Author

# Dennis A. Yoder

Bio: Dennis A. Yoder is an academic researcher from Glenn Research Center. The author has contributed to research in topics: Turbulence & Nozzle. The author has an hindex of 14, co-authored 41 publications receiving 565 citations.

##### Papers

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TL;DR: In this article, three two-equation turbulence models developed specifically to improve prediction of jet flowfields are investigated and compared for a reference nozzle producing heated and unheated jets at a low acoustic Mach number of 0.5 to avoid complications of large compressibility effects.

Abstract: Three two-equation turbulence models developed specifically to improve prediction of jet flowfields are investigated. These models are the Tam-Ganesan k-e formulation, a standard k-e model with modification for heated jets referred to as the PAB temperature correction, and a standard k-e model employing variable diffusion for the k and e equations. Two standard two-equation models are also investigated for comparison with the modified formulations. The standard models are the Chien k-e and Menter shear stress transport formulations. All of the models were investigated for a reference nozzle producing heated and unheated jets at a low acoustic Mach number of 0.5 to avoid complications of large compressibility effects. The primary deficiency of the standard models was the delayed initial jet mixing rate. All of the modified turbulence model formulations provided improved mean flow predictions relative to the standard models. The improved mixing rate enabled by the Tam-Ganesan model and the variable diffusion correction resulted from increased turbulent diffusion enabled by both models. The Tam-Ganesan model and PAB temperature correction improved predictions of mean axial velocities for the heated jet, but did not improve prediction of the calculated turbulent kinetic energy fields.

95 citations

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TL;DR: In this paper, the authors highlight some of the fundamental issues in modeling free shear flows for propulsion applications, present a review of past modeling efforts, and identify areas where further research is needed.

49 citations

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TL;DR: In this paper, the authors provide an assessment of current turbulent flow calculation methods for hypersonic propulsion flowpaths, particularly the scramjet engine, and the results from calculations of a direct connect supersonic combustion experiment are also used to address the effects of turbulence model selection and in particular settings for the turbulent Prandtl and Schmidt numbers.

Abstract: This report provides an assessment of current turbulent flow calculation methods for hypersonic propulsion flowpaths, particularly the scramjet engine. Emphasis is placed on Reynolds-averaged Navier–Stokes (RANS) methods, but some discussion of newer methods such as large eddy simulation (LES) is also provided. The report is organized by considering technical issues throughout the scramjet-powered vehicle flowpath, including laminar-to-turbulent boundary layer transition, shock wave/turbulent boundary layer interactions, scalar transport modeling (specifically the significance of turbulent Prandtl and Schmidt numbers), and compressible mixing. Unit problems are primarily used to conduct the assessment. In the combustor, results from calculations of a direct connect supersonic combustion experiment are also used to address the effects of turbulence model selection and in particular settings for the turbulent Prandtl and Schmidt numbers. It is concluded that RANS turbulence modeling shortfalls are still a major limitation to the accuracy of hypersonic propulsion simulations, whether considering individual components or an overall system. Newer methods such as LES-based techniques may be promising, but are not yet at a maturity to be used routinely by the hypersonic propulsion community. The need for fundamental experiments to provide data for turbulence model development and validation is discussed.

41 citations

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01 Apr 1999

TL;DR: The two equation k-epsilon turbulence model of Chien has been implemented in the Wind Navier-Stokes flow solver and results indicate that the WIND model functions very similarly to that in NPARC, though the WWIND code appears to he slightly more accurate in the treatment of the near-wall region.

Abstract: The two equation k-epsilon turbulence model of Chien has been implemented in the WIND Navier-Stokes flow solver. Details of the numerical solution algorithm, initialization procedure, and stability enhancements are described. Results obtained with this version of the model are compared with those from the Chien k-epsilon model in the NPARC Navier-Stokes code and from the WIND SST model for three validation cases: the incompressible flow over a smooth flat plate, the incompressible flow over a backward facing step, and the shock-induced flow separation inside a transonic diffuser. The k-epsilon model results indicate that the WIND model functions very similarly to that in NPARC, though the WIND code appears to he slightly more accurate in the treatment of the near-wall region. Comparisons of the k-epsilon model results with those from the SST model were less definitive, as each model exhibited strengths and weaknesses for each particular case.

38 citations

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TL;DR: In this paper, the leakage performance of a brush seal with gaseous working fluids at static and low rotor speed conditions was studied and the effects of packing a lubricant into the bristles and also of reversing the pressure drop across the seal were studied.

