Research Publications/Outputs

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An aerodynamic CFD analysis of inlet swirl in a micro-gas turbine combustor
(2023-07) Meyers, Bronwyn C; Grobler, Jan-Hendrik; Snedden, GC
A combustor was designed for a 200N micro-gas turbine [1, 2] using the NREC preliminary combustor design method [1, 2, 3]. During the design process, there are various aspects where there are no definitive methodologies for specifying the design detail, such as the design of the hole-sets, and multiple options can be derived that can satisfy the required mass flow split and pressure drop for a particular hole-set.
Decoupling store and parent aerodynamics for fast prediction of subsonic store trajectories
(2024-09) Mthembu, N; Ndlovu, Hlamulo P; Ndebele, Bright B; Jamison, Kevin A; Zwane, Lindokuhle
A method optimised for efficient prediction of subsonic store separation trajectories is described and demonstrated using a wind-tunnel test case. The FastTraj method uses a decoupled flow field approach where it is assumed that in most attached flow subsonic store separation scenarios the presence of the store has little impact on the perturbed flow field generated by the parent aircraft. The inviscid perturbed flow field of the parent aircraft is computed using computational fluid dynamics codes and is captured using a grid. The store aerodynamic model is generated elsewhere and Missile Datcom is used to segment the store model to approximate the effect of the perturbed flow field changing along the length of the store. The 6-DOF trajectory solver interpolates the aerodynamic grid from the parent aircraft to determine the local flow vector at each reference point on the segmented store, in addition to the local flow vector due to the motion of each segment. Good comparisons with the wind-tunnel data are achieved showing that the method’s speed is not at the expense of accuracy and that it is necessary to segment the store to achieve good results.
Fatigue properties of additively manufactured tool steel
(2024-09) Johnston, Charmaine M; Tshabalala, Lerato C; Davids, M
Tool steel is routinely used by the Experimental Aerodynamics group at the Council for Scientific and Industrial Research (CSIR), South Africa, to manufacture critical components for wind tunnel testing. This steel is known for its high strength properties in both tension and compression, and has a good combination of machinability, ductility, and fracture toughness. The emergence of the Additive Manufacturing (AM) technology provides an alternative to traditional manufacturing procedures in the production of wind tunnel model parts and instrumentation; however, use of the AM technology requires knowledge, inter alia, of the fatigue characteristics of the AM materials. Test specimens were manufactured from tool steel powder using the Selective Laser Melting (SLM) technology and subjected to fatigue and tensile tests. The thermal treatments were used for stress relieving and aging the additively manufactured part; the processes used in this project were found to have an adverse effect on the properties of the material.
Fatigue properties of additively manufactured tool steel
(2024-09) Johnston, Charmaine M; Tshabalala, Lerato C; Davids, M
Tool steel is routinely used by the Experimental Aerodynamics group at the Council for Scientific and Industrial Research (CSIR), South Africa, to manufacture critical components for wind tunnel testing. This steel is known for its high strength properties in both tension and compression, and has a good combination of machinability, ductility, and fracture toughness. The emergence of the Additive Manufacturing (AM) technology provides an alternative to traditional manufacturing procedures in the production of wind tunnel model parts and instrumentation; however, use of the AM technology requires knowledge, inter alia, of the fatigue characteristics of the AM materials. Test specimens were manufactured from tool steel powder using the Selective Laser Melting (SLM) technology and subjected to fatigue and tensile tests. The thermal treatments were used for stress relieving and aging the additively manufactured part; the processes used in this project were found to have an adverse effect on the properties of the material.
Feasibility of rotor fault detection from a fluid dynamics perspective
(2020-05) Robbins, SL; Heyns, PS; Heyns, Johan A
The majority of condition monitoring techniques employed today consider the acquisitioning and analysis of structural responses as a means of profiling machine condition and performing fault detection. Modern research and newer technologies are driving towards non-contact and non-invasive methods for better machine characterisation. Yet current literature lacks investigations into the monitoring and detection of anomalous conditions using fluid dynamic behaviour. If one considers unshrouded rotors which are exposed to a full field of fluid interaction such as helicopter rotors and wind turbines amongst others, such an approach could potentially be beneficial. In this work, time-dependent fluid dynamic data is numerically simulated around a helicopter tail rotor blade using URANS CFD with the Open FOAM software package. Pressures are probed at locations in the field of the rotor and compared to results attained in an experimental investigation where good correlation is seen between the results. A blade is modelled with a seeded fault in the form of a single blade out of plane by 4°. Comparisons are drawn between the blade in its ‘healthy’ and ‘faulty’ configurations. It is observed that the fault can be detected by deviations in the amplitudes of the pressure signals for a single revolution at the probed locations in the field. These deviations manifest as increases in the frequency spectrum at frequencies equivalent to the rotational rate (1 per revolution frequencies). The results described are assessed for their fidelity when the pressure is probed at different locations in the domain of the rotor. Deviations in the pressure profiles over the surface of the blades are also seen for the asymmetric rotor configuration, but may prove too sensitive for practical application.
