Pawel Flaszynski

An Experimental and Numerical Study of Tip Vortex Cavitation

An Experimental and Numerical Study of Tip Vortex Cavitation The article presents the results of the research project concerning tip vortex cavitation. This form of cavitation is very important in operation of many types of rotary hydraulic machines, including pumps, turbines and marine propellers. Tip vortex cavitation generates noise, vibration and erosion. It should be eliminated or significantly limited during the design of these types of machines. The objective of the project was to develop an accurate and reliable method for numerical prediction of tip vortex cavitation, which could serve this purpose. The project consisted of the laboratory experiments and numerical calculations. In the laboratory experiments tip vortex cavitation was generated behind a hydrofoil in the cavitation tunnel and the velocity field around the cavitating kernel was measured using the Particle Image Velocimetry method. Measurements were conducted in three cross-sections of the cavitating tip vortex for a number of angles of attack of the hydrofoil and for several values of the cavitation index. In the course of numerical calculations two commercial CFD codes were used: Fluent and CFX. Several available approaches to numerical modeling of tip vortex cavitation were applied and tested, attempting to reproduce the experimental conditions. The results of calculations were compared with the collected experimental data. The most promising computational approach was identified.

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.

Numerical prediction of steady and unsteady tip vortex cavitation on hydrofoils

ABSTRACT The article presents the numerical method for prediction of tip vortex cavitation generated on hydrofoils. This method has been developed in the course of numerical and experimental research described in earlier publications. The objective of the research was to design the optimum discrete grid structure for this specific computational task and to select the best turbulence model for such an application The article includes a short description of the method and a computational example demonstrating its performance. In this example the results of numerical prediction of the cavitating tip vortex obtained from two commercial CFD codes are compared with experimental photographs taken in the cavitation tunnel in the corresponding flow conditions. Altogether nine different flow conditions are tested and analyzed, but only selected results are included. The accuracy of the numerical predictions is discussed and the reasons for minor existing discrepancies are identified. The unsteady tip vortex calculations are also presented, showing the fluctuations of the transverse velocity components predicted for three cross-sections of the cavitating vortex kernel.

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.

SHOCK WAVE BOUNDARY LAYER INTERACTION INVESTIGATION: CONTROL BY ROD VORTEX GENERATORS AND THEIR APPLICATION ON HELICOPTER ROTOR BLADES

The paper describes the numerical simulations of a new passive flow control device (Rod Vortex Generator RVG) and the possibilities to induce streamwise vortices for controlling of a shock wave boundary layer interaction. Firstly, a row of rods were placed at the lower wall of a curved wall nozzle with negative pressure gradient. The lower wall is designed in order to mimic similar flow conditions as for wings or helicopter rotor blades. The severe flow conditions (M = 1.43) result in a strong reverse flow which is controlled by the proposed vortex generators. On the other hand, the application of RVGs on helicopter rotor blades was analyzed. In the case of forward flight conditions, flow separation is usually present at the advancing side due to shock wave boundary layer interaction while dynamic stall appears at the retreating side. The numerical results of the flow past the AH-1G helicopter rotor blade were validated against flight test data and the flow separation on the advancing side was reduced by the proposed technology improving the aerodynamic performance (ratio thrust / torque).

A method for analysing ram pressure characteristics of impeller pump rotor

A method for analysing ram pressure characteristics of impeller pump rotor This paper presents a method in which typical tests of centrifugal pump are used to obtain information on real value of discharge angle of flow leaving the rotor. The method can be applied to properly choose inlet angle to blade palisade of centrifugal guide vanes in the case when to perform measurements of velocity fields behind the rotor more precisely is not possible.