Carlos Velez

Reacting Unsteady Reynolds-Averaged Navier–Stokes with the Tabulated Premixed Conditional Moment Closure Method

The tabulated premixed conditional moment closure model has shown the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable run times in a Reynolds-averaged Navier–Stokes formulation. The tabulated premixed conditional moment closure model is a table lookup combustion model that tabulates species, reaction rates, and thermodynamic data for use by the computational-fluid-dynamics code during run time. In this work, the tabulated premixed conditional moment closure model is extended to unsteady Reynolds-averaged Navier–Stokes. The new model is validated against particle image velocimetry and laser Raman measurements of an enclosed turbulent reacting methane jet from the German Aerospace Center. The flame’s reaction progress variable, its variance, and the scalar dissipation rate are calculated by the computational fluid dynamics in three dimensions. These three parameters are used to index detailed species information from the table for use by the computational-fluid-...

LES Simulation of an Enclosed Turbulent Reacting Methane Jet With the Tabulated Premixed CMC Method

The Tabulated Premixed Conditional Moment Closure Method (T-PCMC) has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed conditional moment closure method is extended to Large Eddy Simulation. The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy [2]. The experimental data has a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity and temperature are provided.The T-PCMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code using three controlling variables; the reaction progress variable, variance and local scalar dissipation rate. The local scalar dissipation is used to account for the affects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. Sub-grid scale models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature and major species are compared to the experimental data. Once validated, this “low runtime” CFD turbulent combustion model will have great utility for designing the next generation of lean premixed gas turbine combustors.Copyright

Experimental study of transverse jet mapping using PLIF

Planar Laser Induced Fluorescence (PLIF) with acetone seeding is applied to measure the scalar fields of an axisymmetric freejet and an inclined jet-in-crossflow as applicable to film cooling. From the scalar fields, jet-mixing and trajectory characteristics are obtained. In order to validate the technique, the canonical example of a nonreacting freejet of Reynolds Numbers 900-9000 is investigated. After validating the technique with the axisymmetric jet, the jet-in-crossflow was tested with various velocity ratios and jet injection angles. Results indicate the degree of wall separation for different injection angles and demonstrate both the time-averaged trajectories as well as near-wall concentration results for varying jet momentum fluxes. Consistent with literature findings, the orthogonal jet trajectory for varying blowing ratios collapses when scaled by the jet-to-freestream velocity ratio and hole diameter, r_d. Similar collapsing is demonstrated in the case of a nonorthogonal jet. Computational Fluid Dynamic (CFD) simualtions using the OpenFOAM software is used to compare predictions with a select experimental case, and yields reasonable agreement.

Rotorcraft blade-vortex street interactions; critical aerodynamic aspects

Numerical investigations of helicopter blade-vortex mechanism of interaction are performed using large eddy simulation (LES). The simulations were performed for a Reynolds number, Re = 1.3 x 10 6 , based on the chord, c, of the airfoil (NACA0012). Computations are carried out for two different types of blade-vortex interactions, concerning single and respectively two vortices blade interaction. It was observed that for single vortex-blade interaction, the blade-vortex interaction becomes less significant with the increase of vertical miss distance. Larger amplitudes of aerodynamic coefficients were observed for the case of two vortices-blade interaction when compared with the single vortex blade interactions.

Novel design of an ocean wave power device utilizing a bi-directional turbine

This paper details an innovative design for a wave energy harvester that converts the heaving motion of waves into electrical power. The conceptual design utilizes a unique bi-directional turbine system that develops a torque in a given direction, independent of whether the fluid is moving upward or downward. The result is power production both as the buoy is heaved upward by a wave as well as while the buoy falls after the wave passes. Although a Wells turbine is a bi-directional turbine currently in use, the proposed bi-directional design, unlike the Wells turbine, is intended to use the ocean water as the working fluid. In addition, in the proposed design, stator blades redirect the fluid to flow nearly parallel to the blade angle, as opposed to the nearly perpendicular flow that acts on the Wells blade. A simple computational fluid dynamics (CFD) program demonstrated the feasibility of the proposed bi-directional design, indicating a 22.3% torque increase over a NACA 0012 Wells turbine blade of equal size.

