Turbulent Conditions Research Articles

Evaluation of landing procedures for a high-altitude platform with skid-type landing gear based on pilot-in-the-loop simulations

AbstractIn the context of the project HAP, the German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform. The underlying vehicle is a fixed-wing aircraft that is supposed to be stationed in the stratosphere for 30 days. Due to, among others, low achievable rates of descent, the use of skids as landing gear and its high susceptibility to wind, landing this aircraft is a very challenging task. Hence, it requires a landing procedure specifically tailored to the aircraft’s particularities. Furthermore, this procedure needs to be easy to follow by pilots especially in adverse atmospheric conditions. This paper deals with a pilot-in-the-loop simulation campaign conducted to assess a landing procedure developed for the high-altitude platform in earlier works. Within this campaign, the pilots are supposed to land the aircraft following this developed procedure in atmospheric turbulence conditions. In addition, they also land the aircraft following a second procedure, which is based on a conventional landing. In doing so, the altitude at which a flare is performed and/or the propellers are shut down is varied. Finally, the novel procedure’s overall feasibility from a piloting point of view and its potential to reduce the risks during landing are assessed. The results show that the procedure proves to reduce the risk of inadvertent ground contact of the aircraft payload compartment, which is associated with serious damage to aircraft structure and payload. However, since the novel procedure is challenging for the pilots, some improvements to the procedure are proposed.

Foreign Policy of the Union State: Latin-Caribbean Direction of the Russia-Belarus Integration

The research is aimed at studying the Union State foreign policy in the Latin-Caribbean direction in new geopolitical conditions and its role in the emerging architecture of world economy and geopolitics. The mechanism for implementing the Union State foreign policy has been determined. It is shown that the external contour of the Russia-Belarus integration is not the sum of foreign policies, but is being implemented within the framework of their legal framework: pursuing a coordinated foreign policy, the parties maintain a flexible approach and are not limited by the framework of the foreign policy institutions of the Union. The author presents basic areas of project cooperation between Russia, Belarus and the states of the Latin-Caribbean region establishing priorities of cooperation.Aim. To appraise the significance and potential of Latin-Caribbean direction in the Union State foreign policy in the current conditions of economic turbulence and geopolitical escalation.Tasks. To identify the main areas of cooperation, to analyze current trends and influencing factors, and to determine the prospects for interaction.Methods. A combination of general scientific theoretical and special methods is used. The method of comparative analysis and the logical method are of prime importance. When working with regulatory and legislative sources, the normative method is used.Results. The potential of cooperation between the Union State and the countries of Latin-Caribbean America has not been fully realized, however, an accelerated diversification of partnership between the countries is being practiced as well as an expansion of areas of interaction based on economic feasibility and political motivation.Conclusions. Under current conditions of global political and economic turbulence, the Latin-Caribbean direction of the Union’s foreign policy is an important part in building effective international cooperation and developing new trans-regional logistics routes.

Simulation of unsteady ice accretion on horizontal axis wind turbine blade sections in turbulent wind shear condition

This study presents a comprehensive simulation approach to quantify power losses in horizontal axis wind turbines under environmental icing conditions. It investigates how wind shear and turbulence affect a 2.5 MW wind turbine's performance, particularly under ice accretion. Turbulence intensity, ranging from 1% to 20%, impacts the relative flow fluctuations and angle of attack on the blade sections, influencing the aerodynamic penalty ratio. The incoming wind speed and the flow angle at various blade sections were determined using the unsteady blade element momentum method, considering vortex induction effects and Prandtl and Glauert corrections. For ice accretion analysis, a fully unsteady simulation of computational grid motion due to ice accretion was performed, along with the solution of the multiphase flow of water dispersed particles in cold air, derived from the psychrometric chart. The findings highlight the significant impact of the incoming turbulent wind fluctuations on the dispersion of the ice shape formed at sections corresponding to their radial position on the blade according to the momentary angle of attack fluctuations. The formation of ice profiles along the blade has led to a subsequent degradation in the aerodynamic efficiency of the blade sections, which is directly proportional to the escalation in turbulence intensity. This phenomenon leads to a continual reduction in the power output of the wind turbine. This research provides valuable insights into the performance of wind turbines under icing conditions in real wind fluctuations.

