Tunnel Conditions Research Articles

Measurement and Modeling of Subscale Open-Return Unsteady Wind-Tunnel Behavior

Unsteady-flow wind tunnels typically employ control louvers installed in the wind-tunnel circuit to produce rapid changes in the test-section flow velocity. For these wind tunnels, an open-return circuit is advantageous because of the lower mass of air that must be accelerated by the louver forcing. However, in addition to inertial effects, the wind-tunnel behavior is also affected by the interaction of the pressure disturbances from the louvers and their reflection from the open boundary conditions of the wind tunnel, resulting in a windspeed response that is nonintuitively related to the louver motion. In this paper, an experimental investigation into the unsteady behavior of a model-scale, open-return wind tunnel is described. An incompressible method of characteristics model for the wind tunnel is shown to successfully predict the wind-tunnel dynamic behavior, and an approach to produce controlled windspeed histories that compensates for the wind-tunnel response is demonstrated.

Role of streak secondary instabilities on free-stream turbulence-induced transition

We study the stability of a zero-pressure gradient boundary layer subjected to free-stream disturbances by means of local stability analysis. The dataset under study corresponds to a direct numerical simulation (DNS) of a flat plate with a sharp leading edge in realistic wind tunnel conditions, with a turbulence level of 3.45 % at the leading edge. We present a method to track the convective evolution of the secondary instabilities of streaks by performing sequential stability calculations following the wave packet, connecting successive unstable eigenfunctions. A scattered nature, in time and space, of secondary instabilities is seen in the stability calculations. These instabilities can be detected before they reach finite amplitude in the DNS, preceding the nucleation of turbulent spots, and whose appearance is well correlated to the transition onset. This represents further evidence regarding the relevance of secondary instabilities of streaks in the bypass transition in realistic flow conditions. Consistent with the spatio-temporal nature of this problem, our approach allows us to integrate directly the local growth rates to obtain the spatial amplification ratio of the individual instabilities, where it is shown that instabilities reaching an $N$ -factor in the range [2.5,4] can be directly correlated to more than 65 % of the nucleation events. Interestingly, it is found that high amplification is not only attained by modes with high growth rates, but also by instabilities with sustained low growth rates for a long time.

Locating people in tunnels using Wi-Fi technology

The aim of the project is to investigate the possibility of using people's mobile phones to locate people in a tunnel environment using the mobile phone's Wi-Fi connection. In total, 39 different trials were carried out under different conditions in a road tunnel in Stockholm, Sweden. In the trials, the Wi-Fi-based predicted location has been compared with the actual location of the recruited 16 participants in the tunnel. The conditions include the number of people in a group, the number of available access points in the tunnel, whether the mobile phone has an active or passive connection, whether a person is moving or standing still and whether the mobile phone is held in the hand or is stored in the person's pocket. The results indicate that the mean value for the distance between actual and predicted locations is in the order of 20 m or less, which is higher than reported in other studies. Despite this, there is a good potential to locate individuals in a tunnel emergency as the distance between emergency exits is often much longer than the uncertainties in the predicted locations of people. Improving the location algorithms will possibly reduce the uncertainty of the predicted location.

Centrifuge model test of the influence of tunnel excavation with different spacings on existing tunnels

The continuous development and utilization of underground space has led to an increasing number of short-distance constructions between new and existing tunnels. New tunnel construction affects the surrounding strata and destroys the structure and operation of the adjacent existing tunnel. Therefore, investigating the influence of new tunnels on the deformation of existing tunnels is crucial. Four centrifugal model tests simulating tunnel excavation processes were conducted to study the influence of tunnel excavation with different spacings on existing tunnels. Liquid was drained one section at a time to simulate the formation loss ratio produced by tunnel excavation and unloading during centrifuge operation, which eliminated the error caused by centrifuge shutdown–restart. Test results indicated that new tunnel excavation led to uneven settlement of the existing tunnel, and the settlement of the existing tunnel was greater than that of the two sides. Under the same burying condition of the new tunnel, the smaller the net distance between the new and existing tunnels, the greater the influence on the vertical and horizontal displacement of the existing tunnel, and the smaller the settlement of the ground surface. New tunnel excavation caused tensile stress near the excavation surface of the existing tunnel. A smaller clear distance resulted in a higher tensile stress. The centrifugal model tests provide technical support for tunnel construction and underground space development.

