Passive Boundary Layer Separation Control on a NACA2415 Aerofoil at High Reynolds Numbers

The design and analysis of a passive flow control system for a NACA2415 airfoil is under-taken. There exists a vast body of knowledge on airfoil boundary layer control with the use of controlled mass flux, but there is little work investigating passive mass flux-based methods. A simple duct system that uses the upper surface pressure gradient to force blowing near the leading edge and suction near the trailing edge is proposed and evaluated. 2D RANS analyses at Rec ≈ 1.27 × 106 were used to generate potential configurations for experimental tests. Initial computational results suggest drag reductions of approxi-mately 2 − 7% as well as lift increases of 4 − 5% at α = 10◦ and α = 12.5◦. A carbon composite-aluminum structure model that implements the most effective configurations, according to the CFD predictions, has been designed and fabricated. Experiments are performed to evaluate the CFD results and the feasibility the duct system

Utveckling av en Ny Kanal för grundläggande forskning av Turbulent strömning

Turbulent channel flows are of great interest for investigations of modified wall boundary conditions due to their well-understood characteristics and their broad applicability. In a reversal of typical trends, they can often be more difficult to investigate experimentally than to simulate owing to the far-reaching influence of corner effects as well as the need for development lengths in excess of 200 channel half-heights in order to produce high-quality flow. In order to rovice experimental results to compare directly with current and future computational studies conducted in the FSG group, a new experimental channel flow facility has been designed for use with state-of-the-art optical measurement techniques such as planar and stereoscopic µPIV. To further aid in understanding the flows in and around complex surfaces, a water-NaI solution will be used as the working fluid for refractive-index matched experiments. A holistic design approach has been taken, taking into consideration design, manufacturing, operational, and experimental requirements and limitations. The facility has been designed with modularity as a key focus and the channel is subdivided into three interchangeable sections with the capability to support a wide range of experimental set-ups and configurations with minimal modification. To produce a high-quality flow, the channel has an aspect ratio of 20 : 1 and a development length of 288δ preceding the test section. Based on inital design estimates of pressure losses in the system, a 11 kW centrifugal pump has been specified and is projected to allow the channel to reach its maximum design flow velocity of 10 m s¯¹. Reτ of 2300 can be achieved, allowing for investigations well into the turbulent regime which remain within the range of Reynolds numbers that can be resolved in DNS studies.Turbulenta kanalströmingar är mycket intressanta för undersökningar av modifierade väggrandvilkor på grund av deras väl förstådda egenskaper och allmän tillämpbarhet. MOt typiska trender kan de ofta vara mer komplicerat att undersöka med experimentalla metoder än med strömningsmekaniska beräkningar på grund av påverkan av sekundära flöden i hörn och krav på långa utvecklingssträckor större än 100 kanalhöjder för att garantera strömning av högsta kvalitet. För att ta experimentel data som kan jämföras direkt med aktuella och framtida beräkningsstudier från FSG gruppen, har en ny vattenkanal designats. Kanalen ska utnyttja de senaste optiska mätningsmetoder såsom planar och stetoskopisk µPIV, även med en lösning av vatten och NaI som driftsvätskan för att utföra brytningsindexmatchade experiment. Med ett holistisk utvecklingssätt har tillverknings-, operations-, och experimentella krav och begränsningar beaktats. Kanalen har designats med modularitet som stort fokus och är delad i tre utbytbara sträckor för att tillåta många olika experimentella monteringar och gestaltningar med minimala krav på förändring. För att ge hög strömningskvalitet har kanalen sidförhållande på 20 : 1 och en flödesutvecklingssträcka på 288δ innan mätsträckan. Baserat på inledande beräkning av tryckfallet i hela systemet valdes en 11 kW centrifugalpump. Med den pumpen kommer kanalen att nå sin maximala designhastighet på 10 m s¯¹ vilket ger Reτ = 2300. Detta innebär att undersökningar av turbulenta flöden, inom spännvidden av Reynolds tal som kan simuleras med numeriska metoder, kan utföras

Utveckling av en Ny Kanal för grundläggande forskning av Turbulent strömning

Turbulent channel flows are of great interest for investigations of modified wall boundary conditions due to their well-understood characteristics and their broad applicability. In a reversal of typical trends, they can often be more difficult to investigate experimentally than to simulate owing to the far-reaching influence of corner effects as well as the need for development lengths in excess of 200 channel half-heights in order to produce high-quality flow. In order to rovice experimental results to compare directly with current and future computational studies conducted in the FSG group, a new experimental channel flow facility has been designed for use with state-of-the-art optical measurement techniques such as planar and stereoscopic µPIV. To further aid in understanding the flows in and around complex surfaces, a water-NaI solution will be used as the working fluid for refractive-index matched experiments. A holistic design approach has been taken, taking into consideration design, manufacturing, operational, and experimental requirements and limitations. The facility has been designed with modularity as a key focus and the channel is subdivided into three interchangeable sections with the capability to support a wide range of experimental set-ups and configurations with minimal modification. To produce a high-quality flow, the channel has an aspect ratio of 20 : 1 and a development length of 288δ preceding the test section. Based on inital design estimates of pressure losses in the system, a 11 kW centrifugal pump has been specified and is projected to allow the channel to reach its maximum design flow velocity of 10 m s¯¹. Reτ of 2300 can be achieved, allowing for investigations well into the turbulent regime which remain within the range of Reynolds numbers that can be resolved in DNS studies.Turbulenta kanalströmingar är mycket intressanta för undersökningar av modifierade väggrandvilkor på grund av deras väl förstådda egenskaper och allmän tillämpbarhet. MOt typiska trender kan de ofta vara mer komplicerat att undersöka med experimentalla metoder än med strömningsmekaniska beräkningar på grund av påverkan av sekundära flöden i hörn och krav på långa utvecklingssträckor större än 100 kanalhöjder för att garantera strömning av högsta kvalitet. För att ta experimentel data som kan jämföras direkt med aktuella och framtida beräkningsstudier från FSG gruppen, har en ny vattenkanal designats. Kanalen ska utnyttja de senaste optiska mätningsmetoder såsom planar och stetoskopisk µPIV, även med en lösning av vatten och NaI som driftsvätskan för att utföra brytningsindexmatchade experiment. Med ett holistisk utvecklingssätt har tillverknings-, operations-, och experimentella krav och begränsningar beaktats. Kanalen har designats med modularitet som stort fokus och är delad i tre utbytbara sträckor för att tillåta många olika experimentella monteringar och gestaltningar med minimala krav på förändring. För att ge hög strömningskvalitet har kanalen sidförhållande på 20 : 1 och en flödesutvecklingssträcka på 288δ innan mätsträckan. Baserat på inledande beräkning av tryckfallet i hela systemet valdes en 11 kW centrifugalpump. Med den pumpen kommer kanalen att nå sin maximala designhastighet på 10 m s¯¹ vilket ger Reτ = 2300. Detta innebär att undersökningar av turbulenta flöden, inom spännvidden av Reynolds tal som kan simuleras med numeriska metoder, kan utföras

