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At least 217 records · Page 12

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NASA NTRS1986

Non-linear effects in finite amplitude wave propagation through ducts and nozzles

In this paper an extensive study of non-linear effects in finite amplitude wave propagation through ducts and nozzles is summarized. Some results from earlier studies are included to illustrate the non-linear effects on the transmission characteristics of duct and nozzle terminations. Investigaiations, both experimental and analytical, were carried out to determine the magnitudes of the effects for high intensity pulse propagation. The results derived from these investigations are presented in this paper. They include the effect of the sound intensity on the acoustic characteristics of duct and nozzle terminations, the extent of the non-linearities in the propagation of high intensity impulsive sound inside the duct and out into free field, the acoustic energy dissipation mechanism at a termination as shown by flow visualizations, and quantitative evaluations by experimental and analytical means of the influence of the intensity of a sound pulse on the dissipation of its acoustic power.

Salikuddin, M.↗

NASA NTRS1986

Experimental aerodynamic evaluation of the SSME two-duct, hot gas manifold

An investigation was performed on an improved Space Shuttle Main Engine (SSME) hot gas manifold (HGM) design using a full scale HGM model in cold-flow, air-blowdown tests. The new HGM design replaces the current three transfer ducts with two enlarged elliptical transfer ducts, faired duct inlets, and enlarged fuel bowl. Extensive experimental results have been obtained to verify previous results showing that the two-duct design improved the HGM internal flow path by eliminating separated flow regions, reducing high local velocities, and providing more uniform flow.

Kim, B. Y.↗

NASA NTRS1985

Flow field measurements in a 90 degree turning duct

The objective of this investigation is the experimental evaluation of the influence of inlet turbulence intensity on secondary flow development in a turning duct. The existing 25.4 cm square turning duct (90) facility is being utilized to investigate of bulk turbulence levels on secondary flow development. The large scale duct flow facility allows detailed mean velocity and turbulence quantities to be measured at several streamwise planes in the curved duct. Non-intrusive laser velocimetry is being used to measure the mean and fluctuating components of velocity in all three orthogonal directions. To assure that the turbulence measurements are unbiased by particle lag and other effects, comparison hot wire data will be taken to validate the laser velocimetry system calibration.

Crawford, Roger A.↗

NASA NTRS1987

Inlets, ducts and nozzles

The internal fluid mechanics research program in inlets, ducts, and nozzles is described. The program consists of a balanced effort between the development of computational tools and the conduct of experimental research. The experiments are designed to better understand the fluid flow physics, to develop new or improved flow models, and to provide benchmark quality data sets for validation of the computational methods. The inlet, duct, and nozzle research program is described according to three major classifications of flow phenomena: highly three-dimensional flow fields; shock-boundary layer interactions; and shear layer control. Specific examples of current and future elements of the research program are described for each of these phenomena. In particular, the highly three-dimensional flow field phenomena is highlighted by describing the computational and experiemental research program in transition ducts having a round-to-rectangular area variation. In the case of shock-boundary layer interactions, the specific details of research for normal shock-boundary layer interactions are described. For shear layer control research in vortex generators and the use of aerodynamic excitation for enhancement of the jet mixing process are described. Future research in inlets, ducts, and nozzles will include more emphasis on three-dimensional full Navier-Stokes methods and corresponding experiments designed to concentrate on the appropriate three-dimensional fluid flow physics.

Abbott, John M.↗

NASA NTRS1989

Calculation of turbulence-driven secondary motion in ducts with arbitrary cross section

Calculation methods for turbulent duct flows are generalized for ducts with arbitrary cross-sections. The irregular physical geometry is transformed into a regular one in computational space, and the flow equations are solved with a finite-volume numerical procedure. The turbulent stresses are calculated with an algebraic stress model derived by simplifying model transport equations for the individual Reynolds stresses. Two variants of such a model are considered. These procedures enable the prediction of both the turbulence-driven secondary flow and the anisotropy of the Reynolds stresses, in contrast to some of the earlier calculation methods. Model predictions are compared to experimental data for developed flow in triangular duct, trapezoidal duct and a rod-bundle geometry. The correct trends are predicted, and the quantitative agreement is mostly fair. The simpler variant of the algebraic stress model procured better agreement with the measured data.

Demuren, A. O.↗

NASA NTRS1990

Calculation of turbulence-driven secondary motion in ducts with arbitrary cross-section

Demuren, A. O.↗

NASA NTRS1991

Detonation duct gas generator demonstration program

The feasibility of the generation of detonation waves moving periodically across high speed channel flow is experimentally demonstrated. Such waves are essential to the concept of compressing requirements and increasing the engine pressure compressor with the objective of reducing conventional compressor requirements and increasing the engine thermodynamic efficiency through isochoric energy addition. By generating transient transverse waves, rather than standing waves, shock wave losses are reduced by an order of magnitude. The ultimate objective is to use such detonation ducts downstream of a low pressure gas turbine compressor to produce a high overall pressure ratio thermodynamic cycle. A 4 foot long, 1 inch x 12 inch cross-section, detonation duct was operated in a blow-down mode using compressed air reservoirs. Liquid or vapor propane was injected through injectors or solenoid valves located in the plenum or the duct itself. Detonation waves were generated when the mixture was ignited by a row of spark plugs in the duct wall. Problems with fuel injection and mixing limited the air speeds to about Mach 0.5, frequencies to below 10 Hz, and measured pressure ratios of about 5 to 6. The feasibility of the gas dynamic compression was demonstrated and the critical problem areas were identified.