Heat mitigation in basal compacted clay liners in municipal solid waste landfills.

In municipal solid waste (MSW) landfills, biodegradation of the organic MSW fraction results in elevated waste and basal liner temperatures which have the potential to cause the clay component of the basal liner to experience severe moisture loss over time and eventually undergo desiccation cracking. Cracking of the basal liner's clay component would result in an uncontrolled release of contaminants into the surrounding environment and ultimately give rise to a variety of major environmental concerns. Accordingly, this study examined the variation of temperature-moisture profiles along the depth of a compacted clay liner (CCL) exposed to different constant elevated waste temperatures (CETs) in the absence and presence of two heat reduction techniques, respectively. Rockwool insulation layers with varying thicknesses and galvanized steel cooling pipes with varying flowrates were introduced separately as the two heat reduction techniques. Introduction of both techniques led to a significant attenuation of the temperature rise and desiccation experienced by the CCL in the face of different CETs. An increase in rockwool thickness increments led to a progressive reduction of CCL temperature, while an increase in flow rate under turbulent condition did not have a significant influence on the temperature and desiccation reduction of the CCL. Nevertheless, the present study certainly highlights the potential of the two proposed heat reduction techniques to minimize desiccation and consequently increase the service life of CCLs exposed to different elevated temperatures in MSW landfills.

The Diffusion Tensor of Protons at 1 au: Comparing Simulation, Observation, and Theory

The natural variation in plasma parameters observed at 1 au can lead to a variation in transport parameters, such as diffusion and drift coefficients, for energetic charged particles of solar and galactic origin. Given the importance of these parameters to particle transport studies, this variation is investigated through test particle simulations over a range of energies in the presence of simulated turbulence with properties corresponding to an ensemble of observed turbulence conditions at Earth. The resulting transport coefficients are then compared with observational estimates from the literature, as well as the predictions of several scattering theories. Parallel and perpendicular mean free paths are shown to vary widely, for the former in agreement with prior observational estimates, but not for the latter. Furthermore, a large disparity between the predictions of theory and the simulation results is noted for the perpendicular mean free path. As such, these results indicate that particle transport studies, particularly predictive ones, need to take into account this natural variation in transport coefficients.

Working in precarity: examining mainstream discourses about street hawking in Ghana

Abstract This study sought to analyze how the media and the general public position street hawking in an economic environment typically constrained by neoliberal orthodoxy. We conducted a critical textual analysis of news articles, op-eds, and video clips from some of the most popular news media sources in Ghana and found that while informal work is often done in turbulent material conditions, marginality and precarity of street hawking are exacerbated by media and popular discourses that are anchored by neoliberalism. We also found that such discourses are resisted by counter-discourses. The study challenges neoliberal analyses of work and labor by explicating the tensions between the attraction to neoliberalism and the reality of its failures for informal work.

Sustainable drag reduction in Taylor-Couette flow using riblet superhydrophobic surfaces

Superhydrophobic surfaces (SHSs) have been proven effective in reducing frictional drag force in various flow conditions. However, at high flow speeds, the air plastron on these surfaces collapses, leading to a decline in their effectiveness. In this study, we investigated the frictional drag forces of various SHSs and their combination with surface patterns across a wide range of flow conditions (5.00×102 < Re < 1.12×105) by using an facile coating method. Our experiments involved incorporating a superhydrophobic coating on the inner cylinder of a custom-made Taylor-Couette apparatus, integrated with a rheometer to measure torque applied on the inner rotor as a function of rotational speed. As part of our research, we calculate the effective slip length to assess the drag reduction performance of coatings, revealing an effective slip length of around 63 µm on a flat SHS. Furthermore, we explore the combined effect of superhydrophobic coatings and triangular-shaped riblets on drag reduction in Taylor-Couette flow, comparing the performance of these surfaces based on the riblet’s sharpness and the Reynolds number. Our experimental results show a reduction in measured torque of up to 24 % and 48 % on a V-grooved SHS in laminar and turbulent flow, respectively. Longevity tests confirm that the designed surfaces maintain their superhydrophobicity and drag reduction performance under turbulent flow conditions. Overall, this work introduces a passive drag reduction strategy through surface design, which substantially mitigates the frictional drag force and demonstrating considerable potential for enhanced performance and increased efficiency of Taylor-Couette systems.