Analysis of drivers’ mental workload in V-shaped undersea tunnels based on heart rate variability

To explore the effects of illumination and tunnel longitudinal slope on driving safety in V-shaped undersea tunnels, we conducted a study to analyze changes in drivers’ mental workload caused by Illumination and longitudinal slope variations within the tunnel through field data. The typical V-shaped undersea tunnel crossing Jiaozhou Bay in Qingdao, China, was selected. Thirty drivers were recruited to participate in the driving tests during off-peak hours and 120 sets of electrocardiographic (ECG) signals were collected from drivers under natural driving conditions. The standard deviation of the Normal-to-Normal intervals (SDNN) was used and an outlier test was performed using the box plot. The drivers’ SDNN was used to index drivers’ mental workload under different Illumination and longitudinal slope conditions in the V-shaped undersea tunnel. A model was established to quantify the relationships of illumination and longitudinal slope with the SDNN. The results showed a significant negative correlation between the illumination change rate and the SDNN, i.e., the greater the change rate of illumination was, the smaller the SDNN was (and the greater the mental workload was). While the mental workload of drivers varied on tunnel longitudinal slope compared with illumination. With increased steepness of longitudinal slopes, the driver’s SDNN value decreased, but the SDNN of drivers in the downhill section were smaller than SDNN in the uphill section, reflecting a greater mental workload. Finally, a proposed value interval for the combined design of illumination and slope in undersea tunnels is given in the context of drivers’ mental workload variations.

Effect of paddy stubble powder on germination percentage and growth of chilli seedlings under poly tunnel condition

Effect of paddy stubble powder on germination percentage and growth of chilli seedlings under poly tunnel condition

Deformation characteristics and instability mechanism of transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel

To investigate the deformation characteristics and instability mechanism of the transportation hub under downward traversal conditions of the double-track super-large diameter shield tunnel, take the example of Beijing East Sixth Ring Road into the ground reconstruction project. Using the field experimental monitoring method and numerical simulation method, after verifying the accuracy of the model, this manuscript begins to unfold the analysis. The results show that, without any deformation prevention and control measures, The basement raft of the underground structure of the transportation hub will produce a deformation difference of 18 ​mm, and the tensile stress is more than 1.43 ​MPa, the inhomogeneous deformation and structural cracking will lead to structural instability and groundwater surges, which seriously affects the safe operation of the transportation hub station. When control measures are taken, the deformation and stress of the base raft slab of the underground structure of the transportation hub are within the prescribed limits, which can ensure the safe operation of the station. The displacement of the base slab of the underground structure in the horizontal direction of the cross-section is all pointing to the east, and the overall trend is to shift from the first tunnel to the backward tunnel. The horizontal displacement of the base slab in the direction of the tunnel axis all points to the beginning of the crossing, and the displacement of the slab in the vertical direction is distributed as "rising in the middle and sinking in the surroundings". For a two-lane super-large diameter shield tunnel penetrating an underground structure, there are two mechanical effects: unloading rebound and perimeter rock pressure. The above deformation characteristics are the superposition effect produced by the two, and this fine assessment of the deformation of the raft foundation provides a scientific basis for formulating the deformation control countermeasures of the crossing project. At the same time, it makes up for the blank of the double-track super-large diameter shield tunnel down through the transportation hub project.

Study on the propagation characteristics of gas explosions disturbed by crushed rock in tunnels through gas-containing stratum

Gas explosions pose a serious risk to tunnel construction when through a gas-containing stratum. The crushed rock accumulated in tunnel could have a significant impact on explosion. To understand the mechanism of crushed rock influence on gas explosion, methane/air explosion experiments under the crushed rock with different blockage ratios and void ratios were carried out using an independently designed experimental system. The results show that the crushed rock can significantly affect the explosion intensity, and the various blockage ratios show a higher degree of influence than the void ratio. The crushed rock has the combined effect of accelerating and quenching on the flame, and there has an optimum blockage that dramatically accelerates the flame propagation. The needle-shaped, divergent and reversed flames appeared with high blockage ratio and void ratio conditions. The velocity ratio (ratio of the flame front velocities upstream and downstream of the crushed rock) has an exponential function relationship with the blockage ratio. Under certain void ratio conditions, the maximum explosion overpressure shows a parabolic trend with increasing blockage ratio. This study is helpful to guide the understanding of the explosion characteristics under practical tunnel conditions and the change law of flame structure with crushed rock obstruction.

