| 1. |
- Lim, Shyang Maw, et al.
(författare)
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Wall Treatment Effects on the Heat Transfer in a Radial Turbine Turbocharger
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer Science+Business Media B.V.. - 9783319306001 ; , s. 439-447
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Konferensbidrag (refereegranskat)abstract
- Contradicting results about heat transfer effects on the performance of turbine turbocharger motivated this study. It was aimed to assess the effects that the wall treatment in a numerical sense has on the performance of a radial turbine of automotive turbocharger operating under a continuous flow condition. Adiabatic and non-adiabatic conditions were analyzed by using Unsteady Reynolds Averaged Navier-Stokes (URANS), Large Eddy Simulations (LES) and Detached Eddy Simulations (DES) approaches. When considering heat transfer, heat transfer loss at various locations is highly dependent on the near-wall modelling approach employed. Development of thermal boundary layer in the upstream region of turbine affects how the gas is convected in the downstream components, such as the scroll and the rotor. As long as the deviation in predicting thermal boundary layer does not affect the prediction of gas temperature at the inlet and outlet of the rotor, the difference in turbine power prediction by different near-wall modelling approaches was found to be small.
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| 2. |
- Nadali Najafabadi, Hossein, et al.
(författare)
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On the Characteristics of the Jet in Film Cooling Applications
- 2016
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Ingår i: PROCEEDINGS OF THE 5TH INTERNATIONAL CONFERENCE ON JETS, WAKES AND SEPARATED FLOWS (ICJWSF2015). - Cham : SPRINGER INT PUBLISHING AG. - 9783319306025 - 9783319306001 ; , s. 449-455
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Konferensbidrag (refereegranskat)abstract
- Numerical and experimental investigations are conducted to study the jet characteristics on the pressure side of a film-cooled turbine guide vane. CFD simulations, including both the steady RANS turbulence model, k - omega shear stress transport (SST), as well as the hybrid approach, Scale-Adaptive Simulation (SAS), are utilized to comprehend the turbulent flow structures and the vortex dynamics associated to the film cooling jet. For this purpose the commercial CFD code FLUENT has been utilized to study flow with injection of coolant through fan-shaped holes for two blowing ratios (0.6 and 1.2). Although, both turbulence models predict the vortical structures and jet dynamics similarly, the findings suggest that by resolving large energy containing vortices, the SAS model can improve the modeling of mixing properties and thereby approximation of the surface temperature.
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| 3. |
- Nilsson, Johan, et al.
(författare)
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Passive load control in backward-facing step flow by using chevrons
- 2016
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Ingår i: Proceedings of the 5th International Conference on Jets, Wakes and Separated Flows, ICJWSF 2015. - Cham : Springer International Publishing. - 9783319306001 ; 185, s. 223-239
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Konferensbidrag (refereegranskat)abstract
- The ability of chevrons at the top edge of a backward-facing step to reduce downstream surface pressure fluctuations is investigated numerically. Three different chevron configurations are compared against a baseline case without chevrons. Low frequency reduction in the surface pressure fluctuations is observed for two of the configurations. The chevrons do not appear to have a significant effect on the flow as the mean reattachment length for all configurations is nearly constant and there is only a small increase in streamwise turbulence for one configuration with the other configurations unchanged.
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| 4. |
- Nygård, Alexander, et al.
(författare)
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Analysis of vortical structures in intermittent jets
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer Science+Business Media B.V.. - 9783319306001 ; , s. 3-10
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Konferensbidrag (refereegranskat)abstract
- The manipulation of jets has since long been subject to research, due to the wide range of industrial applications in which they are used. A vast number of numerical and experimental studies concerning the physics of the breakup process of continuous jets have been published. Improvements in mixing and ambient gas entrainment have been reported experimentally when using intermittent injection, although the responsible mechanisms have not yet been completely revealed. This work presents a systematic analysis of the mechanisms of jet breakup and mixing with the surrounding fluid and its relation to vorticity generation and transport. Comparisons aremade between the redistribution of vorticity and the engulfment of ambient fluid into the core region for different injection strategies.
