Experimental analysis of the pressure–velocity correlations of external unsteady flow over rocket launchers

Based on simultaneous wall pressure and velocity measurements, the aerodynamic load of a launcher body model is investigated. Two different configurations are considered in order to study the influence of geometrical artifacts on the after body flow and consequently on the aerodynamic load. After a brief presentation of the experimental setup used to get the unsteady wall pressure and external velocity field, a global analysis of the integrated pressure along the nozzle is presented for both configurations. It is shown that the unsteady load induced on a configuration with attachment device involves characteristic frequencies which fits the mechanical response of the structure whereas no particular behavior is observed on the configuration without attachment device. Then, a Proper Orthogonal Decomposition is successively performed from the wall pressure field and from the external velocity field highlighting the relationship between the most energetic structures of the flow and the involved phenomenon. Finally, a pressure/velocity correlation of the POD modes is presented and the most energetic structures of the velocity field are linked to the unsteady load observed on the nozzle. It is then confirmed the structural influence of the attachment device and its contribution to the unsteady loads acting on the nozzle.ESA TRP: "Unsteady Subscale Force Measurements within a Launch Vehicle Base Buffeting Environment"

EEN VAST AANSPREEKPUNT IN HET ZIEKENHUIS VOOR LAAGGELETTERDE ONCOLOGISCHE PATIËNTEN

Om oncologische patiënten adequaat te begeleiden door de complexe zorgketen hebben zij een vast aanspreekpunt in het ziekenhuis nodig. Veel informatie die in de complexe, langdurige en multidisciplinaire oncologische zorg gegeven wordt, ligt boven het niveau van de patiënt. Dit stelt hoge eisen aan de geletterdheid van de patiënt. Laaggeletterde patiënten zijn vaak ondervertegenwoordigd in wetenschappelijk onderzoek. Door schaamte en het niet herkennen blijft laaggeletterdheid onderbelicht en verbogen in de samenleving en in de zorg. Naar aanleiding van deze probleemstelling is de volgende onderzoeksvraag geformuleerd: “Welke inzichten uit de zorgethiek kunnen gebruikt worden bij de vorming van de taakomschrijving van een vast aanspreekpunt voor laaggeletterde oncologische patiënten? En welke aanbevelingen voor goede oncologische zorg kunnen naar aanleiding daarvan gedaan worden?” De zorgethiek richt zich in een interdisciplinair veld op wat goede zorg in een context gebonden situatie is. Binnen de zorgpraktijk wordt gekeken naar geleefde ervaringen en de geordende samenleving. Om antwoord te krijgen op de onderzoeksvraag is daarom een theoretisch-conceptueel zorgethisch onderzoek verricht. Uit de literatuurstudies rondom laaggeletterdheid in de oncologie en de invulling van een vast aanspreekpunt is gebleken dat er een wrijving bestaat tussen laaggeletterden en zorgverleners door lastige communicatie en het moeilijk te herkennen van laaggeletterdheid. Dit zegt iets over de zorgrelatie wat in de zorgethische reflectie middels het richtinggevende begrip ‘relationaliteit’ wordt uitgediept. De gevonden diversiteit tussen laaggeletterden enerzijds, en de diversiteit in taakomschrijvingen en titels van een vast aanspreekpunt anderzijds, maken zorgverleners en zorgontvangers kwetsbaar. Naar aanleiding van een zorgethische reflectie op kwetsbaarheid is naar voren gekomen wat kwetsbaarheid in deze situatie inhoudt. Tot slot zijn er weinig kartrekkers in zorginstelling en weinig educatie in de zorgopleidingen omtrent laaggeletterdheid. Dit zegt iets te zeggen over wie een stem krijgt en wie niet. Impliciete normen en machtsverhoudingen in de samenleving en de zorg die hier betrekking op hebben, zijn zichtbaar geworden in de zorgethische reflectie omtrent macht. Op basis van deze reflectie zijn een zestal aanbevelingen gedaan ten aanzien van de kenmerken van een vast aanspreekpunt in het ziekenhuis voor laaggeletterde oncologische patiënten

Density Field Reconstruction of an Overexpanded Supersonic Jet using Tomographic Background-Oriented Schlieren

A Tomographic Background-Oriented Schlieren (TBOS) technique is developed to aid in the visualization of compressible flows. An experimental setup was devised around a sub-scale rocket nozzle, in which four cameras were set up in a circular configuration with 30{\deg} angular spacing in azimuth. Measurements were taken of the overexpanded supersonic jet plume at various nozzle pressure ratios (NPR), corresponding to different flow regimes during the start-up and shut-down of rocket nozzles. Measurements were also performed for different camera parameters using different exposure times and f-stops in order to study the effect of measurement accuracy. Density gradients and subsequently two-dimensional line-of-sight integrated density fields for each of the camera projections are recovered from the index of refraction field by solving a Poisson equation. The results of this stage are then used to reconstruct two-dimensional slices of the (time-averaged) density field using a tomographic reconstruction algorithm employing the filtered back-projection and the simultaneous algebraic reconstruction technique. By stacking these two-dimensional slices, the (quasi-) three-dimensional density field is obtained. The accuracy of the implemented method with a relatively low number of sparse cameras is briefly assessed and basic flow features are extracted such as the shock spacing in the overexpanded jet plume

