting capability of a single and double-stage Savonius turbine

The Savonius hydrokinetic turbine is a viable alternative for rural electrification despite its relatively low power coefficient. There are many ways to improve power performance, including the use of multiple-stage turbines. Although many studies have investigated the effects of multi-staging, few have captured their effect on three performance parameters combined: power efficiency, flow structure, and self-starting capability. Therefore, the current study explored and analyzed the extent of these parameters using a multi-stage conventional Savonius turbine in a wind tunnel facility with a varying flow speed of 5 m/s to 9 m/s. The findings suggested that adding a stage increased the power coefficient to a maximum of 138% at 5 m/s, but reached a plateau as the wind speed increased to 9 m/s. The double-stage was discovered to reduce the self-starting speed of the turbine at all rotor angles for self-starting capabilities. The coefficient of static torque results indicated that the maximum static torque for the single and double-stage configurations occurred at 45° and 45°/135° rotor angles, respectively. The qualitative study revealed that the double-stage turbine has a larger wake size at higher wind speeds, resulting in a reduced wake intensity at the rear side of the rotor. The reduced torque variation caused by the additional stage has improved the overall performance of the turbine, making the double-stage configuration more preferable than the single-stage, particularly for low speed, high depth, and narrow river applications.

Scaling formulation of multiphase flow and droplet trajectories with rime ice accretion on a rotating wind turbine blade

In this paper, scaling and similitude are investigated for ice accretion on a rotating wind turbine blade. Numerical CFD icing simulations are performed using FENSAP ICE software to test the scaling methods and verify the results. A small blade section is scaled six times, and each case is tested at specific flow conditions. Scaled conditions for velocity (streamwise and rotational), droplet size, and icing time are examined. CFD solutions for the flow field (air and droplet) are obtained in terms of the velocity, droplet trajectories, pressure coefficient distributions, ice thickness, and ice shapes, by quantifying the significant parameters involved in the icing process. Recommendations for parameters to be used for rime ice scaling on a rotating blade are presented, and numerical results are reported to support those recommendations. Numerical results and test conditions are obtained at sea level in wind tunnel facilities for experimental investigation. This paper presents the formulation of non-dimensionlized governing equations for scaling of the flow field, droplet trajectories, and ice accretion on a rotating blade model. It derives a set of non-dimensional groups which govern the flow parameters for a rotating blade, including the Strouhal number, Froude number, drag coefficient of droplets and droplet based Reynolds number, droplet inertia parameter, and two other new parameters. The scaling methodology can also be utilized to determine alternative test conditions to predict rime ice conditions on a rotating blade. The study provides valuable insight to predict ice accretion on large wind turbine blade sections in the field based on scaled smaller blade sections tested in a laboratory setting.

Automated crack classification for the CERN underground tunnel infrastructure using deep learning

One early sign of tunnel structure deterioration originates in the form of cracking, and therefore crack detection and resultant classification is integral for tunnel structural inspection and maintenance. Conventionally tunnel cracks are manually recorded and classified by trained professionals, which is costly, time-consuming and inevitably subjective. Recent advances in deep learning space have allowed for automatic cracks detection algorithms to be developed and subsequently utilized in structural health assessment of surface buildings, bridges, roads and other civil infrastructure. Nevertheless, these methods of development underperform when implemented for a tunnel structure in an underground environment due to the disparity of illumination combined with the congested image data caused by pipes, steel mesh, wires, and other tunnel facilities. To overcome these challenges, this paper proposes an innovative image-based crack detection method accompanied with crack classification using Convolution Neural Network (CNN) specifically for underground infrastructure environment. Unlike conventional CNN development from scratch, the proposed CNN incorporates Transfer Learning in the form of the VGG16 model with weights transferred from ImageNet. The transfer model was trained under different scenarios in order to find the optimal model for the novel dataset. The various models are trained using over 10′000 images validated on 2′500 images all of which are 256 × 256 pixels in size, these models are all subsequently tested using 30 images 3072 × 4096 pixels in size all of which are collected from the underground infrastructure at CERN. The Transfer Learning model used outperforms that of the traditional CNN training method of training from scratch. The optimum transfer model accomplished better testing metrics 96.6%,87.3%,92.4%,89.3% for Accuracy, Precision, Recall and F1 score respectively all of which were achieved with a shorter training time. The proposed CNN determines the existence and location of cracks within an image which are then subjected to a secondary classification CNN where the crack is categorized into one of the four crack classes which include the three directional classes of Horizontal, vertical and diagonal with the last crack classes incorporated to represent complex crack regions. The secondary classification CNN attains an Accuracy of 92.3% a Precision of 83.9% a Recall value of 82.3 % and a final F1 score of 81.5%. The performance of the proposed methods shows that a CNN crack detector/classifier can effectively overwhelm the unfavourable tunnel environment and accomplish results to a high standard.

