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The purpose of this paper is to design an S‐duct intake for unmanned aerial vehicles (UAVs) applications with good efficiency in a wide range of operating conditions.

A fully‐parametric 3‐D CAD model of the intake was constructed in order to produce different intake configurations, within specific geometric constraints, and to study the influence of geometry variation on efficiency. O‐type blocking methodology was adopted in order to construct the block‐structured mesh of hexahedral elements, used in the simulations. The commercial CFD code ANSYS‐CFX was used to compute the flow field inside the flow domain of each case considered. The Reynolds averaged Navier‐Stokes (RANS) equations are discretized using an implicit, vertex‐based finite volume method, combined with the shear stress transport (SST) two‐equation turbulence model and an automatic wall treatment.

By shortening the axial length the flow separation after the first turning becomes more pronounced and the losses are increasing. For very long ducts the increased internal wall area leads to increased wall friction and, consequently, to increased loss production.

The adoption of Gerlach‐shaped profiles for the design of the S‐duct resulted in a low pressure loss level for the optimal shape, although more uniform distribution of total pressure losses resulted for ducts longer than the optimal one, which should be taken into account in the design process.

The main purpose of this research is to investigate distortion and duct total pressure loss at the duct exit (engine face) of a special S-shaped air intake at different simulated flight regimes with and without lip-screen installation. This air intake is supposed to be equipped with a micro jet engine.

Experimental investigations were performed by using a low subsonic close loop wind tunnel to simulate different flight regimes such as negative stall, cruise, shallow angle climb, steep angle climb and positive stall. In order to investigate flow behaviour along the duct length, static pressure changes were also measured. Test results were plotted in terms of total pressure contours and reduced results were tabulated. Static pressure results were also illustrated in different figures.

Results indicated that duct total pressure loss is within the acceptable range and is less than the 2 percent (allowable value) at various flight regimes, but installation of lip-screen has approximately reduced duct pressure recovery between 5 and 15 percent. Results also showed that mean distortion coefficient at duct exit is between 0.22 and 0.3, which is greater than the amount recommended by many jet engine producers.

It would be desirable to investigate the effects of flow control devices installed on this air intake in future researches.

It is highly recommended to practically examine any designed air intake to make sure it is geometrically optimized.

Current research developed an initial test bed for evaluation of the overall aerodynamic behavior of a previously designed special purpose S-shaped duct air intake. Obtained experimental results will help to analyze the internal flow characteristics of the current model as well as preparing data to compare with the future test results for improving its performance.

This paper aims to design an optimal shape for an annular S-duct, considering both energy losses and exit flow uniformity, starting from a given baseline design. Moreover, this paper seeks to identify the design factors that affect the optimal annular S-duct designs.

The author has carried out computational fluid dynamic (CFD)-based shape optimization relative to five distinct numerical objectives, to understand their interrelations in optimal designs. Starting from a given baseline S-duct design, they have applied control node-induced shape deformations and high-order polynomial response surfaces for modeling the functional relationships between the shape variables and the numerical objectives. A statistical correlation analysis is carried out across the optimal designs.

The author has shown by single-objective optimization that the two typical goals in S-duct design, energy loss minimization and exit flow uniformity, are mutually contradictory. He has presented a multi-objective solution for an optimal shape, reducing the total pressure loss by 15.6 per cent and the normalized absolute radial exit velocity by 34.2 per cent relative to a baseline design. For each of the five numerical objectives, the best optimization results are obtained by using high-order polynomial models.

The methodology is applicable to axisymmetric two-dimensional geometry models.

This paper applies a recently introduced shape optimization methodology to annular S-ducts, and, it is, to the author’s knowledge, the first paper to point out that the two widely studied design objectives for annular S-ducts are contradictory. This paper also addresses the value of using high-order polynomial response surface models in CFD-based shape optimization.

The purpose of air-intake duct used in combat aircrafts is to decelerate the inlet flow and concurrently raise the static pressure recovery at the compressor inlet. Because of side-slip movement during sharp maneuvers of the aircrafts, the airflows ingested into twin air-intake ducts are not same and symmetric at its two inlets but are asymmetric in nature. The asymmetric inlet flow conditions at the twin air-intakes thus caused instabilities and deteriorated aerodynamic performance of aircraft components such as compressors and other downstream components. This study aims to investigate the flow control in a twin air-intake with asymmetric inflows.

The continuity and momentum equations are solved with second-order upwind scheme for computing finite-volume method-based unsteady computational fluid dynamics simulation.

Performance parameters are deteriorated with the increase of inflow asymmetry in the twin air-intake duct. Slotted synthetic jets are used to manage flow separation, thereby increasing aerodynamic performance of the air-intake. A variety of vortical structures are generated from the rectangular slots, convected downstream of the twin air-intake. The use of slotted synthetic jets increases static pressure recovery by 64 per cent whereas reducing total pressure loss coefficient by 63 per cent, distortion coefficient by 58 per cent and swirl coefficient by 55 per cent which is an indicative of better aerodynamic performance of twin air-intake.

The study stresses the need of robust flow control technique to improve the performance of combat air-intake system under extreme maneuvering conditions. The results can be useful in designing air-intake satisfying the stealth features for modern combat aircrafts.

The purpose of this paper is to identify efficient methods and tools for the design of distributed propulsion architectures.

Multi-objective computational aerodynamic design optimisation of an S-Duct shape.

Both duct pressure loss and flow distortion through such a duct can be reduced by wall-curvature changes.

