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At least 109 records · Page 6

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NASA NTRS1977

Form drag, skin friction, and vortex shedding frequencies for subsonic and transonic crossflows on circular cylinder

A series of wind-tunnel tests covering a range of Mach numbers and Reynolds numbers in subsonic and transonic flows was conducted on a circular cylinder placed normal to the flow. Form drag coefficients were determined from surface-pressure measurements and displayed as a function of Mach number to show the drag rise phenomenon. Buried wire gages arranged on the model surface were used to measure skin-friction distributions and vortex-shedding frequencies at different flow conditions. It was found that detectable periodic shedding ceases above M = 0.9. The measured skin-friction distributions indicate the positions of mean separation points clearly; these values are documented for the different flow conditions.

Murthy, V. S.↗

NASA NTRS1991

A dynamical systems analysis of the kinematics of time-periodic vortex shedding past a circular cylinder

Computer flow simulation aided by dynamical systems analysis is used to investigate the kinematics of time-periodic vortex shedding past a two-dimensional circular cylinder in the context of the following general questions: (1) Is a dynamical systems viewpoint useful in the understanding of this and similar problems involving time-periodic shedding behind bluff bodies; and (2) Is it indeed possible, by adopting such a point of view, to complement previous analyses or to understand kinematical aspects of the vortex shedding process that somehow remained hidden in previous approaches. We argue that the answers to these questions are positive. Results are described.

Ottino, Julio M.↗

NASA NTRS1997

Computation of Sound Generated by Viscous Flow Over a Circular Cylinder

The Lighthill acoustic analogy approach combined with Reynolds-averaged Navier Stokes is used to predict the sound generated by unsteady viscous flow past a circular cylinder assuming a correlation length of 10 cylinder diameters. The two-dimensional unsteady flow field is computed using two Navier-Stokes codes at a low Mach number over a range of Reynolds numbers from 100 to 5 million. Both laminar flow as well as turbulent flow with a variety of eddy viscosity turbulence models are employed. Mean drag and Strouhal number are examined, and trends similar to experiments are observed. Computing the noise within the Reynolds number regime where transition to turbulence occurs near the separation point is problematic: laminar flow exhibits chaotic behavior and turbulent flow exhibits strong dependence on the turbulence model employed. Comparisons of far-field noise with experiment at a Reynolds number of 90,000, therefore, vary significantly, depending on the turbulence model. At a high Reynolds number outside this regime, three different turbulence models yield self-consistent results.

Cox, Jared S.↗

NASA NTRS1997

Computation of Vortex Shedding and Radiated Sound for a Circular Cylinder

The Lighthill acoustic analogy approach combined with Reynolds-averaged Navier Stokes is used to predict the sound generated by unsteady viscous flow past a circular cylinder assuming a correlation length of ten cylinder diameters. The two- dimensional unsteady ow field is computed using two Navier-Stokes codes at a low Mach number over a range of Reynolds numbers from 100 to 5 million. Both laminar ow as well as turbulent ow with a variety of eddy viscosity turbulence models are employed. Mean drag and Strouhal number are examined, and trends similar to experiments are observed. Computing the noise within the Reynolds number regime where transition to turbulence occurs near the separation point is problematic: laminar flow exhibits chaotic behavior and turbulent ow exhibits strong dependence on the turbulence model employed. Comparisons of far-field noise with experiment at a Reynolds number of 90,000, therefore, vary significantly, depending on the turbulence model. At a high Reynolds number outside this regime, three different turbulence models yield self-consistent results.

Cox, Jared S.↗

NASA NTRS1984

Heat transfer investigation in the junction region of circular cylinder normal to a flat plate at 90 deg location

External heat-transfer rates were measured on a flat plate in the junction region of a circular cylinder mounted normal to the plate at a location 90 deg from the stagnation point. This configuration simulates the junction of the shroud with gas-turbine vanes. Heat-transfer results are presented for laminar, transition, and turbulent boundary layers for a Mach number of 0.14 with gas temperatures of approximately 750 deg R over a flat plate at room temperature. The measurements were made in air for a unit Reynolds number, Re/cm, range of 11,000 to 58,000. Heat-transfer measurements were conducted in the 70-ft long, 4-in. diameter shock tube. A shock-wave reflection technique was used to produce a flow Mach number of 0.14. Thin-film platinum heat gages were mounted on the flat plate and along the line of the stagnation point of the cylinder to measure the local heat flux in the junction region. The experimental heat-transfer data were correlated with the laminar and turbulent boundary-layer theories for the flat plate. With the cylinder the heat fluxes on the flat plate were greatly increased in the junction region compared to the heat flux for the plate alone.

