Experimental characterization and modelling of a cavitating centrifugal pump operating in fast start-up conditions

The start-up of rocket engine turbopumps is generally performed only in a few seconds. It implies that these pumps reach their nominal operating conditions after only a few rotations. During these first rotations of the blades, the flow evolution in the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed evolution. These phenomena progressively become negligible when the steady behavior is reached. The pump transient behaviour induces significant pressure fluctuations which may result in partial flow vaporization, i.e. cavitation. An existing experimental test rig has been updated in the LML laboratory (Lille, France) for the start-ups of a centrifugal pump. The study focuses on cavitation induced during the pump start-up. Instantaneous measurement of torque, flow rate, inlet and outlet unsteady pressures, and pump rotation velocity enable to characterize the pump behaviour during rapid starting periods. Three different types of fast start-up behaviours have been identified and have been presented at ISROMAC 12 (Duplaa et al, 2008). According to the final operating point, the start-up is characterized either by a single drop of the delivery static pressure, by several low-frequency drops, or by a water hammer phenomenon that can be observed both a the inlet and outlet of the pump. A physical analysis to explain these three different types of transient flow behaviour has been recently proposed (Duplaa et al, 2010). In the present paper, a modelling of the fast start ups in cavitating conditions is proposed. It consists of a two steps adaptation of fast start-up model in non cavitating conditions proposed by Dazin et al (2007). For that, fast X-rays imaging has been performed in the impeller with the collaboration of the French Atomic Agency (CEA) in order to determinate the high frequency evolution of the volume fraction during fast the start-ups. Although the results of the modelling presented here are not definitive, they are very promising

Cavitation inception in fast startup

The start-up of rocket engine turbopumps is generally performed only in a few seconds. It implies that these pumps reach their nominal operating conditions after only a few rotations. During these first rotations of the blades, the flow evolution in the pump is governed by transient phenomena, based mainly on the flow rate and rotation speed evolution. These phenomena progressively become negligible when the steady behaviour is reached. The pump transient behaviour induces significant pressure fluctuations which may result in partial flow vaporization, i.e. cavitation. An existing experimental test rig has been updated in the LML laboratory (Lille, France) for the start-ups of a centrifugal pump. The study focuses on cavitation induced during the pump start-up. Instantaneous measurement of torque, mass flow rate, inlet and outlet unsteady pressures, and pump rotation velocity enable to characterize the pump behaviour during rapid starting periods

Mise en relation analytique de la cinématique de l’écoulement et des performances d’un rotor caréné à Mach de vol intermédiaire

Reaching the European long-term air transport emission reduction goals impose shifting by 2050 toward hybridation/electrification of airplanes as well as global optimization of flight missions. This implies developping distributed propulsion systems through the multiplication of small shrouded rotors operating at high efficiency within a wide range. Present litterature lacks a low-order shrouded rotor model specifically designed to work on such wide operating range. In this paper, the working range of the existing models is benchmarked on the basis of similarity factors built on an innovative expression of the shrouded rotors problem. It is established here that the model of Jardin et al. [1] presents the wider working range thanks to the "homokinetic" surface definition but lacks robustness and needs an additional input that is related to the "homokinetic" surface. The extension of this model to the compressible domain increases its robustness and an empirical model of the "homokinetic" surface helps droping the additional input

Unified classification and characterization of axial turbomachines and propellers

Reaching the mid/long-term air transport emission reduction goals imposed by both European and American standards impose increasing the propulsive systems’ adaptability to various operating conditions, in order to maximize the aircraft overall efficiency all along the flight mission. This implies the enlargement of the design space of propulsive systems such that it can even be operated equally as a compressor or turbine, which leads to rethink the paradigm of designing turbomachines. The continuity in the definition and characterization of different types of turbomachines should be restored which is proposed through this contribution. Analytical relationships allowing to switch between compressor map, propeller map and map are developed. To minimize the inputs of the maps’ conversion relations, a methodology to extract mean flow features from any characterization map is presented, namely the rotor outlet relative flow angle and mean streamline radius. The application of the characterization maps’ conversion relations on a turbofan’s single-stage axial fan and on a propeller allowed their validation through the physical coherence of the results. The flow features extraction methodology also showed very satisfying results with comparison to experiments. Eventually, the ability of the formalism as a powerful performance analysis tool for all kind of turbomachines is stressed out, which makes it the best candidate for the unified treatment of turbomachines

