Tandem Configuration Research Articles

A multi-physics CFD study to investigate the impact of laser beam shaping on metal mixing and molten pool dynamics during laser welding of copper to steel for battery terminal-to-casing connections

This study aims to investigate the impact of laser beam shaping on metal mixing and molten pool dynamics during laser beam welding of Cu-to-steel for battery terminal-to-casing connections. Four beam shapes were tested during LBW of 300 µm Cu to 300 µm nickel-plated steel. Both experiments and simulations were used to study the underlying physics. A CFD model was firstly calibrated against experiments and then deployed to explore the effect of the increasing ring-to-core diameter, as well as a tandem laser spot configuration. The study showed that metal mixing is influenced by the keyhole dynamics and collapse events, but also there is an intricate interplay between keyhole geometry, fluid dynamics via Marangoni forces and buoyancy forces. Notably, the buoyance forces due to the different densities of steel and Cu, along with the recoil pressure contribute to the upward flow of steel towards Cu, and hence impact meaningfully the material mixing. The study pointed-out that the selection of a custom ring-to-core diameter and ring-to-core power is a decision with a trade-off between the need of stabilising the keyhole dynamics and the need to reduce the mixing. Findings indicated that 350 µm ring and 90 µm core with 30% of ring power (weld configuration C3) resulted in more stable dynamics of the keyhole, with significant reduction of collapse events, and ultimately controlled migration of steel towards Cu. Additionally, the pre-heating approach with the tandem beam only led to local fusion of Cu and no significant improvement in keyhole stability was observed.

Homo-tandem-bifacial dye-sensitized solar cell: A new paradigm to boost photoconversion efficiency above limit

Over the last three decades, dye-sensitized solar cells (DSSCs) have received a lot of attention, reaching record efficiencies under AM 1.5G illumination slightly over 10%. However, these values are lower than other competing photovoltaic systems. The performance of DSSCs has to be further enhanced in order to have a substantial influence and application potential in the field of photovoltaics. Herein we propose a new intriguing strategy to take advantage of two concepts well known in the field of photovoltaics, such as the tandem configuration and the bifaciality, never applied at the same time to DSSCs. Thanks to the combination of these strategies, we are noteworthy able to overcome the maximum efficiency ever obtained for a traditional DSSC based on iodide/triiodide redox couple and Ru-based dye, as high as 14.96%. Our findings open the way to further enhancement with optimized DSSCs configuration.

Two-terminal tandem solar cell with Sb2S3/Sb2Se3 absorber pair: achieving 14% power conversion efficiency

Embarking on a journey toward high solar efficiency, this study delves into a two-terminal tandem solar cell (TSC) featuring Sb2S3/Sb2Se3 as an absorber layer. The tandem setup consists of different bandgap (Eg) absorbers to selectively target photon energies: the top cell employs a wide bandgap material to efficiently absorb high-energy photons, while the bottom cell utilizes a lower bandgap material to capture refined photons transmitted from the top cell. This strategy mitigates thermalization and transparent energy losses by assigning distinct photon absorption and conversion roles to the top and bottom cells. Realizing peak efficiency in a tandem configuration rests on the apt choice of active materials for the top and bottom cells. In this regard, a comprehensive study is presented, introducing a TSC architecture that pairs an Sb2S3-based top cell (Eg 1.7 eV) with a Sb2Se3-based bottom cell (Eg 1.2 eV). Through meticulous analysis, the performance of these cells in the tandem setup is analyzed, employing methods such as filtered spectrum analysis and current-matching strategies. The Sb2S3/Sb2Se3 tandem design incorporates a critical tunnel recombination junction facilitated by an ITO layer. Noteworthy is the investigation’s uncovering of impressive metrics for the tandem device, encompassing an open-circuit voltage (VOC) of 1.58 V, a current density (JSC) of 15.50 mA.cm−2, and a fill factor (FF) of 56.90%. This collective attainment culminates in an extraordinary power conversion efficiency of 14%. The insights gleaned from this study hold substantial promise for the future development of monolithic TSC. By adroitly harnessing the distinctive strengths of Sb2S3 and Sb2Se3 materials within a tandem configuration, a clear trajectory is charted toward momentous advancement in solar energy conversion technology.