Development of a chemical mechanism for ammonia/hydrogen blends for engines

ABSTRACT Ammonia/hydrogen blend fuels have been extensively used as alternative fuel for engines. The combustion and emissions characteristics of ammonia/hydrogen engines have been investigated utilising a CFD model. Developing a robust and accurate chemical reaction mechanism for ammonia/hydrogen blend fuels is of utmost importance. In this paper, a chemical mechanism has been developed and validated for the combustion characteristics of ammonia/hydrogen, which includes 31 species and 223 reactions. Extensive validation has been conducted using experimental data as the basis. The obtained data indicate that the simulated values for the ignition delay times of the shock tube and the concentration of the main components in the stirred jet reactor align well with the measured values. The simulated laminar flame speed under turbulent flow conditions shows a remarkable agreement with the corresponding experimental data. The study compared simulated flame evolution values with experimental data from a constant volume combustion bomb. The results indicate that the proposed mechanism is able to produce favourable flame evolution and combustion characteristics. The presented detailed mechanism demonstrates credible overall performance in terms of combustion behaviours, indicating its suitability for effectively modelling ammonia/hydrogen combustion in real engines.

The effect of emulsifier concentration on turbulent drop breakup – An experimental study based on single drop visualizations

HypothesisA modified Weber number can capture the effect of emulsifier concentration and the effect of external stress in turbulent drop breakup. Moreover, the effect of emulsifiers on turbulent drop breakup cannot be adequately understood from classic slow/laminar techniques and quasi steady state interfacial tension. ExperimentsSingle drop breakup visualizations are used to study the effect of polysorbate 20 on turbulent drop deformation and breakup. Comparisons are made to drop tensiometry and emulsification experiments. FindingsA high concentration of the emulsifier increases breakup probability and breakup rate and decreases breakup timescales. These effects scale with a Weber number, indicating a lowering of the effective interfacial tension to 71 % of its pure interface value. This is far less than the observed lowering of interfacial tension as measured by quiescent drop tensiometry. Mechanistically, this shows that adsorption during emulsification cannot be limited by diffusion. Studying the effect cross a range of emulsifier concentrations suggest an elastic resistance at intermediate concentrations, further helping to understand the origin of similar effects previously reported in emulsification experiments. Overall, the results show the need to study emulsifiers under turbulent conditions to understand their effects during emulsification, as opposed to the slow/laminar techniques previously used.

Research on the NI-MLA Method for Enhancing the Spot Position Detection Accuracy of Quadrant Detectors Under Atmospheric Turbulence

The distorted spots induced by atmospheric turbulence significantly degrade the spot position detection accuracy of the quadrant detector (QD). In this paper, we utilize angular measurement and homogenization characteristics of non-imaging microlens array (NI-MLA) systems, effectively reducing the distortion degree of the spots received on the QD target surface, thereby significantly enhancing the spot detection accuracy of the QD. First, based on the principles of geometric optics and Fourier optics, it is proved that the NI-MLA system possesses the angular measurement characteristic (AMC) within the paraxial region while deriving and verifying the focal length of the system. Then, the QD computation curve characteristics of the system under non-turbulence are explored. This study further elucidates the mathematical principle of the NI-MLA system for mitigating the spot position detection random error of QD (SPDRE-QD) and discusses in depth the relationship between the NI-MLA system’s capability to mitigate the SPDRE-QD and the system’s parameters under various turbulence intensities. Finally, it is experimentally verified that the root-mean-square error (RMSE) of the QD computation values using the NI-MLA system are reduced by a significant improvement of at least 2.44 times and up to 17.36 times compared with that of the conventional optical system of QD (COS-QD) under turbulence conditions ranging from weak to strong.

