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In this study, 12 potential wake vortex encounters that were reported at a major European airport have been investigated. Because almost all encounters occurred in ground proximity, most pilots conducted a go-around. The primary purpose of this study is to discriminate between incidents caused by wake vortices or rather by effects like wind shear or turbulence. Detailed knowledge of real-world encounter scenarios and identification of worst-case conditions during the final approach constitute highly relevant background information to assess the standard scenario used for the definition of revised wake turbulence separations.

Wake vortex predictions using the probabilistic two-phase wake vortex model (P2P) are used to investigate the incidents in detail by using data from the flight data recorder, meteorological instrumentation at the airport and numerical weather prediction.

In the best documented cases, the flight tracks through the vortices could be reconstructed in good agreement with wake vortex predictions and recorded aircraft reactions. Out of the eight plausible wake vortex encounters, five were characterized by weak crosswinds below 1.5 m/s combined with tailwinds. This meteorological situation appears favourable for encounters because, on the one hand, weak crosswinds may compensate the self-induced lateral propagation of the upwind vortex, such that it may hover over the runway directly in the flight path of the following aircraft. On the other hand, tailwinds limit the propagation of the so-called end effects caused by the breakdown of lift during touchdown.

The installation of plate lines beyond the runway tails may improve safety by reducing the number of wake vortex encounters.

The conducted investigations provide high originality and value for both science and operational application.

Wake vortices that are generated by an aircraft as a consequence of lift constitute a potential danger to the following aircraft. To predict and avoid dangerous situations, wake vortex transport and decay models have been developed. Being based on different model physics, they can complement each other with their individual strengths. This paper investigates the skill of a Multi-Model Ensemble (MME) approach to improve prediction performance. Therefore, this paper aims to use wake vortex models developed by NASA (APA3.2, APA3.4, TDP2.1) and by DLR (P2P). Furthermore, this paper analyzes the possibility to use the ensemble spread to compute uncertainty envelopes.

An MME approach called Reliability Ensemble Averaging (REA) is adapted and used to the wake vortex predictions. To train the ensemble, a set of wake vortex measurements accomplished at the airports of Frankfurt (WakeFRA), Munich (WakeMUC) and at a special airport Oberpfaffenhofen was applied.

The REA approach can outperform the best member of the ensemble, on average, regarding the root-mean-square error. Moreover, the ensemble delivers reasonable uncertainty envelopes.

Reliable wake vortex predictions may be applicable for both tactical optimization of aircraft separation at airports and airborne wake vortex prediction and avoidance.

Ensemble approaches are widely used in weather forecasting, but they have never been applied to wake vortex predictions. Until today, the uncertainty envelopes for wake vortex forecasts have been computed among others from perturbed initial conditions or perturbed physics as well as from uncertainties from environmental conditions or from safety margins but not from the spread of structurally independent model forecasts.

This paper aims to propose a precise turbulence model for automobile aerodynamics simulation, which can predict flow separation and reattachment phenomena more accurately.

As the results of wake flow simulation with commonly used turbulence models are unsatisfactory, by introducing a nonlinear Reynolds stress term and combining the detached Eddy simulation (DES) model, this paper proposes a nonlinear-low-Reynolds number (LRN)/DES turbulence model. The turbulence model is verified in a backward-facing step case and applied in the flow field analysis of the Ahmed model. Several widely applied turbulence models are compared with the nonlinear-LRN/DES model and the experimental data of the above cases.

Compared with the experimental data and several turbulence models, the nonlinear-LRN/DES model gives better agreement with the experiment and can predict the automobile wake flow structures and aerodynamic characteristics more accurately.

The nonlinear-LRN/DES model proposed in this paper suffers from separation delays when simulating the separation flows above the rear slant of the Ahmed body. Therefore, more factors need to be considered to further improve the accuracy of the model.

This paper proposes a turbulence model that can more accurately simulate the wake flow field structure of automobiles, which is valuable for improving the calculation accuracy of the aerodynamic characteristics of automobiles.

Based on the nonlinear eddy viscosity method and the scale resolved simulation, a nonlinear-LRN/DES turbulence model including the nonlinear Reynolds stress terms for separation and reattachment prediction, as well as the wake vortex structure prediction is first proposed.

From pilot reports, field measurements and numerical simulations, it is known that wake vortices may persist within the glide path in ground proximity, leading to an increased encounter risk. This paper aims to investigate wake vortex behaviour during final approach and landing to understand why landings can be safe nevertheless. Further, it is investigated whether and to which extent the installation of plate lines beyond the runway tails may further accelerate wake vortex decay and thus improve safety by reducing the number of wake vortex encounters.

A hybrid numerical simulation approach is used to investigate vortex evolution from roll-up until final decay during the landing manoeuvre. The simulations are complemented by field measurement data accomplished at Munich Airport and at Special Airport Oberpfaffenhofen.

