Piotr Doerffer

Shock wave – boundary layer interaction control by wall ventilation

Abstract Negative effects of shock wave – boundary layer interaction are restricting the velocity of modern commercial airplanes. Therefore, a lot of research was focused on methods of its control in the last decade. The effectiveness of passive, hybrid and active methods have been investigated and compared with one another. The main results are presented in this paper. These three methods were investigated experimentally. Static pressure distribution along the wall and the cavity were measured. At one location downstream of interaction the stagnation pressure was measured with a Pitot probe above the wall on the whole height of the λ-foot. Comparison of these results allowed us to judge the effectiveness of the method. The Schlieren system and the Mach–Zehnder interferometer were used to visualise the flow field structure.

Continuation of modelling of perforated plate aerodynamics performance

Abstract This paper continues a physical modelling of a transpiration flow, presented in [P.P. Doerffer, R. Bohning, Aerosp. Sci. Technol. 4 (2000) 525–534], by developing a system of gasdynamic equations for the viscous flow in tubes of a perforated plate. Asymptotic expansions give interesting analytical expressions for the pressure loss in the tubes as a function of Mach number in a perforation hole.

Secondary Flow Control and Streamwise Vortices Formation

The structure of a secondary flow in a linear turbine cascade has been investigated. In order to analyse streamwise vortices configuration and to control their formation two types of side wall boundary layer fences have been applied. Results obtained proved that the streamwise fence reduces significantly spanwise extent of secondary flows. Transverse fence has no such effect but causes very significant change of location and the losses level in a passage vortex. Presented results cast some new light on the contribution of passage vortex, horse shoe vortex and a shear plain in between, to the losses maximum where these flow elements are in direct neighbourhood.

Streamwise vortex generator for separation reduction on wind turbine profile

High angles of attack of the wind turbine blades induce severe flow conditions which lead to flow separation and, as the consequence, aerodynamic performance reduction. Implementation of a new type of passive streamwise vortex generator (Rod Vortex Generator - RVG), on a wind turbine profile in order to reduce the flow separation is presented. Numerical model validation is carried out for the S809 aerofoil and a wide range of angles of attack (AoA) employed as reference for flow control cases. Investigation of proposed passive control method involves attached as well as incipient and massive flow separation. A study of chordwise location of RVGs for different inflow conditions is performed. The numerical and experimental results are in good agreement. Obtained numerical results based on the RANS approach reveal a large potential of selected passive devices in reduction of flow separation and increase of aerodynamic performance.

Application of the passive control of shock wave to the reduction of high-speed impulsive noise

Strong, normal shock wave, terminating a local supersonic area on an airfoil (or helicopter blade), not only limits aerodynamic performance but also becomes a source of a high-speed impulsive (HSI) noise. The application of a passive control system (a cavity covered by a perforated plate) on a rotor blade should reduce the noise created by a moving shock. This article covers details of the numerical implementation of the Bohning/Doerffer transpiration law into the SPARC code and includes a validation against the experimental data obtained for the ONERA transonic nozzle with a flat wall. The passive control device is then applied numerically on a helicopter blade in high-speed transonic hover conditions to weaken the shock wave – the main source of HSI noise.

Improvement of Wind Turbine Blade Performance by Means of Rod Vortex Generators

Wind turbines are complex energy conversion fluid-flow machines which entail coupled aero-mechanical issues. From an aero-acoustical point of view, wind turbine blades present two main problems: first, a reduced aerodynamic performance due to flow separation, and second, the level of noise emissions. Flow separation appears on the blade as a result of high angles of attack causing a decrease in the aerodynamic efficiency. In this chapter, the application of rod vortex generators (RVGs) to control and decrease the flow separation—by the creation of streamwise vorticity on the blade—is presented. The NREL Phase VI wind turbine rotor and the S809 airfoil are used as reference cases. The validation of NREL Phase VI model rotor against experimental data is found to be satisfactory. A study into the effects of RVGs’ chordwise location and spanwise distance is presented for selected cases and a range of inflow conditions. It is shown that the proposed RVGs lead to an improvement of the aerodynamic performance, and can be successfully applied by the wind energy industry.

Implementation of k-kL-ω Turbulence Model for Compressible Flow into OpenFOAM

The article deals with results of the implementation of the k-kL-ω turbulence model for compressible transitional flow into OpenFOAM. This model was firstly proposed by Walters and Leylek [2] and utilizes the approach of the laminar kinetic energy in order to predict the transition between laminar and turbulent flows. The performance of the implemented model has been tested for the case of flow over a flat plate and the flow through VKI and SE 1050 turbine cascades. The properties of the implementation of the model for compressible flow simulations into OpenFOAM are discussed.

PERFORATED PLATE AERODYNAMICS FOR PASSIVE SHOCK CONTROL

Transpiration flow through perforated walls plays ever increasing role in aerodynamics due to a frequent application of the flow control by means of blowing or suction. An experimental study is presented here which allowed to determine a transpiration flow characteristic in a form of a simple function. It is very useful for modelling of such flows. Additionally a method of “aerodynamic porosity” determination was proposed which is much more reliable than geometrical description of the porosity. A theoretical analysis of the flow through a perforation hole was also carried out. The flow is considered as compressible and viscous. The gasdynamic analysis led us to a very similar result as obtained from experiment.

Leakage flow reduction in different configuration of labyrinth seal on a turbine blade tip

This paper contains experimental and numerical investigation of the leakage flow over the blade tip in turbine stage. Experiments were conducted in non-rotating linear channel. Test rig was intended to model the geometry of the labyrinth seal of the blades of the lower pressure turbine stage. Investigated model contained two different geometries of labyrinth fins. Moreover smooth and honeycomb stator landing were tested. Experimental measurements have been supported by CFD simulation which gives valuable information of flow structure in labyrinth seal and show complex flow physics in the investigated model.

Streamwise vortex generator for separation reduction on wind turbine rotors

Purpose The purpose of this paper is to describe numerical investigations focused on the reduction of separation and the aerodynamic enhancement of wind turbine blades by a rod vortex generator (RVG). Design/methodology/approach A flow modelling approach through the use of a Reynolds-averaged Navier–Stokes solver is used. The numerical tools are validated with experimental data for the NREL Phase VI rotor and the S809 aerofoil. The effect of rod vortex generator’s (RVG) configuration on aerofoil aerodynamic performance, flow structure and separation is analysed. RVGs’ chordwise locations and spanwise distance are considered, and the optimum configuration of the RVG is applied to the wind turbine rotor. Findings Results show that streamwise vortices created by RVGs lead to modification of flow structure in boundary layer. As a result, the implementation of RVGs on aerofoil has proven to decrease the flow separation and enhance the aerodynamic performance of aerofoils. The effect on flow structure and aerodynamic performance has shown to be dependent on dimensions, chordwise location and spanwise distribution of rods. The implementation of devices with the optimum configuration has shown to increase aerodynamic performance and to significantly reduce separation for selected conditions. Application of rods to the wind turbine rotor has proven to avoid the spanwise penetration of flow separation where applied, leading to reduction of flow separation and to aerodynamic enhancement. Originality/value The proposed RVGs have shown potential to enhance the aerodynamic performance of wind turbine rotors and profiles, making devices an alternative solution to the classical vortex generators for wind turbine applications.