Application of an inverse method for improvement of the measurement capability of the particle image velocimetry method

W pracy przedstawiono koncepcję zwiększenia możliwości pomiarowych metody anemometrii obrazowej (Particie Image Velocimetry - PIV) poprzez zastosowanie zastosowaniu wyniku symulacji numerycznej w procesie analizy danych pomiarowych. Badania przeprowadzono w celu weryfikacji następującej hipotezy: uzyskanie zgodności wyniku pomiaru metodą PR" oraz wyniku numerycznej symulacji przepływu umożliwi wyznaczenie parametrów przepływu, będących poza zakresem pomiarowym metody PIV'. W ramach pracy przeprowadzono testy numeryczne, w których dokonano estymacji parametrów przepływu wokół profilu NAC A0009. Identyfikacj ipodległa prędkość przepływu strumienia niezaburzonego. W celu sprawdzenia poprawności zaproponowanej procedury estymacji parametrycznej, algorytm przetestowano na symulowanych danych pomiarowych. Wyniki badań testowych dowodzą poprawności opracowanych procedur oraz stanowią przyczynek do rozpoczęcia pracy nad nową metodyką analizy wyników7 pomiarów metodą PIV.In the presented paper an application of the inverse method for improvement of the measurement capability of the Particle Image Velocimetry method have been discussed. The paper introduces a new approach for PIV data analysis. In a course of the research following thesis has been verified: fitting of the experimental PIV data and a direct numerical problem solution, will lead to determination of flow parameters unobtainable for PIV method. In order to verify the proposed methodology numerical tests has been performed. The parameters of the flow over NACA0009 airfoil has been estimated. The parameter of has been estimated with developed optimization algorithm. The presented results proved the feasibility of proposed methodology and contributes to development of new PIV data post-processing procedure

Development of Particle Imagine Velocimetry Algorithm

W pracy przedstawiono metodykę wyznaczania wektorowego pola prędkości za pomocą metody anemometrii obrazowej. Szczególną uwagę zwrócono na zwiększenie dokładności uzyskiwanych wyników przy pracy z danymi o słabej jakości. W tym celu opracowany został własny algorytm w środowisku MATLAB. Sprawdzono działanie alternatywnego sposobu wyznaczania przemieszczeń w stosunku dostandardowo stosowanego oraz efektywność metod poprawiania jakości sygnału korelacji podawanych w literaturze. Uzyskane wyniki porównane zostały z wynikami uzyskanymi za pomocą komercyjnego oprogramowania. Badania stanowią wstępną fazę do opracowania algorytmu do wyznaczania wektorowego pola prędkości w płynie za pomocą pomiarów ultrasonograficznych.In current work the Particle Imagine Velocimetry method is being described. The aim of research was to improve the performance of PIV algorithm while working with poor quality input data. Alternative method of displacement estimation and signal enhancement methods was tested by own algorithm developed in MATLAB. Performance of proposed methods was compared with performance of commercial program. This investigation is initial stage of research on developing and validating a vector flow imaging system based on Particle Imagine Velocimetry by fast ultrasound

Robust optical flow estimation applied to particle image velocimetry images for high resolution velocity measurements

The article discusses application of Robust Optical Flow Estimation for increasing of Particle Image Velocimetry measurement resolution. Nowadays, one of the promising approaches for increasing the performance of the PIV systems is application of the Optical Flow Estimation for image analysis. Nevertheless, some of the OF implementations do not perform well in case of motion discontinues typically occurring in the PIV images. The purpose of this study is to validate the performance of the Robust Optical Flow Estimation. The tests were performed on simulated images of vortex flow and the results were compared with displacement fields calculated with the typical correlation PIV algorithm. The velocity for high and medium particle concentration was similar for Optical Flow and PIV-like analysis. Furthermore, the performance of the robust optical flow framework was tested with images corrupted with blurs and occlusions. The tests proved good performance of proposed analysis in case of non-Gaussian sources of measurement errors. The robust estimation framework performed well in the case of common image artefacts and proved to be a promising method for precise PIV flow measurements. The presented approach can be useful in development hybrid OF-PIV post processing software aimed for high-resolution measurements and provide a help in designing of experimental investigation of microscale fluid flow phenomena

