Test Campaign Research Articles

A method to develop a high-fidelity gearbox thermal model based on limited temperature measurements

This paper presents a method to create a high-fidelity gearbox thermal model. A hybrid analytical-empirical model is presented, it is based on the thermal network approach and experiments are used to determine some unknown parameters of the model. A test campaign was led on a four stages helical gear unit and consisted of cooling measurements, no-load tests and loaded tests. These experiments were performed under different rotational speeds and loads. The results show that the developed thermal model provides an accurate prediction of the thermal behavior of different components of the gearbox (namely rolling element bearings and oil) by only using few thermal sensors. These results are corroborated by power losses measurements which demonstrate that the model can estimate the gear unit efficiency.

Experimental study on the resilient and permanent deformation of a compacted waste foundry sand

The use of Waste Foundry Sands (WFS) as a construction material in geotechnical works is strategic because it allows the consumption of large amounts of this waste worldwide, typically discarded in landfills. Beyond the achievement of environmental requirements, the construction industry needs a comprehensive understanding of its mechanical properties, which is a challenge to enhance the recycling or reuse of WFS. This paper investigates the resilient and permanent deformation of a compacted WFS under repeated load. These features are necessary to understand the behavior of this material in the context of pavement design. A campaign of laboratory tests was carried out based on cyclic triaxial tests to measure resilient modulus (RM) and permanent deformation (PD). Specimens were prepared with different densities, which achieved varying compaction energy (600, 1260, and 2700 kJ/m3) but keeping saturation degree varying in a narrow range. Results demonstrated that the resilient modulus ranges from approximately 80 to 380 MPa, with confining stress controlling its behavior and having a small effect on compaction energy. Permanent deformation reaches almost 3 % after 150.000 load cycles for the maximum confining and deviatoric stresses and is controlled by the confining and deviatoric stress. The WFS reached the shakedown state for all the densities and stress-state evaluated, in a pattern below plastic creep shakedown and plastic limit shakedown. The best models to describe the experimental results were investigated, and the fitting parameters were also found. The authors also demonstrated that the resilient modulus measured on the last 100.000 cycles of permanent deformation tests is similar to the values measured on resilient modulus tests, which allows to characterize the resilient and permanent deformation using only the permanent deformation tests.

A data-driven approach for rapid detection of aeroelastic modes from flutter flight test based on limited sensor measurements

Flutter flight test involves the evaluation of the airframe’s aeroelastic stability by applying artificial excitation on the aircraft lifting surfaces. The subsequent responses are captured and analyzed to extract the frequencies and damping characteristics of the system. However, noise contamination, turbulence, non-optimal excitation of modes, and sensor malfunction in one or more sensors make it time-consuming and corrupt the extraction process. In order to expedite the process of identifying and analyzing aeroelastic modes, this study implements a time-delay embedded Dynamic Mode Decomposition technique. This approach is complemented by Robust Principal Component Analysis methodology, and a sparsity promoting criterion which enables the automatic and optimal selection of sparse modes. The anonymized flutter flight test data, provided by the fifth author of this research paper, is utilized in this implementation. The methodology assumes no knowledge of the input excitation, only deals with the responses captured by accelerometer channels, and rapidly identifies the aeroelastic modes. By incorporating a compressed sensing algorithm, the methodology gains the ability to identify aeroelastic modes, even when the number of available sensors is limited. This augmentation greatly enhances the methodology’s robustness and effectiveness, making it an excellent choice for real-time implementation during flutter test campaigns.

AERODYNAMIC IMPACT OF SECONDARY AIR INJECTION FLOWRATES ON THE MAIN ANNULUS FLOW FIELD FOR A TRANSONIC HIGH-PRESSURE TURBINE STAGE

Abstract In this study, the influence of secondary air blowing on the main annulus flow field of a transonic high-pressure turbine (HPT) was investigated experimentally and numerically. The experimental setup was a single-stage, unshrouded turbine with a blading consistent with modern HPTs. The entire testing campaign was conducted in a full annular, rotating, continuous turbine test rig at the Japan Aerospace Exploration Agency (JAXA), which realized the most faithful matching unrivalled of both the primary and secondary stream similarity parameters to reality. An elaborate secondary air system implemented in the hardware enabled it to mimic all the dominant coolant/purge streams representative of advanced hot sections: the full coverage film-cooling on stator and rotor airfoils, disk wheelspace purge air blown forward and aft of the rotor, and coolant injection through the over-tip casing. Detailed three-dimensional flow field measurements for various secondary air flowrates were performed by traversing a pneumatic thermometric combination probe downstream of the rotor. A complete set of numerical simulations was run concurrently with the testing to determine how well they captured the flow physics, particularly the interaction of the ejected secondary streams with the primary flow. The JAXA in-house code, UPACS, and its best practice settings, based on past verification and validation efforts, were employed and not intentionally tuned to better fit the data.

