Prevention of Reynolds-Averaging with Regard to Turbulent Force Densities

Reynolds-averaging of the Navier-Stokes equations is an approach to derive equations of motion for averaged quantities of the flow field. The treatment of averaged quantities in fluid dynamics is justified with the ratio of masses and eigentimes being generally large between a body subject to flow forces and the particles of the fluid itself. A given state of the flow-field exhibits an averaged effect on its surrounding. Contrary, the development of a turbulent flow-field itself is determined by the interaction of fluid elements of comparable masses and eigentimes. Therewith, the averaging of the equations of motion describing the evolution of the flow-field is not immediately reasoned for. While for linear processes the averaging of physical quantities does directly carry through to the averaging of the underlying equations of motion it is a topic of concern for non-linear processes. In view of that it appears meaningful to distinguish between the averaging of a state of quantities and the averaging of evolutionary equations

A multi-camera image acquisition system and its application for the investigation of flow related events

A previously (at ISFV11) presented high-speed video stroboscope developed at the Institute of Aerodynamics and Flow Technology of German Aerospace Center has been improved and extended to a high-resolution, multi-camera recording system. This system allows for the investigation of fast repetitive, e.g. periodic, phenomena and provides a real-time, slow-motion display of these events with simultaneous frame recording. Non-repetitive events can be imaged with the variable framing rate limited by the properties of the applied cameras. This system has been successfully used in various applications as the visualization of micro- and macroscopic flows, diagnostics of fast running machines as turbines and engines (fuel injection, combustion), marine propellers (cavitation), medicine (larynx diagnostics) and zoology (study of the insect fly). It has been also used for the investigation of the flap gap width during the Airbus A340-400 flight tests in the EU-Project “AWIATOR”. Especially for this project, a number of dedicated features have been implemented to the system

ACCURACY OF COMBINED 3D SURFACE DEFORMATION MESUREMENT AND 3D POSITION TRACKING IN A WIND TUNNEL

In this study the accuracy of a combined measurement of 3D surface deformation and the 3D position of an object in a wind tunnel is investigated. The aim of this study is the development of a system for the high accuracy measurement of an objects 3D position and deformation under wind load during simulated rapid maneuvers. In this situation, the 3D position and orientation of the model are considered to be unknown. The point tracking package PointTracker of the DaVis image processing software was used for the automatic detection of the 3D position and orientation of the model. The PointTracker calculates the 3D position from reflective markers placed on the model. The deformation is detected by the StrainMaster3D module of the DaVis software. In this software module a random structure on the model surface is used to calculate the 3D surface with a stereo camera setup. In a first experiment, the two measuring systems are compared by a combined measurement of marker positions and 3D surface from a random structure on a wing model. Deformations are simulated by small rotations of the wing in the wind tunnel. In a second experiment the position of an aircraft model with and without wind load and the deformation of the flaps were measured. The first experiment revealed that the results of the two measuring systems were consistent with an accuracy of about 20µm on a measuring area of 200 x 300 mm measuring deformations ranging from 0 mm to 1.7 mm. In the second experiment, a deformation of about 3.8 mm within the flaps was detected for changing wind load resulting form a change of the attack angle in the range of 10 degree to 10 degree (flaps angle 4 degree). With no wind load, the measured deformation was below 0.4 mm. As a result, the combination of the two measuring systems yields a ready to use system for the pure optical detection of the position, orientation and deformation of models in a wind tunnel with arbitrary movements or accelerations

Comparison of MDM methods at ETW (EWA) (Part II)

The Model Deformation Measurement (MDM) methods of DLR, Onera and ETW have been compared in a wind tunnel test conducted within the EWA workshop “Measurement of wing deformation at ETW”. The participating partners used the same stereo camera system, but different calibration procedures were applied. The introduced MDM method “Image pattern correlation Technique” (IPCT) uses a random dot pattern instead of discrete markers which are used as targets by the MDM method of ONERA and ETW. The comparison of the results for the different methods showed a good consistency

Experiences from Flow Field Measurements in Industrial Transonic Wind Tunnels for Comparison with Numerical Results

The progress made at the development of modern flow measurement techniques as Particle-Image Velocimetry (PIV) and Pressure Sensitive Paint (PSP) allow to provide flow data of increased quality and accuracy. Particularly PIV and PSP are able to capture a huge amount of experimental data during a wind tunnel test campaign. PIV provides instantaneous as well as averaged flow velocity fields in different planes of the flow and allows the detection of large and small spatial flow structures. Using PSP the pressure distribution on a whole surface can be determined giving much more insights in details of the flow topology than would be possible by discrete pressure taps. The combined application of both techniques offer new possibilities for detailed flow investigations but also will provide possible an excellent data base for comparisons with numerical results

Experiences from Flow Field Measurements in Industrial Transonic Wind Tunnels for Comparison with Numerical Results

The progress made at the development of modern flow measurement techniques as Particle-Image Velocimetry (PIV) and Pressure Sensitive Paint (PSP) allow to provide flow data of increased quality and accuracy. Particularly PIV and PSP are able to capture a huge amount of experimental data during a wind tunnel test campaign. PIV provides instantaneous as well as averaged flow velocity fields in different planes of the flow and allows the detection of large and small spatial flow structures. Using PSP the pressure distribution on a whole surface can be determined giving much more insights in details of the flow topology than would be possible by discrete pressure taps. The combined application of both techniques offer new possibilities for detailed flow investigations but also will provide possible an excellent data base for comparisons with numerical results