Design and setup of a wing model in the Minimum-Turbulence-Level wind tunnel

A reinforced fiber-glass model of a NACA 4412 wing profile is designed and set-up in the Minimum-Turbulence-Level (MTL) wind-tunnel facility at KTH Royal Institute of Technology (Sweden), aiming to complement the high-fidelity numerical work performed by our research group on the same airfoil, including direct numerical simulations (DNS) and large-eddy simulations (LES). The model has 65 pressure taps, and the set-up includes two mounting panels designed to allow for particle image velocimetry (PIV) and hot-wire anemometry (HWA) measurements of the boundary layer on the model (both to be performed in a future campaign). In this first experimental campaign pressure scans are carried out at four angles of attack of interest (0, 5, 10 and 12 degrees), and at four different Reynolds numbers based on chord length and inflow velocity (200,000, 400,000, 1,000,000 and 1,640,000). The experimental data is then compared with reference high-fidelity and k- SST RANS simulations. The preliminary results show an excellent agreement with the reference numerical data, specially at the moderate angles of attack.QC 20210525</p

Design and setup of a wing model in the Minimum-Turbulence-Level wind tunnel

A reinforced fiber-glass model of a NACA 4412 wing profile is designed and set-up in the Minimum-Turbulence-Level (MTL) wind-tunnel facility at KTH Royal Institute of Technology (Sweden), aiming to complement the high-fidelity numerical work performed by our research group on the same airfoil, including direct numerical simulations (DNS) and large-eddy simulations (LES). The model has 65 pressure taps, and the set-up includes two mounting panels designed to allow for particle image velocimetry (PIV) and hot-wire anemometry (HWA) measurements of the boundary layer on the model (both to be performed in a future campaign). In this first experimental campaign pressure scans are carried out at four angles of attack of interest (0, 5, 10 and 12 degrees), and at four different Reynolds numbers based on chord length and inflow velocity (200,000, 400,000, 1,000,000 and 1,640,000). The experimental data is then compared with reference high-fidelity and k- SST RANS simulations. The preliminary results show an excellent agreement with the reference numerical data, specially at the moderate angles of attack.QC 20210525</p

Experimental and numerical investigation of turbulent boundary layers with strong pressure gradients

A detailled investigation of a turbulent boundary-layer flow subjected to a strong adverse pressure gradient (APG) is presented. The main goal is to define a test case for the validation and improvement of RANS-turbulence models from wind-tunnel measurement data collected over the course of multiple measurement campaigns, including volumetric Lagrangian Particle Tracking (LPT) and stereoscopic PIV (SPIV), and oil-film interferometry. The boundary layer at a zero-pressure gradient (ZPG) reference position upstream of the pressure gradient region is found to exhibit a mild deviation from a canonical flow in the sense that the boundary layer thickness and hence the Reynolds number based on the momentum loss thickness Reθ are larger than for a canonical flow. Moreover a mild deviation in skin-friction coefficient and shape factor is found. The experimental data using LPT and SPIV in a spanwise domain around the centerplane show an increase of the boundary layer thickness compared to a canonical flow and a spanwise variability. This can possibly be attributed to the wake flow of the turning vanes upstream of the nozzle and the test-section. For the mean velocity profiles, this leads to a deviation in the law-of-the-wake region compared to canonical flows. The inner region, which is essential for the turbulence modelling and validation, is largely unaffected and agrees well with canonical flows. The Reynolds stresses are also in good agreement with canonical flows. Regarding the ultimate aim to define the computational set-up for RANS simulations, a pragmatic approach is pursued. The inlet length of the test-section is increased to account for the larger boundary layer thickness, corresponding to an adjustment of the virtual origin of the boundary layer. This leads to a good matching with the experimental mean velocity profile and the boundary layer parameters at the ZPG reference position. Downstream, in the pressure gradient region, which is the focus region for the improvement and validation of RANS turbulence models, the deviation between the RANS results and the experimental data is found to be almost insensitive with respect to minor changes in the computational set-up. In the strong APG region, the clearly most important deviation between the numerical predictions and the experimental data is due to the RANS turbulence models used