Spatially-Resolved Freestream Velocity Measurements At The NASA Langley 31-Inch Mach 10 Air Tunnel Using FLEET

Freestream velocity measurements in the NASA Langley 31-inch Mach 10 wind tunnel are reported in this paper using Femtosecond Laser Electronic Excitation Tagging (FLEET). The freestream measurements acquired during the January 2023 test campaign were the first direct measurement of freestream velocity in this hypersonic wind tunnel facility. Spatial distributions of time-averaged and instantaneous velocity measurements were obtained at all three typical wind tunnel freestream unit Reynolds number conditions of Re∞ /L = 1800000 [1/m] , 3600000 [1/m], and 6400000 [1/m], though the current paper focuses on centerline measurements for the three Re∞ /L and spatial distributions for one Re∞ /L. Measured values for time-averaged velocity and mean of the instantaneous velocity at the wind tunnel centerline agree within 5 m/s or 0.4% of the calculated velocity from the facility data acquisition system. Measurements acquired at locations away from the wind tunnel centerline reveal the spatial extent of the core flow of the hypersonic facility.

Unsteady Aerodynamics of Delta Kites for Airborne Wind Energy Under Dynamic Stall Conditions

ABSTRACTThree unsteady aerodynamic tools at different levels of fidelity and computational cost were used to investigate the unsteady aerodynamic behavior of a delta kite applied to airborne wind energy. The first tool is an in‐house unsteady panel method that is fast but delivers low to mid fidelity predictions. The second tool uses the open‐source CFD code SU2 to solve the unsteady Reynolds‐averaged Navier–Stokes equations with the SST turbulence model. At an intermediate level of fidelity, a semiempirical dynamic stall model that combines the panel method with a phenomenological dynamic stall module is proposed. The latter has free parameters that are fine‐tuned with CFD results from the second tool. The research on the dynamic stall model has been inspired by two flight test campaigns suggesting dynamic stall phenomena possibly driven by the periodic variation of the angle of attack (aerodynamic pitching motion) during crosswind maneuvers. The recorded inflow along the flight path was prescribed in the three aerodynamic tools. As expected, the price to pay for the low computational cost of the panel method is its inability to capture the dynamic stall phenomenon. The results from unsteady CFD qualitatively matched the experimental data identifying a leading‐edge vortex that forms and detaches cyclically during the pitching motion. Using RANS data, the semiempirical tool was fined‐tuned to reproduce the dynamic stall behavior, becoming an accurate and fast aerodynamic tool for coupling with any kite flight simulator. Further discussions on the effects of kite aerostructural deflections are included.

A Composite Fuselage under Mechanical Load: a case study for Guided Wave-based SHM

The introduction of composite materials in aeronautics has brought numerous advantages, along with unique damage and failure modes. The structure health is currently ensured by a damage-tolerant design and non-destructive inspections. Among other techniques, Guided Wave-based Structural Health Monitoring (GW-SHM) has gained interest as a cost and time effective alternative to traditional non-destructive techniques. One of the main challenges for GW-SHM is the influence of environmental and operational conditions on the damage identification capability. Aircraft structures undergo a broad range of mechanical load conditions, affecting the GW-SHM system. The study of load influence is meaningful in view of applications where the SHM system is expected to work under varying load conditions. Such applications may be in-flight monitoring, but also on-ground only usage and structural test monitoring. A full-scale CFRP door surrounding structure was instrumented with a GW-SHM system and tested under mechanical load. A hydraulic test rig was used to apply three representative load cases in quasi-static conditions on the structure. A network of robust piezocomposite transducers to monitor the structure has been designed and manufactured. The network is organized in arrays, which include the transducers, cabling and a connecting base plate for optimized sensor installation. A multiplexing module is directly connected to the base plate enabling a fast and reliable sensor connection, a drastic cable weight reduction, and a modular design. The combined influence of load and temperature on the propagation of Guided Waves has been assessed. Finally, a data-driven approach to damage identification has allowed the detection and localization of barely visible impact damage introduced during the test campaign.