Jakościowe wizualizacje przepływów ściśliwych

The paper demonstrates the feasibility of quantitative flow visualisation methods for investigation of transonic and supersonic flows. Two methods and their application for retrieving compressible flow field properties has been described: Background Oriented Schlieren (BOS) and Particle Image Velocimetry (PIV). Recently introduced BOS technique extends the capabilities of classical Schlieren technique by use of digital image processing and allow to measure density gradients field. In the presented paper a review of applications of BOS technique has been presented. The PIV is well established technique for whole field velocity measurements. This paper presents application of PIV for determination of the shock wave position above airfoil in transonic flow regime. The study showed that application of quantitative flow visualisation techniques allows to gain new insights on the complex phenomenon of supersonic and transonic flow over airfoils like shock-boundary layer interaction and shock induced flow separation.Artykuł przedstawia możliwości zastosowania jakościowych metod wizualizacji przepływu do badań przepływów ściśliwych. Przedstawiono dwie metody umożliwiające pomiar parametrów pola przepływającego płynu: anemometrię obrazową oraz technikę fotografii smugowej opartej na obrazowaniu tła. Ostatnio opracowana nowa metodyka pozwala na rozwinięcie klasycznej techniki Schlierena, dzięki wykorzystaniu cyfrowej analizy obrazu umożliwia jakościowy pomiar gradientów gęstości. W publikacji przedstawiono przegląd zastosowań techniki fotografii smugowej wykorzystującego obrazowanie tła do jakościowego pomiaru zmian gęstości przepływów ściśliwych. Anemometrii obrazowa jest techniką wizualizacyjną, umożliwiającą bezinwazyjny pomiar pola prędkości przepływającego płynu. W publikacji przedstawiono zastosowanie anemometrii obrazowej do wyznaczenia pozycji fali uderzeniowej ponad powierzchnią profilu dla okołodzwiękowych prędkości przepływu. Przedstawione wyniki wykazały, iż zastosowanie technik jakościowej wizualizacji przepływu umożliwia pogłębienie analizy badanych zjawisk w warunkach przepływu okołodźwiękowego i naddźwiękowego, takich jak oddziaływanie fali uderzeniowej z warstwą przyścienną oraz oderwania przepływu spowodowanego falą uderzeniową

Identification of the boundary layer shock wave interaction type in transonic flow regime

The paper presents various approaches to wind tunnel data analysis when identifying the shock wave boundary layer interaction type. The investigation was carried out in the transonic flow regime in the N-3 Wind Tunnel of Institute of Aviation. The Mach number was 0.7 and Reynolds number was approximate equal 2.85 million. The object of the research was a laminar airfoil in configuration without and with turbuliser device mounted on the upper model surface. In order to achieve turbulent boundary layer in front of the shock wave the carborundum strip was used. The effect of the varying angle of incidence on the flow filed was investigated. During experimental research, different means and test methods were applied (pressure measurements, Schlieren and oil visualisation, Particle Image Velocimetry (PIV), hot-film anemometry). The results were analysed in terms of the shock wave boundary interaction type. Most of results were in good agreement with theoretical models reported in the literature. The study showed that combination of various measurement techniques should be used in the shock wave boundary investigations in order to achieve more consistent and reliable conclusions. The results of the presented research can also be used for better understanding other mechanisms i.e. the boundary layer shock wave separation process in transonic flow regime

PIV measurements of the vortex ring state of the main rotor of a helicopter

W pracy przedstawiono wyniki badań wizualizacyjnych w tunelu aerodynamicznym przeprowadzonych w celu zbadania stanu pierścienia wirowego na wirniku nośnym śmigłowca. Badania wizualizacyjne przeprowadzono metodą anemometrii obrazowej (PIV). Cechą charakterystyczną opadania śmigłowca w warunkach stanu pierścienia wirowego (VRS, Vortex Ring State) jest powstanie wokół wirnika cyrkulacyjnego ruchu strug powietrza po torach w kształcie pierścieni. W przeprowadzonych badaniach warunki VRS uzyskano poprzez umieszczenie modelu śmigłowca w przestrzeni pomiarowej tunelu tak, aby oś wirnika nośnego pokrywała się z osią symetrii przestrzeni pomiarowej. Wykonane analizy potwierdziły skuteczność sytemu PIV stosowanego w Laboratorium Badań Aerodynamicznych Instytutu Lotnictwa do badań opływu śmigłowa z pracującym wirnikiem oraz stanowią przyczynek do kontynuacji badań nad dynamiką powstania stanu pierścienia wirowego na wirniku nośnym śmigłowca.The paper presents results of the investigation of the vortex ring state (VRS, settling with power) of the main rotor of a helicopter with the use of Particle Image Velocimetry (PIV) method. One of the most distinguished features in the conditions known as settling with power is a formation of toroidal vortices around the rotor of a helicopter. In order to provide the necessary conditions for the development of VRS the rotation axis of the main rotor and the axis of symmetry of the wind tunnel’s test section were set coaxially. The results of the measurements proved the feasibility of the Applied Aerodynamics Laboratory’s PIV system for investigations of the flow over a powered rotor in a test section of the wind tunnel. The presented results constitute a contribution to performance of a more detailed research on the development of the VRS of the main rotor of a helicopter