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| 5. |
- Segalini, Antonio
(författare)
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Experimental and analytical investigation of forest clearings
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer. - 9783319306001 ; , s. 339-346
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Konferensbidrag (refereegranskat)abstract
- A numerical model of forest clearings is proposed based on the linearised Euler equations. The forest is replaced by distributed body forces that decrease the flow momentum entrained inside the canopy. The model is compared with available wind-tunnel measurements of clearings areas. It is observed that the model deviates from themeasurements over the forest surface, but the performance improve over the clearing surface, probably associated to an incorrect evaluation of the forest intensity. The proposed model suggests that the clearing is associated to an internal boundary layer with intensity function of the clearing length.
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| 6. |
- Szász, Robert-Zoltán, et al.
(författare)
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Algorithm for automatic quantification of flashback and flash forward events from high-speed chemiluminescence recordings
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer Science+Business Media B.V.. - 9783319306001 - 9783319306025 ; , s. 519-526
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Konferensbidrag (refereegranskat)abstract
- Three methods are employed to identify and quantify flashback and flash forward events based on chemiluminescence recordings of swirling flames. The approaches differ in the procedure to determine the instantaneous flame position. The results revealed that the most robust method is to determine a threshold relative to the instantaneous maximum intensity. Analysis of the complete dataset indicated that flashback events are significantly slower than flash forward events.
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| 7. |
- Trip, Renzo, et al.
(författare)
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An experimental study on the relation between the wake inlet conditions and the near wake topology
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer Science+Business Media B.V.. - 9783319306001 ; , s. 133-138
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Konferensbidrag (refereegranskat)abstract
- A study on the relation between the wake inlet conditions and the wake characteristics of a bluff body by means of Particle Image Velocimetry is presented. The wake inlet condition, being a laminar boundary layer at the trailing edge of the body, are varied by means of wall-suction. Measurements are carried out at Reh = 6.7 × 103 based on the body thickness h. The induced radius of curvature of the streamlines is shown to be a promising parameter in explaining the increase in base drag and decrease in vortex shedding frequency associated with a thinner boundary layer.
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| 8. |
- Vinuesa, R., et al.
(författare)
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Characterization of the massively separated wake behind a square cylinder by means of direct numerical simulation
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer Science+Business Media B.V.. - 9783319306001 ; , s. 259-266
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Konferensbidrag (refereegranskat)abstract
- The massively separated wake behind a wall-mounted square cylinder is investigated by means of direct numerical simulation (DNS). The effect of inflow conditions is assessed by considering two different cases with matching momentum thickness Reynolds numbers Reθ ≃ 1000 at the location of the cylinder: one with a fully-turbulent boundary layer as inflow condition, and another one with a laminar boundary layer. The main simulation is performed by using the spectral element code Nek5000. While in the laminar-inflow simulation the horseshoe vortex forming around the cylinder can be observed in the instantaneous flow fields, this is not the case in the turbulent-inflow simulation. Besides, the streaks in the turbulent case become greatly attenuated on both sides of the obstacle. By analyzing the Reynolds shear stress uv, we show that this is due to the modulation of the horseshoe vortex by the turbulence from the incoming boundary layer.
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| 9. |
- Örlü, Ramis, et al.
(författare)
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Generalization of the diagnostic plot to higher-order moments in turbulent boundary layers
- 2016
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Ingår i: Springer Proceedings in Physics. - Cham : Springer. - 9783319306001 ; , s. 333-338
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Konferensbidrag (refereegranskat)abstract
- The present work extends the diagnostic plot concept for the streamwise turbulence intensity in wall-bounded turbulent flows [Alfredsson and Örlü, Eur. J. Mech. B/Fluids 42, 403 (2010)], and generalizes it for higher-order (even and odd) moments, thereby providing a general description of the probability density distribution of streamwise velocity fluctuations. Turbulent boundary layer data up to a friction Reynolds number of 20000 are employed and demonstrate the feasibility of the diagnostic plot to scale data throughout the logarithmic and wake regions.
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