Unlocking the full potential of monolithic perovskite/biPoly™ Si tandem devices through in-depth analysis and detailed engineering

Perovskite/Si tandem solar cells have emerged as one highly promising tandem configuration of tandem devices for 1-Sun photovoltaic systems. Up to now, heterojunction (HJ) cells have been the dominant silicon bottom cell structure and holds the record efficiency of dual-junction perovskite/Si tandem cells, whereas the investigation on perovskite/Si tandem cells using Si bottom cells that dominate today's mass markets (such as PERC and TOPCon) is still limited. In this work, we delve into the crucial optical and electrical engineering aspects required for perovskite/Si devices based on bifacial TOPCon structures (biPoly™), which has high efficiency potential as a single-junction Si cell, enables TCO-free contacts and is expected to be compatible with current mass production technologies. Simulations predict that such devices can potentially achieve a current density of 20.4 mA/cm2 despite of the parasitic absorption in poly-Si layers, comparable to that of HJ-based perovskite-Si tandem devices. We also demonstrate through simulations that edge and peripheral recombination effects can be mitigated by selecting an appropriate substrate size and employing locally doped poly-Si layers. Such improvements are also preliminarily verified with a prototype device. By carefully designing device structures and advancing fabrication techniques, perovskite/biPoly™ Si tandem cells can come closer to realizing the full potential of biPoly™ cells and achieve efficiencies comparable to those observed in devices utilizing HJ cells.

An investigation of water gas shift reaction in a Pd-alloy membrane reactor with an optimized crossflow configuration

In this study, the performance of a high-temperature water gas shift reaction (WGSR) using a Fe-Cr catalyst along with a Pd alloy membrane was simulated by computational fluid dynamics (CFD). The influences of using Pd membranes, catalytic layer thickness ratio (R/R0), Reynolds number, and steam-to-CO ratio (S/C) on the reaction were investigated by comparing CO conversion and hydrogen recovery (HR). In the CFD simulation, one-tube and four-tube systems were simulated at 500 °C. This study also compared the performance between tandem and optimized configurations. The results show that the CO conversion can be improved up to 22.9% when the WGSR reactor system uses a Pd membrane compared to the system without a Pd membrane. The system has the best hydrogen recovery performance at S/C = 4 and R/R0 larger than 1.5. At Re=5, the optimized configuration for CO conversion has better performance when R/R0 is larger than 1.75. Compared to the tandem configuration, the optimized configuration also shows better performance for HR at every R/R0. The results indicate that a Pd membrane and optimized configuration can significantly improve CO conversion and that R/R0 and S/C optimization is very important for effective reactor performance.

Design of CZTS/CZTSe tandem solar cells with enhanced performance

The replacement of toxic and expensive materials with non-toxic, earth-abundant alternatives is an urgent necessity in the field of solar cells. Due to their environmentally friendly and optical properties, CZTS and CZTSe kesterite materials have been proposed as promising alternative compounds in thin film solar cell applications. In this study, a numerical investigation of a CZTS/CZTSe tandem solar cell structure is conducted using SILVACO software. In this structure, CZTS and CZTSe serve as the main absorbers in the top and bottom sub-cells, respectively. However, the bottom sub-cells require thick absorbers, which leads to a decrease in overall performance due to the limited diffusion length of minority carriers in the applied materials. A separate study of individually top and bottom cells was conducted, and their results closely matched those reported by world champions. Effects of the top absorber thickness were examined for the tandem configuration, which resulted in a conversion efficiency (η) of 15.71%. In order to enhance the performance of the tandem solar cell, a creation of a diffusion electric field in the absorbers of the sub-cells through gradient doping is proposed. The results demonstrated a significant improvement in performance, with gradient doping densities of 2 × 1014-1019 cm−3 and 1.5 × 1015-1019 cm−3 in the CZTS and CZTSe layers, respectively, yielding a remarkable conversion efficiency of 23.38%.