IDENTIFICATION OF THE BOUNDARY LAYER SHOCK WAVE INTERACTION TYPE IN TRANSONIC FLOW REGIME

The paper presents various approaches to wind tunnel data analysis when identifying the shock wave boundary layer interaction type. The investigation was carried out in the transonic flow regime in the N-3 Wind Tunnel of Institute of Aviation. The Mach number was 0.7 and Reynolds number was approximate equal 2.85 million. The object of the research was a laminar airfoil in configuration without and with turbuliser device mounted on the upper model surface. In order to achieve turbulent boundary layer in front of the shock wave the carborundum strip was used. The effect of the varying angle of incidence on the flow filed was investigated. During experimental research, different means and test methods were applied (pressure measurements, Schlieren and oil visualisation, Particle Image Velocimetry (PIV), hot-film anemometry). The results were analysed in terms of the shock wave boundary interaction type. Most of results were in good agreement with theoretical models reported in the literature. The study showed that combination of various measurement techniques should be used in the shock wave boundary investigations in order to achieve more consistent and reliable conclusions. The results of the presented research can also be used for better understanding other mechanisms i.e. the boundary layer shock wave separation process in transonic flow regime

PIV measurements of flow separation over laminar airfoil at transonic speeds

The paper presents results of transonic flow field visualization over a laminar airfoil in high-speed wind tunnel. Quite recently, considerable attention has been paid to experimental investigations of an interaction between the shock and the boundary layer for aerodynamics applications. The purpose of the paper is to investigate development of the flow separation over laminar airfoil at transonic speeds. In a course of presented studies, the Particle Image Velocimetry (PIV) method was used for instantaneous velocity measurements of flow field in the test section of N-3 Institute of Aviation transonic wind tunnel. The object of the research was a laminar airfoil inclined at various angles. The effect of the varying angle of incidence on the flow filed was investigated. The freestream Mach number was 0.7. The results of the PIV measurements were analysed in order to identify the type of the separation from the measured velocity fields. Three forms of separation for low, medium and high angle of incidence was distinguished. The results are in good agreement with theoretical models reported in the literature. The study showed that application of quantitative flow visualisation technique allowed gaining new insights on the complex phenomenon of transonic flow over airfoil. The results of the presented research can be used for better understanding of the mechanism of the flow separation process in transonic flow over airfoils and fluid structure interactions

A Research Methodology for Wind Tunnel Investigation of Development and Demise of a Vortex Ring State

Jednym z zagrożeń bezpieczeństwa lotu śmigłowców jest stan pierścienia wirowego (ang. Vortex Ring State - VRS). W niniejszej pracy przedstawiono metodykę oraz przykładowe wyniki badań eksperymentalnych dotyczących zagadnienia VRS, przeprowadzonych w tunelu aerodynamicznym Instytutu Lotnictwa. Badanym obiektem był zdalnie sterowany śmigłowiec, umieszczony w przestrzeni pomiarowej tunelu niskich prędkości o średnicy 1,5 m. Zakres badań obejmował pomiary wagowe za pomocą wagi tensometrycznej oraz badania wizualizacyjne metodą anemometrii obrazowej (PIV). W trakcie prowadzonych testów zarejestrowano spadek siły ciągu generowanej przez wirnik nośny śmigłowca towarzyszący wejściu w stan pierścienia wirowego oraz dokonano wizualizacji powstałych struktur wirowych. Uzyskane wyniki potwierdziły, że przyjęta metodyka jest skuteczna do analizy procesu rozwoju i zanikania pierścienia wirowego na wirniku nośnym śmigłowca.The Vortex Ring State (VRS) of the main rotor is one of the threats for the safety of a helicopter. Therefore this phenomenon has been intensively investigated for several years, in order to understand the mechanisms of its development and the possibilities of avoiding the danger flight regime. The paper presents a research methodology applied for investigations of development of the VRS of the main rotor of a helicopter. The object of investigation was a model of a helicopter with a powered rotor, placed in a low-speed wind tunnel with test section diameter of 1.5 m. The investigation includes a strain gage measurements and flow visualization with the Particle Image Velocimetry (PIV) method. The results show the decrease in the thrust generated by the main rotor due to the VRS. The velocity field, measured with PIV method, shows the process of the VRS forming, development and demise. The results proved the feasibility of the presented methodology for investigation of the Vortex Ring State

Ground effect influence on the aerodynamic characteristics of ultralight high-wing aircraft : wind tunnel tests

The ground proximity may significantly improve the performance of the aircraft, but in some conditions, it affects its stability. The gain of lift which and reduction of drag during low altitude flight is known as the wing in ground effect (WIG effect). It may concern aircrafts or WIG-crafts (ground effect vehicles). In the article experimental results of the wind tunnel test of an aircraft in ground effect has been presented. The main aim of the test was to investigate the ground effect influence on aerodynamic characteristic of the of the ultralight high-wing aircraft model during early take off, taxiing or final landing stage. Investigation was carried out in the 1.5 m diameter low speed T-1 wind tunnel in the Institute of Aviation in Warsaw. The velocity was 32 m/s and Reynolds number related to the aerodynamic chord was equal about 0.37·106. Tests were performed for chosen angles of attack in range 0-10⁰. During investigation, the strain gauge balance measurements and Particle Image Velocimetry (PIV) flow visualization technique were applied. Tested model position was relatively close to the ground. It was found, that the ground proximity has significant influence on the pitching moment. The normal force was increased and the axial force is decreased due to the WIG effect, which is compatible with the theory. It has significant meaning for control aircraft issue and safety