Two-point statistics in non-homogeneous rotating turbulence

Time-resolved two-dimensional two-component particle image velocimetry measurements with high spatial resolution are carried out in a water tank agitated by four blades rotating at constant speed. Different blade geometries and rotation speeds are tested for the purpose of modifying turbulent flow conditions. In all cases where no baffles are used to break the rotation, the Zeman length is an order of magnitude smaller than the Taylor length. Compared with the cases with baffles which break the rotation, in the unbaffled cases turbulence production and/or mean advection are significant and the turbulence nonlinearity is dramatically reduced for the horizontal (i.e. normal to the axis of rotation) two-point turbulence fluctuating velocities. This nonlinearity reduction is manifest not only in the interscale turbulent energy transfer but also in the interspace turbulent energy transfer, which nearly vanishes. However, the nonlinearity is not reduced for the vertical two-point turbulence fluctuating velocities: the corresponding interscale turbulent transfer rate is in fact intensified, and its dependence on the two-point separation distance, as well as that of the corresponding interspace turbulent transfer rate, which does not vanish, is significantly modified. Even though non-homogeneities are very different for different blades and rotation speeds in the unbaffled cases, the horizontal fluctuating velocity's second-order structure function collapses with scalings which resemble predictions for homogeneous turbulence subject to strong rotation. The vertical fluctuating velocity's second-order structure function does not collapse for different blade geometries by neither these nor the Kolmogorov predictions.

Theoretical Model and Experimental Study of Slurry Erosion by Flowing Dilute Sulfuric Acid Under Turbulent Conditions

Theoretical Model and Experimental Study of Slurry Erosion by Flowing Dilute Sulfuric Acid Under Turbulent Conditions

Atmosphere turbulence effects on a multiple apertures free space optical communication systems

Abstract Wireless communication signals experienced fluctuations in intensity due to atmospheric turbulence. The presented work uses a multi-input-multi-output (MIMO) system to study the performance free-space optical (FSO) communication over a diverse atmospheric turbulence condition channel. The findings produced demonstrate how various channel models perform in FSO system at varying levels of channel turbulence. From 7.9 for the Weak turbulence to 45.3 for the strong turbulence, the turbulence attenuation rises linearly. The data could be transmitted via a link length of up to 1 km with strong turbulence. Strong turbulence could have higher Q-factor, yet is constrained by short distance (1 km) in comparison with weak turbulence, which has greater distance (3.8 km), therefore communication quality is lower. For moderate and weak turbulence, the maximum link is around 1.5 km and 3.8 km, respectively. This study is useful for designing a stable FSO system for regional environments suffer from frequent fluctuated weather turbulence such as the Middle East and South Asia.

Tracing Dissent: A Study of Simulated Gendered Memories in V. V. Ganeshananthan’s Brotherless Night

This article critically examines the interplay of memory, gender, and political consciousness in V. V. Ganeshananthan’s Brotherless Night against the backdrop of the Sri Lankan Civil War in the 1980s. Focusing on the protagonist, Sashi, the study employs theories of memory and gender studies to illuminate how her gendered memories contribute to the formation of political consciousness during the conflict. Sashi’s gendered memories emerge as a crucial lens through which the traumatic events of the war are remembered. By navigating the complexity of war, Sashi’s memories function as a form of dissent against dominant narratives, carving out a representation of subversive forms of memory often marginalized in such turbulent conditions. The concept of “simulated memories” by Kourken Michaelian can be used to analyze the narrative, wherein Sashi reconstructs major historical events she did not directly witness. This act of imaginative reconstruction, combined with the violence she has witnessed, forms a cogent narrative that transforms readers into secondary witnesses of the war. By engaging with theoretical frameworks of memory and gender studies, the study contributes to a deeper understanding of the intricate dynamics between personal memory, gendered experiences, and the political landscape in times of conflict.