Decay of the supersonic turbulent wakes from micro-ramps

The wakes resulting from micro-ramps immersed in a supersonic turbulent boundary layer at Ma = 2.0 are investigated by means of particle image velocimetry. Two micro-ramps are investigated with height of 60% and 80% of the undisturbed boundary layer, respectively. The measurement domain is placed at the symmetry plane of the ramp and encompasses the range from 10 to 32 ramp heights downstream of the ramp. The decay of the flow field properties is evaluated in terms of time-averaged and root-mean-square (RMS) statistics. In the time-averaged flow field, the recovery from the imparted momentum deficit and the decay of upwash motion are analyzed. The RMS fluctuations of the velocity components exhibit strong anisotropy at the most upstream location and develop into a more isotropic regime downstream. The self-similarity properties of velocity components and fluctuation components along wall-normal direction are followed. The investigation of the unsteady large scale motion is carried out by means of snapshot analysis and by a statistical approach based on the spatial auto-correlation function. The Kelvin-Helmholtz (K-H) instability at the upper shear layer is observed to develop further with the onset of vortex pairing. The average distance between vortices is statistically estimated using the spatial auto-correlation. A marked transition with the wavelength increase is observed across the pairing regime. The K-H instability, initially observed only at the upper shear layer also begins to appear in the lower shear layer as soon as the wake is elevated sufficiently off the wall. The auto-correlation statistics confirm the coherence of counter-rotating vortices from the upper and lower sides, indicating the formation of vortex rings downstream of the pairing region

Application of AA-PSP to hypersonic flows: the double ramp model

Anodized Aluminium Pressure Sensitive Paint (AA-PSP) is known for its rapid response characteristics, making it a highly desirable technique when studying high-speed phenomenon on a global scale. The current study examines the efficacy of the AA-PSP technique, which is prepared with a more practical approach than that reported in literature, in analysing the flow characteristics of a double ramp model placed in hypersonic flow of M = 5. Three different flow angles of 0°, −2°, and −4° are studied. Two-dimensional colour schlieren visualisation, using a colour wheel, is employed alongside high sensitivity Kulite pressure tap data to corroborate the AA-PSP findings. The AA-PSP results show good correlation between the qualitative schlieren and ±8.9% discrepency with the quantitative pressure tap data. The more practical AA-PSP preparation proposed in the current study, which uses aluminium alloy 6-series rather than pure aluminium, is proved to have the response time and the accuracy to be applied to unsteady high-speed flows

Numerical and experimental investigations of the supersonic microramp wake

The flow past a microramp immersed in a supersonic turbulent boundary layer is studied by means of numerical simulations with the implicit large-eddy simulation technique and experiments conducted with tomographic particle image velocimetry. The experimental data are mostly used to verify the validity of the numerical results by ample comparisons on the time-averaged velocity, turbulent statistics, and vortex intensity. Although some discrepancies are observed on the intensity of the upwash motion generated by the streamwise vortex pair, the rates of the recovery of momentum deficit and the decay of streamwise vortex pair intensity are found in good agreement. The instantaneous flow organization is inspected, making use of the flow realizations available from implicit large-eddy simulation. The flow behind the microramp exhibits significant large-scale unsteady fluctuations. Notably, the quasi-conical shear layer enclosing the wake is strongly undulated under the action of Kelvin–Helmholtz (K–H) vortices. The resulted vortices induce localized high-speed arches in the outer region and a deceleration within the wake associated with ejection of low-momentum fluid. Because of the presence of the K–H vortex, the streamwise vortex filaments exhibit downward and outward motions. The further evolution of vortical structures within the wake features the development of K–H vortices from arch shape to full ring in the far wake, under the effects of the streamwise vortices, which induce an inward motion of the vortex legs and eventually connect the vortex at the bottom

An experimental realisation of steady spanwise forcing for turbulent drag reduction

We present an experimental realisation of spatial spanwise forcing in a turbulent boundary layer flow, aimed at reducing the frictional drag. The forcing is achieved by a series of spanwise running belts, running in alternating spanwise direction, thereby generating a steady spatial square-wave forcing. Stereoscopic particle image velocimetry is used to investigate the impact of actuation on the flow in terms of turbulence statistics, performance characteristics, and spanwise velocity profiles, for a waveform of $\lambda_x^+ = 401$. An extension of the classical spatial Stokes layer theory is proposed based on the linear superposition of Fourier modes to describe the non-sinusoidal boundary condition. The experimentally obtained spanwise profiles show good agreement with the extended theoretical model. In line with reported numerical studies, we confirm that a significant flow control effect can be realised with this type of forcing. The results reveal a maximum drag reduction of 26% and a maximum net power savings of 8%. In view of the limited spatial extent of the actuation surface in the current setup, the drag reduction is expected to increase further as a result of its streamwise transient. The second-order turbulence statistics are attenuated up to a wall-normal height of $y^+ \approx 100$, with a maximum streamwise stress reduction of 44% and a reduction of integral turbulence kinetic energy production of 39%

Investigation of the double ramp in hypersonic flow using luminescent measurement systems

Compression ramp flows in supersonic and hypersonic environments present unique flow patterns for shock wave-boundary layer interaction studies. They also represent the generic geometry of two-dimensional inlets and deflected control surfaces for re-entry vehicles. Therefore, a detailed knowledge of the flow behaviour created by such geometries is critical for optimum design. The flow is made more complicated due to the presence of separation regions and streamwise Görtler vortices. The objective of the current research is to study the behaviour and characteristics of the flow over the double ramp model placed in hypersonic flow at freestream Mach number of 5. Three different incidence angles of 0°, −2°, and −4° are studied using colour Schlieren and luminescent paints consisting of anodized aluminium pressure-sensitive paint (AA-PSP) and the temperature-sensitive paint (TSP) technique. The colour Schlieren provides description of the external flow while the global surface pressure and temperature distribution is obtained through the AA-PSP and TSP methods. The TSP technique also proves that it is very effective in identifying the location and properties of the Görtler vortices; revealing the effect of incidence on the magnitude and pattern of Görtler vortices formed

Icy moons' geysers: from laboratory to theory

Stars and planetary system