Synthetic jet actuation for load control

The reduction of wind turbine blade loads is an important issue in the reduction of the costs of energy production. Reduction of the loads of a non-cyclic nature requires so-called smart rotor control, which involves the application of distributed actuators and sensors to provide fast and local changes in aerodynamic performance. This paper investigates the use of synthetic jets for smart rotor control. Synthetic jets are formed by ingesting low-momentum fluid from the boundary layer along the blade into a cavity and subsequently ejecting this fluid with a higher momentum. We focus on the observed flow phenomena and the ability to use these to obtain the desired changes of the aerodynamic properties of a blade section. To this end, numerical simulations and wind tunnel experiments of synthetic jet actuation on a non-rotating NACA0018 airfoil have been performed. The synthetic jets are long spanwise slits, located close to the trailing edge and directed perpendicularly to the surface of the airfoil. Due to limitations of the present experimental setup in terms of performance of the synthetic jets, the main focus is on the numerical flow simulations. The present results show that high-frequency synthetic jet actuation close to the trailing edge can induce changes in the effective angle of attack up to approximately 2.9°

Size and density redistribution by a rod obstacle in a cluster jet for quasi-phase matching of high harmonic generation

We investigate the the possibility to realize a fully coherent XUV light source generating wavelengths down to 4 nm by using high-order harmonic generation (HHG) in an ionized medium. Due to the strong ionization, current p We investigate the possibility to realize a fully coherent XUV light source generating wavelengths down to 4 nm by using high-order harmonic generation (HHG) in an ionized medium. Due to the strong ionization, current phase-matching techniques for HHG are not suitable. Instead, we will investigate quasi-phase matching (QPM) over an extended interaction length to increase the output pulse energy. For this, we will prepare a cluster jet from a 5 mm long supersonic nozzle operated at high backing pressure (up to 75 bar). The modulation for QPM is obtained by placing either an array of wires or slits on top of the exit of the nozzle. Here, we report on the characterization of the modulated argon cluster jet. We apply Rayleigh scattering imaging and interferometry to infer the cluster size and total atomic number density distribution in the jet. Initial experiments concern the modulation of the jet by placing a 2 mm rod above the nozzle. The rst results on the cluster size and density distribution will be compared with the simulation results from our 2D fluid dynamics model

Compressible flow simulation on unstructured grids using multi-dimensional upwind schemes

Aerospace Engineerin

A stable and conservative high-order solver for the Reynolds-Averaged

This paper describes the development of an highly efficient parallel multiblock structured code for aerodynamic applications. The goal of our research is to assess whether or not high-order energy stable schemes are more efficient for such problems. The spatial part of the Reynolds-Averaged Navier-Stokes equations are solved making use of high-order energy stable discretization techniques based on Summation By Parts (SBP) finite difference operators and Simultaneous Approximation Term (SAT) boundary treatment [1, 2, 3, 4]. The SBP/SAT schemes we employ are up to 5th order accurate. The solver is conservative, implicit and fully coupled with a modified version of the Spalart-Allmaras turbulence model[5]. Thanks to the energy stability property of the SBP/SAT schemes, a significantly reduced amount of artificial dissipation is needed compared to schemes which do not posses this (or a similar) property. As it will be shown in the results, this leads to an higher accuracy of the numerical solutions

Compressible Turbulent Flow Numerical Simulations of Tip Vortex Cavitation

For an elliptic Arndt’s hydrofoil numerical simulations of vortex cavitation are presented. An equilibrium cavitation model is employed. This single-fluid model assumes local thermodynamic and mechanical equilibrium in the mixture region of the flow, is employed. Furthermore, for characterizing the thermodynamic state of the system, precomputed multiphase thermodynamic tables containing data for the appropriate equations of state for each of the phases are used and a fast, accurate, and efficient look-up approach is employed for interpolating the data. The numerical simulations are carried out using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations for compressible flow. The URANS equations of motion are discretized using an finite volume method for unstructured grids. The numerical simulations clearly show the formation of the tip vortex cavitation in the flow about the elliptic hydrofoil

Efficiency Benchmarking of an Energy Stable High-Order Finite Difference Discretization

In this paper, results are presented for a number of benchmark cases, proposed at the 2nd International Workshop on High-Order CFD Methods in Cologne, Germany, in 2013. A robust high-order-accurate finite difference method was used that was developed during the last 10–15 years. The robustness stems from the fact that the entire numerical procedure, including various kinds of boundary conditions, can be proven stable. This paper outlines the methodology, and it summarizes results presented at the workshop along with some more data and test

Unsteady simulations of rotor stator interactions using SBP-SAT schemes: status and challenges

Recent developments in the SBP-SAT method have made available high-order interpolation operators (Mattsson and Carpenter, SIAM J Sci Comput 32(4):2298–2320, 2010). Such operators allow the coupling of different SBP methods across nonconforming interfaces of multiblock grids while retaining the three fundamental properties of the SBP-SAT method: strict stability, accuracy, and conservation. As these interpolation operators allow a more flexible computational mesh, they are appealing for complex geometries. Moreover, they are well suited for problems involving sliding meshes, like rotor/stator interactions, wind turbines, helicopters, and turbomachinery simulations in general, since sliding interfaces are (almost) always nonconforming.With such applications in mind, this paper presents an accuracy analysis of these interpolation operators when applied to fluid dynamics problems on moving grids. The classical problem of an inviscid vortex transported by a uniform flow is analyzed: the flow is governed by the unsteady Euler equations and the vortex crosses a sliding interface. Furthermore, preliminary studies on a rotor/stator interaction are also presented