Predicting structure performance of urban critical infrastructure: an augmented attention-based LSTM model

PurposeAccurate prediction of the structural condition of urban critical infrastructure is crucial for predictive maintenance. However, the existing prediction methods lack precision due to limitations in utilizing heterogeneous sensing data and domain knowledge as well as insufficient generalizability resulting from limited data samples. This paper integrates implicit and qualitative expert knowledge into quantifiable values in tunnel condition assessment and proposes a tunnel structure prediction algorithm that augments a state-of-the-art attention-based long short-term memory (LSTM) model with expert rating knowledge to achieve robust prediction results to reasonably allocate maintenance resources.Design/methodology/approachThrough formalizing domain experts' knowledge into quantitative tunnel condition index (TCI) with analytic hierarchy process (AHP), a fusion approach using sequence smoothing and sliding time window techniques is applied to the TCI and time-series sensing data. By incorporating both sensing data and expert ratings, an attention-based LSTM model is developed to improve prediction accuracy and reduce the uncertainty of structural influencing factors.FindingsThe empirical experiment in Dalian Road Tunnel in Shanghai, China showcases the effectiveness of the proposed method, which can comprehensively evaluate the tunnel structure condition and significantly improve prediction performance.Originality/valueThis study proposes a novel structure condition prediction algorithm that augments a state-of-the-art attention-based LSTM model with expert rating knowledge for robust prediction of structure condition of complex projects.

Effect of surface energy on the contamination characteristics of porcelain double umbrella insulators

To explore the influence of surface energy on the contamination characteristics of insulators, COMSOL Multiphysics software was used to simulate the contamination characteristics of XWP 2-160 insulators under wind tunnel conditions, and the rationality of the modified expression of the dynamic deposition model of the contaminated particles was verified. The change of contamination characteristics before and after changing the surface energy of insulators under natural conditions was simulated and analyzed. The results show that under the original surface energy (72 mJ/m 2) and low surface energy (6.7 mJ/m 2) with the increase in particle size, the contamination amount of an insulator surface area decreases first and then increases. When the wind speed is 2 m/s, the change in the particle size has the most pronounced effect on the amount of contamination. The amounts of contamination for the low surface energy are 64–75%, 60–95%, 55–91% and 54–78% lower than those for the original surface energy for particle sizes of 10, 15, 20 and 25 μm, respectively. For the same wind speed, when the size of contamination particles increases, the difference between the ratio of DC and AC contamination accumulation is gradually increasing because of the influence of the electric field force. From the perspective of the insulator preparation process, the development of low surface energy insulators can improve their anti-fouling performance.

Mechanical properties of partially bonded rock anchors in squeezing large-deformation soft rock tunnels