Reliable bi-functional nickel-phosphate /TiO2 integration enables stable n-GaAs photoanode for water oxidation under alkaline condition

Hydrogen is one of the most widely used essential chemicals worldwide, and it is also employed in the production of many other chemicals, especially carbon-free energy fuels produced via photoelectrochemical (PEC) water splitting. At present, gallium arsenide represents the most efficient photoanode material for PEC water oxidation, but it is known to either be anodically photocorroded or photopassivated by native metal oxides in the competitive reaction, limiting efficiency and stability. Here, we report chemically etched GaAs that is decorated with thin titanium dioxide (~30 nm-thick, crystalline) surface passivation layer along with nickel-phosphate (Ni-Pi) cocatalyst as a surface hole-sink layer. The integration of Ni-Pi bifunctional co-catalyst results in a highly efficient GaAs electrode with a ~ 100 mV cathodic shift of the onset potential. In this work, the electrode also has enhanced photostability under 110 h testing for PEC water oxidation at a steady current density Jph > 25 mA·cm−2. The Et-GaAs/TiO2/Ni-Pi║Ni-Pi tandem configuration results in the best unassisted bias-free water splitting device with the highest Jph (~7.6 mA·cm−2) and a stable solar-to-hydrogen conversion efficiency of 9.5%.

Experimental study on performance assessment of photovoltaic/thermal-thermoelectric generator systems: Bifacial and tandem types

The utilization of photovoltaic/thermal-thermoelectric generator (PV/T-TEG) systems holds great promise for achieving efficient utilization of the full solar spectrum. However, the conventional tandem structure design fails to effectively address the issue of temperature mismatch between the PV and TEG components during operation, highlighting the need for an innovative solution. To address this limitation, an innovative bifacial PV/T-TEG system was developed in this study. A practical test setup was employed to compare the performance of the conventional tandem system with the novel bifacial system under controlled laboratory conditions. The influences of solar radiation and water flow rate on the temperature, electrical, and thermal characteristics of both system configurations were thoroughly investigated and analyzed. The experimental findings unequivocally demonstrate that the recommended bifacial system exhibits lower average PV module temperature and a larger temperature difference in the TEG component when compared to the conventional tandem configuration. Specifically, the temperature reduction in the PV component could be higher than 18 K, while the improvement in temperature difference in the TEG component was larger than 5 K. Moreover, both the PV and TEG components show significantly enhanced power output. The PV power output experiences an improvement ranging from 4.7% to 12.7%, while the maximum power enhancement ratio for TEG reaches 27.8%. Additionally, a notable enhancement of 17% in thermal efficiency is observed when comparing the two systems. The thermal efficiency of the bifacial system improves by 8.37%, and for the tandem system, the improvement is 10.73%, achieved by adjusting the water flow rates.

Vortex dynamics and on the mechanism of vertical force enhancement in inclined stroke flapping wings

The rigorous numerical investigation of the class of inclined stroke plane flapping wings has brought to light the vertical force enhancement due to dipole jet interaction. In this study, the class of inclined stroke plane flapping wings with varying inter-plane distances and stroke inclinations are studied for vertical force generation. The configurations with stroke plane angles of 60° and 75° are found to produce significantly high vertical forces. Further, wake structures of the tandem flapping wing in an inclined stroke plane show various types of dipole vortex shedding and dipole jet interactions. The identified types of dipole jet interactions help in the understanding of vertical force trends of the forewing, hindwing, and hence the tandem wing configuration as a whole. It reveals the potential dipole jet interaction producing the highest vertical force in tandem wing configurations. In all, the study can classify the flows of the tandem wing configurations based on vortex shedding during hovering conditions and understand its vertical force enhancements. This not only helps in getting physical insights into the vortex dynamics of inclined stroke plane flapping wings but also in the design optimisation of the tandem wing configurations in biomimetic Micro Air vehicles (MAVs).

