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The aerodynamic interaction of vehicles in platoon formation generates complex unsteady flow phenomena that strongly influence drag performance. This study investigates the unsteady aerodynamic drag and associated flow structures of two simplified Ahmed body models (30° slant angle) traveling in platoon using transient Computational Fluid Dynamics (CFD). Unsteady Reynolds-Averaged Navier–Stokes (URANS) and Improved Delayed Detached Eddy Simulation (IDDES) are employed to analyze the effect of longitudinal spacing ratios, d/L=0.1–2.0. Following a mesh independence study, a grid with 13.3 million cells is adopted to resolve the flow field and quantify drag unsteadiness for both the lead and trailing vehicles across spacing configurations. Validation is performed by comparing the predicted drag coefficients with experimental measurements. Results show that the lead vehicle experiences a substantial drag reduction, with the coefficient decreasing to 0.16 at close spacing, before rising to 0.40 (URANS) and 0.37 (IDDES) at d/L=2. In contrast, the trailing vehicle exhibits only minor drag variation across d/L=0.5–2, ranging between 0.35 and 0.37. Additional analyses include pressure coefficient distributions, instantaneous velocity fields, and vortex structures identified through Q-criterion visualizations. Comparisons indicate that IDDES captures finer flow structures and better reflects   the unsteadiness of drag than URANS. Overall, the results suggest that the lead vehicle benefits most from platooning, achieving up to 60% drag reduction at small spacings, whereas the trailing vehicle gains comparatively little.

In the present work, the three-dimensional heat and fluid flows around staggered pin-fin arrays are predicted using two hybrid RANS/LES models (an improved delayed detached eddy simulation (IDDES) model and a stress-blended eddy simulation (SBES) model), and one transitional unsteady Reynolds averaged Navier-Stokes (URANS) model, called k-ω SSTLM. The periodic segment geometry with a total of nine pins is considered with a channel height of 2D and a distance of 2.5D between each pin. The corresponding Reynolds number based on the pin diameter and the maximum velocity between pins is 10,000. The two hybrid RANS/LES results show the superior prediction of the mean velocity profiles around the pins, pressure distributions on the pin wall, and Nusselt number distributions. However, the transitional model, k-ω SSTLM, shows large discrepancies except in front of the pins where the flow is not fully developed. The vortical structures are well resolved by the two hybrid RANS/LES models. The SBES model is particularly adept at capturing the 3-D vortex structures after the pins. The effects of the blending function switching between RANS and LES mode of the two hybrid RANS/LES models are also investigated.

Aerodynamic noise level has become an important performance index of civil aircraft, and it is drawing more and more attention. Most airframe noise research based on CFD method is aimed at aircraft individual parts at present, while lack of noise prediction for the complex high fidelity full aircraft model. Due to the interaction between aircraft parts, noise prediction between single part and the actual configuration are very different in the aspect of calculation conditions, noise generation and propagation. Only by using more realistic model can the noise be accurately predicted. In this paper, high-resolution mesh and high-precision hybrid RANS/LES method, combined with the FW-H acoustic analogy method, are employed to predict the noise of a turboprop's high-fidelity 1/6 scale model of landing configure. The improved delayed detached eddy simulation (IDDES) method was used to simulate the flow in the near-field sound source region, and the sound source characteristics of the whole turboprop are obtained. In addition to the two important noise sources-flap side edge and wing tip, numerical simulation also found other two important noise sources resulting from the interaction between parts-interaction between nacelle wake and flap, and the complex flow between flap inner side and fuselage. Results of far-field noise show that in the longitudinal symmetry plane of the fuselage, the noise mainly propagates to the lower front and over back direction, and the dipole characteristics are very obvious. In the plane perpendicular to the incoming flow, the noise in the transverse direction is weaker. 民用飞机机体噪声水平已成为衡量飞机性能的重要指标，受到了越来越多的关注。当前基于CFD数值模拟的机体噪声预测研究大多针对飞机单独部件开展，缺乏对全机高保真复杂构型的噪声预测。由于部件之间的干扰，针对部件的噪声预测在计算条件、噪声的产生及传播等方面均和实际构型之间存在很大的差异，因此采用高保真真实飞机模型才能对飞机机体噪声进行更准确的预测。采用精细化高分辨率网格与高精度混合RANS/LES方法，结合FW-H声类比方法，对涡桨飞机高保真1/6缩比模型在降落状态下的气动噪声进行了数值预测研究。采用改进的延迟分离涡模拟（IDDES）方法对近场声源区流动进行模拟，得到了涡桨飞机全机的近场声源特性。除了捕捉到襟翼侧缘和翼尖2个重要噪声源之外，还发现了由短舱尾迹和后缘襟翼之间的干扰引起的噪声源、襟翼内侧和机身之间的复杂流动引起的噪声源。远场噪声研究结果显示，在机身的纵向对称面内，噪声主要向前下方和后上方传播，偶极子特性十分明显。在垂直于来流的平面内，横向噪声较弱。