Large scale monitoring of a highway bridge with remote sensing and distributed fiber optic techniques during load tests

Many bridges in western countries are at the end of their lifetime and hence Structural Health Monitoring is vital to ensure their safe operation. Load test are one way to assess the utilization grade and to decide if actions have to be taken. We report on a comprehensive monitoring campaign of load tests of a large highway bridge on the Brenner highway. The Brenner highway is the main alpine truck crossing passages from Germany to Italy. Several different remote sensing techniques like static and dynamic laser scanning, robotic total station measurements and interferometric radar were used to determine displacements of the bridge deck and girders. Strain changes and bending were observed with distributed fiber optic sensing. Furthermore, the movements of the bridge bearings were determined with IoT tilt sensors. Data was acquired during static and dynamic load tests. We demonstrate that the utilization grade of the bridge can be assessed by an integrated analysis of the different sensor data in combination with a numerical model of the structure. As a consequence of the investigations it was decided by the highway operator to close one of the three lanes of the bridge.

Application of semiempirical correlations for multidimensional heat transfer in rocket engine cooling channels

Heat transfer in cooling channels of liquid rocket engine thrust chambers is an intrinsically multidimensional problem due to the geometry of the channels, often rectangular in section, and the asymmetric distribution of heat input from the hot combustion gas. In this study, the possibility of addressing this problem with semiempirical correlations for the coolant heat transfer and multidimensional numerical simulations for the heat conduction in the wall is investigated. Using experimental data from a test campaign of a cooling channel representative of liquid rocket engine conditions, semiempirical correlations are derived. Both cases of constant and variable heat transfer coefficient along the perimeter of the channel section are considered. The resulting correlations are then used to evaluate their reliability in reproducing the experimental wall temperature data from the same test campaign. For comparison, a correlation taken from the open literature and obtained with experimental data of circular heated tubes is also considered. The results demonstrate that correlations based on a constant heat transfer coefficient fail to reproduce with sufficient accuracy the test cases characterized by higher wall temperatures, while correlations based on a variable heat transfer coefficient overestimate the wall temperature in the initial sections of the channel.

Dynamic reduction technique for nonlinear analysis of spur gear pairs

In this study the dynamic response of a spur gear pair is analyzed using a novel nonlinear approach. The actual rolling motion and engagement of the system is simulated using a set of reduced order models obtained in a pre-processing phase using the minimal amount of master degrees of freedom without loss of accuracy or generality. The flexibility of the gear bodies is included by a refined finite element model, and no geometry simplification is introduced while also retaining all nonlinearity sources. To reduce the computational cost the time-varying mesh stiffness is also pre-computed and used depending on the instantaneous loading conditions. Contact loss is also taken into account, and reconnection events are treated as vibro impacts. The results are compared against high quality and demanding experimental results with a computational cost several orders of magnitude lower than models with similar accuracy. Different loading conditions are investigated during the sweep-up and down maneuvers. Mainly, the dynamic transmission error is analyzed, showing remarkable agreement with the test campaign’s results. Different nonlinear phenomena such as hysteretic jumps and sub- and super-harmonic resonances are correctly predicted by the proposed model in terms of both frequency and amplitude. This method allows quick and accurate nonlinear analyses overcoming current limitations and is open to further complications to include other components and effects.

Vibration Correlation Technique: Methodology Applied to Buckling of Large-Scale Sandwich Cylindrical Shell

This paper assesses the Vibration Correlation Technique's (VCT) applicability within the context of sandwich cylindrical shells through detailed numerical investigation. The study utilizes a sandwich shell from NASA's Shell Buckling Knockdown Factor project. Finite element models are implemented, incorporating initial mid-surface and thickness imperfections to replicate NASA's buckling test campaign. The numerical results are compared to the experimental data, validating the nonlinear solution with an approximate deviation of 1%. Subsequently, the VCT experimental campaign is numerically conducted through free vibration analyses at different load levels, enabling a comprehensive evaluation of VCT's applicability. The results verified the effectiveness of the VCT, demonstrating a deviation of less than 10% when estimating the buckling load for load levels below 65% of the nonlinear buckling load. Overall, the findings confirm the non-destructive nature of the VCT when employed on such structures, supporting future practical applications.