Nagamatsu, H. T.↗

NASA NTRS1996

Progress on LES of Flow Past a Circular Cylinder

The objective of the present research is to assess the usefulness of large-eddy simulation (LES) methodology for flows in complex geometries. Flow past a circular cylinder has been calculated using a central-difference based solver, and the results have been compared to those obtained by a solver that employs higher-order upwind biased schemes (Beaudan & Moin, 1994). This comparison allows us to assess the suitability of these schemes for LES in complex geometry flows.

Mittal, R.↗

NASA NTRS1981

Correct generalized solar radiation pressure force on a circular cylinder in an arbitrary orientation

In response to the inconsistency seen in Geogevic (1973) with respect to the solution for solar radiation pressure in the case of a circular cylinder, a succinct derivation of the correct solution is presented. Numerical comparisons of the two sets of results confirm that the new formulation yields physically reasonable results for both general and special cases. A detailed graphic representation of the mathematical model used is included.

Tang, C. C. H.↗

NASA NTRS1946

Flight Investigation at High Speeds of the Drag of Three Airfoils and a Circular Cylinder Representing Full-Scale Propeller Shanks

Tests have been made at high speeds to determine the drag of models, simulating propeller shanks, in the form of a circular cylinder and three airfoils, the NACA 16-025, the NACA 16-040, and the NACA 16-040 with the rear 25 percent chord cut off. All the models had a maximum thickness of 4 1/2 inches to conform with average propeller-shank dimensions and a span of 20 1/4 inches. For the tests the models were supported perpendicular to the lower surface of the wing of an XP-51 airplane. A wake-survey rake mounted below the wing directly behind the models was used to determine profile drag of Mach numbers of 0.3 to 0.8 over a small range of angle of attack. The drag of the cylinder was also determined from pressure-distribution and force measurements.

Barlow, William H↗

NASA NTRS1986

Coherent shedding from a circular cylinder at critical, supercritical, and transcritical Reynolds numbers

Results are summarized from NASA-Langley studies of the mean drag and unsteady flow parameters of the flow around a circular cylinder at critical, supercritical and transcritical Re. Flow velocities of Mach 0.05-0.40 in the Low Turbulence Pressure Tunnel were used in conjunction with Re from 250,000-6.2 million. Data were collected in the wake and along the walls using pressure transducers. Corrections which were devised to calculate the Strouhal numbers in the presence of broadband signatures in the supercritical regime are described. The tests revealed, as found in previous tests, a discontinuity in the Strouhal number (from 0.2-0.43) in the supercritical regime.

Horvath, Thomas J.↗

NASA NTRS1987

Details of the computed flowfield over a circular cylinder at Reynolds number 1200

The application of an upwind-biased implicit approximate factorization Navier-Stokes algorithm to the unsteady impulsive start-up flow over a circular cylinder at Reynolds number 1200 is described. The complete form of the compressible Navier-Stokes equations is used, and the algorithm is second-order accurate in both space and time. The development with time of the shape and size of the separated vortical flow region is computed, as well as the time-variation of several boundary layer parameters and profile shapes. Computations, in general, show excellent agreement with experiment, although the present method predicts a more rapid onset of reversed flow on the cylinder than evidenced in experiment. The changes that the vortical region behind the cylinder undergoes as the symmetric flow transitions to periodic vortex shedding are discussed. The flow becomes periodic with a Strouhal frequency of 0.222, which compares well with the experimental value of approximately 0.21. The effect of grid density on the development of the unsteady flow is also shown.

