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The exponential growth in computational capabilities and the increasing reliability of current simulation tools have fostered the use of computational fluid dynamics (CFD) in the design of pioneering aircraft engine architectures, such as the counter rotating open rotor (CROR) engine. Today, this design process is led by tight performance and noise constraints from a very early stage, thus requiring deep investigations of the aerodynamic and acoustic behaviour of the fluid flow. The purpose of this study is to track the trajectory of tip vortices, which is of critical importance to understand and prevent potential vortex–blade interactions with subsequent rows, as this condition strongly influences the aerodynamic and structural performance and acoustic footprints of the engine.

In this paper, a flow feature detection methodology is applied to a particular CROR test case with the goal of visualizing and tracking the development of these coherent structures from the tip of front rotating blades. The suitability and performance of four typical region-based methodologies and one line-based (LB) criteria are firstly evaluated. Then, two novel seeding methodologies are presented as an attempt to improve the performance of the LB algorithm previously investigated.

It was demonstrated that the new seeding algorithms increase the probability of the selected seeds to grow into a tip vortex line and reduce the user’s dependence upon the selection of candidate seeds, providing faster and more accurate answers during the design-to-noise iterative process.

Apart from the new vortex detection initialization methodologies, the paper also attempts to assist the user in the endeavour of extracting rotating structures from their own CFD simulations.

The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan.

A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region.

It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes.

Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy.

The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.

This study aims to investigate the effectiveness of two types of winglets, multi-tip and raked, on the performance of sinusoidal and simple leading-edge wings and compares it by a numerical method.

The wing configuration in this study is rectangular and uses NACA0020 section, and all simulations are performed by a numerical method based on finite volume and base pressure algorithm in Reynolds 2 × [10]^5. In the mentioned numerical method, the flow is considered turbulent, and the k-ω-SST model is used. To calculate the stresses on the wing surface, the mesh is extended to below the viscous layer, and a second-order upstream accuracy is used to calculate the convection flux.

The use of raked and multi-tip winglets for the sinusoidal edge of the wing improved aerodynamic performance by 5.12 and 2.28%, respectively, and the greatest effect of these two winglets was on increasing the lifting force and reducing the inductive drag, respectively. Also, by examining the distribution of induced vortices around the configurations, it was found that the curvature of the sinusoidal wing tip at the angles of attack before stall reduced the strength of the induced vortices and, the use of winglet during and after stall, caused increased aerodynamic performance of the sinusoidal wing.

The whale is an international species of aquatic animal found in most of the world’s oceans. It has large fin aspect ratios that have a series of bulges at the edge of the attack, which improves the aerodynamic performance near and after stall. Today, one of the fields of research is the use of this idea in the wings of micro air vehicle.

Winglet reduces induced drag in simple wings. So far, the effect of winglets on wings with sinusoidal attack edges has not been investigated.

A new method for predicting rotor wake in low speed and hovering flight is described to investigate the motion of the helical tip vortex. Beginning with the generalized wake model, a semi‐empirical correction for the vortex core effect on rotor wake is made and free wake calculation is carried out. As an example of its engineering application, the calculated downwash velocity field along the rocket launch line is presented and simply analysed. In terms of theory, the method developed here may provide of a referable basis for further study the formation mode of the tip vortex and vortex core interior structure.

THE study of the flight of birds has provided and will still provide much valuable information for tiie progress of human flight. Many suggestions for the improvements of wings by the use of special wing tips owe their existence to the observation of nature. In spite of such suggestions, free‐flight experimentation—as far as published work goes—is still rather rare and restricted in scope. This reluctance may be due to practical design considerations (handling) as well as to the necessity of making the conventional aileron as efficient as possible; it may also be caused by the impression that experiment in this direction is not worth the effort.

The design of main rotor blade tips is of interest to helicopter manufactures since the tip details affect the performance and acoustics of the rotor. The paper aims to discuss this issue.

In this paper, computation fluid dynamics is used to simulate the flow around hovering helicopter blades with different tip designs. For each type of blade tip a parametric study on the shape is also conducted for comparison calculations were performed the constant rotor thrust condition. The collective pitch and the cone angles of the blades were determined by at an iterative trimming process.

Analysis of the distributed blade loads shows that the tip geometry has a significant influence on aerodynamics and aeroacoustics especially for stations where blade loading is high.

The aeroacoustic characteristics of the rotors were obtained using Ffowcs Williams-Hawkings equations.

The purpose of this study is to investigate the aerodynamic characteristics of a low-to-moderate-aspect-ratio, tapered, untwisted, unswept wing, equipped of sheared wing tips.

In this work, wind tunnel tests were made to study the influence in aerodynamic characteristics over a typical low-to-moderate-aspect-ratio wing of a general aviation aircraft, equipped with sheared – swept and tapered planar – wing tips. An experimental parametric study of different wing tips was tested. Variations in its leading and trailing edge sweep angle as well as variations in wing tip taper ratio were considered. Sheared wing tips modify the flow pattern in the outboard region of the wing producing a vortex flow at the wing tip leading edge, enhancing lift at high angles of attack.

The induced drag is responsible for nearly 50% of aircraft total drag and can be reduced through modifications to the wing tip. Some wing tip models present complex geometries and many of them present benefits in particular flight conditions. Results have demonstrated that sweeping the wing tip leading edge between 60 and 65 degrees offers an increment in wing aerodynamic efficiency, especially at high lift conditions. However, results have demonstrated that moderate wing tip taper ratio (0.50) has better aerodynamic benefits than highly tapered wing tips (from 0.25 to 0.15), even with little less wing tip leading edge sweep angle (from 57 to 62 degrees). The moderate wing tip taper ratio (0.50) offers more wing area and wing span than the wings with highly tapered wing tips, for the same aspect ratio wing.

Although many studies have been reported on the aerodynamics of wing tips, most of them presented complex non-planar geometries and were developed for cruise flight in high subsonic regime (low lift coefficient). In this work, an exploration and parametric study through wind tunnel tests were made, to evaluate the influence in aerodynamic characteristics of a low-to-moderate-aspect-ratio, tapered, untwisted, unswept wing, equipped of sheared wing tips (wing tips highly swept and tapered).

Helicopter rotor blades are usually aerodynamically limited by the severe conditions present in every revolution: strong shock wave boundary layer interaction on the advancing side and dynamic stall on the retreating side. Therefore, different flow control strategies might be applied to improve the aerodynamic performance.

The present research is focussed on the application of passive rod vortex generators (RVGs) to control the flow separation induced by strong shock waves on helicopter rotor blades. The formation and development in time of the streamwise vortices are also investigated for a channel flow.

The proposed RVGs are able to generate streamwise vortices as strong as the well-known air-jet vortex generators. It has been demonstrated a faster vortex formation for the rod type. Therefore, this flow control device is preferred for applications in which a quick vortex formation is required. Besides, RVGs were implemented on helicopters rotor blades improving their aerodynamic performance (ratio thrust/power consumption).

A new type of vortex generator (rod) has been investigated in several configurations (channel flow and rotor blades).

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.