Partially bonded rock anchors are crucial structural tunnel support elements whose effectiveness depends on their interactions with the surrounding rock. This study combined laboratory experiments and numerical simulations to examine the mechanical behavior of partially bonded rock anchors under pull-out tests, focusing on the influence of bonded lengths. The axial strain of the anchor body and the vertical strain of the concrete block along the anchor axis were tested using distributed optical fibers. The results indicated that the anchor body stress remained relatively constant in the unbonded sections but gradually decreased as the depth into the bonded section increased. Simultaneously, the significant compressive stress range induced by the rock anchor in the concrete block decreased rapidly as the bonded length increased. Subsequently, the effects of different bonded lengths, unbonded section positions, and bonding combinations on the mechanical behavior and support effectiveness of partially bonded rock anchors in highly stressed soft rock tunnels undergoing substantial deformation were investigated using numerical simulations in ABAQUS. These findings suggest that rock anchors with longer bonded lengths have better control of the rock between the anchors. Simultaneously, the maximum axial stress of rock anchors tended to increase with longer bonded lengths. The rock displacement tended to be obviously larger when the unbonded section was set at the end of the rock anchors compared with when the unbonded section was set in the middle. The rock displacement was larger when the unbonded section was set at the outer end of the rock anchors, indicating that setting unbonded sections near the tunnel wall was detrimental to controlling rock deformation while improving structural safety. Setting one unbonded section near the tunnel wall and another unbonded section in the middle of the rock anchors resulted in excellent structural safety and rock deformation control. Furthermore, fully bonded rock anchors were compared with partially bonded rock anchors based on suitable bonding combinations in the deformation section of Muzhailing Tunnel. The results indicated that the fully bonded rock anchors experienced axial forces exceeding the yielding load in the early stages of support, with noticeable early yielding of the anchor plate. In contrast, the unbonded sections in the partially bonded rock anchors did not yield in either the bonded anchor body or the anchor plate. Partially bonded rock anchors exhibited better overall stability and reliability under high-deformation tunnel conditions.

Fly by Feel: Flow Event Detection via Bioinspired Wind-Hairs

Bio-inspired flexible pillar-like wind-hairs show promise for the future of flying by feel by detecting critical flow events on an aerofoil during flight. To be able to characterise specific flow disturbances from the response of such sensors, quantitative PIV measurements of such flow-disturbance patterns were compared with sensor outputs under controlled conditions. Experiments were performed in a flow channel with an aerofoil equipped with a 2D array of such sensors when in uniform inflow conditions compared to when a well-defined gust was introduced upstream and was passing by. The gust was generated through the sudden deployment of a row of flaps on the suction side of a symmetric wing that was placed upstream of the aerofoil with the sensors. The resulting flow disturbance generated a starting vortex with two legs, which resembled a horseshoe-type vortex shed into the wake. Under the same tunnel conditions, PIV measurements were taken downstream of the gust generator to characterise the starting vortex, while further measurements were taken with the sensing pillars on the aerofoil in the same location. The disturbance pattern was compared to the pillar response to demonstrate the potential of flow-sensing pillars. It was found that the pillars could detect the arrival time and structural pattern of the flow disturbance, showing the characteristics of the induced flow field of the starting vortex when passing by. Therefore, such sensor arrays can detect the “footprint” of disturbances as temporal and spatial signatures, allowing us to distinguish those from others or noise.

Streamlining multi-hole probe calibration using artificial neural networks

Accurately measuring the three-dimensional flow field characteristics in complex flow fields, particularly in turbomachines, is of utmost importance and is commonly achieved through experimental methods. Multi-hole pressure probes are a proven measuring technique to provide precise readings of flow characteristics in both two-dimensional (2D) and three-dimensional (3D) flow fields. However, manufacturing imperfections have an impact on their measuring accuracy so each probe has a slightly different measuring behavior. In order to take these specific characteristics into account a thorough calibration process prior to utilization has to be applied. This calibration process involves positioning the probe in various flow conditions in a wind tunnel and collecting all relevant data. A model is then established to correlate the measured pressure distribution across the probe holes with known flow conditions. Unfortunately, this calibration process is time-consuming and requires costly equipment.To address these challenges, this study introduces a novel calibration technique that leverages advanced machine learning methods, specifically artificial neural networks (ANNs), to significantly streamline the process. ANNs are renowned for their ability to model diverse systems and adapt and generalize well, making them a promising solution for simplifying the calibration of multi-hole probes. In this research, an ANN calibration model was developed specifically for a 5-hole probe, and its configuration was optimized through an automated hyperparameter optimization process. The performance of the ANN model was then compared to that of a conventional polynomial model. After confirming its accuracy, the ANN model was successfully re-adapted and applied to new probes, requiring minimal calibration data collection. The results highlight the potential of ANNs in probe calibration, as they enable a simplified process that demands fewer calibration data points.