Distributed electric propulsion is an emerging research topic, with a key advantage being its potential for enhanced lift performance through aerodynamic propeller-wing interactions. To address the lack of research on the flow mechanism of distributed propulsion systems, quasi-steady Reynolds-averaged Navier-Stokes numerical simulations were conducted on a simplified 2.5D distributed propulsion system to analyze the impact of parameters such as advance ratio, spanwise propeller distance (tip-to-tip distance), and angle of attack. The parameters study revealed that achieving optimal distributed propulsion system performance requires a trade-off with propeller efficiency. At low angles of attack, propeller efficiency increases by up to 4% with increasing spanwise propeller distance. However, this trend reversed at high angles of attack. The system lift coefficient shows a maximum increase of approximately 100% compared to the isolated system. The converging flow generated by distributed propellers on the suction side of the wing contributes to lift enhancement. At high angles of attack, the small spanwise propeller distance configuration benefits mainly from the wing on the ascending blade side (P-) within the slipstream region, while the medium configuration derives lift primarily from the wing section adjacent to the ascending blade side (P-) in the non-slipstream region. The flap exhibits an inverse low-pressure distribution compared to the wing. SST-IDDES method results indicate that the spiral vortex on the suction surface of the wing on the ascending blade side contributes to increased lift for the distributed propulsion system. The study clarifies the impact of flow field structures induced by distributed propeller-wing interactions on the aerodynamic performance of distributed propulsion systems, establishing a theoretical foundation for the aerodynamic optimization of systems.

Three new types of acoustic insulation facilities, namely, full-enclosed (FEAB), bilateral-inverted-L-shaped (BILSAB), and inverted-L-shaped (ILSAB) acoustic barriers, are gradually receiving application along high-speed railways. A moving high-speed train (HST) may induce a nonlinear aerodynamic impact on the acoustic barrier. The HST may also experience a rapid change in its aerodynamic loads, reducing its stability and causing discomfort to passengers. Hence, nonlinear aerodynamic effects of three new types of high-speed railway acoustic insulation facilities when an HST passes by are compared based on model experiments and improved delayed detached eddy simulations (IDDES). Results show that: (i) When a HST runs at 350 km/h, the coefficient of pressure difference on the FEAB is 5.64 and 8.78 times higher than in the BILSAB and ILSAB, respectively. (ii) The amplitude of drag force coefficient of the head car when entering the FEAB is 2.80 and 2.95 times that of the BILSAB and ILSAB, respectively. The amplitude of lift coefficient of the tail car when running through the BILSAB is 1.27 and 1.37 times that of the FEAB and ILSAB. The amplitude of side force coefficient of the tail car when running through the ILSAB is 1.18 and 1.24 times that of the FEAB and BILSAB. (iii) For the tail car, the standard deviation of C x when running inside the FEAB is 2.18 and 2.15 times that of the BILSAB and ILSAB, respectively. The standard deviation of C y when running inside the FEAB is 1.42 and 1.51 times that of the BILSAB and ILSAB, respectively. The standard deviation of C y when running inside the FEAB is 1.48 and 1.15 times that of the BILSAB and ILSAB, respectively. The results of this research may provide reference value for optimizing the structural patterns and improving the train’s operating stability.

In this work, we present the first three-dimensional (3D) computational investigation of wind turbine airfoils over 360° angles of attack to predict unsteady aerodynamic loads and vortex-shedding characteristics. To this end, static–airfoil simulations are performed for the FFA-W3 airfoil family at a Reynolds number of 107 with the Improved Delayed Detached Eddy Simulation turbulence model. Aerodynamic forces reveal that the onset of boundary-layer instabilities and flow separation does not necessarily coincide with the onset of stall. In addition, a comparison with two-dimensional simulation data and flat plate theory extension of airfoil polars, suggest that, in the deep stall regime, 3D effects remain critical for predicting both the unsteady loads and the vortex-shedding dynamics. For all airfoils, the vortex-shedding frequencies are found to be inversely proportional to the wake width. In the case of slender airfoils, the frequencies are nearly independent of the airfoil thickness, and their corresponding Strouhal number St is approximately 0.15. Based on the calculated St, the potential for shedding frequencies to coincide with the natural frequencies of the International Energy Agency 15 MW reference wind turbine blades is investigated. The analysis shows that vortex-induced vibrations occur primarily at angles of attack of around ±90° for all airfoils.