During touchdown, the so-called end effects trigger pressure disturbances and helical vortex structures that appear to ensure vortex decay rates in ground proximity needed to guarantee the required safety targets of aviation. Light detection and ranging (LIDAR) measurements indicate that vortex decay indeed can be accelerated by a plate line installed on the ground surface. The lifetime of the most safety relevant, long-lived and strongest vortices can be reduced by one-third.

The installation of plate lines beyond the runway tails may improve safety by reducing the number of wake vortex encounters and increase the efficiency of wake vortex advisory systems.

The novel numerical simulation technique and the acquired insights into the wake vortex phenomena occurring during landing as well as the demonstration of the functionality of the patented plate line provide high originality and value for both science and operational application.

The purpose of this paper is to provide an approach to predict rotor thrust and hub moments under in ground effect (IGE) in transient flight. Target of the research is developing a new integrated methodology that can be applied in the simulation of rotor flow field IGE.

Free-wake model and panel method are two methods used to predict ground influence on rotor flow field. However, these methods can result in unphysical phenomena, such as wake vortex moving below the ground during simulation and fluctuation taking place on vortices near ground, which is named noise problem. Thus, a new tactic called “constant volume rectification” is developed to rectify the unreal vortex location, and a third-order time-stepping algorithm called CB3D (Center difference and Backward difference 3rd-order scheme with numerical Dissipation) with strengthened stability is proposed to replace the existing second-order time-stepping algorithm CB2D (Center difference and Backward difference 2nd-order scheme with numerical Dissipation) to inhibit the development of discrete error.

The new free-wake model is effective and stable in predicting the characteristics of the rotor flow field in steady and transient flights under IGE. The newly developed CB3D scheme is more stable and more suitable for wake prediction of rotor under IGE than the CB2D scheme. At different advance ratios, the predicted flow regimes of recirculation and ground vortex agree well with the test images. In the accelerating condition, the predicted variations of rotor thrust and hub moments with advance ratios are consistent with the corresponding experimental results. It is found that the slow movement of wake geometry with advance ratio in the accelerating condition is the cause of the delay in the variation tendency of rotor forces compared to that in steady condition.

The proposed model can be used in rotor designing and helicopter flight dynamics simulation because of its favorable stability and relatively low computational cost.

This paper proposes several new methods to make the time-stepping wake model highly appropriate for rotor aerodynamics prediction under IGE. These methods provide new perspectives in solving the unstable and unphysical problems that often arise in vortex–ground interaction in rotor free-wake prediction.

The purpose of this paper is to evaluate the prediction capability of comprehensive structural dynamics (CSD) analysis codes for the higher harmonic control aeroacoustic rotor test (HART) II data.

A nonlinear flexible multibody dynamics analysis code DYMORE, as well as the comprehensive analytical model of rotorcraft aerodynamics and dynamics (CAMRAD) II, are used to perform the task. The predicted results on rotating free vibration analysis, airloads, blade elastic motions, and structural moments are correlated with the measured data for the baseline, minimum noise, and minimum vibration cases.

The DYMORE analysis results with a free wake model show a good performance in capturing blade vortex interaction peaks in the prediction of section normal forces but apparently with a phase shift problem. The high‐frequency behavior in the airloads signal does not affect much on the aeroelastic response and structural moments of the rotor.

The present approach uses two separate CSD codes to systematically validate the HART II data. The accuracy of each code on structural dynamic aspects of HART II rotor is assessed using a consistent set of inputs. The effects of blade tip deflections on the interaction of blades and their trailed vortices leading to a reduced noise emission are also investigated.

The purpose of this paper is to present and validate an efficient time‐marching free‐vortex method for rotor wake analysis and study the rotor wake dynamics in transient and maneuvering flight conditions.

The rotor wake is represented by vortex filament elements. The equations governing the convection, strain and viscous diffusion of the vortex elements are derived from incompressible Navier‐Stokes equations based on the viscous splitting algorithm. The initial core size of the blade tip vortices is directly computed by a vortex sheet roll‐up model. Then, a second‐order time‐marching algorithm is developed for solving the governing equations. The algorithm is formulated in explicit form to improve computing efficiency. To avoid the numerical instability, a high order variable artificial dissipative term is directly introduced into the algorithm. Finally, the developed method is applied to examine rotor wake geometries in steady‐state and maneuvering flight conditions. Comparisons between predictions and experimental results are made for rotor wake geometries, induced inflow distributions and rotor transient responses, to help validate the new method.

The algorithm is found to be numerically stable and efficient. The predicted rotor responses have good agreement with experimental data. The transient behavior of the wake dominates the rotor responses following rapid control inputs in hover. The wake curvature effect induced by rotor pitching or rolling rate significantly changes the rotor off‐axis response.

This method should be further validated using experimental measurements of full‐scale helicopter rotors.

The paper presents a new time‐marching free‐vortex wake method, which is suitable for application in helicopter flight simulation.

The primary purpose of this paper is to investigate the characteristics of the unsteady flow field in the wake of Eppler‐361 airfoil undergoing harmonic pitch oscillation in both pre‐stall and post‐stall regimes.