Assessment of Anisotropic Elastic Parameters Using Laboratory Triaxial and In-Situ Pressuremeter Tests in Opalinus Clay

AbstractOpalinus Clay is a stratified shale that exhibits anisotropic deformation properties. In this work, the transversely isotropic deformation parameters of Opalinus Clay are summarized from recent undrained triaxial test campaigns. Relatively consistent values are found for Poisson’s ratios representing different orientations, regardless of the lithofacies and the effective confining stresses used in the tests. Pressuremeter tests were performed at the Mont Terri Rock Laboratory in two boreholes perpendicular and parallel to bedding, respectively. The elastic moduli normal to the borehole wall (borehole moduli) are determined using unloading data obtained at multiple diametric caliper axes and exhibit strong anisotropy for the tests in the borehole parallel to bedding. The anisotropic borehole moduli are predicted based on Amadei and Savage’s (Int J Rock Mech Min Sci 28:383–396, 1991. https://doi.org/10.1016/0148-9062(91)90077-Y) analytical solution using the laboratory-derived Poisson’s ratios and the shear modulus derived from pressuremeter tests in the borehole perpendicular to bedding. The prediction overestimates the magnitude of the borehole moduli but underestimates their anisotropic ratio compared to that from pressuremeter measurement. Drilling a borehole parallel to the bedding of Opalinus Clay is known to induce a local borehole damage zone preferentially developed normal to bedding. The results from a finite element analysis that incorporates this local damage are in better agreement with the pressuremeter measurement.

Kinetic Model Implementation of Fluidized Bed Devolatilization

Computational modeling is a powerful tool for studying and investigating the behavior of fluidized bed gasifiers and the modeling of the initial devolatilization step is necessary to provide a reliable description of the whole process involving the feedstock decomposition and the subsequent gasification reaction. In this work, a bench-scale fluidized bed reactor was used to examine the devolatilization of different carbonaceous materials within the temperature range from 650 to 850 °C. The experimental test campaign was used to derive the linear correlation factor to describe the devolatilization in terms of product distribution as a function of temperature and highlight the different behavior between lignocellulosic and plastic feedstocks. Furthermore, the experimental data were used to develop concise kinetic expressions able to fit the experimental devolatilization times ranging from 75 in the case of poplar at a lower temperature and 22 s for the Organic Fraction of Municipal Solid Waste (OFMSW) at a higher temperature. The obtained model produces a simple kinetic expression where the size of the particle is enclosed in the kinetic parameters. The kinetic model sided by the application of linear correlations describes the overall thermal decomposition in a fluidized bed, simplifying its modeling in commercial simulation software, even when particles are considered as point-like bodies.

Surface Pressure Measurement of Truncated, Linear Aerospike Nozzles Utilising Secondary Injection for Aerodynamic Thrust Vectoring

A cold-gas test campaign has been conducted at the DLR’s P6.2 test bench in Lampoldshausen, with the objective of investigating the linear aerospike nozzle flow in interaction with secondary injection thrust vector control (SITVC). In this campaign, the influence of nozzle truncation, injection position and injection pressure on the nozzle surface and base pressure is analysed using pressure probes and Schlieren flow-visualisation techniques. The effects of injection position and truncation on the nozzle surface pressure development are comparable for all geometric variations, resulting in a locally increased static pressure upstream and a locally decreased static pressure downstream of the injection. The magnitude and dimension of these high- and low-pressure regions are correlated with the injection pressure. However, the influence of injection position and truncation on the base pressure is not entirely predictable by the named parameters, indicating an interdependence between both geometric parameters. Finally, the required pressure ratio of injection to the primary flow to ensure sonic injection has been analysed on TUD’s cold-gas test bench. This allows the respective injection position-dependent threshold to be identified. The analysis reveals that these experiments have been conducted under transsonic injection conditions.