Comparison study of mechanical characteristics between conventional shield tunnel and shield tunnel with mortise-groove cross-section in ground fissure site

ABSTRACT Under the condition of the shield tunnel intersecting the ground fissure section at a right angle, a physical model test was conducted at a geometric scale ratio of 1:30. This test aimed to compare and analyze the force and deformation of the conventional shield tunnel and shield tunnel after adopting measures to mitigate the effects of ground fissure dislocation. Meanwhile, a finite-element numerical simulation of a conventional shield tunnel under the same working conditions was performed. The physical model test results align closely with the outcomes predicted by numerical calculations. The deformation observed in the shield tunnel primarily consisted of vertical shear deformation near the ground fissure, accompanied by a minor torsional deformation. In grade IV ground fissure sites, both the conventional shield tunnel and shield tunnel with mortise-groove cross-section after taking measures exhibit a basic level of safety. However, only the shield tunnel, after taking measures, is safe when the ground fissure develops to grade III. By contrast, the conventional shield tunnel generates significant shear deformation at the first circumferential seam in the footwall of the ground fissure, which easily causes the joints inside the circumferential seam to yield shear. When the ground fissure grade was raised to II, the conventional shield tunnel and shield tunnel with mortise-groove cross-section after taking measures experienced relatively serious damage.

Analysis of different dimensions of a virtual wind tunnel and different wall conditions

Growing interest in improving the performance of vehicles is a subject that allows for continuous research. One such branch of these researchers is energy and consumption performance. These performances describe, on a global level, the need for lower fuel consumption but also a higher energy and power performance. Therefore, to create this balance, direct control of polluting emissions, especially C02 emissions, is necessary. Creating the best mix between low fuel consumption, maximum power of internal combustion engine and low pollutant emissions is influenced by many factors. One such factor, of prime importance, is represented by the aerodynamics of vehicle, in particular the aerodynamic performance, which needs to be tested to be confirmed, so numerical values are needed. Therefore, different ways of testing in the physical or virtual environment are necessary. To facilitate the optimization of a vehicle from an aerodynamic point of view, the most practical way is the virtual wind tunnel, given the possibility to test, at the same time, more configurations. But the CFD (Computational Fluid Dynamics) simulations, sometimes, have the disadvantage of very long compilation times. So, in the presented paper the construction of an optimal virtual wind tunnel for trucks will be presented, focusing on the test area (chamber) and several configurations will be presented such as: different proximity of the tunnel walls to the tested object so a different geometry of the test chamber and condition for the type of floor with different roughness than base case to simulate a more realistic road surface. Following the CFD simulations, it was observed the influence that increasing the dimensions of the test chamber has on the results obtained, so that moving the walls away from the test model generates much more realistic results. In addition, another thing that has an impact is the roughness of the floor, which, in this particular case, generate a 10% difference between the values obtained. Therefore, it will be possible to optimize the tunnel as best as possible to have results as close as possible to reality and in a reduced time.

Hole-tunneling Si0.82Ge0.18/Si triple-barrier resonant tunneling diodes with high peak current of 297 kA/cm2 fabricated by sputter epitaxy

Hole-tunneling Si0.82Ge0.18/Si asymmetric triple-barrier (TB) resonant tunneling diodes (p-RTDs) were created by sputter epitaxy instead of conventional chemical vapor phase epitaxy. As a result, a peak current density (PCD) of 297 kA/cm2 with a peak-to-valley current ratio of 7.3 was recorded at room temperature. The observed high planarity of the films grown by sputter epitaxy is also considered one of the factors behind the high PCD. From the results of self-consistent theoretical calculations of current–voltage characteristics using box-shaped potentials as a first approximation and considering space charge effects of quantum wells, heavy-hole-to-heavy-hole and light-hole-to-light-hole state transitions under the tunneling conditions of the TB potential structure applied in this study were found to be inherent current paths. Moreover, the light and heavy hole currents contribute almost equally to the overall device current, resulting in a theoretical PCD of 637 kA/cm2, which is close to the experimental result. Further analytical simulations with adjusted series resistance and thickness of the nondoped layer allowed the alignment of the theoretically obtained PCD voltage position with the experimentally obtained one. Thus, the theoretical and analytical calculations explain the operation mechanisms of SiGe/Si p-RTDs, and the proposed fabrication method using our sputter epitaxy method is very useful for the actual production of high-PCD SiGe/Si p-RTDs operating at room temperature.