Tunnel Facility Based Vehicle Localization in Highway Tunnel Using 3D LIDAR

Vehicle localization in highway tunnels is a challenging issue for autonomous vehicle navigation. Since GPS signals from satellites cannot be received inside a highway tunnel, map-aided localization is essential. However, the environment around the tunnel is composed mostly of an elliptical wall. Thereby, the unique feature points for map matching are few unlike the case outdoors. As a result, it is a very difficult condition to perform vehicle navigation in the tunnel with existing map-aided localization. In this paper, we propose tunnel facility-based precise vehicle localization in highway tunnels using 3D LIDAR. For vehicle localization in a highway tunnel, a point landmark map that stores the center points of tunnel facilities and a probability distribution map that stores the probability distributions of the lane markings are used. Point landmark-based localization is possible regardless of the number of feature points, if only representative points of an object can be extracted. Therefore, it is a suitable localization method for highway tunnels where the feature points are few. The tunnel facility points were extracted using 3D LIDAR. Position estimation is conducted using an EKF-based navigation filter. The proposed localization algorithm is verified through experiments using actual highway driving data. The experimental results verify that the tunnel facility-based vehicle localization yields precise results in real time.

Surface roughness and model scale influences on forebody aerothermodynamics

In this study, the surface roughness and model scale influences on forebody aerothermodynamics were examined experimentally. The scaling effect of measured surface pressure and heat flux according to the model scale was observed, and the effect of surface roughness on scaling was considered. The experiment was conducted using a shock tunnel facility with a nominal freestream Mach number of 6. The measured surface pressure and heat flux were compared with the numerical results and theory. Considering the experimental data, a relatively small difference between the models considered with a different roughness was observed in case of pressure. However, a noticeable difference was observed in case of heat flux, in which the cause of the increase in heat flux with the increase in the roughness is thought to be due to the roughness-induced disturbance. The surface heat flux away from the stagnation point is found to be inversely proportional to the square root of model size, a similar trend with that at the stagnation point.

Pseudo-equivalent deterministic excitation method application for experimental reproduction of a structural response to a turbulent boundary layer excitation.

In the transportation engineering field, the turbulent boundary layer over a structure is one of the most relevant sources of structural vibration and emitted noise. Wind tunnels are still one of the best options for vibroacoustic experimental analyses for this specific problem. However, it is also true that this experimental method is not always affordable, due to several limitations-settings hard to control, time and money consumption, discrepancies among laboratories-that wind tunnel facilities present. It has already developed different methodologies to address this necessity, most of them based on the use of loudspeakers or shakers. In this work, an existing numerical method, called the pseudo-equivalent deterministic excitation method (PEDEM), is further developed for the experimental purpose of reproducing the experimental structural response of a panel subjected to a turbulent boundary layer (TBL) excitation, by using an equivalent rain-on-the-roof excitation instead; different formulations are used for the application of this approximated TBL excitation. The experimental application of PEDEM, here called X-PEDEM, is validated by comparison with experimental results of two different panels analysed in two different wind tunnel facilities.

Capability analysis of computational fluid dynamics models in wind shield study on Queensferry Crossing, Scotland

Bridge aerodynamic studies are essential in ensuring the safety and acceptable performance of long-span bridges vulnerable to the effects of cross-winds. Aerodynamic studies were traditionally carried out in wind tunnel facilities, but there are now greater opportunities for using computational fluid dynamics (CFD) modelling. Few three-dimensional (3D) aerodynamic simulations of lightweight vehicles on bridges exist, but limited validation and verification work has been carried out. In the study reported in this paper, 3D CFD models were developed for Queensferry Crossing – a cable-stayed bridge in Scotland – containing wind shields and sample vehicles. The models considered the wind effects from a range of yaw wind angles and subsequently determined the aerodynamic coefficients of vehicles. The models were verified by means of a mesh sensitivity study, a domain sensitivity study and comparisons with wind tunnel tests. The models were then validated using the same modelling process but with a different type of wind shield and again comparing the results with wind tunnel test data for the same configuration. The results showed that CFD modelling can determine aerodynamic coefficients to a level of accuracy similar to that of wind tunnel tests.