Structural and Aeroelastic Studies of Wing Model with Metal Additive Manufacturing for Transonic Wind Tunnel Test by NACA 0008 Example

Additive manufacturing (AM) technology has a potential to improve manufacturing costs and may help to achieve high-performance aerospace structures. One of the application candidates would be a wind tunnel wing model. A wing tunnel model requires sophisticated designs and precise fabrications for accurate experiments, which frequently increase manufacturing costs. A flutter wind tunnel testing, especially, requires a significant cost due to strict requirements in terms of structural and aeroelastic characteristics avoiding structural failures and producing a flutter within the wind tunnel test environment. The additive manufacturing technique may help to reduce the expensive testing cost and allows investigation of aeroelastic characteristics of new designs in aerospace structures as needed. In this paper, a metal wing model made with the additive manufacturing technique for a transonic flutter test is studied. Structural/aeroelastic characteristics of an additively manufactured wing model are evaluated numerically and experimentally. The transonic wind tunnel experiment demonstrated the feasibility of the metal AM-based wings in a transonic flutter wind tunnel testing showing the capability to provide reliable experimental data, which was consistent with numerical solutions.

Mathematical model of fuselage oscillations at transonic flight speeds

Ensuring the safety of supersonic aircraft flights and aerospace systems in the transonic range of M flight numbers still remains an urgent scientific and applied problem. This is caused by the peculiarities of the aerodynamic surfaces flow by inhomogeneous (transonic) air and is due to the emergence of various aeroelastic phenomena in these flight modes and the current lack of a generally accepted model of transonic flutter, even for aerodynamic control surfaces. Based on a joint analysis of the conditions for the formation of shock waves on the surface of the aerodynamic profile, changes in the parameters of supersonic flow across the Prandtl-Meyer expansion fan, and the hypothesis of "dynamic curvature of the aerodynamic profile", the approximate laws of interaction of elastic bending vibrations of the fuselage with fluctuations in shock waves were obtained. The obtained regularities are used to substantiate a mathematical model for estimating excited forces and excited bending moments of the fuselage. The analysis of the obtained mathematical model confirms the theoretical possibility of the appearance of fuselage forms of transonic flutter in supersonic aircraft, which was observed in the flight experiment and which is due to the interaction of shock waves with the angular velocity of the fuselage elastic bending vibrations. With the accepted in the article input geometrical data of a fuselage aerodynamic surfaces’ profile, the maximum possible values of fuselage bending moments are obtained using the developed mathematical model. The obtained mathematical model can be used for a preliminary approximate assessment of the transonic flutter fuselage forms characteristics in supersonic aircraft and aerospace systems.

Resolving Pitching Airfoil Transonic Aerodynamics by Cfd Data Modeling

A detailed numerical study of harmonically pitching airfoils of NACA00 series is presented here. Based on the analysis of the CFD results, a hypothesis is made that a simple data model can capture the dynamics of the airfoils in pitch. The data model is based on the cl ?? (lift coefficient - angle of attack) hysteresis loops that retain generic geometrical characteristics for a wide range of reduced frequency, k, encountered in flutter in transonic flows for all the NACA00 airfoils considered. The model was trained on a subset of the considered NACA00 airfoils and then tested on the remaining NACA00 set, for a subset of the reduced frequencies. The model predictions of the cl ? ? hysteresis loops for the test set are shown to be in excellent agreement with the CFD results for the range of k typical of transonic flutter. The data model offers a paradigm shift in the prediction of transonic flow dynamics of pitching airfoils and will guide the development of a new transfer function that will be incorporated in a new aeroelastic framework leading to an appropriate transonic flutter model for use in the development of future aircraft.

Verification tests of a new blade flutter research facility

Long term strategic changes in power generation approaches will require more flexibility for large power generating turbines as an unavoidable consequence of the increasing share of power generated by alternative energy sources. Demanded flexibility for the power turbine output will augment undesired flow phenomena in the low-pressure turbine module, which will consequently enhance blade flutter problems of long slender blades in turbine last stages. In order to advance the understanding of blade flutter onset conditions, the Institute of Thermomechanics of the Czech Academy of Sciences instigated an advanced research program on blade flutter research in high-speed turbomachines. A new innovative test facility for Blade Forced Flutter research was designed and built in the High-Speed Laboratory of the Institute of Thermomechanics. The concept of the new test facility is based on extensive experience with an older Transonic Flutter Cascade facility operated at the NASA Glenn Research Center in Cleveland, Ohio. At present, the first phase of verification tests of the new facility is in progress. The ongoing steady-state tests are intended for exploration of a newly proposed quasi-stationary method to investigate instigating flow conditions leading to an onset of intense blade flutter. Results of some opening tests under steady flow conditions are presented in the paper. The blade drive mechanism for unsteady tests with oscillating blades has not yet been installed in the facility. The presented paper is a work-in-progress report on the ongoing research of complex blade flutter problems.