Initial simplified study requires higher fidelity computational fluid dynamics & design sensitivity follow-up.

Shape optimisation of an S-Duct intake can improve intake efficiency and reduce the risk of engine-intake compatibility problems.

Potential to advance lower emissions impact from distributed propulsion aircraft.

Both the duct loss and flow distortion can be simultaneously reduced by significant amounts.

The aim of this work was to focus on the creation of a mathematical model for the optimization problem and the methodology for selection of the most important parameters. The engine mount design optimization problem requires a selection of the most important parameters, which influence the final solution.

A two-tier optimization algorithm was considered. The geometry of the engine mount is optimized by first taking into account the sum of loads, and the weight is minimized next.

Several parameters were selected as the essential set of factors for the engine mount design and for optimization to get the minimal weight for the system of the engine and engine mount.

As a case study, the single turboprop engine attached to the front part of fuselage – the so-called tractor propeller configuration – was considered.

This paper contains the proposed methodology, which is going to be used in the efficient systems and propulsion for small aircraft (ESPOSA) project to optimize the newly designed engine mount.

This paper presents a new developed methodology that could be useful for engine mount design.

This study aims to feature the application of the artificial compressibility method (ACM) for the numerical prediction of two-dimensional (2D) axisymmetric swirling flows.

The respective academic numerical solver, named IGal2D, is based on the axisymmetric Reynolds-averaged Navier–Stokes (RANS) equations, arranged in a pseudo-Cartesian form, enhanced by the addition of the circumferential momentum equation. Discretization of spatial derivative terms within the governing equations is performed via unstructured 2D grid layouts, with a node-centered finite-volume scheme. For the evaluation of inviscid fluxes, the upwind Roe’s approximate Riemann solver is applied, coupled with a higher-order accurate spatial reconstruction, whereas an element-based approach is used for the calculation of gradients required for the viscous ones. Time integration is succeeded through a second-order accurate four-stage Runge-Kutta method, adopting additionally a local time-stepping technique. Further acceleration, in terms of computational time, is achieved by using an agglomeration multigrid scheme, incorporating the full approximation scheme in a V-cycle process, within an efficient edge-based data structure.

A detailed validation of the proposed numerical methodology is performed by encountering both inviscid and viscous (laminar and turbulent) swirling flows with axial symmetry. IGal2D is compared against the commercial software ANSYS fluent – by using appropriate metrics and characteristic flow quantities – but also against experimental measurements, confirming the proposed methodology’s potential to predict such flows in terms of accuracy.

This study provides a robust methodology for the accurate prediction of swirling flows by combining the axisymmetric RANS equations with ACM. In addition, a detailed description of the convective flux Jacobian is provided, filling a respective gap in research literature.

The purpose of this paper is to provide a design solution of an engine intake duct suitable for delivering air to the compressor of a gas turbine engine of a general aviation turboprop aircraft, where the initial duct shape suffers a problem of flow distortion due to flow separation at the compressor inlet.

Aerodynamic design uses a three-dimensional inverse-by-optimization approach where the deviation from a desirable target pressure distribution is minimized by means of the adjoint method.

By virtue of a minimization algorithm, the specified target pressure distribution does not necessarily have to be fully realizable to drive the initial pressure distribution towards one with a favourable pressure gradient. The resulting optimized engine intake duct features a deceleration region, in a diverging channel, followed by an acceleration region, in a contracting channel, inhibiting flow separation on the compressor inlet plane.

The flow separation at the compressor inlet has been eliminated allowing proper installation of the engine and flight testing of the aircraft.

Placement and shaping of the intake duct of a turboshaft and turboprop gas turbine engine is a common industrial problem which can be challenging when the available space is limited. The inverse-by-optimization approach based on a reduced flow model, i.e. inviscid flow based on the Euler equations, and a specification of a simple target pressure distribution constitutes an efficient method to overcome the challenge.

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 purpose of this paper is to obtain a better understanding of the rotor–stator interaction in the vaneless region of a centrifugal pump.

A third-order sub-grid scale (SGS) model containing the rotation rate tensor named the dynamic cubic non-linear model (DCNM) is used for simulating the flow field in a centrifugal pump with a vaned diffuser. The pressure coefficient and velocity distributions are compared with the experimental data. Focusing on the vaneless region, the pressure pulsation, Reynolds stress pulsation and Reynolds stress transport equation are analyzed.

The comparison of the calculation results with the experimental data indicates that the DCNM can accurately capture the distributions of pressure and velocity in the vaneless region. Based on the instantaneous pressure signals, the pressure pulsation is analyzed to show that in the vaneless region, the dominant frequency near the impeller is twice the blade passing frequency, whereas it is equal to the blade passing frequency near the diffuser. Further exploration of the Reynolds stress pulsation shows the correlation between the two variables. Additionally, the extreme low frequency of Reynolds stress near the diffuser is found to be related to the rotation instability. To explore the turbulence characteristics in the vaneless region, the Reynolds stress transportation equation is studied. In the vaneless region, the rotation term of the Reynolds stress transport equation is negligible compared to the production term, although the rotation instability is obvious near the diffuser. The production of the Reynolds stress plays the role of redistributing the energy from the uu component to the vv component, except for the region near the impeller outlet.

The third-order SGS model DCNM has proved to be promising in simulating the rotor–stator interaction. The analysis of the rotation instability and the Reynolds stress transport equation shed light on the further understanding of the rotor–stator interaction.