Uncertainty evaluation for velocity–area methods

Velocity–area methods are used for flow rate calculation in various industries. Applied within a fully turbulent flow regime, modest uncertainties can be expected. If the flow profile cannot be described as “log-like”, the recommended measurement positions and integration techniques exhibit larger errors. To reduce these errors, an adapted measurement scheme is proposed. The velocity field inside a Venturi contour is simulated using computational fluid dynamics and validated using laser Doppler anemometry. An analytical formulation for the Reynolds number dependence of the profile is derived. By assuming an analytical velocity profile, an uncertainty evaluation for the flow rate calculation is performed according to the “Guide to the expression of uncertainty in measurement”. The overall uncertainty of the flow rate inside the Venturi contour is determined to be 0.5 % compared to 0.67 % for a fully developed turbulent flow

Seeding-free inlet flow distortion measurement by filtered Rayleigh scattering: diagnostic approach and verification

The expected close coupling between engine and fuselage of future aero-engine architectures will lead to highly distorted inflows at the engine face, presenting a major design risk for efficient and reliable engine operation. In particular, the increase in flow unsteadiness is perceived as a significant challenge. In this context, the Cranfield Complex Intake Test Facility (CCITF) is currently being installed at Cranfield University to reproduce the anticipated level of total pressure and swirl distortion arising from novel, closely coupled airframe-engine configurations. To address the expected demand for much more comprehensive flow field data, it is intended to establish the filtered Rayleigh scattering (FRS) technique for non-intrusive testing of aero-engine intake flows. Unlike the previously used particle image velocimetry (PIV) or Doppler global velocimetry (DGV), which are limited to the measurement of a single flow quantity, FRS can be used for the combined planar measurement of velocity and scalar fields without the need to add a flow tracer. In this study, an FRS concept with the ability to simultaneously measure high-accuracy time-averaged and time-resolved three-component velocity, static pressure and temperature fields is verified on a simplified mock-up of the CCITF facility. Time-averaged results show excellent agreement with benchmark laser Doppler anemometry (LDA) velocities, static pressure probe measurements and analytical temperature calculations. Moreover, it is shown that the developed concept can be used to determine multiple flow variables from a single-frequency measurement, opening the path towards time-resolved multi-parameter measurements by FRS

Towards time-resolved multi-property measurements by filtered Rayleigh scattering: diagnostic approach and verification

The use of multiple perspective views is a possible pathway towards the combined measurement of multiple time-resolved flow properties by filtered Rayleigh scattering (FRS). In this study, a six view observation concept is experimentally verified on a aspirated pipe flow. The concept was introduced in our previous work, and it has the ability to simultaneously measure high-accuracy time-averaged and time-resolved three-component velocity, pressure and temperature fields. To simulate time-resolution, multi-view FRS data at a single optimised excitation frequency are selected and processed for multiple flow properties. Time-averaged and quasi-time-resolved FRS results show very good agreement with differential pressure probe measurements and analytical temperature calculations and lie within ±2 m/s of complementary laser Doppler anemometry (LDA) velocity measurements for all operating points. The introduction of a multistage fitting procedure for the time-resolved analysis leads to a significant improvement of the precision by factors of 4 and 3 for temperature and axial velocity and 18 for pressure. Moreover, both processing methods show their capacity to resolve flow structures in a swirling flow configuration. It is demonstrated that the developed multi-view concept can be used to determine multiple flow variables from a singlefrequency measurement, opening the path towards time-resolved multi-parameter measurements by FRS

Seeding-free inlet flow distortion measurements using filtered Rayleigh scattering: integration in a complex intake test facility

Highly integrated propulsion systems to achieve fuel savings and reduction of emissions in future aircrafts call for new measurement methods to assess inlet conditions at the engine fan face. Propulsion systems are expected to operate at higher levels of total pressure, total temperature, and swirl distortion due to flow interaction with aerodynamic surfaces and inherent flow distortion within convoluted intakes. Filtered Rayleigh Scattering (FRS) offers capability to assess all these quantities at once, and without the need of seeding particles which cannot be used for in-flight measurements. This paper aims at increasing the technology readiness level of this measurement technique through the application on a lab-scale S-duct diffuser tests and benchmark against Stereo-Particle Image Velocimetry (S-PIV) measurements. Methods to improve the optical integration and mitigate the effect of varying background conditions are hereby explored. Overall, this represents a step forward in the use of FRS as a turnkey solution for the testing and development phase of future propulsion systems

Non-intrusive flow diagnostics for unsteady inlet flow distortion measurements in novel aircraft architectures