Development of a Dynamically Re-Configurable Radio-Frequency Interference Detection System for L-Band Microwave Radiometers.

Real-Time RFI Detection and Flagging (RT-RDF) for microwave radiometers is a versatile new FPGA algorithm designed to detect and flag Radio-Frequency Interference (RFI) in microwave radiometers. This block utilizes computationally-efficient techniques to identify and analyze RF signals, allowing the system to take appropriate measures to mitigate interference and maintain reliable performance. With L-Band microwave radiometry as the main application, this RFI detection algorithm focuses on the Kurtogram and Spectrogram to detect non-Gaussian behavior. To gain further modularity, an FFT-based filter bank is used to divide the receiver's bandwidth into several sub-bands within the band of interest of the instrument, depending on the application. Multiple blanking strategies can then be applied in each band using the provided detection flags. The algorithm can be re-configured in the field, for example with dynamic integration times to support operation in different environments, or configurable thresholds to account for variable RFI environments. A validation and testing campaign has been performed on multiple scenarios with the ARIEL commercial microwave radiometer, and the results confirm the excellent performance of the system.

Out-of-plane bending properties of cross laminated timber (CLT)

In Europe the structural timber building product cross laminated timber (CLT) is regulated via European Technical Assessments (ETAs), which require large and voluminous test campaigns to obtain. So far, there is no standardised CLT strength class system nor a set of harmonised properties. Such a strength class system and tabulated values could be accompanied by a set of so-called load-bearing models, analogous to the current regulations for glued laminated timber (GLT). The aims of this contribution are to comprehensively analyse the first known load-bearing model for out-of-plane bending of CLT from 2006 and to validate and benchmark this approach with possible further candidates. The aim is to initiate the establishment of a European strength class system for CLT based on its out-of-plane bending properties, for a more reliable, regulatory compliant structural building product and for enhancing its market acceptance. Therefore, a comprehensive analysis of various potential influencing parameters on out-of-plane CLT bending properties is effected by means of stochastic-numerical investigations as well as a large amount of test campaigns, the latter in the form of a retrospective study. The first approach from 2006, in particular in its adapted version, is successfully validated and confirmed as a valuable candidate for the future regulation of CLT due to its overall more accurate and more reliable strength predictions compared with the other candidates. In addition, models for the density and the modulus of elasticity parallel to the grain, as currently defined for glulam, are confirmed to be applicable also for CLT. An analysis of the variation in the properties of the base material and CLT motivates additional efforts towards grading and quality assurance in order to meet the expectations of the nominal strength class of boards and to fulfil minimum requirements for finger joint quality to better utilise the high performance of CLT and to increase its reliability.

Experimental assessment of high-energy high nickel-content NMC lithium-ion battery cycle life at cold temperatures

An essential element for the diffusion and environmental impact assessment of electrochemical storage systems is their lifetime. This lifetime also impacts the overall cost of the equipment in which the storage system is used. At the same time, a number of applications, e.g. electric vehicles, do not allow a temperature control of the batteries, although the performances of the latter are very strongly linked to them. The phenomena investigated, such as aging, behavior at low temperature and rapid charge for low temperature, are complex and difficult to model. Only the establishment of databases representative of the conditions of use can lead to elements of response. The exploitation of these databases by artificial intelligence tools is certainly relevant but requires a learning on data representative of the conditions of use and of the phenomena to be evaluated.The work presented in this paper is in this context and is intended to model the influence of the rapid charge at low temperature (0 °C, −10 °C, −20 °C) on the lifetime (initial capacity loss) of lithium-Ion NMC elements. The problem with data-based approaches is the large number of tests required and the development in relevant experimental designs. Faced to this challenge, a consortium of French laboratories and manufacturers has been working together since the 2000s to carry out this type of work. The paper proposes to present a test campaign and summarizes the main results to assess the service life (loss of capacity) for a fast-charging application at low temperature and position them against the manufacturer data established at 25 °C. The impact of two partial discharge processes (50 %) will also be assessed. In a last part, we show that for low temperatures, even for the nominal charge current the life time is reduced to few dozens of cycles and a mechanical destruction of the cell with no activation of the current interrupt device is achieved. This study demonstrates and quantifies the very important impact of low-temperature charging processes on the lifetime of high energy lithium-ion NMC batteries.