Rumsey, C. L.↗

NASA NTRS1961

Effect of Groundboard Height on the Aerodynamic Characteristics of a Lifting Circular Cylinder Using Tangential Blowing from Surface Slots for Lift Generation

A wind-tunnel investigation has been made to determine the ground effect on the aerodynamic characteristics of a lifting circular cylinder using tangential blowing from surface slots to generate high lift coefficients. The tests were made on a semispan model having a length 4 times the cylinder diameter and an end plate of 2.5 diameters. The tests were made at low speeds at a Reynolds number of approximately 290,000, over a range of momentum coefficients from 0.14 to 4.60, and over a range of groundboard heights from 1.5 to 10 cylinder diameters. The investigation showed an earlier stall angle and a large loss of lift coefficient as the groundboard was brought close to the cylinder when large lift coefficients were being generated. For example, at a momentum coefficient of 4.60 the maximum lift coefficient was reduced from a value of 20.3 at a groundboard height of 10 cylinder diameters to a value of 8.7 at a groundboard height of 1.5 cylinder diameters. In contrast to this there was little effect on the lift characteristics of changes in groundboard height when lift coefficients of about 4.5 were being generated. At a height of 1.5 cylinder diameters the drag coefficients generally increased rapidly when the slot position angle for maximum lift was exceeded. Slightly below the slot position angle for maximum lift, the groundboard had a beneficial effect, that is, the drag for a given lift was less near the groundboard than away from the groundboard. The variation of maximum circulation lift coefficient (maximum lift coefficient minus momentum coefficient) obtained in this investigation is in general agreement with a theory developed for a jet-flap wing which assumes that the loss in circulation is the result of blockage of the main stream beneath the wing.

Lockwood, Vernard E.↗

NASA NTRS1989

Simulating transitional flow and heat transfer over the flat plate and circular cylinder using a K-epsilon turbulence model

A boundary layer computer code, called TEXSTAN, has been used to simulate external, transitional, fluid flow and heat transfer over the flat plate and circular cylinder. Turbulence modeling was accomplished by using a low-Reynolds number K-epsilon turbulence model. The study was made for free-stream turbulence intensities less than 15 percent. The comparison of the flat plate heat transfer predictions to experimental data showed good agreement, for the location of transition as well as in the heat transfer coefficient. The typical discrepancy in predicting the heat transfer coefficient was less than 5 percent of the measured value.

Sullivan, T. J.↗

NASA NTRS1988

Correlations of velocity and temperature fluctuations in the stagnation-point flow of circular cylinder in turbulent flow

Boundary layer flow and turbulence transport analyses to study the influence of the free-stream turbulence on the surface heat transfer rate and the skin friction around the stagnation point of a circular cylinder in a turbulent flow are presented. The analyses are formulated with the turbulent boundary layer equations, the Reynolds stress transport equations and the k - epsilon two-equation turbulence modeling. The analyses are used to calculate the time-averaged turbulence double correlations, the mean flow properties, the surface heat transfer rate and the skin friction with an isotropic turbulence in the freestream. The analytical results are described and compared with the existing experimental measurements. Depending on the free-stream turbulence properties, the turbulence kinetic energy can increase or decrease as the flow moves toward the surface. However, the turbulence kinetic energy induces large Reynolds normal stresses at the boundary layer edge. The Reynolds normal stresses change the boundary layer profiles of the time-averaged double correlations of the velocity and temperature fluctuations, the surface heat transfer rate and the skin friction. The free-stream turbulence dissipation rate can affect the stagnation-point heat transfer rate but the influence of the free-stream temperature fluctuation on the heat transfer rate is insignificant.

Wang, Chi R.↗

NASA NTRS1984

Mass transfer from a circular cylinder: Effects of flow unsteadiness and slight nonuniformities

Experiments were performed to determine the effect of periodic variations in the angle of the flow incident to a turbine blade on its leading edge heat load. To model this situation, measurements were made on a circular cylinder oscillating rotationally in a uniform steady flow. A naphthalene mass transfer technique was developed and used in the experiments and heat transfer rates are inferred from the results. The investigation consisted of two parts. In the first, a stationary cylinder was used and the transfer rate was measured for Re = 75,000 to 110,000 and turbulence levels from .34 percent to 4.9 percent. Comparisons with both theory and the results of others demonstrate that the accuracy and repeatability of the developed mass transfer technique is about + or - 2 percent, a large improvement over similar methods. In the second part identical flow conditions were used but the cylinder was oscillated. A Strouhal number range from .0071 to .1406 was covered. Comparisons of the unsteady and steady results indicate that the magnitude of the effect of oscillation is small and dependent on the incident turbulence conditions.