(Invited) New Approaches to Photoelectrochemical Cascade Reactions and Protection of Photoelectrodes

A half-century of research has positioned direct photoelectrochemical (PEC) fuel generation as a promising technology that still requires substantial development. Work on the hydrogen evolution reaction (HER) has provided a strong basis for realizing the generation of more complex fuels through the carbon dioxide reduction reaction (CO2RR), but multiple challenges remain. The CO2RR requires larger driving forces and integration of multiple catalysts in order to selectively generate multi-carbonproducts, while still presenting many unsolved issues from HER, such stabilizing photoelectrodes under operation. In this talk I will discuss advances in the integration of multiple catalytic microenvironments in a single photoelectrochemical device, and progress toward the stabilization of photoelectrodes for fuel generation.First, I will highlight the adaptation of three-terminal tandem (3TT) photovoltaic technology to photoelectrochemical applications. In our 3TT devices, a two-junction III-V solar cell device has an additional contact, enabling two unique catalyst sites operating at different voltages under the same illumination. Idealized circuit modeling shows the promise of these 3TT devices compared to traditional two-terminal, two-junction devices, particularly with respect to spectral tolerance. We have adapted the structure of 3TT photovoltaics to function as PEC devices and developed multiple catalysts for integration into the two solution contact sites. We demonstrate progress toward light-driven cascade catalysis for multi-carbon CO2RR products.Second, I will highlight our approaches to protective schemes for photoelectrodes: one which is independent of semiconductor chemistry, and one which is driven by that chemistry. In the first approach, transparent conductive encapsulants (TCEs) are demonstrated as photoabsorber-agnostic protective layers. Unlike many protection schemes, these TCEs can be applied to semiconductors post-processing and without substantial modification, providing facile and robust protection. We have characterized the electrochemical performance of TCEs and demonstrate their integration with multiple semiconductors for the reduction of methyl viologen as a proxy for PEC fuel formation. In the second approach, we use the knowledge generated over fifty years of photoelectrode research to develop a new material, ZnTiN2, which can be directly integrated with established semiconductors and which will degrade under PEC conditions. We leverage this degradation to create protective layers which may be self-healing, and demonstrate rapid refinement of ZnTiN2 optoelectronic properties enabling integration with other semiconductors in tandem configurations.

Electromagnetic energy harvesting via flow-induced vibration of flexible diaphragm in the presence of square cylinders at varied incidence angles: An experimental investigation

This study designs an electromagnetic energy harvester that uses a magnet in translation within a coil to harness energy from flow-induced vibrations when wall confinement affects a change in the wake formation behind a bluff body. An attached permanent magnet surrounded by a coil is attached to a flow channel with a flexible diaphragm, and a square cylinder acts as the bluff body that generates a vortex-induced street, thereby oscillating the diaphragm and generating electrical energy. The main novelty presented in the current investigation is developing a quick and efficient way of capturing fluid energy for practical applications, at the cost of augmented mechatronical complexity. Fluid flow and electromagnetic induction convert flow energy into electrical energy, and the influences of the Reynolds number (Re = 3000, 4000, and 5000) and the position of square cylinders (X*=X/D) on the dynamic characteristics are considered. As a result of different incidence angles (α) and spacing between two identical square cylinders (L*=L/D), Reynolds number and incidence angles have significant effects on the harvesting of energy. Additionally, based on experimental data, an output voltage of 0.04 V can be generated when the excitation pressure oscillates at about 20 Hz. Whether a single square or two identical squares are arranged, the 45-degree incidence angle is the most suitable arrangement for power conversion, and L*=4 can produce maximum energy for all configurations. Finally, the experimental results provide deeper insight into the physics behind the relationship between square spacing, rotation angle, and energy harvesting. Regarding hydroelastic energy extraction, tandem diamond configurations have substantial advantages over square ones. With high amplitudes and high frequencies, tandem diamond cylinders can generate mechanical power even beyond typical circular cross-sections. Furthermore, complementary numerical simulations are presented to provide a solid foundation for the reasoning behind the variation in extracted energy as well as complement the experiment results. By conducting numerical simulations, it is found that changing the incidence angle can significantly alter the flow patterns, which is attributable to the sequential formation of a primary vortex from the lee of the bluff body.