Numerical Investigation of Model Support, Closed Engine Nacelle and Scale Effect on a Wind Tunnel Test Model

In the frame of the H2020 MORE&LESS project co-funded by European Commission, a test campaign for a hypersonic vehicle demonstrator took place at the INCAS Trisonic Facility. CFD analysis was used to quantify the effects of the wind tunnel model support, the closed engine nacelle, and to perform the Reynolds number extrapolation. Three sets of simulations were used in order to generate the corrections. The wind tunnel configuration with sting, sting cavity, and closed nacelle was used as the baseline, with the aim of matching the experimental results as precisely as possible. A configuration with a flow-through nacelle and the shock cone in the appropriate position for each Mach number and no sting or cavity was used to determine the effect of the sting and the closed nacelle. For the Reynolds extrapolation, a 1:1 model was used, with the boundary conditions deriving from the theoretical trajectory of the vehicle. The CFD results for the wind tunnel configuration closely align with the experimental data. Significant differences between the three configurations can be observed just for the pitching moment, and those are caused by the presence of the sting and the open nacelle. The difference in Reynolds number does not seem to have a significant effect on the aerodynamic coefficients.

DTT toroidal field conductor samples test in Sultan: DC and AC characterization

The superconducting magnet system of the Divertor Tokamak Test (DTT) facility, composed of 18 toroidal field (TF) coils, 6 poloidal field coils and a central solenoid, has been designed and many procurements have been launched. Some manufacturing aspects and some conductor features require characterization under relevant close-to-operative conditions. To confirm the design choices in all details, cryogenic tests in qualified facilities have been foreseen. In this work, the results of the TF samples characterization at the SULTAN facility at the Swiss Plasma Centre (SPC, EPFL) are presented. The 3 week test campaign started on July the 8th, 2022. The DTT TF SULTAN sample was made of two Nb3Sn cable-in-conduit conductor ‘legs’, namely ‘TF-A’ and ‘TF-B’, made with wires produced by Kiswire Advanced Technology, differing for the cabling twist pitch sequence only, and designed to work in DTT at 42.5 kA at 11.9 T peak field. The extensive characterization comprised 3000 electro-magnetic (EM) cycles and two warm-up-cool-down (WUCD) steps, and in detail it included: AC measurements on the virgin conductors, on cyclic loaded conductors and after WUCDs; DC tests at 10.85 T/42.5 kA with intermediate EM cycles at 10.85 T/45 kA before and after WUCDs; DC tests using partial Lorentz force loads, and Minimum Quench Energy tests at 9 T/42.5 kA after cycles and WUCDs. The results of the DC measurement analysis verified the design, in terms of current sharing temperature (T cs) and critical current (I c), as both samples are over the minimum acceptance values. In particular, the ‘TF-A’ sample, characterized by a so-called ‘long twist pitch’ cabling sequence, showed higher performance without any degradation with loading and WUCD cycles, whereas sample ‘TF-B’ presented an initial T cs reduction that afterwards substantially remained unchanged. In terms of strain acting at the Nb3Sn filaments level, this result can be described by a lower effective strain in the ‘TF-A’ sample. AC losses were measured with a calorimetric method as a function of frequency for each series of AC sinusoidal pulsing measurements, and the characteristic coupling time constants were determined.

Nonlinear dynamics of a horizontal rotor with asymmetric magnetic supports

In this paper, a horizontal rotor with passive anisotropic asymmetric magnetic bearings nonlinear model is developed. The model is based on the experimental evidence of an educational demonstrator, a powerful benchmark which highlights features of rotordynamics systems. An experimental setup is developed using laser sensors to track the displacements of the rotor and tachometer to record the rotor angular speed. Several test campaigns are performed with different initial conditions to characterise the educational demonstrator. The first test campaign is oriented to identify the system structural properties, while the second one is focused on the nonlinearity identification. The rotor modelling is divided into three stages with progressive increase in complexity, starting from the overall linear structural behaviour to the nonlinear subharmonic resonance phenomenon. The model is developed with a generalised approach suitable for a wide range of operating conditions and rotor configurations. Progressively, the developed rotor models are compared to highlight their limitations and advantages. Finally, rotor trajectory analysis and time–frequency analysis are used in the numerical-to-experimental comparison.