The first step towards decarbonized air mobility in South Africa: A hydrogen powered unmanned aerial vehicle
(2022-11) Jamison, Kevin A; Naidoo, Purusha; Ramotsabi, Katleho
The South African government is investing in the use of hydrogen fuel as a pathway towards decarbonising transport sectors. Hydrogen is likely to be a viable option for decarbonising air transport and it is being investigated intensively around the world. The merits of hydrogen as an air transport fuel relative to other alternatives are discussed. To localise expertise in hydrogen powered aviation in South Africa it was decided that a small hydrogen fuel cell powered unmanned aerial vehicle (UAV) would be developed as a first step. Once hydrogen powered flight is demonstrated at the UAV scale then the expertise gained can be scaled up to the general aviation sector and ultimately, commercial aviation. A concept of the UAV and its hydrogen fuel cell propulsion unit is presented and discussed.
Flat Plate Flutter in a Supersonic Flow Field
(2024-07) Ndebele, Bright B
The interaction of a two-dimensional cantilevered elastic flat plate with a supersonic flow field was investigated numerically using StarCCM+. The plate was 0.4 m in length and inclined at 15∘ to the freestream at three Mach numbers (1.2, 1.35, and 1.45). The flat plate was assumed to be aluminium. Using StarCCM+, the inviscid Navier-Stokes equations were solved, and the fluid-structure interaction resolved. This way, the flow field around the plate and the plate deflection were calculated. The results indicated that at Mach 1.2, the plate exhibited a steadystate deflection, while at the other investigated Mach numbers, limit cycles were observed. The deformation of the plate caused a flow compression at the top, resulting in a weak shock at Mach 1.2 and strong shocks at 1.35 and 1.45. These findings provide insight into the dynamic response of the plate and the corresponding flow characteristics at different Mach numbers.
The numerical aerodynamic investigation of swirling inlet flow in a vaporizer tube micro-gas turbine combustor
(2022-09) Meyers, Bronwyn C; Grobler, Jan-Hendrik; Snedden, GC
A combustor was designed for a 200N micro-gas turbine for the model aircraft industry using the NREC design method. Multiple designs resulted which varied in terms of annular area split configuration, hole area splits and relative hole positions. In a previous study two likely preferable designs were selected using a devised scoring method. For this study, the effect of inlet (diffuser outlet) swirl on the internal aerodynamics of the two combustor designs previously chosen was investigated using a RANS CFD analysis. For each of the two designs a set of varying flow angles was applied at the inlet to the simulation domain. The effect on the establishment of the primary zone features is of specific interest; however, the effects and consequences of the swirl throughout the combustor were investigated. Some of the results such as mass flow splits and pressure drop are already quantitative in nature, however, the evaluation of the quality of the recirculation zone, mixing and outlet plane flow are of a more qualitative nature. A scoring system was previously devised in order to apply a quantitative value to the qualitative aspects of the flow, such as Recirculation zone (Rz), Outlet and Mixing, which are initially analysed subjectively. For each feature, the designs were subjectively evaluated relative to each other and given a rating/score. This scoring methodology for ranking different combustor designs proved to be an effective method for evaluating the effect of inlet swirl on the flow features and behaviour of the chosen combustor designs and thus provide an indication of the likely performance changes to be expected. The methodology was able to indicate which of the two top designs was the better option when considering inlet swirl, however the potential for improvement was revealed when considering scoring in a global context. This study suggests that for this engine, the inlet swirl could allow for the removal of NGV before the turbine since the flow is fairly well conditioned and “pre-turned” due to the swirling flow progressing to the outlet of the combustor. The removal of the traditional NGV allows for a reduction in NGV pressure losses which compensates for the increased combustor pressure loss experienced due to increased inlet swirl.
