Search results

This study aims to simulate gust effects on the aeroelastic behavior of a flexible aircraft. The dynamic response of the system for different discreet gust excitations is obtained using numerical simulations.

Coupled dynamics, including rigid and flexible body coordinates, are considered for modeling the dynamic behavior of the aircraft. Wing is considered flexible and other parts are considered rigid. Wing is modeled with nonlinear Euler Bernoulli beam. Moreover, unsteady aerodynamics based on the Wagner function are used for aerodynamic loading, and the results are compared with those of quasi-steady aerodynamics.

Von Kármán continuous gust is applied to this aircraft. In addition, the discrete “1- cosine” gust with different gust lengths is applied to the aircraft, and the maximum and minimum accelerations are computed. It is shown that the nonlinear modeling of the system represents the actual behavior and causes limit cycle oscillation phenomena.

This methodology can yield a relatively simple dynamic model for high aspect ratio aircrafts to provide insights into the vehicles’ dynamics, which can be available early in the design cycle.

Hydraulic instabilities are one of the most important reasons causing vibrations and fatigues in hydraulic turbines. The present paper aims to find the relationship between pressure pulsations and fatigues of key parts of a Kaplan turbine.

3D unsteady numerical simulations were preformed for a number of operating conditions at high heads for a prototype Kaplan turbine, with the numerical results verified by online monitoring data. The contact method and the weak fluid‐structure interaction method were used to calculate the stresses in the multi‐body mechanism of the Kaplan turbine runner body based on the unsteady flow simulation result.

The results show that vortices in the vaneless space between the guide vanes and blades cause large pressure pulsations and vibrations for high heads with small guide vane openings. The dynamic stresses in the runner body parts are small for high heads with large guide vane openings, but are large for high heads with small guide vane openings.

A comprehensive numerical method including computational fluid dynamics analyses, finite element analyses and the contact method for multi‐body dynamics has been used to identity the sources of unit vibrations and key part failures.

The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical integrity of the launcher can be compromised by shock wave/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments.

This paper aims to report numerical and experimental investigations on the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experimental investigations based on Schlieren visualizations are conducted in a transonic wind tunnel and are then compared with numerical predictions based on unsteady Reynolds averaged Navier–Stokes and large eddy simulation (LES) approaches. The effect of buffeting on the structure is finally studied by solving the equation of the dynamics.

Buffeting is both experimentally and numerically revealed. Experiments highlight 3D oscillations of the shock wave in the manner of a wind-flapping flag. LES computations identify a lambda-shaped shock wave foot width oscillations, which noticeably impact aerodynamic loads. At last, the experiments highlight the chaotic behavior of the shock wave as it shifts from an oscillatory periodic to an erratic 3D flapping state. Fluid structure computations show that the aerodynamic response of the airfoil tends to damp the structural vibrations and to mitigate the effect of buffeting.

While buffeting has been extensively studied for classical supercritical profiles, this study focuses on diamond airfoils. Moreover, a fluid structure computation has been conducted to point out the effect of buffeting.

This paper aims to focus on the effect of normal load, sliding speed and temperature on the coefficient of friction of Al 6061-T6 alloy under dry sliding conditions.

Dry sliding experiments were conducted using rotary type pin on disk tribometer. Pins with 3 mm radius of contact and circular disks of 165 mm diameter were fabricated to simulate Hertzian contact configuration. Experiments were conducted by applying three different normal loads (1, 1.5 and 2 kg) and three different sliding speeds (1.25, 2 and 3 m/s) at different temperatures [room temperature (31 ± 1 °C), 60 °C, 100 °C and 150 °C].

Coefficient of friction at end of the first cycle of sliding, stabilized stage, unsteady state and steady state are reported elaborately in this study. Adhesive and abrasive wear mechanisms were observed in the dry sliding of Al 6061- T6 alloy contacts from the microscopic analysis of worn contact surfaces. The coefficient of friction was more influenced by the increase in normal load than the increase in sliding speed and temperature.

The results obtained from this study are significant for the design of aluminium-to-aluminium contacts in aerospace engineering and automobile engineering.

This study reveals the coefficient of friction of aluminium-to-aluminium (Al 6061-T6 alloy) contacts under cylinder on flat contact configuration.

The details of predicting the aerodynamic forces of maneuvering helicopter rotors are discussed in this paper. A new approach to modeling the unsteady rotor aerodynamic forces is presented based on the insight into nonuniform induced velocity distribution, inflow dynamics and unsteady airfoil behavior. For a specified maneuver, the rotor control inputs and helicopter flight attitudes during the maneuvering are first obtained using inverse solution technique, and then the unsteady rotor forces are numerically simulated by synthetically applying the vortex theory, dynamic inflow theory and unsteady airfoil aerodynamic models. Good results of the sample calculations of lateral jink and pop‐up maneuvers are obtained.

The purpose of this paper is to elucidate the detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition.

Unsteady flows in a centrifugal pump volute at non-cavitation and cavitation conditions are investigated by using a computation fluid dynamics framework combining the re-normalization group k-e turbulence model and the mass transport cavitation model.

