A Low Speed Compressor Test Rig for Flutter Investigations

A test facility for aereolastic investigations has been installed at the chair of Aero Engines at the Technische Universität Berlin. The test rig provides data for tool and code validation and is used for basic aeroelastic experiments. It is a low speed wind tunnel which allows free and controlled flutter testing. The test section contains a linear cascade with eleven compressor blades. Nine of them are elastically suspended. The paper presents a detailed description of the test facility, results to evaluate the overall flow quality and an aeroelastic model to predict the flutter velocity and critical interblade phase angles. Hot-wire anemometry has been applied to examine the inlet flow for several Mach- and Reynolds numbers. The results show small turbulence intensities. The blade surface pressure distribution and the flow field of the blade’s suction and pressure side has been accessed by oil flow visualization.

Ground Vibration Test Planning of a Fighter Aircraft by Using a Rough Finite Element Model

Certification process is one of the crucial procedures for safety in the design of a new aerial platform. Flight flutter testing is the most critical component for the certification process. Usually a flutter analysis is performed beforehand for the planning of flight flutter testing of an aircraft which mostly requires the Finite Element Model (FEM) together with Ground Vibration Testing (GVT) to construct the structural dynamic model of the complete aircraft for the flutter analyses. GVT is not only required for new aircraft design but also when considerable changes are made to an existing aircraft or when new external load configurations are introduced. Experimental methods require high effort, high budget, long time, and much repetition. Therefore, the computational and theoretical studies seem more applicable in the early phase. However, GVT of an available fighter aircraft in defense projects becomes an issue for the designers if a detailed FEM of the aircraft is not available prior to test. Hence, planning of the GVT in early stage is vital for project leaders. In this study, a rough FEM of a fighter aircraft is developed and correlated to available GVT data for planning purpose. The representative mode shapes are evaluated by estimation of the several sections of the aircraft. It is also shown that a rough FEM of the aircraft can be utilized for determination of the measurement and excitation points on the aircraft in planning stage. The geometrical properties, physical limitations and basic requirements of GVT are also taken into account for an efficient planning.

Transmissibilty-Based Operational Modal Analysis for Flight Flutter Testing Using Exogenous Inputs

During the recent years several new tools have been introduced by the Vrije Universiteit Brussel in the field of Operational Modal Analysis (OMA) such as the transmissibility based approach and the the frequency-domain OMAX concept. One advantage of the transmissibility based approach is that the ambient forces may be coloured (non-white), if they are fully correlated. The main advantage of the OMAX concept is the fact that it combines the advantages of Operational and Experimental Modal Analysis: ambient (unknown) forces as well as artificial (known) forces are processed simultaneously resulting in improved modal parameters. In this paper, the transmissibility based output-only approach is combined with the input/output OMAX concept. This results in a new methodology in the field of operational modal analysis allowing the estimation of (scaled) modal parameters in the presence of arbitrary ambient (unknown) forces and artificial (known) forces.