| 1. |
- Adamu, Abdulmalik, et al.
(författare)
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An investigation of superstructure length on bi-stable ship wake flow
- 2024
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Ingår i: Ocean Engineering. - 0029-8018. ; 312
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Tidskriftsartikel (refereegranskat)abstract
- The variation in the geometry of a ship model has the potential to eliminate the flow asymmetry in ship wake and improve its aerodynamic performance. This study investigates the impact of the length of superstructure on the wake flow bi-stability of the ship model using IDDES at Re = 8 × 104. Also, this article studied the effect of ship's funnel structure using two models, with and without funnel, on the wake flow asymmetry, providing smooth transition into the study of the length of superstructure. The result indicates that when the funnel is removed, the length of flow reattachment after separation at the hanger increases for the top step and decreases for the second step for the case with no funnel. The asymmetric flow at wake persists, however, the configuration is different, showing difference in flow state. When the length of the superstructure is reduced, the turbulence at the wake increases, the size of recirculation bubble at the flight deck and behind the stern reduces and the overall pressure area decreases significantly. Behind the stern, all three cases indicate an asymmetrical flow, however, compared to Case 1, the asymmetry at the flight deck in Case 2 is weak, while a symmetrical flow is achieved with Case 3. Consequently, this research proposes a novel approach to improving wake flow and ensure safe aircraft take-off and landing operations on the ship deck.
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| 2. |
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| 3. |
- Basara, Branislav, 1964, et al.
(författare)
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A further enhancement of the PANS method for calculations with moving meshes or with transient boundaries
- 2015
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Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 0, s. 287-290
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Konferensbidrag (refereegranskat)abstract
- The Partial Averaged Navier-Stokes (PANS) model changes seamlessly from Reynolds-Averaged Navier-Stokes (RANS) to the direct numerical solution of the Navier-Stokes equations (DNS) as the unresolvedto-total ratios of kinetic energy and dissipation are varied. An efficient use of the PANS method relies on a definition and calculations of resolution parameters. In the standard approach, the integral scale of turbulence is obtained by using resolved turbulence calculated as difference between instantaneous filtered velocity and the averaged velocity field. Such approach is impractical for cases with moving geometries or with transient boundaries and for example, especially for calculations of engines, which will be shown in this paper, due to a long cycle-to-cycle averaging in order to supply the optimum resolution parameter. This paper deals with an alternative approach which doesn't need a time average velocity field.
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| 4. |
- Basara, Branislav, 1964, et al.
(författare)
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Calculations of turbulent flow through a staggered tube bank
- 2017
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Ingår i: Proceedings of the Thermal and Fluids Engineering Summer Conference. - 2379-1748. ; 2017-April, s. 1563-1566
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Konferensbidrag (refereegranskat)abstract
- The primary aim of this paper is to numerically investigate the crossflow in a staggered tube bank by using a variable-resolution method. Experimental data of Simonin and Barcoude (1988) is available in the ERCOFTAC database. There are also few ERCOFTAC workshops, e.g. 1993, 19999, which were considering this test case primarily for checking the performance of the Reynolds-Averaged Navier-Stokes (RANS) models. Therefore, there are number of results with very different models which can be found in the literature. The work presented here aims to add one more set of results but this time with recently advanced variable resolution method, namely the Partially-Averaged Navier-Stokes (PANS). This method (Girimaji, 2006) belongs to so called bridging or seamless methods. The PANS approach adjusts seamlessly from the Reynolds-Averaged Navier-Stokes (RANS) to the Direct Numerical Solution (DNS) of the Navier-Stokes equation. The results are largely improved by using the PANS as for example shown in Basara (2015). This turbulence bridging method is derived from the RANS model equations. It inevitably improves results when compared with its corresponding RANS model if more scales of motions are resolved. This is done by varying the unresolved-to-total ratios of kinetic energy and dissipation. In the practice, the parameter which determines the unresolved-to-total kinetic energy ratio is defined by using the grid spacing and calculated integral length scale of turbulence. When the grid size is smaller, then more of the turbulent kinetic energy can be resolved. Usually, the integral scale of turbulence is obtained by summing up resolved turbulence, calculated as difference between instantaneous filtered velocity and the averaged velocity field, and unresolved turbulence obtained from its own equation. The turbulence model adopted in the present PANS variant is the four-equation ζ - f formulation (Hanjalic et al., 2004) which is the variant of more known v2-f model based on the elliptic relaxation concept.). As this model represents a practical and accurate RANS choice for a wide range of industrial applications, especially when used in conjunction with the universal wall approach (Popovac and Hanjalic, 2007, Basara, 2006), its PANS variant therefore guarantees that the proper near-wall model is used when fkis of a higher value. Therefore, the near-wall PANS variant of Basara et al. (2011) was used in the present study. The PANS model is implemented into the commercial CFD code AVL FIRE (AVL FIRE Manual, 2011).