Tantalum Nitride‐Enabled Solar Water Splitting with Efficiency Above 10%

AbstractDesigning photoanode semiconducting materials with visible‐light absorption and minimal charge‐carrier recombination for achieving efficient solar‐to‐hydrogen (STH) conversion is challenging. Here, hybrid Ta3N5 nanorods and thin films are developed on transparent GaN/Al2O3 substrates. A Ta3N5 photoanode with a loaded cocatalyst achieves the best current density, i.e. 10.8 mA cm−2, at 1.23 V versus the reversible hydrogen electrode under simulated AM 1.5G solar illumination. In a tandem configuration with dual‐CuInSe2 photovoltaic cells, this semi‐transparent photoanode achieves a reproducible STH energy conversion efficiency of ≈12% (the highest among photocatalytic materials), and remains at more than 10% for 6.7 h of tandem device operation. Detailed transient absorption spectroscopy and theoretical analysis indicates that this high performance originates from efficient light absorption and hole utilization inside the Ta3N5 material. The results show the feasibility of suppressing dominant optical and charge‐carrier‐ recombination losses by using nanostructured visible‐light‐absorbing materials for practical STH conversion.

Experimental Study of an Asymmetric Tandem Wing Configuration for Drone Application

A low-speed wind tunnel investigation characterizing the performance of an asymmetric tandem wing is presented. Wind tunnel data were supported by numerical modeling and flow visualization. The opposing wing halves of a rectangular AR=6.23 wing were systematically shifted fore and aft along a central fuselage to yield asymmetry. The results show that the lift curve slope, minimum drag coefficient, and Oswald efficiency factor are weakly affected by asymmetry, a result supported by numerical computations. The maximum lift-to-drag ratio, however, dropped essentially linearly with increasing asymmetry, a consequence of the reduced aspect ratio of each wing half decreasing the lift coefficient for minimum drag. Comparison of the experimental results with a symmetric wing with conventional empennage suggests that an asymmetric tandem wing configuration may be a viable geometry for deployable flight vehicles such as tube-launched drones.

Study of lift enhancing mechanisms via comparison of the flapping trajectory of tandem flapping foil

Designing an aero/hydrovehicle that mimics natural swimmers such as fish is a challenging task. In the present study, an attempt has been made to mimic the fish tail motion that generates the lift energy. Two fishtail trajectories are replaced with two National Advisory Committee for Aeronautics 0012 foils in a tandem configuration for energy extraction. The energy induced due to lift force of the hind wing while flapping along fishtailed trajectory in single and tandem configurations is determined and compared with that of the simple flapping foil having heave and pitch motion only. The impact of various factors such as foil gap (G), phase angle (φ), and influence of Strouhal number (St) on the energy extraction performance is also investigated at a Reynolds (Re) number of 1173. The results show that a fishtail motion trajectory and foil gap ratio of 3c–4c (c being chord length) would enhance the energy extraction performance of the hindwing. The present research provides a new vision for the improvement of biomimetic power generators, as it aims to improve energy efficiency through the use of wake vortices.

Effects of wake interaction on energy extraction performance of tandem semi-active flapping foils

A numerical investigation was carried out to analyze the interactions between semi-active tandem flapping foils at various tandem distances with a chord-based Reynolds number of 1100. Results indicate that with a tandem distance of less than 1.5 chord lengths and released in-phase, both foils exhibited terminal periodic motions with a nonzero mean stagger distance. In contrast, under the other conditions, the two foils ended up with periodic flapping motions without stagger. Due to the high-pressure region near the leading edge of the aft foil, the heaving motion of the fore foil resulted in lower energy extraction performance than that of single foil, when the tandem distance was less than 5 chord lengths. However, as the tandem distance increased, the fore foil acted like a single foil. The aft foil demonstrated significant fluctuations in performance parameters when subjected to the wake of the fore foil. The favorable interaction between the wake and aft foil resulted in lower power consumption for pitching and enabled the aft foil to extract an additional 15.2% power compared to a single foil. Conversely, during the unfavorable wake–foil interaction, the pitching motion of the aft foil consumed more energy than energy extraction from the heaving motion, leading to net energy consumption. The initial inter-foil pitching phase difference also significantly influenced the performance of the aft foil. Two models, the global phase and the wake phase model, affect these tandem configurations, both proving effective in capturing these effects with the wake phase model displaying notable efficacy.