Planar Laser-Induced Fluorescence Experiments and Modeling Study of Jets in Crossflow

Planar Laser Induced Fluorescence (PLIF) with acetone seeding was applied to measure the scalar fields of an axisymmetric freejet and an inclined jet-in-crossflow as applicable to film cooling. From the scalar fields, jet-mixing and trajectory characteristics were obtained. In order to validate the technique, the canonical example of a nonreacting freejet of Reynolds Numbers 900-9000 was investigated. Desired structural characteristics were observed and showed strong agreement with computational modeling. After validating the technique with the axisymmetric jet, the jet-in-crossflow was tested with various velocity ratios and jet injection angles. Results indicated the degree of wall separation for different injection angles and demonstrate both the time-averaged trajectories as well as select near-wall concentration results for varying jet momentum fluxes. Consistent with literature findings, the orthogonal jet trajectory for varying blowing ratios collapsed when scaled by the jet-to-freestream velocity ratio and hole diameter, rd. Similar collapsing was demonstrated in the cases of a non-orthogonal jets. Computational Fluid Dynamic (CFD) simulations using the OpenFOAM software were used to compare predictions with select experimental cases, and yielded reasonable agreement. Insight into the importance and structure of the counter rotating vortex pair and general flowfield turbulence was highlighted by cross validation between CFD and experimental results.

Flow past flat plate at angle of attack; numerical studies using S-A, LES and IDDES

One of the main issues in using large-eddy simulation (LES) for high Reynolds number flows in bounded domain is the requirement of very fine grid resolution near the wall. The hybrid RANS/LES methodology aims to reduce the high computational effort of wallresolved LES. In the present study we carry out numerical computations by the means of detached-eddy simulation (DES), delayed detached eddy simulation (DDES) and improved DDES (IDDES). The computations are carried out for flow past flat plate at angle of attack

Aerodynamic aspects of helicopter blade-vortex interaction; the interaction with vortex streets considering the icing effect

Numerical investigations of helicopter blade-vortex mechanism of interaction are performed using large eddy simulation (LES). The simulations were performed for a Reynolds number, Re = 1.3 x 10 6 , based on the chord, c, of the airfoil (NACA0012). Computations are carried out for two different types of blade-vortex interactions, concerning single and respectively two vortices blade interaction. It was observed that for single vortex-blade interaction, the blade-vortex interaction becomes less significant with the increase of vertical miss distance. Larger amplitudes of aerodynamic coefficients were observed for the case of two vortices-blade interaction when compared with the single vortex blade interactions.

Numerical studies of high-speed cavity flows using LES, DDES and IDDES

Cavity flows arise in many aerospace applications, such as wheel wells, weapons bays, and other fuselage openings for telescopes and sensors. There are two key processes of feedback-loop mechanism which are not fully understood. First, the direct relation between feedback acoustic waves and shedding vortex at leading lip had not been clearly visualized both in experimental and numerical studies. Second, the generation mechanism of feedback acoustic waves is not clear yet, especially for high-speed cavity flows involving shock waves, Mach waves and high-speed convective shear-layer. In the present work we employ computational fluid dynamics to gain an understanding of these phenomena.

Reduction of helicopter BVI noise using synthetic jets; a numerical study using large-eddy simulation

A novel technique regarding the reduction of helicopter blade-vortex interaction noise is proposed. The proposed technique is based on the idea of injecting air at the leading edge of the blade to alter the vortex characteristics (strength and core size). The numerical investigations are performed using the large-eddy simulation (LES) approach. The simulations were performed for a Reynolds number, Re = 1.3 x 10 6 , based on the NACA0012 airfoil chord and free-stream velocity. The present study shows that by injecting air at the leading edge of the blade, the influence of blade-vortex interaction on the aerodynamic coefficients and aeroacoustic noise is significantly reduced.