To reduce the crosswind effect on high-speed trains, in this paper, by using the Improved Delayed Detached Eddy Simulation (IDDES) method and the SST turbulence model, a novel blowing measure is studied and compared by considering different positions of blowing slots on the train surface. The concerned blowing positions on the train surface include the top position (Top); windward side (WWS): the upper position (WU), middle position (WM), and lower position (WL); and leeward side (LWS): the upper position (LU), middle position (LM), and lower position (LL). The results show that in regard to the rolling moment coefficient around the leeward rail, C Mx lee , the mitigation effect with LM for the head car is the largest, and the mitigation effect with WL for the middle car and tail car is superior to other cases. The corresponding drop percentages are 18.5%, 21.7%, and 30.8% for the head car, middle car, and tail car, respectively. The flow structures indicate that the blowing positions on the lower half of WWS and upper half of LWS would form a protective air gap to weaken the impact of coming flows and delay the vortex separation on LWS, and thus the train aerodynamic performance is improved.

The present study aims to assess the effects of two different underlying RANS models on overall behavior of the IDDES methodology when applied to different flow configurations ranging from fully attached (plane channel flow) to separated flows (periodic hill flow). This includes investigating prediction accuracy of first and second order statistics, response to grid refinement, grey area dynamics and triggering mechanism. Further, several criteria have been investigated to assess reliability and quality of the methodology when operating in scale resolving mode. It turns out that irrespective of the near wall modeling strategy, the IDDES methodology does not satisfy all criteria required to make this methodology reliable when applied to various flow configurations at different Reynolds numbers with different grid resolutions. Further, it is found that using more advanced underlying RANS model to improve prediction accuracy of the near wall dynamics results in extension of the grey area, which may delay the transition to scale resolving mode. This systematic study for attached and separated flows suggests that the shortcomings of IDDES methodology mostly lie in inaccurate prediction of the dynamics inside the grey area and demands further investigation in this direction to make this methodology capable of dealing with different flow situations reliably.

The paper deals with the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct. The Improved Delayed Detached Eddy Simulation (IDDES) approach based on the Shear Stress Transport (SST) model is used, which in this paper is applied to a turbulent reacting flow with finite rate chemical reactions. An original Adaptive Implicit Scheme for unsteady simulations of turbulent flows with combustion, which was successfully used in IDDES simulation, is described. The simulation results are compared with the experimental database obtained at the LAERTE experimental workbench of the ONERA—The French Aerospace Laboratory. Comparison of IDDES with experimental results shows a strong sensitivity of the simulation results to the surface roughness and temperature of the duct walls. The results of IDDES modeling are in good agreement with experimental pressure distributions along the wall and with the results of videoregistration of the excited radical chemiluminescence.

The impact of train heights on train aerodynamic performance is studied by using an improved delayed detached-eddy simulation (IDDES) method. The correctness of the numerical method has been verified by the existing wind tunnel and moving model experiments data. The aerodynamic drag, lift, slipstream, and wake flow are compared for three train heights. The results presented that the drag and lift increased by 6.2% and 23.8% respectively, with an increase in train height from 3.89 m to 4.19 m. Compared with the 3.89 m case, the maximum time-averaged slipstream at the platform location for 4.04 and 4.19 m cases are increased by 2.0% and 4.3% respectively. Meanwhile, the wake topology for three cases is described and analyzed quantitatively. The downwash angle of the wake longitudinal flow is increased with the increasing train height, resulting in the mixing of the downwash flow and the ground flow in advance. The wake in the higher trains tends to develop outward and downward. Besides, the higher trains will also bring greater transient aerodynamic loads to the equipment above the train. It's recommended to shorten the maintenance period of the electrical equipment above the higher trains to ensure the devices' safety. Abbreviations: CFL: Courant-Friedrichs-Lewy; COT: Center of the track; FDR: Flow development region; FFT: Fast Fourier transform; GF: Ground-fixed reference system; ICE3: Intercity Express 3; IDDES: Improved delayed detached-eddy simulation; LES: Large-eddy simulation; LV: Longitudinal vortex; MME: Moving model experiments; NBL: Negative bifurcation line; PBL: Positive bifurcation line; PSD: Power spectral density; RANS: Reynolds averaged Navier - Stokes; SF: Stable focus; SP: Saddle point; STBR: Single-track ballast and rails; SV: Spanwise vortex; TF: Train-fixed reference system; TOR: Top of the track; TSI: Technical specification for interoperability; UN: Unstable node; WPR: Wake propagation region