Effect of Rubidium Fluoride on Grain Sintering and Optoelectronic Properties of Nanostructured CuInSe2 Thin Films Obtained by Solution Processing

Chalcopyrite CuInSe2 (CISe) and Cu(In, Ga)(S, Se)2 (CIGS) absorber layers, have emerged as promising alternatives in the solar cell field due to their unique properties such as power conversion efficiencies (PCEs) above 20 %, direct bandgap, and high absorption coefficient. This enables the making of high-quality PV devices with absorbers from 2 μm thick, significantly reducing the use of raw materials. Additionally, the CISe absorber layer is a desirable material for Perovskite/CIS tandem configuration with a narrow band gap at the bottom that has demonstrated PCEs close to 25 %, and potential applications in lightweight and/or flexible substrates. Recently, the addition of alkali elements such as sodium, potassium, rubidium, and cesium via post-deposition techniques (PDTs) has demonstrated an improvement in CIGS-based solar cells’ performance. In this study, 10, 20, and 30 nm thick layers of rubidium fluoride were post-deposited on CISe-films made by solution processing techniques and then selenized under a selenium-argon atmosphere to improve the CISe photoelectronic properties such as the number of charge carriers collected and grain growth, critical characteristics to ensure useful photovoltaic devices. Thus, the effect of rubidium fluorine on CISe-based solar cells was analyzed using several characterization techniques. According to the results, thin films made by an amine-thiol mixture with uniform atomic composition were obtained. The crystallinity and grain growth improved with an increase in rubidium fluoride addition. Moreover, with 10 nm of rubidium fluoride, an improvement in the lifetime of the charge carrier, photoluminescence intensity, and the number of carriers collected by the solar cells was obtained.

Deflection-Based Approach for Flexible Pavement Design in Thailand

The Department of Highways (DOH), Thailand, has adopted both empirical and mechanistic approaches for flexible pavement analysis and design. Recently, the deflection-based design approach has been comprehensively reviewed by the DOH for the possible adoption of national design standards and practices. One of the key reasons is that Thailand’s road authorities, i.e., the DOH and the Department of Rural Roads (DRR), have considered the falling weight deflectometer (FWD) for the new construction and rehabilitation of road pavements. In addition, the FWD is widely accepted as the non-destructive test for deflection measurement and structural capacity evaluation. Ultimately, the implication of FWD deflections for in-house pavement analysis and design shall be developed and proposed to Thailand’s road authorities. Therefore, this study presents the deflection-based approach of flexible pavement design in Thailand. The FWD and a standard Thai truck were selected as the main loading applications in this study. A typical FWD loading stress of 700–800 kPa was practically adopted by the DOH and compared with a standard 10-wheel 25-ton truck with a tandem axle-dual wheel configuration with a tire pressure of 690 kPa. The layered elastic analysis was performed to calculate the pavement responses. The results suggest that the flexible pavement design based on a deflection-based approach is simple, practical, and conservative.

Investigation on the flow-induced vibration of tandem cylinders with varying diameters at subcritical Reynolds numbers

The flow interference among multiple cylinders is highly complex, and investigating it holds substantial engineering relevance. This paper considering three different arrangements at subcritical Reynolds numbers, a series of experiments were conducted to study the flow-induced vibrations (FIV) of rigid cylinders in tandem with variable diameters. Both cylinders are free to respond in both in-line (IL) and cross-flow (CF) directions. Utilizing a dynamic data acquisition system to obtain micro-strain time history information. The reference cylinder diameter (D) of 30 mm was employed as the standard for the spacing ratio (S/D). Both cylinders were exposed to uniform water flow at varying S/D: 3.0, 4.0, 6.0, and 8.0. A parametric investigation was conducted to analyze the effects of the relative spacing of the cylinders on the vibration response of the system. The results indicate that vibration intensity escalates as flow velocity increases. For the same cylinders, unsteady wave-induced vibrations (WIV) behind the upstream cylinder hinder the appearance of the lower branch of the amplitude response. Furthermore, the S/D substantially influences the cylinder vibration response. In the arrangement where the small cylinder is located upstream, the downstream cylinder undergoes WIV under smaller S/D, and the shielding effect is inconspicuous. In contrast, when the larger cylinder is located upstream, the shielding effect intensifies, leading to synchronous vibrations of the upstream and downstream cylinders. The S/D appears to exert minimal influence on the vibration under these conditions. In summary, the interference between cylinders in tandem configurations significantly impacts the vibration characteristics of the cylinders.