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| 5. |
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| 6. |
- Basara, Branislav, 1964, et al.
(författare)
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Effects of convection schemes on hybrid RANS-LES calculations
- 2018
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Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer International Publishing. - 1612-2909 .- 1860-0824. ; 137, s. 145-155
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Tidskriftsartikel (refereegranskat)abstract
- Nowadays it is commonly accepted to report on convections schemes in the case of Large Eddy Simulations. However, this is still not mandatory for the hybrid Reynolds-Averaged Navier-Stokes (RANS)—LES calculations. Therefore, this paper intends to show that the effects of convection scheme is equally important for hybrid RANS-LES calculations as well as for LES runs. We choose here the Partially-Averaged Navier–Stokes (PANS) model as the representative hybrid RANS-LES model but the conclusions derived in this work are equally applicable to other methods. The aim of the paper is to provide a proper criterion from the employment of higher order differencing schemes. The paper will assess two approaches, namely step functions where central-differencing scheme is used in the regions with a lower unresolved turbulent kinetic energy and a continuous function which depends on the ratio between unresolved and total kinetic energy. The results will be presented for the flow around the square cylinder. Direct numerical simulation (DNS) data and measurements are available for comparisons.
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| 7. |
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| 8. |
- Basara, B., et al.
(författare)
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Near-Wall Formulation of the Partially Averaged Navier-Stokes Turbulence Model
- 2011
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Ingår i: AIAA Journal. - : American Institute of Aeronautics and Astronautics (AIAA). - 1533-385X .- 0001-1452. ; 49:12, s. 2627-2636
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Tidskriftsartikel (refereegranskat)abstract
- The variable-resolution partially averaged Navier-Stokes bridging strategy is applied to the four-equation k-epsilon-zeta-f turbulence model. In this approach, the popular two-equation model is enhanced with an additional transport equation for the velocity scale ratio zeta and an equation for the elliptic relaxation function f for the purpose of improved near-wall behavior. By using the elliptic relaxation technique to model the wall blocking effect, the new four-equation partially averaged Navier-Stokes model retains the simplicity of the previous two-equation partially averaged Navier-Stokes versions but significantly improves predictions in the near-wall region. The proposed partially averaged Navier-Stokes k-epsilon-zeta-f model is evaluated in a turbulent channel flow and flow around a three-dimensional circular cylinder mounted vertically on a flat plate. The results clearly show benefits of the improved near-wall modeling and extend partially averaged Navier-Stokes applicability to a broader range of smooth bluff-body separated flows.
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| 9. |
- Basara, Branislav, 1964, et al.
(författare)
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PANS methodology applied to elliptic-relaxation based eddy viscosity transport model
- 2010
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Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1612-2909 .- 1860-0824. - 9783642141386 ; 110, s. 63-69
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Konferensbidrag (refereegranskat)abstract
- The Partially-Averaged Navier-Stokes (PANS) approach is a recently proposed method which changes seamlessly from the Reynolds-Averaged Navier-Stokes (RANS) model equations to the direct numerical solution (DNS) of the Navier-Stokes equations as the unresolved-to-total ratios of kinetic energy and dissipation are varied. Two variants of the PANS model are derived up to now, one based on the k-epsilon formulation and the other based on the k-omega formulation. We introduce here another variant which is based on four equation eddy viscosity transport model, namely zeta-f turbulence model. Benefits of using such near wall model inside the PANS concept are clearly presented in this paper.
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| 10. |
- Basara, Branislav, 1964, et al.
(författare)
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PANS VS. LES FOR COMPUTATIONS OF THE FLOW AROUND A 3D BLUFF BODY
- 2008
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Ingår i: “7th International ERCOFTAC Symposium on “Engineering Turbulence Modelling and Measurements”, June 4-6, 2008, Limassol, Cyprus..
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Konferensbidrag (refereegranskat)abstract
- This paper presents comparisons between recentlyproposed Partially-Averaged Navier-Stokes(PANS) method with the Large Eddy Simulation(LES) for the flow around the Ahmed bluff body.PANS model changes seamlessly from Reynolds-Averaged Navier-Stokes (RANS) to the direct numericalsolution of the Navier-Stokes equations(DNS) as the unresolved-to-total ratios of kinetic energyand dissipation are varied. The parameter whichdetermines the unresolved-to-total kinetic energy ratiois defined based on the grid spacing and it is dynamicallyadjusted at each point at the end of everytime step. The main target of this paper is to show ifPANS obtains comparable results with LES calculationson finer meshes and improves results on coarsermeshes. In other words, the question to be answeredis whether PANS can provide the optimum solutionfor every computational mesh. This will be achievedby comparing PANS calculations on two differentcomputational meshes: 3.4 mil.(grid A), and 8.0 mil.(grid B), with LES calculations on grid A and additionaltwo grids consisting of 9.5 mil. cells (grid C)and 16.5 mil. cells (grid D).
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