Laminar separation bubbles form on the back surfaces of aero-engine LP turbine blades. In recent years significant weight and cost reductions and performance improvements have been achieved through a better understanding of the behavior of such separation bubbles. A project is underway at the Universita¨t Stuttgart to study a possible technique to suppress laminar separation bubbles using actuated transition. This paper reports on DNS results with and without actuation for different frequencies, amplitudes and Reynolds numbers, revealing the nature of the transitional process. Early results from an experimental simulation are included. In addition numerical simulations of fluidic oscillators which are capable to provide the required frequencies at a size which would fit into an LP turbine are presented.

The public reporting burden for this collection of information is estimated to average 1 hour per response, inclu gathering and maintaining the data needed, and completing and reviewing the collection of informatio,". oend cor of information, including suggestions for reducing the burden, to Department of Defend', Washington He: (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid C PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS./VFRL-SR-AR-TR-04- Successful operation of next-generation unmanned air vehicles will demand a high level of autonomy. Autonomous low-level operation in a high-threat environment dictates a need for on-hoard, robust, reliable and efficient trajectory optimization, in this report, we develop and demonstrate an innovative combination of traditional analytical and numerical solution procedures to produce efficient, robust and reliable means for nonlinear Light path optimization in the presence of time-varying obstacles and threats. The solution procedure exploits the natural tune-scale separation that exists in the aircraft dynamics using singular perturbation theory. A reduced order problem involving only the kinematics of the position subspace is treated numerically. The nonlinear aircraft dynamics are to be treated analytically in phase II using a boundary layer analysis that results in an optimal feedback guidance solution. The developed algorithms were coupled with a neural network adaptive autopilot and integrated in an existing unmanned test-bed. This report documents the phase I effort, which produced a demonstration of the developed algorithm in near-real-time flight simulation, and included a simple evaluation of tracking computed trajectories on a rotary wing UAV. SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENT Report Documentation Page On-Line Trajectory Optimization for Autonomous Air VehiclesTechnical AbstractSuccessful operation of next-generation unmanned air vehicles will demand a high level of autonomy. Autonomous low-level operation in a high-threat environment dictates a need for on-board, robust, reliable and efficient trajectory optimization. In this report, we develop and demonstrate an irmovative combination of traditional analytical and numerical solution procedures to produce efficient, robust and reHable means for nonlinear flight path optimization in the presence of time-varying obstacles and threats. The solution procedure exploits the natural time-scale separation that exists in the aircraft dynamics using singular perturbation theory. A reduced order problem involving only the kinematics of the position subspace is treated numerically. The nonlinear aircraft dynamics are to be treated analytically in phase II using a boundary layer analysis that results in an optimal feedback guidance solution. The developed algorithms were coupled with...

The present paper is devoted to the detailed experimental study of weakly nonlinear resonant interactions of Tollmien-Schlichting waves in a specially designed 2D non self-similar boundary layer on an airfoil. The influence of the fundamental frequency on the efficiency of the tuned subharmonic resonance is investigated as well as the influence of frequency and spanwise wavenumber detunings. The results are compared with Direct Numerical Simulations based on a vorticity-velocity formulation of the complete Navier-Stokes equations. Good overall agreement is achieved.

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Aerodynamics of circular cylinders with conical shaped pointed forebodies is studied experimentally at a subcritical Reynolds number of around 10 5 Attention is focused primarily on the side force coefficient at high angles of attack which has a maximum value comparable to that of lift and drag The main objective is to minimize the side force, which may lead to a large undesirable yawing moment Effectiveness of several procedures such as surface roughness helical strakes modified tip geometries, and tip rotation is assessed Results suggest nose boom and tip rotation to be promising in achieving this objective Nomenclature A = cyclinder cross sectional area wd 2 /4of conical sections (Fig 1) Re = Reynolds number pVd/n, S = side force V -freestream velocity o: = angle of attack a i <*2 <*3 -a p ex angles of conical forebodies (Fig 1) fji = viscosity of air P = density of air co = angular velocity of conical tip