DSpace Collection:http://hdl.handle.net/10204/9072016-02-09T16:08:54Z2016-02-09T16:08:54ZA computationally efficient 3D finite-volume scheme for violent liquid–gas sloshingOxtoby, OFMalan, AGHeyns, JAhttp://hdl.handle.net/10204/83392015-12-18T21:55:22Z2015-10-01T00:00:00ZTitle: A computationally efficient 3D finite-volume scheme for violent liquid–gas sloshing
Authors: Oxtoby, OF; Malan, AG; Heyns, JA
Abstract: We describe a semi-implicit volume-of-fluid free-surface-modelling methodology for flow problems involving violent free-surface motion. For efficient computation, a hybrid-unstructured edge-based vertex-centred finite volume discretisation is employed, while the solution methodology is entirely matrix free. Pressures are solved using a matrix-free preconditioned generalised minimum residual algorithm and explicit time-stepping is employed for the momentum and interface-tracking equations. The high resolution artificial compressive (HiRAC) volume-of-fluid method is used for accurate capturing of the free surface in violent flow regimes while allowing natural applicability to hybrid-unstructured meshes. The code is parallelised for solution on distributed-memory architectures and evaluated against 2D and 3D benchmark problems. Good parallel scaling is demonstrated, with almost linear speed-up down to 6000 cells per core. Finally, the code is applied to an industrial-type problem involving resonant excitation of a fuel tank, and a comparison with experimental results is made in this violent sloshing regime.
Description: Copyright: 2015 Wiley. This is the pre-print version of the work. The definitive version is published in the International Journal for Numerical Methods in Fluids, Vol. 79(6), pp 306–3212015-10-01T00:00:00ZEulerian derivation of non-inertial Navier-Stokes equations for compressible flow in constant, pure rotationCombrinck, MLDala, LNLipatov, Ihttp://hdl.handle.net/10204/82282015-11-03T21:55:16Z2015-07-01T00:00:00ZTitle: Eulerian derivation of non-inertial Navier-Stokes equations for compressible flow in constant, pure rotation
Authors: Combrinck, ML; Dala, LN; Lipatov, I
Abstract: This paper presents an Eulerian derivation of the noninertial Navier-Stokes equations for compressible flow in constant, pure rotation. The method that is presented is an extension of work done by Kageyama & Hyodo where the momentum equation in incompressible conditions was derived. It is shown that no fictitious effects are present in the noninertial mass and energy conservation equations. The origin of the Coriolis and centrifugal forces in the momentum equation is shown.
Description: 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics - HEFAT 2015, Kruger National Park, South Africa, 20-23 July 20152015-07-01T00:00:00ZDeveloping the Inundu fast-jet electronics test and evaluation podJamison, KNkodi, Thttp://hdl.handle.net/10204/82252015-11-03T21:55:16Z2015-09-01T00:00:00ZTitle: Developing the Inundu fast-jet electronics test and evaluation pod
Authors: Jamison, K; Nkodi, T
Abstract: The development of the Inundu fast-jet electronics test and evaluation pod is described as a case study in the development of technology demonstrators. This pod is required to provide a “laboratory” environment for its electronics payload despite the rigors of being carried by fast-jet aircraft. This requirement, along with the need to be easily integrated with a wide variety of carriage aircraft resulted in a challenging development project.
Description: Eleventh SA INCOSE Conference - Systems Engineering - Shifting the barriers, CSIR International Convention Centre, Pretoria, 16-18 September 2015.2015-09-01T00:00:00ZDynamic stability of a seaplane in takeoffDala, Lhttp://hdl.handle.net/10204/81712015-10-12T21:55:15Z2015-01-01T00:00:00ZTitle: Dynamic stability of a seaplane in takeoff
Authors: Dala, L
Abstract: This research is based on the investigation into the dynamic stability associated with seaplanes during take-off. Various forces acting on a hydroplaning hull form have been empirically defined. Such empirical data have shown that under a certain set of conditions, a hydroplaning hull will begin to porpoise, an instability oscillation in both the vertical direction, and about the centre of gravity In order to investigate the porpoising motion, a shallow water flume was used. It was the first time that such facility has been used to simulate the dynamic motion of hydroplaning hull forms. An experimental method derived from the store release experiments was derived for the dynamics measurements. The equipment developed has led to an analysis of a flat plate hull porpoising in a supercritical channel. The porpoising limit has then been very well defined.
