SETU Carlow Campushttps://research.thea.ie/handle/20.500.12065/21642024-02-23T07:33:00Z2024-02-23T07:33:00ZNumerical study of oblique detonation wave control for fuel blendsKore, RushikeshVashishtha, Ashishhttps://research.thea.ie/handle/20.500.12065/45382023-06-20T03:00:48Z2023-01-01T00:00:00ZNumerical study of oblique detonation wave control for fuel blends
Kore, Rushikesh; Vashishtha, Ashish
The current study is motivated to develop control strategies for oblique detonation wave formation on a finite length wedge in a premixed methane-air mixture. The effectiveness of hydrogen blends (0 - 100%) to methaneair premixed mixture (at 300 K) on Chapmann Jouguet (CJ) detonation and oblique detonation wave formation are analyzed for different pressures (20 kPa - 100 kPa) and incoming velocities (2.4 - 3.2 km/s) by using 1-D Zeldovich-von Neumann-Doering (ZND) calculations. It was found that induction length and induction time reduces with higher blends of hydrogen in CJ-ZND analysis as well as oblique detonation wave ZND analysis. Similar effects are observed by adding small amount of reaction promoters (H2O2 or O3) as additives up to 15000 PPM. The two-dimensional numerical simulations for the oblique shock wave (OSW) to oblique detonation wave (ODW) transition for different blends and additions in fuel-air mixtures are performed for wedge at angle θ = 26◦ for incoming flow velocity of 2800 m/s, pressure of 20 kPa and temperature of 300 K. The unsteady reactive Navier-Stokes RANS equations are solved with adaptive grid refinement and robust SAGE chemistry solver on CONVERGE platform using reduced version of GRI mechanism along with ozone sub-chemistry. Two dimensional simulations confirms smooth transition with initiation length 1 cm for stoichiometric hydrogen-air and no ODW formation for methane-air premixed mixtures for 10 cm wedge length. It is also found that 50% hydrogen blending and 10000 PPM of ozone addition to stoichiometric methane-air mixture can establish ODW with initiation lengths of 3.9 cm and 4.0 cm, respectively on a finite length wedge.
2023-01-01T00:00:00ZUnsteady DSMC Simulation of blunt nose with spike at hypersonic rarefield flowsRavuri, NishitaScully, StephenVashishtha, Ashishhttps://research.thea.ie/handle/20.500.12065/45372023-06-20T03:02:02Z2023-03-29T00:00:00ZUnsteady DSMC Simulation of blunt nose with spike at hypersonic rarefield flows
Ravuri, Nishita; Scully, Stephen; Vashishtha, Ashish
To design an efficient ram-air intake for an air-breathing propulsion system for VLEO (Very-Low) / SLEO (Super Low) Earth Orbit satellites requires consideration of the unsteady effects in the hypersonic low-density or rarefied environment. This study aims to analyze the unsteady effects due to shock instabilities on a forward facing spike geometry attached to a flat blunt nose in low-density hypersonic flows. The Direct Simulation Monte-Carlo (DSMC) approach is used to study two flow-conditions: 1) ground test facility (V∞ = 2075 m/s, Kn = 1.4×10−3 ) and 2) at an altitude of 100 km (V∞ = 8557 m/s, Kn = 0.45) for a spiked blunt nose with flat face. It was found that gas surface interaction (specular and diffuse reflection) results in changing dynamics of flow field for both conditions. The large amplitude shock fluctuations are not observed in lower density environments as compared to continuum flow in previous literature. The diffuse reflection leads to higher drag and higher unsteadiness at Vin fty = 2075 m/s, when compare to specular reflection, while lower drag and unsteadiness at high Knudsen number case of Vin fty = 8557 m/s.
2023-03-29T00:00:00ZMach number dependence of flow instability around a spiked bodyVashishtha, AshishKhurana, Shashankhttps://research.thea.ie/handle/20.500.12065/45322023-06-17T04:32:08Z2023-05-05T00:00:00ZMach number dependence of flow instability around a spiked body
Vashishtha, Ashish; Khurana, Shashank
A forward-facing aerospike have been identified as a passive flow control device for enhancing the aerodynamic efficiency and reducing the heat transfer in high-speed flows. In addition, it has been reported that the presence of a spike brings in unsteadiness in the form of oscillation and pulsation to the structure. Previous researchers have investigated the aerothermodynamic coefficients, together with offering a detailed explanation of the flow physics and associated unsteadiness, and their dependence on the spike's geometric characteristics (spike nose, and length-to-fore-body diameter ratio, L/D). This work focuses on ascertaining the role of flow speeds (free-stream Mach number), and their energy content, in governing the physics around a spiked body, which is yet to be established. Numerical investigation has been carried out using axisymmetric Navier-Stokes laminar flow solver for Mach number range of 2.0 to 7.0. A round-tip spike with flat-face cylindrical after-body have been simulated for spike length ratio of L/D=2.0, with spike diameter to fore-body diameter of 0.1. The flow unsteadiness has been analyzed with drag and pressure coefficients variation at different Mach numbers. It was found that the flow field around the spiked blunt nose behaves in pulsation mode at lower Mach numbers 2, 3 and transition to oscillatory mode at higher Mach numbers 5, 6 and 7, while remain almost stable at Mach 4. The limit of Strouhal Number for characterizing the pulsation and oscillation modes at various Mach numbers for spike length of L/D = 2 with flat after-body is observed as 0.2, however it may very well depend on other geometric parameters of spike and after-body.
2023-05-05T00:00:00ZAn assessment of radiation models utilized in CFD for thermal and fluid analysis in interior building spaces with large glazingSamuel, Yona ArikeConfrey, ThomasVashishtha, AshishCallaghan, DeanNolan, Cathalhttps://research.thea.ie/handle/20.500.12065/45312023-06-17T04:32:10Z2023-01-01T00:00:00ZAn assessment of radiation models utilized in CFD for thermal and fluid analysis in interior building spaces with large glazing
Samuel, Yona Arike; Confrey, Thomas; Vashishtha, Ashish; Callaghan, Dean; Nolan, Cathal
This paper investigates the effects of using the S2S and the DO method in the CFD simulation of a cavity to identify
a convenient model for simulating radiative heat transfer. A 3D model for an office room fitted with a sizeable controllable glass
window was developed to carry out a transient analysis of a room's thermal performance when the glass is at its opaque state while accounting for each of the models. A transient user-defined function (UDF) boundary condition, based on radiative heat flux, was set as an incident solar load boundary condition on the dynamic glazing to study the dispersed temperature and the airflow in the room. Various configurations of the enclosed room with initial wall boundary condition and airflow in the room were considered
under the effects of different parameters such as thermal properties, Rayleigh (Ra) and Grashof (Gr) numbers, surface emissivity,
and absorption. Radiative CFD results were compared, and the importance of accounting for radiation was noted. The S2S displayed good performance, whereas unexpected temperature distribution was observed with the DO method. Although heat transfer depends on the transmitting material's thermal properties, further analysis has shown that the S2S, along with the SST k-ꞷ viscous turbulence model, using piecewise linear approximation, is a reliable CFD model setting for performing a thermal analysis of a highly glazed enclosed room. The results were also compared to a previous 2D analysis of an enclosed space without accounting for radiation. Results had shown that the interior temperature was less than 2% for the S2S when radiation was overlooked. Further study would involve the validation of the computed room temperature with experimental data which will show the efficiency of the two radiation model methods in performing the thermal performance of a building.
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