Experimental measurements were carried out to study the characteristics of the unsteady flow field within the wake of an airfoil. All of the experiments were conducted in a low‐speed wind tunnel, and the velocity field was measured by a hot‐wire anemometry. The airfoil was given a harmonic pitching motion about its half chord axis at two reduced frequencies of 0.091 and 0.273. All experimental data were taken at the oscillation amplitude of 8°. During the experiments, the mean angle of attack was altered from 2.5 to 10° that this made it possible to study the wake in both pre‐stall and post‐stall regimes.

From the results, it can be concluded that different velocity profiles are formed in the wake at different phase angles. In addition, the hysteresis of the velocity field in the wake is captured between increasing and decreasing incidences. It is also found that the velocity field in the wake is strongly affected by the operating conditions of the airfoil, e.g. mean angle of attack, reduced frequency and instantaneous angle of attack. Huge variations in the profiles of the wake are observed at high instantaneous angles of attack when the mean angle of attack is 10°, i.e. when the airfoil experiences significant oscillations beyond the static stall. It is concluded that this is due to dynamic stall phenomenon.

Findings of the present study give valuable information, which can be used to characterize wakes of micro air vehicles, helicopter's rotor blades, and wind turbine blades. In addition to this, present findings can be used to predict dynamic stall of the above applications.

The paper is the first to investigate the unsteady wake of Eppler‐361 airfoil and to predict the dynamic stall phenomenon of this airfoil.

Computational fluid dynamics (CFD)/computational structural dynamics (CSD) coupling analysis is an important method in the research of helicopter aeroelasticity due to its high precision. However, this method still suffers from some problems, such as wake dissipation and large computational cost. In this study, a new coupling method and a new air load correction method that combine the free wake model with the CFD/CSD method are proposed to maintain computational efficiency whilst solving the wake dissipation problem of the prior coupling methods.

A new coupling method and a new air load correction method that combine the free wake model with the CFD/CSD method are proposed. With the introduction of the free wake model, the CFD solver can adopt two-order accuracy schemes and fewer aerodynamic grids, thus maintaining computational efficiency whilst solving the wake dissipation problem of the prior coupling methods.

Compared with the predictions of the prior methods and flight test data, those of the proposed method are more accurate and closer to the test data. The difference between the two methods in high-speed forward flight is minimal.

Because of the chosen research approach, the research results may lack generalisability. Therefore, researchers are encouraged to test the proposed method further.

In this paper, a CFD/CSD/free wake coupling method is proposed to improve the computational accuracy of the traditional CFD/CSD coupled method and ensure the computational efficiency.

The purpose of the paper is to predict the aerodynamic performance of a complete scale model H-Darrieus vertical axis wind turbine (VAWT) with end plates at different operating conditions. This paper aims at understanding the flow physics around a model VAWT for three different tip speed ratios corresponding to three different flow regimes.

This study achieves a first three-dimensional hybrid lattice Boltzmann method/very large eddy simulation (LBM-VLES) model for a complete scaled model VAWT with end plates and mast using the solver PowerFLOW. The power curve predicted from the numerical simulations is compared with the experimental data collected at Erlangen University. This study highlights the complexity of the turbulent flow features that are seen at three different operational regimes of the turbine using instantaneous flow structures, mean velocity, pressure iso-contours, blade loading and skin friction plots.

The power curve predicted using the LBM-VLES approach and setup provides a good overall match with the experimental power curve, with the peak and drop after the operational point being captured. Variable turbulent flow structures are seen over the azimuthal revolution that depends on the tip speed ratio (TSR). Significant dynamic stall structures are seen in the upwind phase and at the end of the downwind phase of rotation in the deep stall regime. Strong blade wake interactions and turbulent flow structures are seen inside the rotor at higher TSRs.

The computational cost and time for such high-fidelity simulations using the LBM-VLES remains expensive. Each simulation requires around a week using supercomputing facilities. Further studies need to be performed to improve analytical VAWT models using inputs/calibration from high fidelity simulation databases. As a future work, the impact of turbulent and nonuniform inflow conditions that are more representative of a typical urban environment also needs to be investigated.

The LBM methodology is shown to be a reliable approach for VAWT power prediction. Dynamic stall and blade wake interactions reduce the aerodynamic performance of a VAWT. An ideal operation close to the peak of the power curve should be favored based on the local wind resource, as this point exhibits a smoother variation of forces improving operational performance. The 3D flow features also exhibit a significant wake asymmetry that could impact the optimal layout of VAWT clusters to increase their power density. The present work also highlights the importance of 3D simulations of the complete model including the support structures such as end plates and mast.

Accurate predictions of power performance for Darrieus VAWTs could help in better siting of wind turbines thus improving return of investment and reducing levelized cost of energy. It could promote the development of onsite electricity generation, especially for industrial sites/urban areas and renew interest for VAWT wind farms.

A first high-fidelity simulation of a complete VAWT with end plates and supporting structures has been performed using the LBM approach and compared with experimental data. The 3D flow physics has been analyzed at different operating regimes of the turbine. These physical insights and prediction capabilities of this approach could be useful for commercial VAWT manufacturers.