Abstract: The leakage performance of a brush seal with gaseous working fluids at static and low rotor speed conditions was studied. The leakage results are included for air, helium, and carbon dioxide at several bristle/rotor interferences. Also, the effects of packing a lubricant into the bristles and also of reversing the pressure drop across the seal were studied. Results were compared to that of an annular seal at similar operating conditions. In order to generalize the results, they were correlated using corresponding state theory. The brush seal tested had a bore diameter of 3.792 cm (1.4930 in), a fence height of 0.0635 cm (0.025 in), and 1800 bristles/cm circumference (4500 bristles/in circumference). Various bristle/rotor radial interferences were achieved by using a tapered rotor. The brush seal reduced the leakage in comparison to the annular seal, up to 9.5 times. Reversing the pressure drop across the brush seal produced leakage rates approx. the same as that of the annular seal. Addition of a lubricant reduced the leakage by 2.5 times. The air and carbon dioxide data were successfully correlated using corresponding state theory. However, the helium data followed a different curve than the air and carbon dioxide data.

38 citations

##### Cited by

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TL;DR: The Structure of Turbulent Shear Flow by Dr. A.Townsend as mentioned in this paper is a well-known work in the field of fluid dynamics and has been used extensively in many applications.

Abstract: The Structure of Turbulent Shear Flow By Dr. A. A. Townsend. Pp. xii + 315. 8¾ in. × 5½ in. (Cambridge: At the University Press.) 40s.

1,050 citations

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TL;DR: This work considers the numerical solution of the compressible Reynolds-averaged Navier–Stokes and k–ω turbulence model equations by means of DG space discretization and implicit time integration, and presents the results obtained in the computation of the turbulent flow over a flat plate and the turbulent unsteady wake developing behind a turbine blade.

434 citations

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TL;DR: The use of large-eddy simulation (LES) methods for calculation of turbulent flows has increased substantially in recent years as discussed by the authors, and the availability of LES and hybrid Reynolds-averaged Navier-Stokes (RANS)/LES in general-purpose codes is discussed.

Abstract: Usage of large-eddy simulation (LES) methods for calculation of turbulent flows has increased substantially in recent years. This paper attempts to 1) provide an assessment of the current capabilities of LES, 2) outline some recommended practices for using LES, and 3) identify future research needs. The assessment considers flow problems for which LES can be successfully applied today and flow problems for which LES still has limitations. The availability of LES and hybrid Reynolds-averaged Navier-Stokes (RANS)/LES in general-purpose codes is discussed. Several important issues for which the LES community has not yet reached a consensus are discussed. These include grid sensitivity studies, application of unstructured grid methods, upwind-biased solvers, and turbulence (subgrid) modeling including continuous hybrid RANS/LES approaches. A section on recommended practices and key considerations tries to provide guidance on some of the important items that need to be addressed in using LES. The paper concludes with a discussion of future research directions, with a focus on work needed to advance the capabilities and reliability of LES for analysis of turbulent flows.

419 citations

01 Nov 2006

TL;DR: Ganapathisubramani et al. as discussed by the authors investigated the relationship between the upstream boundary layer and the lowfrequency, large-scale unsteadiness of the separated flow in a Mach 2 compression ramp interaction by performing wide-field particle image velocimetry (PIV) and planar laser scattering (PLS) measurements in streamwise-spanwise planes.

Abstract: The relationship between the upstream boundary layer and the low-frequency, large-scale unsteadiness of the separated flow in a Mach 2 compression ramp interaction is investigated by performing wide-field particle image velocimetry (PIV) and planar laser scattering (PLS) measurements in streamwise–spanwise planes. Planar laser scattering measurements in the upstream boundary layer indicate the presence of spanwise strips of elongated regions of uniform momentum with lengths greater than 40?. These long coherent structures have been observed in a Mach 2 supersonic boundary layer (Ganapathisubramani, Clemens & Dolling 2006) and they exhibit strong similarities to those that have been found in incompressible boundary layers (Tomkins & Adrian 2003; Ganapathisubramani, Longmire & Marusic 2003). At a wall-normal location of y/?=0.2, the inferred instantaneous separation line of the separation region is found to oscillate between x/?=?3 and ?1 (where x/?=0 is the ramp corner). The instantaneous spanwise separation line is found to respond to the elongated regions of uniform momentum. It is shown that high- and low-momentum regions are correlated with smaller and larger size of the separation region, respectively. Furthermore, the instantaneous separation line exhibits large-scale undulations that conform to the low- and high-speed regions in the upstream boundary layer. The low-frequency unsteadiness of the separation region/shock foot observed in numerous previous studies can be explained by a turbulent mechanism that includes these elongated regions of uniform momentum

253 citations

01 Jan 2016

TL;DR: Physical and computational aspects of convective heat transfer, but end up in malicious downloads, where people are facing with some harmful virus inside their computer.

Abstract: Thank you for reading physical and computational aspects of convective heat transfer. Maybe you have knowledge that, people have search hundreds times for their chosen readings like this physical and computational aspects of convective heat transfer, but end up in malicious downloads. Rather than reading a good book with a cup of tea in the afternoon, instead they are facing with some harmful virus inside their computer.

238 citations