DSpace Repository

Welcome to the NLR Reports Repository

Royal NLR conducts research, which is published in reports. Only a minor part of these reports is made public. This repository holds these public, so called Technical Publications (TP), mainly produced from 1996 up till now.

Technical publications published before 1996 may be obtained using the request-form. Other types of NLR-reports are Contract Reports (CR) and Technical Reports (TR), which in general are not public. You may however request a copy by using the request-form. In some cases permission may be granted, depending on specific properties and contractor of the report. Reports will be supplied as pdf-file.

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Recent Submissions

Modeling Comparison of a Two-Phase Mechanically Pumped Loop with a Conventional Ethylene Glycol Water Single-Phase Mechanically Pumped Loop for Fuel-Cell Cooling in TheMa4HERA
(MDPI, 2026) Weijer, A.F. van de; Es, J. van; Gerner, H.J. van; Nijenhuis, A.K. te; Biesheuvel, J.; Delpu, G.; Cherdouh, F.; Peimbert, E.T.; Gantus, R.A.; Trolliet, P.; Galzin, G.; Labaste Mauhe, L.
The fuel-cell (FC) technology currently being considered to reduce aircraft greenhouse gas emissions may require large and heavy cooling systems. The paper introduces the two-phase (2Φ) Mechanically Pumped Loop (MPL) for FC cooling and compares it numerically with the conventional Ethylene Glycol Water (EGW) single-phase (1Φ) cooling system for a 1.2 MW heat-dissipation load. Considering an operating temperature of 90 °C, the system mass of the 2Φ MPL with and without an accumulator is found to be, respectively, 33% and 64% lower than the EGW system. Furthermore, the frontal area of the ram air heat exchanger (HX) was found to be 19% smaller, reducing ram air drag. An increase of the operating temperature to 130 °C was found to reduce the cooling system mass by 21% for the 1Φ MPL, and 22 to 29% for the 2Φ MPL. The frontal area of the ram air HX was found to be reduced by 44% and 40% for the 1Φ and 2Φ MPL, respectively. These results demonstrate the considerable performance gain of the 2Φ MPL over the 1Φ MPL for FC cooling, and the benefits of increasing the operating temperature for the cooling system.
Low-Dissipation Simulation Methods and Models for Turbulent Subsonic Flow
(Springer Nature, 2020) Rozema, W.; Verstappen, R.W.C.P.; Veldman, A.E.P.; Kok, J.C.
The simulation of turbulent flows by means of computational fluid dynamics is highly challenging. The costs of an accurate direct numerical simulation (DNS) are usually too high, and engineers typically resort to cheaper coarse-grained models of the flow, such as large-eddy simulation (LES). To be suitable for the computation of turbulence, methods should not numerically dissipate the turbulent flow structures. Therefore, energy-conserving discretizations are investigated, which do not dissipate energy and are inherently stable because the discrete convective terms cannot spuriously generate kinetic energy. They have been known for incompressible flow, but the development of such methods for compressible flow is more recent. This paper will focus on the latter: LES and DNS for turbulent subsonic flow. A new theoretical framework for the analysis of energy conservation in compressible flow is proposed, in a mathematical notation of square-root variables, inner products, and differential operator symmetries. As a result, the discrete equations exactly conserve not only the primary variables (mass, momentum and energy), but also the convective terms preserve (secondary) discrete kinetic and internal energy. Numerical experiments confirm that simulations are stable without the addition of artificial dissipation. Next, minimum-dissipation eddy-viscosity models are reviewed, which try to minimize the dissipation needed for preventing sub-grid scales from polluting the numerical solution. A new model suitable for anisotropic grids is proposed: the anisotropic minimum-dissipation model. This model appropriately switches off for laminar and transitional flow, and is consistent with the exact sub-filter tensor on anisotropic grids. The methods and models are first assessed on several academic test cases: channel flow, homogeneous decaying turbulence and the temporal mixing layer. As a practical application, accurate simulations of the transitional flow over a delta wing have been performed.
The slip velocity of nearly neutrally buoyant tracers for large-scale PIV
(Springer Nature, 2021) Engler Faleiros, D.; Tuinstra, M.; Sciacchitano, A.; Scarano, F.
The behaviour of nearly neutrally buoyant tracers is studied by means of experiments with helium-filled soap bubbles and numerical simulations. The current models used for estimating the slip velocity of heavy micro particles and neutrally buoyant particles are reviewed and extended to include the effect of unsteady forces and particle Reynolds number. The particle motion is analysed via numerical simulations of a rectilinear oscillatory flow and in the flow around an airfoil within a particle flow parameter space that is typical of large-scale PIV experiments. An empirical relation is obtained that estimates the particle slip velocity, depending on the particle-to-fluid density ratio, the particle Reynolds number and frequency of the local flow fluctuations. The model developed is applied to assess the slip velocity of helium-filled soap bubbles in a large-scale experiment conducted at the German–Dutch wind (DNW) tunnels in the flow around an airfoil, with chord Reynolds numbers up to three millions. Furthermore, a procedure is proposed that can be used to retrieve the bubbles mean density and dispersion from measurements of mean velocity and fluctuations, respectively.
Numerical Whirl–Flutter analysis of a tiltrotor semi-span wind tunnel model
(Springer Nature, 2022) Cocco, A.; Mazzetti, S.; Masarati, P.; Hof, S.C. van 't; Timmerman, B.
This work presents the modeling and preliminary Whirl–Flutter stability results achieved within the Advanced Testbed for TILtrotor Aeroelastics (ATTILA) CleanSky2 project. The project addresses the design, manufacturing, and testing of a semi-span wind-tunnel model of the Next Generation Civil TiltRotor. The preliminary multibody models developed in support of the wind-tunnel testbed design are described, illustrating the modeling technique of each subcomponent of the model, namely the wing, the rotor, the blades, and the yoke. The methodologies used to analyze the stability of systems subjected to periodic aerodynamic excitation when the problem is modeled using full-featured multibody solvers are presented in support of Whirl–Flutter identification during wind-tunnel testing.
Scaled flight testing supporting the development of radical new aircraft
(SFTE, 2023) Jentink, H.W.; Bremmers, F.
Scaled flight testing can contribute to valuable reduction of risk and cost in the development of a radical new aircraft. The role of scaled flight testing in the aircraft development process is described, where it is essential that the relationships between the small-scale and full-scale results are properly defined. The validity of results of scaled flight testing for predicting the full-scale aircraft properties is addressed next. A 1:8.5 scaled version of a typical large passenger aircraft was built, tested in the wind tunnel and flight tested. During the flight tests an accurate flight test instrumentation system measured the scaled aircraft flight parameters. Results of the scaled flight testing have been compared with full-scale test results which validates the value of the scaled flight testing methodology. In a next step the scaled flight testing methodology is applied to investigate and demonstrated the benefits of distributed electric propulsion. The scaled aircraft has been re-built in the same shape but the jet propulsion is replaced by propulsion with six propellers. The development, manufacturing, wind tunnel test and taxi tests are described, flight tests still have to be performed. Finally the role of the flight test engineer in the scaled flight test campaigns has been compared with the role of a flight test engineer in a typical full-scale flight test campaign. The roles were chosen very similar and that worked out very well in these scaled flight test campaigns.