Numerical studies on small rotor configurations with validation using acoustic wind tunnel data

This paper addresses the acoustic and aerodynamic characteristics of small rotor configurations, including the influence of the rotor–rotor interactions. For this purpose, a Rotor/Rotor/Pylon configuration is chosen for both the test and numerical simulations. The wind tunnel experiments on various rotor configuration were performed in DLR’s Acoustic Wind Tunnel Braunschweig (AWB). The experiments involve isolated rotors, and rotors in tandem and coaxial configuration in hover and forward flight. For numerical simulations, an unsteady free wake 3D panel method (UPM) is used to account for aerodynamic non-linear effects associated with the mutual interference among the Rotor/Rotor/Pylon configurations. The effect of the pylon is simulated using potential theory in form of a panelized body. Finally, the sound propagation into the far field is calculated with DLR’s FW–H code APSIM, using UPM blade surface pressure as input. The validation effort is supported by CFD TAU steady simulations on selected hover test cases. The experiments and numerical results indicate that the noise at the blade passing frequency (BPF) and its higher harmonics is the dominant source of the noise for the present rotor selection. The extra subharmonics between two BPFs appearing in the results are caused by the small geometric discrepancy between the blades as well as the motor noise. Broadband noise is also observed in the experiment, but its contribution to the overall sound pressure is very small and can be neglected. The simulation of the acoustic scattering from the rotor support system for the isolated rotor cases indicated an influence about 1–3 dB on the overall sound pressure of the polar microphones. In both the coaxial and the tandem configuration, the acoustic interferences are particularly well visible in the numerical simulations and cause a more complex noise directivity. There is almost no change in time-averaged inflow by applying phase angles. In the coaxial condition, in hover, the phase delay between rotors does not change the maximum noise level. In forward flight, the phase delay can influence the maximum level of the noise radiation. In both coaxial and tandem configuration, the position of the downstream rotor is key for the noise radiation, and therefore, avoiding the interaction with upstream wake can reduce the noise radiation.

Wake tail plane interactions for a tandem wing configuration in high-speed stall conditions

In this work, wake-tail plane interactions are investigated for a tandem wing configuration in buffet conditions, consisting of two untapered and unswept wing segments, using hybrid Reynolds-Averaged Navier–Stokes / Large Eddy Simulations (RANS/LES) with the Automated Zonal Detached Eddy Simulation (AZDES) method. The buffet on the front wing and the development of its turbulent wake are characterized, including a spectral analysis of the fluctuations in the wake and a modal analysis of the flow. The impact of the wake on the aerodynamics and loads of the rear wing is then studied, with a spectral analysis of its lift and surface pressure oscillations. Finally, the influence of the position and the incidence angle of the rear wing is investigated. For the considered flow conditions, 2D buffet is present on the front wing. During the downstream movement of the shock, the amount of separation reaches its minimum and small vortices are present in the wake. During the upstream movement of the shock, the amount of separation is at its maximum and large turbulent structures are present accompanied by high fluctuation levels. A distinct peak in the corresponding spectra can be associated with vortex shedding behind the wing. The impingement of the wake leads to a strong variation of the loading of the rear wing. A low-frequent oscillation of the lift, attributed to the change of the intensity of the downwash generated by the front segment, can be distinguished from high-frequent fluctuations that are caused by the impingement of the wake’s turbulent structures.