Linear Frequency Domain Method For Aerodynamic Applications

Kurzfassung

Applications such as load alleviation involve a wide range of parameters including a multitude of different Mach numbers, angles of attack and load cases and therefore create the demand for rapid prediction of unsteady air loads. First, there is a need for an enhanced prediction accuracy including viscous effects and shocks for a more reliable judgement of aerodynamic behavior compared to the classically-used methods based on the potential theory for such applications. Secondly, short turnaround times must be guaranteed, and this in turn means to find a suitable replacement of the tedious and time-consuming un- steady Navier-Stokes solvers. Driven by these requirements for accurate and fast prediction of air loads, a time-linearized unsteady Navier-Stokes method was developed also known as linear frequency domain method (LFD). The LFD in the DLRs TAU suite is based on the modeling of a damped harmonic oscillator, and it has been shown to be accurate and efficient for the evaluation of unsteady air loads at transonic and partly separated flow conditions [1]. Since then, the LFD method has been continuously extended and applied for various applications. The scope of target applications of the LFD has been growing consistently including different topics in aeroelasticity, where the determined surface pressure and surface skin friction distributions make an important contribution. Moreover, the time-linearized method can also be used for the efficient evaluation of flight dynamic (flight mechanical) characteristics relevant for the stability and control behavior of an aircraft. Furthermore, gust loads were successfully predicted which are important for structural and control surface design [2, 3] as well as control system performance. A recent and demanding application was the extension of the LFD method for fluidic actuators. Thus, the LFD was adopted for simulating pulsating blowing to avoid the enormously long transient phase inherently occurring during time-marching Navier-Stokes simulations. Several applications involving industrial relevant configurations are presented and discussed to outline the maturity of the method and to demonstrate the versatility of the technique.