Marziale, M. L.↗

NASA NTRS1990

Experimental observations on the relationship between stagnation region flow oscillations and eddy shedding for circular cylinder

Measurements indicate a direct coupling between the dominant frequencies of flow oscillations at the leading-edge stagnation region, laminar-separation unsteadiness, and the vortex shedding. An array of surface mounted, micro-thin hot-films were used to simultaneously determine the state of the boundary layer along the surfaced of a circular cylinder, and vortex shedding was monitored by a hot wire placed in its wake.

Mangalam, S. M.↗

NASA NTRS1987

Application of turbulence modeling to predict surface heat transfer in stagnation flow region of circular cylinder

A theoretical analysis and numerical calculations for the turbulent flow field and for the effect of free-stream turbulence on the surface heat transfer rate of a stagnation flow are presented. The emphasis is on the modeling of turbulence and its augmentation of surface heat transfer rate. The flow field considered is the region near the forward stagnation point of a circular cylinder in a uniform turbulent mean flow. The free stream is steady and incompressible with a Reynolds number of the order of 10 to the 5th power and turbulence intensity of less than 5 percent. For this analysis, the flow field is divided into three regions: (1) a uniform free-stream region where the turbulence is homogeneous and isotropic; (2) an external viscid flow region where the turbulence is distorted by the variation of the mean flow velocity; and, (3) an anisotropic turbulent boundary layer region over the cylinder surface. The turbulence modeling techniques used are the kappa-epsilon two-equation model in the external flow region and the time-averaged turbulence transport equation in the boundary layer region. The turbulence double correlations, the mean velocity, and the mean temperature within the boundary layer are solved numerically from the transport equations. The surface heat transfer rate is calculated as functions of the free-stream turbulence longitudinal microlength scale, the turbulence intensity, and the Reynolds number.

Wang, Chi R.↗

NASA NTRS2003

Evaluation of a Second-Order Accurate Navier-Stokes Code for Detached Eddy Simulation Past a Circular Cylinder

We evaluate the applicability of a production computational fluid dynamics code for conducting detached eddy simulation for unsteady flows. A second-order accurate Navier-Stokes code developed at NASA Langley Research Center, known as TLNS3D, is used for these simulations. We focus our attention on high Reynolds number flow (Re = 5 x 10(sup 4) - 1.4 x 10(sup 5)) past a circular cylinder to simulate flows with large-scale separations. We consider two types of flow situations: one in which the flow at the separation point is laminar, and the other in which the flow is already turbulent when it detaches from the surface of the cylinder. Solutions are presented for two- and three-dimensional calculations using both the unsteady Reynolds-averaged Navier-Stokes paradigm and the detached eddy simulation treatment. All calculations use the standard Spalart-Allmaras turbulence model as the base model.

Vatsa, Veer N.↗

NASA NTRS1994

User manual for EXCALIBUR: A FE-BI numerical laboratory for cavity-backed antennas in a circular cylinder, version 1.2

The Finite Element-Boundary Integral (FE-BI) technique was used to analyze the scattering and radiation properties of cavity-backed patch antennas recessed in a metallic groundplane. A program, CAVITY3D, was written and found to yield accurate results for large arrays without the usual high memory and computational demand associated with competing formulations. Recently, the FE-BI approach was extended to cavity-backed antennas recessed in an infinite, metallic circular cylinder. EXCALIBUR is a computer program written in the Radiation Laboratory of the University of Michigan which implements this formulation. This user manual gives a brief introduction to EXCALIBUR and some hints as to its proper use. As with all computational electromagnetics programs (especially finite element programs), skilled use and best performance are only obtained through experience. However, several important aspects of the program such as portability, geometry generation, interpretation of results, and custom modification are addressed.

Kempel, Leo C.↗