Description: Copyright: 2015 American Institute of Aeronautics and Astronautics. This is the pre-print version of the work. The definitive version is published in the Journal of Aircraft, vol. 52(3), pp 964-9712015-01-01T00:00:00ZOptimisation of a novel trailing edge concept for a high lift deviceBotha, JDMDala, LSchaber, Shttp://hdl.handle.net/10204/78892015-03-13T13:07:35Z2014-09-01T00:00:00ZTitle: Optimisation of a novel trailing edge concept for a high lift device
Authors: Botha, JDM; Dala, L; Schaber, S
Abstract: A novel concept (referred to as the flap extension) is implemented on the leading edge of the flap of a three element high lift device. The concept is optimised using two optimisation approaches based on Genetic Algorithm optimisations. A zero order approach which makes simplifying assumptions to achieve an optimised solution: and a direct approach which employs an optimisation in ANSYS DesignXplorer using RANS calculations. The concept was seen to increase lift locally at the flap. The solution to the zero order optimisation showed a decreased stall angle and decreased maximum lift coefficient against angle of attack due to early stall onset at the flap. The DesignXplorer optimised solution matched that of the baseline solution very closely. Computational Aeroacoustic simulations were performed using the DES (Detached Eddy Simulation) model, in 2D, on the baseline and DesignXplorer optimised solution. The DesignXplorer optimised concept steadied the shear layer that bounds the spoiler cove thus reducing noise from this vicinity by 10dB at frequencies over 7 000Hz.
Description: 29th Congress of the International Council of the Aeronautical Sciences (ICAS), St Petersburg, Russia 7-12 September 20142014-09-01T00:00:00ZDynamic transition from Mach to regular reflection of shock waves in a steady flowNaidoo, KSkews, BWhttp://hdl.handle.net/10204/78062014-12-03T21:55:15Z2014-07-01T00:00:00ZTitle: Dynamic transition from Mach to regular reflection of shock waves in a steady flow
Authors: Naidoo, K; Skews, BW
Abstract: The steady, two-dimensional transition criteria between regular and Mach reflection are well established. Little has been done on the dynamic effect on transition due to a rapidly rotating wedge. Results from experiments and computations done on steady and unsteady shock wave transition from Mach reflection to regular reflection, MR RR, are described. The measured motion and the initial shock incidence was used to mimic the experiment with a two-dimensional numerical code. The maximum rotation speed achieved at transition was approximately 2500°s(sup-1). Rapid wedge rotation was shown to have a significant measurable effect on transition. The code was also applied to the dependence of dynamic MR RR transition on other variables in the parameter space. These include rotation about the leading or trailing edge, initial incidence and rotation speed at two free-stream conditions. Impulsively started rotation in these cases was used with the rotation specified by M(subE)= c/a(sub8) where is constant angular velocity (negative anticlockwise), c the distance from the edge considered to the pivot point and a8 the free-stream sound speed. For the Mach numbers and range of rotation speeds tested, both the wedge and shock angle at transition decreased with increased rotation speed. The sensitivity of the transition angle to changing the rotation point from the trailing edge to the experimental model pivot point was investigated briefly at a free-stream Mach number of M=2.98 with M(subE)=-0.1. The wedge angle at transition increased by 1.5° and the shock angle at transition decreased by 1.5°, a significant variation. The effect of the initial incidence was also investigated. By reducing the initial wedge angle from 24.5 to 23.5° for these initial conditions the shock angle at transition decreased by approximately 1.8°, also a marked sensitivity. The flow field development for impulsive rotation about the wedge trailing and leading edges at M=1.93 for M(subE)=-0.075 was analysed in some detail. The flow field development is very sensitive to the rotation centre, more especially at large rotation rates. Four phases of the Mach stem development were identified in both cases. For rotation about the wedge leading edge the Mach stem height remains constant until the expansion waves arrive at the triple point. This is followed by an increase in Mach stem height, which then remains constant for a short period after which it decreases until transition to RR. For rotation about the wedge trailing edge the impulsive start generates a disturbance on the incident wave which propagates down the wave, through the triple point and down the Mach stem. The stem height is constant until the arrival of the incident wave disturbance. This causes a sudden decrease in Mach stem height. Subsequently, the Mach stem height remains constant for a short time, before it decreases until transition to RR. Similar effects in the variation of stem height with wedge angle occur at the higher Mach number of 2.98. It was demonstrated that MR can be maintained for a while at zero wedge incidence with a sufficiently large rotation rate of M(subE)=-0.1, with M=1.93, for both leading and trailing edge pivot points.
Description: Copyright: 2014 Cambridge University Press. This is an ABSTRACT ONLY. The definitive version is published in Journal of Fluid Mechanics, vol. 750, pp 385-4002014-07-01T00:00:00Z