Development of combined hypersonic test facility for aerothermodynamic testing.

In this study, a combined test facility was developed using a combination of an arc-jet tunnel and a shock tunnel for aerothermodynamic testing. The performance validation of individual parts was performed, and results were obtained from the combined test. A small-scale Huels-type arc-jet tunnel was used to preheat the test model by aerodynamic heating before conducting the experiments in the shock tunnel to duplicate the hot surfaces of flight objects encountered during hypersonic flight. The high-enthalpy flow in the arc-jet tunnel provided a heat flux of 1.99±0.03 MW/m2 for a flat-faced model of 10 mm diameters, and the flow condition of the shock tunnel used in this study simulated a Mach 5 flight at a pressure altitude of about 24 km. The two combined experiments employing different shape and material models were carried out to examine the effect of aerothermodynamic phenomena. In the first experiment, the effect of ablation-induced shape change on the fluid-structure was investigated using a cone model manufactured of AL6061 material. The effect of surface roughness on the fluid-structure was examined in the second experiment, which used a hemisphere model constructed of STS303 material. Although substantial findings could not be validated due to the limits of qualitative evaluations utilizing visualization methods, however preheating-related changes in surface roughness were found. As a follow-up study, a force measuring experiment based on the test procedures is being carried out at this facility utilizing a preheated model with an accelerometer. The performance and experimental results obtained using this integrated setup are discussed in detail, highlighting the potential of this combined hypersonic test facility.

Airfoil friction drag reduction based on grid-type and super-dense array plasma actuators

To improve the cruise flight performance of aircraft, two new configurations of plasma actuators (grid-type and super-dense array) were investigated to reduce the turbulent skin friction drag of a low-speed airfoil. The induced jet characteristics of the two actuators in quiescent air were diagnosed with high-speed particle image velocimetry (PIV), and their drag reduction efficiencies were examined under different operating conditions in a wind tunnel. The results showed that the grid-type plasma actuator was capable of producing a wall-normal jet array (peak magnitude: 1.07 m/s) similar to that generated in a micro-blowing technique, while the super-dense array plasma actuator created a wavy wall-parallel jet (magnitude: 0.94 m/s) due to the discrete spanwise electrostatic forces. Under a comparable electrical power consumption level, the super-dense array plasma actuator array significantly outperformed the grid-type configuration, reducing the total airfoil friction drag by approximately 22% at a free-stream velocity of 20 m/s. The magnitude of drag reduction was proportional to the dimensionless jet velocity ratio (r), and a threshold r = 0.014 existed under which little impact on airfoil drag could be discerned.

Influence of high tunnel conditions and cultivars on the growth, yield, and fruit qualityof strawberry in northern Türkiye

Influence of high tunnel conditions and cultivars on the growth, yield, and fruit qualityof strawberry in northern Türkiye

Experimental study of frosting characteristics of trace water vapor under cryogenic wind tunnel conditions

In cryogenic wind tunnels, the working fluid mixed with trace amounts of water vapor may form frost on the test model, which could affect the testing results. To investigate the frosting phenomenon under trace water condition, an experimental system is built for visualizing the frosting process on a cryogenic surface. The effects of variable factors on frost formation are analyzed focusing on the growth characteristics of frost layer. Under trace water and cryogenic surface conditions, the water vapor desublimates into crystals without obvious condensation. As the surface temperature increases from −183 ℃ to −123 ℃, the frost becomes thicker and more porous due to the thinner outer boundary layer. When the water vapor content rises from 30 ppm to 500 ppm, the frost morphology transforms from a flat layer to frost clumps with visible dendritic structure. Additionally, the decrease in nitrogen flow temperature and the increases in ambient pressure and surface roughness of the cryogenic surface are conducive to the development of the branches on the frost crystal, which accelerate the growth of the frost layer. Furthermore, a dimensionless correlation is proposed for predicting the frost thickness under cryogenic and trace water conditions, with an overall error within ±20 %.