Boleslaw Stasicki

Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

High-powered light emitting diodes (LED) are investigated for possible uses as light sources in flow diagnostics, in particular, as an alternative to laser-based illumination in particle imaging flow velocimetry in side-scatter imaging arrangements. Recent developments in solid state illumination resulted in mass-produced LEDs that provide average radiant power in excess of 10 W. By operating these LEDs with short duration, pulsed currents that are considerably beyond their continuous current damage threshold, light pulses can be generated that are sufficient to illuminate and image micron-sized particles in flow velocimetry. Time-resolved PIV measurements in water at a framing rate of 2 kHz are presented. The feasibility of LED-based PIV measurements in air is also demonstrated.

Recent applications of particle image velocimetry in aerodynamic research

Abstract Particle image velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. For the first time the PIV technique allows the recording of a complete velocity field in a plane of the flow within a few microseconds. The PIV technique thereby provides information about unsteady flow fields which is difficult to obtain with other experimental techniques. The short acquisition times and fast availability of data reduce the operational time, and hence cost, in large scale wind tunnels and test facilities. At DLR a variety of PIV systems for use in industrial wind tunnels has been developed in the past decade. The flexibility of these portable systems is illustrated by presenting several results of recent PIV applications. More recently the original photographic means of PIV image recording has been partially replaced by high resolution electronic imaging which can provide PIV data nearly on-line. Images recorded by either system use the same multiple-pass, cross-correlation analysis software, whose algorithms are briefly described. Several examples of actual applications are given: the flow issuing from a jet nozzle was imaged by a specially developed high-speed video camera at close proximity. A high resolution dual-frame digital camera was applied in the study of helicopter rotor aerodynamics and wake vortex measurements of an airplane model. Further, large image sequences exceeding 100 PIV recordings provided detailed information on the structure of a turbulent boundary layer.

Digital video camera for application of particle image velocimetry in high-speed flows

A high-speed digital camera based on video technology for application of particle image velocimetry in wind tunnels is described. The camera contains two independently triggerable interline CCD sensors which are mounted on two faces of a cube beam splitter permitting the use of a single lens. Each of the sensors has a minimal exposure time of 0.8 microsecond(s) with a trigger response time of less than 1 microsecond(s) . The asynchronous reset capability permits the camera to trigger directly off a pulsed laser with a repetition rate differing from the standard 25 Hz CCIR video frame rate. Captured images are digitized within and stored in RAM the camera which can be read through the parallel port of a computer. The camera is software configurable with the settings being non-volatile. Technical aspect such as sensor alignment and calibration through software are described. Close-up PIV measurements on a free jet illustrated that, in the future, the camera can be successfully utilized at imaging high-speed flows over a small field of view covering several cm2, such as the flow between turbine blades. Further, the electronic shutter permits its use in luminous environments such as illuminated laboratories, wind tunnels or flames.

Application of image pattern correlation for non-intrusive deformation measurements of fast rotating objects on aircrafts

The Image Pattern Correlation Technique (IPCT) in combination with high-speed stroboscopic imaging enables nonintrusive measurements of surface deformation of fast vibrating or rotating objects. This paper describes a dedicated instrumentation for the measurement of the deformation of aircraft propellers as well as the results of its application. The further ideas of imaging technologies based on the collected experiences, in particular the high-power pulsed object illumination based on semiconductor light sources are also presented.

Application of high-speed videography for in-flight deformation measurements of aircraft propellers

A combination of high-speed stroboscopic imaging with the Image Pattern Correlation Technique (IPCT) enables for non-intrusive measurement of surface deformation of fast vibrating or rotating objects. In this paper the dedicated instrumentation for the measurement of the deformation of aircraft propellers as well as first results of its application will be described.

Recent developments of image based measurement methods for application to transonic flows in industrial wind tunnels

Abstract The experimental investigation of unsteady complex flow fields in wind tunnels requires advanced measurement techniques. The most important of such image based measurement techniques are those for the measurement of planar flow velocity fields, planar pressure distribution, model location and deformation, model temperature and quantitative high speed flow visualization. The applications as carried out by DLR range from low speed flows to transonic flows, from high lift configurations to propellers and rotors, from wake vortex investigations in catapult facilities and water towing tanks to investigations of vortex break down phenomena on delta wings. The capability to use image based measurement techniques in transonic flows requires dedicated technical developments and experienced scientists due to the special environment of a transonic wind tunnel. In this paper an overview of the state-of-the art of the application of image based measurement techniques in transonic flows as performed by DLRs Institute of Aerodynamics and Flow Technology will be given.

