A robust extension to the triple plane pressure mode matching method by filtering convective perturbations

Time-periodic CFD simulations are widely used to investigate turbomachinery components. The triple-plane pressure mode matching method (TPP) developed by Ovenden and Rienstra extracts the acoustic part in such simulations. Experience shows that this method is subject to significant errors when the amplitude of pseudo-sound is high compared to sound. Pseudo-sound are unsteady pressure fluctuations with a convective character. The presented extension to the TPP improves the splitting between acoustics and the rest of the unsteady flow field. The method is simple: i) the acoustic eigenmodes are analytically determined for a uniform mean flow as in the original TPP; ii) the suggested model for convective pressure perturbations uses the convective wavenumber as axial wavenumber and the same orthogonal radial shape functions as for the acoustic modes. The reliability is demonstrated on the simulation data of a low-pressure fan. As acoustic and convective perturbations are separated, the accuracy of the results increases close to sources, allowing a reduction of the computational costs by shortening the simulation domain. The extended method is as robust as the original one--giving the same results for the acoustic modes in absence of convective perturbations.Comment: Accepted 15-05-11 by International Journal of Aeroacoustics to be published in the special issue focusing on turbomachinery aeroacoustic

Stochastic method to simulate fan broadband noise

Die vorliegende Arbeit beschäftigt sich mit der Anwendung des Random-Particle-Mesh-Verfahrens (RPM) zur Simulation von Fanbreitbandschall. Aus zeitgemittelten, turbulenten Größen erzeugt das Verfahren zeitabhängige Fluktuationen, die zur Vorhersage der Schallentstehung hinreichend sind. Es wird isotrope, freie Turbulenz in Form von divergenzfreien Geschwindigkeitsfluktuationen synthetisiert. Die Untersuchungen sind ohne Beschränkung der Allgemeinheit auf zwei Raumdimensionen beschränkt. Es wird ein hybrides Verfahren vorgeschlagen, das dem RPM-Verfahren eine Strömungslösung auf Basis der (U)RANS-Gleichungen voranstellt und eine zeitgleiche Ausbreitungsrechnung durch Lösen der linearisierten Euler Gleichungen im Zeitbereich vorsieht. Die freie Turbulenz wird störungsfrei in das Ausbreitungsgebiet einkoppelt; der eigentliche Schallentstehungsmechanismus ist so Teil der Ausbreitungsgleichungen. Um die Vergleichbarkeit des RPM-Verfahrens mit Messungen zu gewährleisten, wird ein effizientes Verfahren vorgestellt, das es erlaubt, realistische isotrope Spektren zu realisieren. Dieses Verfahren bedient sich der Superposition mehrerer Gauss-Spektren, um analytisch ein Zielspektrum zu realisieren. Dadurch wird die Beschränkung des RPM-Verfahren auf Gauss-Spektren aufgehoben. Das vorgeschlagene hybride Verfahren wird zunächst bei stationärer Anregung für die Vorhersage von Vorderkanteninteraktionsschall erfolgreich an der analytischen Lösung zur harmonischen und zur breitbandigen Turbulenz-Schaufel-Interaktion validiert. Die Erweiterung auf stochastisch realisierte Turbulenz wird in zwei Anwendungen für Vorderkanteninteraktionsschall -- ein lastfreies NACA0012-Profil und ein angestelltes NACA65(12)-10-Profil im Freistrahl -- nachgerechnet und erfolgreich gegen Messungen verglichen. Das bis dato stationäre Verfahren wird zur Anwendung auf Fans erweitert, wobei die Hintergrundströmung und die mittleren, turbulenten Größen sich periodisch ändern. Die resultierenden Fluktuationen sind damit zyklostationär. Die mittleren Größen werden hierfür aus einer URANS-Simulation entnommen. Durch das vorgestellte Verfahren können die Teilaspekte der Zyklostationarität einzeln untersucht werden. Ausgehend von einer Stromlinie in der Kanalmitte, wird die Statorschaufelreihe als 2D-Kaskade modelliert. Die Turbulenzsynthetisierung und CAA-Simulation erfolgen in 2D. Dadurch kann effizient die abgestrahlte Gesamtschallleistung des Breitbandschalls stromauf und stromab der Statorreihe vorhergesagt werden. Bei einer Validierung gegen Messungen am NASA SDT-Modellfan sind die Trends wiedergegeben und die Abweichungen der Schallleistung liegen innerhalb von 5 dB. Abschließend werden die einzelnen Effekte der Zyklostationarität hierarchisch und exemplarisch am DLR-UHBR-Fan untersucht. Es wird gezeigt, dass die Quellen zur Schallentstehung an den verschiedenen Statorschaufeln unkorreliert sind. Wird in der Kaskade nicht die volle Schaufelanzahl berücksichtigt, werden im Spektrum Cut-on-Frequenzen sichtbar. Davon abgesehen, sind die Pegel und der Trend des Spektrums einer vollen Kaskade wiedergegeben. Der Einfluss der Zyklostationarität auf die mittleren akustischen Spektren scheint vernachlässigbar, obwohl die Zeitsignale sich deutlich unterscheiden. Ausschließlich die Berücksichtigung der periodischen Hintergrundströmung ändert das Spektrum signifikant. Ursachen dafür werden diskutiert, aber können nicht abschließend geklärt werden.This thesis deals with the application of the Random-Particle-Mesh (RPM) method for fan broadband noise predictions. The RPM method generates time-varying turbulent fluctuations on the basis of time-averaged turbulent characteristics. These fluctuations are fully sufficient for the prediction of acoustic noise. Free, isotropic turbulence is synthesised as divergence free velocity fluctuations. Without loss of generality the investigations in the thesis are restricted to two spacial dimensions. A hybrid method is proposed, which complements the RPM method by a preceding flow solver, solving the (U)RANS equations, and a synchronous CAA solver, solving the linearised Euler equations in time domain. Two robust coupling methods of the synthesised fluctuations into the CAA domain are used. The fluctuations are noiselessly coupled as free turbulence upstream of the source region. In this way the sound generation mechanisms are part of the CAA. An efficient method, realising realistic isotropic spectra, is derived to achieve comparability with measurements. This method utilises a superposition of multiple Gaussian spectra to analytically realise a target spectrum. In this way the limitation of the RPM method to Gaussian spectra is removed. Initially the suggested hybrid method is applied for stationary excitation. The leading edge noise due to the impingement of harmonic and broadband gusts onto an infinitely-thin, finite-long airfoil is successfully predicted and validated by the analytical solution. Two isolated-airfoil applications for leading edge noise -- an unloaded NACA0012 profile and a loaded NACA65(12)-10 profile in a free stream -- are recomputed and successfully compared to the measurements. The stationary method is extended to the application on fans by taking the periodic variation of the background flow and of the mean turbulent characteristics into account. The resulting fluctuations are therefore cyclostationary. The periodic mean values are taken from a URANS simulation. The presented method allows to investigate the different aspects of cyclostationarity separately. Based on a streamline in the duct centre a stator blade row is modelled as a 2D cascade. The turbulence synthetisation and CAA simulation are carried out in 2D. This allows to efficiently predict the radiated acoustic power of the broadband noise upstream and downstream of the stator blade row. A validation against measurements of the NASA-SDT fan reproduces the trends. The deviation of the sound power levels are within 5 dB. Finally the different effects of the cyclostationarity are hierarchically and exemplarily investigated on the DLR-UHBR fan. It is shown that the sound sources at the different stator blades are uncorrelated. If not all stator blades are taken into account in the cascade, cut-on frequencies can be identified in the spectrum. Apart from that the levels and trends are reproduced by the reduced cascade. The influence of the cyclostationarity on the average acoustic spectra appears negligible even though the time signal differ significantly. Solely the consideration of the periodic background flow changes the spectrum significantly. Reasons are discussed, but cannot be concluded so far