Wake Structures and Performance of Wind Turbine Rotor With Harmonic Surging Motions Under Laminar and Turbulent Inflows

ABSTRACTThis study presents a comprehensive numerical analysis of a full‐scale horizontal‐axis floating offshore wind turbine (FOWT) rotor subjected to harmonic surging motions under both laminar and turbulent inflow conditions. Utilizing high‐fidelity computational fluid dynamics (CFD) simulations, namely, large eddy simulation (LES) with actuator line model (ALM), this research investigates the rotor performance, wake characteristics, and wake structures of a surging FOWT in detail. The study delves into the influence of varying inflow turbulence intensities, surging settings, and their interplay on the aerodynamic performance and the wake aerodynamics of a FOWT rotor. The results show that, through employing the phase‐averaging technique, surge‐induced periodic coherent structures (SIPeCS) can be identified in the wake of all the surging cases studied, irrespective of the inflow conditions and the surging settings. Additionally, the findings show that the faster wake recovery observed in the surging cases is not caused by enhancing the instability‐induced turbulence level, a previously accepted hypothesis. Instead, the results indicate that it is due to the enhanced advection process resulting from the induction fields of SIPeCS that causes the wake to recover faster. The analysis of rotor performance shows that the time‐averaged rotor performances are affected by the intricate aerodynamics arising from the surging motions. With certain surging settings, the time‐averaged thrust and the time‐averaged power of a surging rotor are found to be simultaneously lower and higher compared with those of a fixed rotor. Furthermore, the study underscores the importance of considering both the magnitude of surging and the rate of surging simultaneously to fully characterize the hysteresis load on a surging rotor.

The European Green Deal and turbulence for non-member states

The European Green Deal (EGD) has had a significant impact on EU member states. In this article, we examine the extent to which it can also have large consequences for non-members. Based on a qualitative approach comparing Norway and the UK, and drawing on a burgeoning literature on ‘turbulence’, we ask whether the EGD creates turbulence in non-member states, what the nature of this turbulence is, and whether the extent and nature of turbulence varies with how closely affiliated a non-member is with the EU. Despite the ambitious climate policies of both countries, we identify a significant amount of turbulence generated by the EGD. Interestingly, we also find that turbulence increases with a closer EU-affiliation. However, our analysis also reveals an impressive capacity in both countries to adapt to their turbulent conditions, and a surprising durability of climate and energy policy in the face of turbulence.

Thermo-hydraulic performance of concentric tube heat exchangers with turbulent flow: Predictive correlations and iterative methods for pumping power and heat transfer

This research addresses the problem of predicting the thermo-hydraulic performance of concentric tube heat exchangers (CTHE) under turbulent flow conditions, a critical aspect in energy-efficient industrial systems such as HVAC, power generation, and chemical processing. Existing studies often lack accurate predictive methods for balancing heat transfer performance with pumping power requirements. To tackle this issue, novel correlations and an iterative Newton–Raphson method were developed for predicting pumping power and heat transfer rates. Three-dimensional CFD simulations of a water-to-water counter-flow CTHE were conducted, with Reynolds numbers ranging from 4000 to 8000 for both the hot and cold fluids. The simulations employed the Reynolds-Averaged Navier–Stokes (RANS) equations with the k−ω SST turbulence model. The results demonstrated that increasing the Reynolds number enhances both heat transfer rates and pumping power, with the cold fluid requiring consistently higher pumping power. New correlations were developed to predict pumping power, capturing the impact of both entry and fully developed flow regions. These correlations showed an average error of less than 2.33% when compared with the CFD data. The iterative Newton–Raphson method for predicting heat transfer rates demonstrated high accuracy, with an average error of 0.66% for heat transfer rate, 0.03% for hot fluid outlet temperature, and 0.01% for cold fluid outlet temperature. Additionally, we identified optimal operating conditions for efficient cooling and heating based on the heat capacity ratio (Cr). The novelty of this work lies in the development of new, highly accurate predictive correlations and iterative methods for optimizing CTHE performance, going beyond existing literature by providing comprehensive insights into the relationship between pumping power, heat transfer efficiency, and flow conditions.