In-flight measurements of propeller blade deformation on a VUT100 cobra aeroplane using a co-rotating camera system

Knowledge of propeller or rotor blade behaviour under real operating conditions is crucial for optimizing the performance of a propeller or rotor system. A team of researchers, technicians and engineers from Avia Propeller, DLR, EVEKTOR and HARDsoft developed a rotating stereo camera system dedicated to in-flight blade deformation measurements. The whole system, co-rotating with the propeller at its full speed and hence exposed to high centrifugal forces and strong vibration, had been successfully tested on an EVEKTOR VUT 100 COBRA aeroplane in Kunovice (CZ) within the project AIM2—advanced in-flight measurement techniques funded by the European Commission (contract no. 266107). This paper will describe the work, starting from drawing the first sketch of the system up to performing the successful flight test. Apart from a description of the measurement hardware and the applied IPCT method, the paper will give some impressions of the flight test activities and discuss the results obtained from the measurements.

In-flight measurements of aircraft propeller deformation by means of an autarkic fast rotating imaging system

ABSTRACT The non-intrusive in-flight measurement of the deformation and pitch of the aircraft propeller is a demanding task. The idea of an imaging system integrated and rotating with the aircraft propeller has been presented on the 30 th International Congress on High-Speed Imaging and Photonics (ICHSIP30) in 2012. Since then this system has been constructed and tested in the laboratory as well as on the real aircraft. In this paper we outline the principle of Image Pattern Correlation Technique (IPCT) based on Digital Image Correlation (DIC) and describe the construction of a dedicated autarkic 3D camera system placed on the investigated propeller and rotating at its full speed. Furthermore, the results of the first ground and in-flight tests are shown and discussed. This development has been found by the European Commission within the 7 th frame project AIM 2 (contract no. 266107). Keywords: propeller blade deformation, non-intrusive measurement, 3D imaging, IPCT, DIC, video stroboscope, phase shifter, stochastic dot pattern, in-flight test

High-power LED light sources for optical measurement systems operated in continuous and overdriven pulsed modes

The rapid progress of light emitting diode (LED) technology has recently resulted in the availability of high power devices with unprecedented light emission intensities comparable to those of visible laser light sources. On this basis two versatile devices have been developed, constructed and tested. The first one is a high-power, single-LED illuminator equipped with exchangeable projection lenses providing a homogenous light spot of defined diameter. The second device is a multi-LED illuminator array consisting of a number of high-power LEDs, each integrated with a separate collimating lens. These devices can emit R, G, CG, B, UV or white light and can be operated in pulsed or continuous wave (CW) mode. Using an external trigger signal they can be easily synchronized with cameras or other devices. The mode of operation and all parameters can be controlled by software. Various experiments have shown that these devices have become a versatile and competitive alternative to laser and xenon lamp based light sources. The principle, design, achieved performances and application examples are given in this paper.

Rotating Camera System for In-Flight Propeller Blade Deformation Measurements

The behaviour of the blades of a propeller or rotor during operation is crucial for its performance and operational saftey. Particularly the bending and twisting of the blades under load are of high interesst, because they directly influence the local angle of attack and thus the performance of the propeller. Up to now only local deformation measurements by means of strain gauges or acclerometers were feasible. The required cabling thereby limits the maximum number of sensors and thus avoids areal measurements. Furthermore, the application of the sensors can influence the mechanical and aerodynamic properties of the blade. A direct shape or location measurement is also not possible with those techniques. The presented measurement method IPCT (“Image Pattern Correlation Technique”) in addition with the application of the newly developed rotating camera system now enables the non-intrusive measurement of the shape and location of propeller- and rotor blades in-flight with a high accuracy. In the beginning of the paper, the measurement technique and the rotating camera are outlined. Later, the performed ground tests and the conducted flight test activities are described briefly and first measurement results are shown. The major part of the development of the rotating camera was funded by the European Commission within the FP7 project \(\text{ AIM }^{2}\) (contract no. 266107).