The flow field in pump volute is very complicated at part load condition with large pressure gradient and intensive vortex movement. Under cavitation conditions, the dominant frequency for most of the monitoring points in volute transit from the blade passing frequency to a lower frequency. Generally, the maximum amplitudes of pressure fluctuations in volute at serious cavitation condition is twice than that at non-cavitation condition because of the violent disturbances caused by cavitation shedding and explosion.

The detailed flow field and cavitation effect in the centrifugal pump volute at partial load condition are revealed and analysed.

This paper aims to focus on mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters.

The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and state‐space represented indicial‐based unsteady aerodynamics. The model is represented by a set of nonlinear partial differential equations for the main rotor within a state‐space representation for all other parts of helicopter dynamics. The coupled rotor and fuselage formulation enforces the use of numerical solution techniques for trim and linearization calculations. The mathematical model validation is carried out by comparing model responses against flight test data for a known configuration.

Improvements in dynamic prediction of both on‐axis and cross‐coupled responses of helicopter to pilot inputs are observed.

Further work is required for investigation of the unsteady aerodynamics, a state‐space representation, within various compatible dynamic inflow models to describe the helicopter response characteristics.

The results of this work support ongoing research on the development of highly accurate helicopter flight dynamic mathematical models. These models are used as engineering tools both for designing new aerial products such as modernized agile helicopters and optimization of the old version products at minimum time and expense.

Provides further information on the mathematical model development problems associated with advanced helicopter flight dynamics research.

Ground vibration testing (GVT) results can be used as system parameters for predicting flutter, which is essential for aeroelastic clearance. This paper aims to compute GVT-based flutter in time domain, using unsteady air loads by matrix polynomial approximations.

The experimental parameters, namely, frequencies and mode shapes are interpolated to build an equivalent finite element model. The unsteady aerodynamic forces extracted from MSC NASTRAN are approximated using matrix polynomial approximations. The system matrices are condensed to the required shaker location points to build an aeroelastic reduced order state space model in SIMULINK.

The computed aerodynamic forces are successfully reduced to few input locations (optimal) for flutter simulation on unknown structural system (where stiffness and mass are not known) through a case study. It is demonstrated that GVT data and the computed unsteady aerodynamic forces of a system are adequate to represent its aeroelastic behaviour.

Airforce of every nation continuously upgrades its fleet with advanced weapon systems (stores), which demands aeroelastic flutter clearance. As the original equipment manufacturers does not provide the design data (stiffness and mass) to its customers, a new methodology to build an aeroelastic system of unknown aircraft is devised.

A hybrid approach is proposed, involving GVT data to build an aeroelastic state space system, using rationally approximated air loads (matrix polynomial approximations) computed on a virtual FE model for ground flutter simulation.

The design of a space launcher requires some considerations about the unsteady loads and heat transfer occurring at the base of the structure. In particular, these phenomena are predominant during the early stage of the flight. This paper aims to evaluate the ability of the unstructured, high order finite-volume CFD solver FLUSEPA, developed by Airbus Safran Launchers, to accurately describe these phenomena.

This paper first performs a steady simulation on a base flow around a four-clustered rocket configuration. Results are compared with NASA experiments and Loci-CHEM simulations. Then, unsteady simulations of supersonic H2/air reacting mixing layer based on the experiment of Miller, Bowman and Mungal are performed. Three meshes with different cells number are used to study the impact of spatial resolution. Instantaneous and time-averaged concentrations are compared with the combined OH/acetone planar laser-induced fluorescence imaging from the experiment.

FLUSEPA satisfactorily predicts the base heat flux at the base of a four-clustered rocket configuration. NASA Loci-CHEM reactive simulations indicate that afterburning plays an important role and should not be neglected. The unsteady reactive computation of a supersonic mixing layer shows that FLUSEPA is also able to accurately predict flow structures and interactions. However, the complexity of the experiment and the lack of details concerning the facility prevents from obtaining satisfactory converged results.

This study is the first step on the development of a cost-effective method aiming at predicting unsteady loads and heat transfer on space launchers using an unsteady and reactive model for the CDF calculations. It uses original techniques such as conservative CHIMERA-like overset grids, local re-centering of fluxes and local adaptive time-stepping to reduce computational cost while being robust and accurate.

Part II of the two‐part paper describes an aeroelastic analysis program and its application for stability computations of turbomachinery blade rows. Unsteady Euler or Navier‐Stokes equations are solved on dynamically deforming, body fitted, and grid to obtain the aeroelastic characteristics. Blade structural response is modeled using a modal representation of the blade and the work‐per‐cycle method is used to evaluate the stability characteristics. Non‐zero inter‐blade phase angle is modeled using phase‐lagged boundary conditions. Results are presented for a flat plate helical fan, a turbine cascade and a high‐speed fan, to highlight the aeroelastic analysis method, and its capability and accuracy. Obtained results showed good correlation with existing experimental, analytical and numerical results. Numerical analysis also showed that given the computational resources available currently, engineering solutions with good accuracy are possible using higher fidelity analyses.