Optimizing Winglet Cant Angle for Enhanced Aircraft Wing Performance Using CFD Simulation and Hybrid ANN‐GA

ABSTRACTWinglets are an extended angled or vertical projected at the wing tips used to reduce the drag encountered during the flight of an aircraft. The main aim of this research was to study the effects of winglets on NACA 4412 airfoil at 15° angle of attack. The simulation was done on the basis of the aerodynamic properties such as lift (CL), drag (CD), and lift/drag (CL/CD) ratio for both with and without the winglets at various cant angles. The designing was carried out in ANSYS Design Modeler for both with and without winglet. Further, the meshing part was again carried out in ANSYS Mesh. K‐Epsilon (two equation) turbulence model is used for the simulation at the inlet speed of 100 m/s, since it is the most common model used to simulate the mean flow characteristics for high turbulent conditions. Further, the cant angle has been optimized to get the maximum coefficient of lift using Nelder Mead, Genetic Algorithm, and Genetic Algorithm with ANN optimization techniques.

Spectral characteristics of a rotating solar prominence in multiple wavelengths

We present synthetic spectra corresponding to a 2.5D magnetohydrodynamic simulation of a rotating prominence in the k Ly alpha , and Ly beta lines. The prominence rotation resulted from angular momentum conservation within a flux rope where asymmetric heating imposed a net rotation prior to the thermal-instability-driven condensation phase. The spectra were created using a library built on the framework called which provides boundary conditions for incorporating the limb-darkened irradiation of the solar disk on isolated structures such as prominences. Our spectra show distinctive rotational signatures for the k Ly alpha , and Ly beta lines, even in the presence of complex, turbulent solar atmospheric conditions. However, these signals are barely detectable for the and spectral lines. Most notably, we find only a very faint rotational signal in the line, thus reigniting the discussion on the existence of sustained rotation in prominences.

Error rates of optically pre-amplified PPM wireless systems with coding and arbitrary optical filter response

We present novel results for the uncoded and coded bit-error probability (BEP) of optically pre-amplified pulse-position modulation (PPM) wireless systems. For uncoded systems, a novel analytic method for the evaluation of the BEP is derived. The method takes into account the non-ideal optical filter response and utilizes a finite Karhunen–Loève series expansion to calculate the BEP. Using the proposed approach, it is possible to accurately evaluate the PPM BEP for arbitrarily shaped filters where the well-established χ2 method only provides approximate results. Considering a Lorentzian filter response, the discrepancy between the two methods amounts to 0.5 dB in a variety of filter bandwidths and PPM modulation orders. The Lorentzian filter response was chosen as an illustrative practical example whose series can be calculated analytically. The proposed method is also valid for any type of optical filter for which the Karhunen–Loève series expansion can be calculated analytically or numerically. Due to the finite number of terms that are required irrespective of the signal energy level, the proposed method can also be applied without loss of accuracy to assess the system performance under the effects of turbulence and adverse weather conditions. For coded systems with Lorentzian filters, Monte-Carlo simulations are utilized to evaluate the BEP performance of the 5G LDPC codes, and it is demonstrated that they impart an energy gain up to 3.3 dB for 4–PPM and 2.3 dB for 16–PPM at a target BEP of 10−5. The optimal code rates are also discussed for several combinations of the optical filter bandwidth and PPM modulation order and it is shown that in almost all of the cases the optimal code rate is 11/13. Moreover, the sum-product and min-sum decoders perform within 0.1 dB from each other for the best code rates, which points towards the utilization of the min-sum decoder in all settings, since its operation does not require knowledge of the filter parameters. Finally, the comparison between the coded systems with Lorentzian and ideal passband filters exhibits the same 0.5 dB discrepancy that was observed for uncoded systems.