Inlet flow distortion is expected to play a major role in future aircraft architectures where complex air induction systems are required to couple the engine with the airframe. The highly unsteady distortions generated by such intake systems can be detrimental to engine performance and were previously linked with loss of engine stability and potentially catastrophic consequences. During aircraft design, inlet flow distortion is typically evaluated at the aerodynamic interface plane, which is defined as a cross-flow plane located at a specific upstream distance from the engine fan. Industrial testing currently puts more emphasis on steady state distortions despite the fact that, historically, unsteady distortions were acknowledged as equally important. This was partially due to the limitations of intrusive measurement methods to deliver unsteady data of high spatial resolution in combination with their high cost and complexity. However, as the development of aircraft with fuselage-integrated engine concepts progresses, the combination of different types of flow distortions is expected to have a strong impact on the engine’s stability margin. Therefore, the need for novel measurement methods able to meet the anticipated demand for more comprehensive flow information is now more critical than ever. In reviewing the capabilities of various non-intrusive methods for inlet distortion measurements, Filtered Rayleigh Scattering (FRS) is found to have the highest potential for synchronously characterising multiple types of inlet flow distortions, since the method has the proven ability to simultaneously measure velocity, static pressure and temperature fields in challenging experimental environments. The attributes of the FRS method are further analysed aiming to deliver a roadmap for its application on ground-based and in-flight measurement environments.European Union funding: 88652

Setup and validation of a laseroptical flow standard for the metrological traceabilility of a high temperature flow test-rig

Gedruckt erschienen im Verlag Carl Schünemann GmbH, ISBN 978-3-95606-385-5Die klassischen gravimetrischen oder volumetrischen Methoden zur Kalibrierung von Durchflussmessgeräten sind aufgrund ihrer drucklosen Ausführung in ihrer Anwendung für das Medium Wasser auf Temperaturen unter 100 °C beschränkt. Eine Kalibrierung unter Prozessbedingungen ist daher zum Beispiel für Anwendungen in der Kraftwerkstechnik nicht möglich. Zur Ausweitung des metrologisch abgesicherten Kalibrierbereichs wird in der vorliegenden Arbeit eine Methode zur druckbeaufschlagten Rückführung von Durchflusssensoren auf Basis der Laser-Doppler-Anemometrie entwickelt, umgesetzt und validiert. Mittels Laser-Doppler-Anemometrie wird die Geschwindigkeitsverteilung des strömenden Fluids in einer Rohrleitung gemessen, die Integration des Geschwindigkeitsfeldes über dem Messquerschnitt bestimmt den Durchfluss. Kernstück der Arbeit ist eine umfassende Analyse der Messunsicherheit des laseroptischen Durchflussnormals. Zur Bestimmung der Messunsicherheit werden unter anderem die folgenden Einflussgrößen in ihrer Auswirkung auf den Volumenstrom quantifiziert: Datenrate, Turbulenz, Wandeffekt, Gradienteneffekt, Strahlverfolgungsrechnung und Diskretisierungsverfahren. Die realisierte Messunsicherheit liegt zwischen 0,15 und 0,19 % (k = 2). Zur Validierung des Unsicherheitsbudgets werden Vergleichsmessungen des laseroptischen Volumenstromnormals mit einer gravimetrischen Durchflussmessanlage, die eine Unsicherheit von 0,04 % (k = 2) bietet, durchgeführt. Die festgestellten absoluten Abweichungen betragen im Mittel 0,04 und maximal 0,09 %. Abschließend wird die Übertragbarkeit der Ergebnisse auf die Anwendung bei höherer Mediumtemperatur diskutiert.The commonly applied volumetric or gravimetric traceability chain for water flow is only feasible for temperatures below 100 °C, due to the non-pressurized design. A calibration in respect to the process condition which apply in a thermal powerplant is therefore not possible. In order to expand the field of metrological traceable flow calibrations, this thesis outlines the concept, realisation and validation of a traceable laseroptical flow standard, which enables a pressurized calibration of flow meters. Laser Doppler Anemometry measurements are performend to determine the spatial velocity profile in the crossection of a pipe. The flow rate is derived by integration of the velocity profile. The main topic of this thesis is an extensive uncertainty analysis for the laseroptical flow standard. The following influencing quantities, among others, have been quantified in respect to their effect on the volume flow rate: datarate, turbulence, wall effect, gradient effect, ray tracing and discretisiation. A resulting measuring uncertainty between 0.15 and 0.19 % (k = 2) has been achieved. A validation of the uncertainty budget has been made by comparision of the laseroptical flow standard to a gravimetric flow test rig, which is characterized by an uncertainty of 0.04 % (k = 2). The asserted mean of the absolute deviation is 0.04, and the maximum deviation 0.09 %. Concluding remarks for the transferability of the results to higher medium temperatures are given

Entwicklung eines laseroptischen Punktsensors auf Basis der Filtered Rayleigh Scattering Technik zum Einsatz unter kryogenen Bedingungen

Die vorliegende Veröffentlichung beschreibt die Entwicklung und den Test eines berührungslosen Strömungssensors auf Basis des Filtered Rayleigh Scattering Prinzips für den Einsatz im European Transonic Windtunnel (ETW) unter kryogenen Bedingungen. Der dazu notwendige Sensor wurde in mehreren Schritten entwickelt und unter kryogenen Bedingungen im Windkanal getestet. Der innovative Ansatz besteht aus der Kombination von kryo-tauglicher, nicht-intrusiver endoskopischer Hardware mit schneller Messwerterfassung bei konstanter Laserfrequenz, um das bereits entwickelte und erfolgreich getestete langsame Frequenzscan-Verfahren für stationäre flächige Messungen in ein instationäres Punktmessverfahren zu überführen