Igor Klioutchnikov

Investigation of Unsteady Transonic Airfoil Flow

Numerical and experimental investigations of the flow over a supercritical airfoil are performed at the Shock Wave Laboratory. The transonic airfoil flow contains complex structures such as local supersonic regions and local separation regions, shock-boundary layer interaction, vortex-wake interaction and boundary layer transition. Furthermore, a phenomenon of upstream moving waves is observed in the experiments as well as in the numerical simulations. This paper focus on the numerical investigation of the upstream moving wave phenomenon in the two-dimensional unsteady transonic airfoil flow. The influence of the Reynolds number, Mach number and the incidence on the mean and unsteady flow properties is analyzed. A direct eect of the Mach number and incidence is observed on the wave phenomenon, whereas the Reynolds number influences the time averaged flow field and hereby indirect the upstream moving waves.

Wave processes in transonic airfoil flows

Upstream moving pressure waves are observed in transonic flows over airfoils already for decades. They can be generated actively by flap or airfoil oscillations [6]. But, they are also naturally present in airfoil flows [1, 4]. Upstream moving pressure waves can lead to flow instabilities by forcing shock and stagnation point oscillations. Furthermore, it is expected that they affect the laminar-turbulent transition [5]. Hence, the phenomenon is of great engineering interest.

A Numerical Investigation of the Flow through a New Fast Acting Valve for Diaphragmless Shock Tubes

In shock tubes, driver and driven section are usually separated by a diaphragm, which produces nearly ideal shock waves due to its instant rapture. However, known disadvantages of diaphragms motivate the investigation of diaphragmless shock tubes. One of these concepts is to replace a diaphram by a rapidly opening piston.

Numerical Simulation of Upstream Moving Pressure Waves in Transonic Airfoil Flow

Results from a numerical investigation of the unsteady transonic flow around a supercritical BAC 3-11 airfoil will be presented here. The focus of this paper is the phenomenon of upstream moving pressure waves. The used solver is based on the finite difference discretisation of high order accuracy (N > 5) and explicit time integration. The mechanisms of pressure wave generation, their development and the influences of the inflow parameter like Mach, Reynolds number and angle of attack are investigated in two-dimensional flow simulations. To analyse the three-dimensional effects simulation of the three-dimensional transonic flow is performed for selected inflow conditions and its preliminary results will be presented.

Experimental and Numerical Investigation of Unsteady Transonic Airfoil Flow

A summary of experimental and numerical results concerning the phenomenon of upstream moving pressure waves in the transonic flow regime is presented. As experimental and numerical time-resolved shadowgraphs show, such waves initiate near the sharp trailing edge of a supercritical airfoil and in the wake, propagate upstream in the subsonic region of the flow, and strengthen before becoming apparently weaker and almost disappear near the leading edge. Using high order numerical simulation several mechanisms of wave generation based on vortex dynamics as well as vortex/trailing edge interactions and wake fluctuations are distinguished. These waves on the upper side of the airfoil are also captured with pressure transducers mounted in the airfoil model as pressure oscillations of dominant frequencies ranging between 1 to 2 kHz. Furthermore, the statistical analysis of the pressure histories allowed for the determination of wave propagation direction, strength and speed.

Unsteady Transonic Airfoil Flow Simulations using High-Order WENO Schemes

The flow over a supercritical airfoil in the transonic regime contains a lot of complex physical phenomena and interactions. High demands are made on the numerical model for an accurate numerical investigation of such a flow type. High-order (N ≥ 5) WENO (Weighted Essentially Nonoscillatory) schemes are appropriate for the numerical simulation of transonic flows, as they have the capability to capture shocks, resolve vortices, and predict their interactions. A high-order finite difference WENO scheme is applied to simulate the unsteady flow over the supercritical BAC3-11 [1] airfoil. The numerical results are compared with experiments carried out in a transonic shock tube and found in good agreement with the experimental data. The influences of Ma and Re number are studied.

Direct Numerical Simulation of Tonal Noise in Sub- and Transonic Airfoil Flow

Tonal noise phenomenon is studied by Direct Numerical Simulation of the sub- and transonic flow around the symmetric NACA 0012 airfoil. A fifth-order Weighted Essentially Non-Oscillatory and a fourth-order explicit Runge-Kutta scheme are utilized. A main focus of this paper is the validation of the method and a grid study for an airfoil flow at a moderate Reynolds number. Therefore, the results of a Direct Numerical Simulation of subsonic flow are compared to experiments. Both, the results of the numerical and experimental flow show the tonal noise phenomenon. The interaction of the Tollmien-Schlichting waves and the trailing edge is studied visually enabling to easily understand the physical principles of the tonal noise phenomena. Additionally, for a transonic flow the non-linear pressure wave propagation, merging and frequency shift is considered.

Coaxial Jets Entering into a Hot Environment

The instability of shear layers of compressible turbulent flows is on one hand a fundamental physical problem and on the other one present in a wide range of applications. Typical of these are free single and coaxial supersonic nozzle jets. The associated shear layers are due to an inflection point of the velocity profil at the nozzle exit.

Wave processes on a supercritical airfoil

A shock tube with a rectangular test section is utilized to study the transonic flow about an airfoil model of a constant chord length. Upstream moving pressure waves are observed in experiment as well as in numerical simulation of a supercritical airfoil flow for different flow regimes. Both experimental and numerical results show that the observed waves are coupled with vortex generation in the boundary layer as well as wake fluctuations. The measured wave frequencies are in the order of 1-2 kHz. Using statistical means the wave speeds and wave propagation direction could be determined.