Exergetic Drag Characteristic Curves

This paper aims to perform a drag breakdown of an airfoil and a wing by using the exergetic method. Moreover, a new far-field wave anergy extraction method is presented. The resulting exergetic drag curves are proposed as additional characteristic curves for external aerodynamic assessment of airfoils or any other bodies. CFD analyses of a NACA 0012 airfoil and a rectangular wing at subsonic and transonic conditions were used as test cases to present the concept. This new approach allows to deeply understand the aerodynamic behavior of a body and provides an alternative point of view to the classical near-field and far-field based drag curves

Epsilon: An Open Source Tool for Exergy-Based Aerodynamic Analysis

This paper presents the open source code called “Epsilon”. It is a tool suited for the aerodynamic analysis of CFD and wind tunnel data by using the exergy method. Other methods are also provided (near-field, far-field, Lamb vector). The architecture of the code is presented as well as a qualitative description of the analysis capabilities provided by the tool. Some reference test cases are presented and an accuracy assessment of the exergy analysis is performed. The software is released to the public along with this conference paper

Vortex Exergy Prediction

This paper aims to provide a prediction method for the transverse exergy of the wing’s trailing vortices. It relates the transverse exergy at each point of the entire downstream survey plane to the vorticity inside the wake. This allows reducing the survey area to the wake region only, leading to a useful expression for the calculation of the transverse exergy from wind tunnel measurements. The proposed equation offers a significant improvement respect to the Maskell method especially at high-angle of attack condition. CFD analyses of a NACA 0012 rectangular wing at subsonic and transonic conditions were used as test cases to present the concept

A velocity decomposition method for exergy-based drag prediction

The exergy method is a powerful tool for aerodynamic analysis and drag prediction. However, its formulation still requires further improvements in order to obtain a useful drag breakdown for the analysis of wind tunnel data (like the far-field methods). The far-field drag breakdown is achieved by using a velocity decomposition technique but the related formulation is not well suited for the exergy method. Thus, the main objective of this work is to develop a new velocity decomposition suited for the exergy analysis and to propose a related exergy-based drag breakdown formulation for wind tunnel applications

2D Flow Field Analysis by the Exergetic Method

This paper aims to perform an analysis of the flow field around an airfoil by using the exergetic method. It offers a new way to analyze the aerodynamics based on an energetic reasoning rather than a classical mechanical point of view (used on the far-field method). The objective is to explore the usage of this method as a tool for the aerodynamic assessment of a classical airfoil: the exergetic parameters are related with physical phenomena, and specially used to detect the origin of losses. CFD analyses of a NACA 0012 airfoil at subsonic and transonic conditions were used as test cases to present the concept

Performance prediction methodology and analysis of a variable pitch fan turbofan engine

The objective of this paper is development and application of a methodology for preliminary analysis of variable pitch fan (VPF), both as a separate component and as a module integrated into a short-medium range geared turbofan engine developed within European FP7 project ENOVAL. For this purpose, a high bypass ratio two spool geared turbofan engine model was constructed in software PROOSIS. A VPF performance modeling methodology was then developed using 3D steady RANS CFD produced fan maps as baseline; the CFD maps characterized five discrete fan pitch angle settings. In order to represent those maps in PROOSIS and add the pitch angle as a degree of freedom, they were transformed into the Map Fitting Tool (MFT) reference frame. Once the complete VPF turbofan model was in place, engine mission optimization experiments were carried out. The resulting performance is characterized by a good capability to control the fan surge margin, without degrading the engine fuel consumption. This paper represents a new contribution on the topic firstly by coupling a 0D engine performance code with a 3D RANS calculation, and then by introducing the concept of MFT maps with an additional degree of freedom as the interface between the two