Economic impact of clinical decision support interventions based on electronic health records

Background!#!Unnecessary healthcare utilization, non-adherence to current clinical guidelines, or insufficient personalized care are perpetual challenges and remain potential major cost-drivers for healthcare systems around the world. Implementing decision support systems into clinical care is promised to improve quality of care and thereby yield substantial effects on reducing healthcare expenditure. In this article, we evaluate the economic impact of clinical decision support (CDS) interventions based on electronic health records (EHR).!##!Methods!#!We searched for studies published after 2014 using MEDLINE, CENTRAL, WEB OF SCIENCE, EBSCO, and TUFTS CEA registry databases that encompass an economic evaluation or consider cost outcome measures of EHR based CDS interventions. Thereupon, we identified best practice application areas and categorized the investigated interventions according to an existing taxonomy of front-end CDS tools.!##!Results and discussion!#!Twenty-seven studies are investigated in this review. Of those, twenty-two studies indicate a reduction of healthcare expenditure after implementing an EHR based CDS system, especially towards prevalent application areas, such as unnecessary laboratory testing, duplicate order entry, efficient transfusion practice, or reduction of antibiotic prescriptions. On the contrary, order facilitators and undiscovered malfunctions revealed to be threats and could lead to new cost drivers in healthcare. While high upfront and maintenance costs of CDS systems are a worldwide implementation barrier, most studies do not consider implementation cost. Finally, four included economic evaluation studies report mixed monetary outcome results and thus highlight the importance of further high-quality economic evaluations for these CDS systems.!##!Conclusion!#!Current research studies lack consideration of comparative cost-outcome metrics as well as detailed cost components in their analyses. Nonetheless, the positive economic impact of EHR based CDS interventions is highly promising, especially with regard to reducing waste in healthcare

Simultaneous Computation of Surface and Volume Sources for Fan Broadband Noise with the Random-Particle-Mesh Method

The relative contribution of broadband noise has steadily increased over the last decades as the mechanisms creating tones are now well understood and can be efficiently reduced. For fan-design capabilities an interim or intermediate solution is needed between restrictive analytical models and full-resolved costly simulations. Ewert et al.1 proposed an affordable way to simulate broadband noise with a CAA solver in the time domain while accounting for the complex geometry and background flow. The Random-Particle-Mesh (RPM) method reconstructs the turbulent fluctuations based on a RANS calculation. Turbulence source is coupled to the Acoustic Perturbation Equations solved by a CAA solver. The approach was applied sucessfully for slat noise and generic trailing-edge noise problems. Our investigations showed that this coupling method does not work sufficiently for lead- ing edge noise of generic airfoil configurations if the vortex sound sources are determined from an incident vorticity field that does not include the additional effect of scattered vorticity shed from the trailing edge of the airfoil due to the presence of a Kutta condition. The objective of this article is to extend and validate the coupling between the RPM and the CAA domain to explicitly include the enforcement of the Kutta condition into the CAA model for homogeneous and potential flow. This is achieved by adding another domain which computes the vorticity–wall interaction. Theoretically the approach should be sufficient to separate the surface from the volu- metric sources. This works very well for a flat plate. But we apply this on a NACA0012 airfoil in potential flow which gives unreasonable results. We discuss the issue and offer ideas for this cause