Selecting munition design features and operational concepts using a trade study supported by simulated operational scenarios
(2021-09) Jamison, Kevin A; Roux, Jeanne M; Zwane, Lindokuhle
A development of an existing munition aimed at an entirely new target set was planned. A trade study was performed to identify the key design features and employment concepts that generate the optimum outcomes in a demanding operational scenario. The trade study was configured as a Multi-Attribute Tradespace Exploration (MATE) using a trade study matrix that considers the key design and operational variables to be investigated. The baseline munition concept was parameterised such that design changes are described by those key variables. For each set of tradespace variables the baseline munition design was optimised to maximise its operational range while complying with constraints and meeting the design requirements. The characteristics of each optimised munition was determined for input into a simulation model of an operational scenario modelling the operational environment and the threat systems to determine the best performing munition solution. This paper outlines the implementation of the MATE approach and the lessons learned that can be incorporated in the broader systems engineering discipline.
A systems engineering framework for integrating stores with aircraft
(2023-10) Jamison, Kevin A
Military and some civilian aircraft need to carry stores to perform their mission. There is a huge diversity of carriage aircraft and types of stores ranging from missiles, drop tanks, space launchers, and rescue equipment. Adding stores to aircraft has a significant impact on the airworthiness of the carriage aircraft. Stores affect aircraft in multiple ways, making the integration of stores a complex multidisciplinary engineering problem that is often costly to resolve. The current regulatory and technical framework for store integration is reviewed. A systems engineering approach to store integration is presented where both aircraft and stores are designed from the outset to facilitate store integration. While some examples of this being done can be found, much still needs to be done to facilitate cost-effective store integration. Two case studies are presented and discussed showing the utility of this approach.
Thermal aging of additively manufactured maraging steel
(2024-12) Davids, Micaela; Johnston, Charmaine M; Tshabalala, Lerato C
The mechanical properties of Additively Manufactured M300 Maraging Steel were tested after two thermal treatments. It was found that the stress-relief process resulted in tensile strength comparable to the powder specification, but low ductility compared to the specifications, whilst the addition of an aging process resulted in substandard tensile strength and extreme brittleness. The results of a hardness test and the tensile properties achieved suggest that the material was embrittled by both thermal processes. The samples were inspected using an Optical Microscope (OM) after testing.
Two dimensional vortex shedding from a rotating cluster of cylinders
(2023-09) Ndebele, Bright B; Gledhill, IMA
The dynamics of two-dimensional vortex shedding from a rotating cluster of three cylinders was investigated using Computational Fluid Dynamics (CFD) and Dynamic Mode Decomposition (DMD). The cluster was formed from three circles with equal diameters in mutual contact and allowed to rotate about an axis passing through the cluster centroid. While immersed in an incompressible fluid with Reynolds number of 100, the cluster was allowed to rotate at non-dimensionalised rotation rates (Ω) between 0 and 1. The rotation rates were non-dimensionalised using the free-stream velocity and the cluster characteristic diameter, the latter being equal to the diameter of the circle circumscribing the cluster. CFD simulations were performed using StarCCM+. Dynamic Mode Decomposition based on the two-dimensional vorticity field was used to decompose the field into its fundamental mode-shapes. It was then possible to relate the mode-shapes to lift and drag. Transverse and longitudinal mode-shapes corresponded to lift and drag, respectively. Lift–drag polars showed a more complex pattern dependent on Ω in which the flow fields could be classified into three regimes: Ω less than 0.3, greater than 0.5, and between 0.3 and 0.5. In general, the polars formed open curves in contrast to those of static cylinders, which were closed. However, some cases, such as Ω = 0.01, 0.22, and 0.28, formed closed curves. Whether a lift-drag polar was closed or open was deduced to be determined by the ratio of Strouhal numbers calculated using lift and drag time series, with closed curves forming when the ratio is an integer.
Validation of CSIR wind tunnel calibration data under different barometric conditions using comparisons with a reference laboratory
(2024-09) Dikgale, Moyahabo S
This paper presents the validation of the calibration data of the Council of Scientific and Industrial Research (CSIR) Calibration Wind Tunnel by evaluating its accuracy under different barometric conditions. Using a reference laboratory with established calibration standards as a benchmark, we compared the CSIR wind tunnel's measurements against those from the reference facility across a range of wind speeds. Our methodology involved a series of controlled calibration designed to assess the consistency and reliability of the wind tunnel's calibration data in different atmospheric conditions. The results demonstrated that the CSIR wind tunnel maintains a high degree of accuracy and reliability, with deviations falling within acceptable limits relative to the reference laboratory's data. This validation highlights the robustness of the CSIR wind tunnel calibration process and its capability to deliver precise wind speed measurements’ calibration across different environmental conditions.
Wind tunnel testing - A career at high speed - while standing still! 1990-2022
(2022-11) Morelli, Mauro F
This item is the John Weston Memorial Lecture and comprises a conference presentation providing details on a career involving wind tunnel testing (1990-2022).

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