Wortman, Andrew↗

NASA NTRS1991

An experimental comparison of nonswirling and swirling flow in a circular-to-rectangular transition duct

Circular-to-rectangular transition duct flows with and without inlet swirl were investigated experimentally in order to determine the effect of inlet swirl on the transition duct flow field and to provide detailed duct flow data for comparison with numerical code predictions. Coefficients based on detailed measurements of velocity, total pressure and static pressure, acquired in four cross stream planes within a circular-to-rectangular transition duct, with and without inlet swirl, are presented, as are surface static pressure and surface oil film visualization results.

Reichert, B. A.↗

NASA NTRS1991

Computation of a circular-to-rectangular transition duct flow field

This paper presents the results of a Computational Fluid Dynamics (CFD) calibration study of flow through a circular-to-rectangular transition duct. The design of these ducts is critical to the optimum performance of aircraft with rectangular exhaust nozzles, since these ducts transfer the flow from the gas turbine engine to the exhaust nozzle. Two duct inflow conditions are considered, the first with straight inflow and the second with swirling inflow. Both flows contain realistic wall boundary layers. The first case permits examination of the effects of the geometric transition on the flowfield, while the second case adds in the rotational flow effect that can be present from the gas turbine engine. The flowfields associated with the two cases have been shown, both with CFD and experiment, to have significant differences. The Navier-Stokes CFD code PARC with the Baldwin and Lomax turbulence model was used in this study. The turbulence model had to be modified for both cases in order to achieve accurate determination of the edge of the wall bounded vorticity layers and thus turbulent viscosity. The results of this calibration study will be valuable to aircraft designers who rely on CFD to assist in the design and evaluation of propulsion systems.

Sirbaugh, J. R.↗

NASA NTRS1992

Effect of type of load on stress analysis of thin-walled ducts

The standard procedure for qualifying the design of duct (pipe) systems in the Space Shuttle Main Engine (SSME) has been fairly well defined. However, since pipe elbows are quite common and important in the SSME duct systems, a clear understanding of the detailed stress profile of the components is necessary for accurate structural and life assessments. This study was initiated to predict the stress profile at/near the tangent point along the cross section of the duct under various types of loads. Also, this study was further extended to understand the stiffening effect on stresses due to pressure at the tangent point. The intention of this study was to identify the importance of selecting proper locations for mounting strain gauges and to utilize the obtained results to anchor dynamic models for accurate structural and life assessments of the SSME ducts under a dynamic environment. The finite element method was utilized in this study.

Min, J. B.↗

NASA NTRS1992

A computational study of advanced exhaust system transition ducts with experimental validation

The current study is an application of CFD to a 'real' design and analysis environment. A subsonic, three-dimensional parabolized Navier-Stokes (PNS) code is used to construct stall margin design charts for optimum-length advanced exhaust systems' circular-to-rectangular transition ducts. Computer code validation has been conducted to examine the capability of wall static pressure predictions. The comparison of measured and computed wall static pressures indicates a reasonable accuracy of the PNS computer code results. Computations have also been conducted on 15 transition ducts, three area ratios, and five aspect ratios. The three area ratios investigated are constant area ratio of unity, moderate contracting area ratio of 0.8, and highly contracting area ratio of 0.5. The degree of mean flow acceleration is identified as a dominant parameter in establishing the minimum duct length requirement. The effect of increasing aspect ratio in the minimum length transition duct is to increase the length requirement, as well as to increase the mass-averaged total pressure losses. The design guidelines constructed from this investigation may aid in the design and manufacture of advanced exhaust systems for modern fighter aircraft.

Wu, C.↗

NASA NTRS1993

Navier-Stokes analysis of three-dimensional S-ducts

Full 3D Navier-Stokes computational results are presented for compressible flows within nondiffusing and diffusing S-ducts. The present study provides an understanding of the performance characteristics of typical S-ducts with attached and separated flows and provides a frame of reference for future computational fluid dynamic studies of internal flows with strong secondary flows. The predicted results, which were obtained using both H- and O-grids, are compared with the experimental wall pressures, static and total pressure fields, and velocity vectors. In addition, computed boundary-layer thickness, velocity profiles in wall coordinates and skin friction values are presented. The inviscid contributions to the secondary flows are quantified. The S-duct entrance Mach number was 0.6, and the Reynolds number was 1.76 x 10 exp 6 based on the upstream duct diameter.

Harloff, G. J.↗

NASA NTRS1993

Experimental and numerical investigation of supersonic turbulent flow in an annular duct

Experimental and numerical results are presented for developing supersonic turbulent flow in an annular duct formed by a circular centerbody and outer shroud. The experimental results are based on data taken in a new flow facility that was designed to generate a shock-free, supersonic annular flow. Numerical computations were performed using the Baldwin-Lomax turbulence model for comparison with experimentally measured profiles. The results demonstrate that computed and measured profiles are in excellent agreement, so that studies can now be conducted of shock wave/boundary layer interaction phenomena within the duct, such as those induced by changes in downstream duct geometry or by the placement of struts between the duct walls.

Williams, K. E.↗

NASA NTRS1993

Numerical simulation of a shock wave/turbulent boundary layer interaction in a duct

A numerical investigation of the interaction of an incident oblique shock wave with a turbulent duct flow is presented. The investigation consists of solving the three-dimensional, unsteady, compressible, mass averaged Navier-Stokes equations, using an implicit finite volume, lower-upper time marching code and incorporates the three-dimensional Baldwin-Lomax turbulence model. Computed results are obtained Mach number 2.9 for a turning angle of 13 degrees and Reynolds number based on duct width of 1.36 x 10 exp 7. Under various inlet conditions, the results clearly depict the flow characteristics, including the shock geometry, the separated flow region, the wall pressure distribution, and the skin friction distribution. The findings provide a physical understanding of the three-dimensional vortex structure of the flow in a duct in which a shock wave interacts with a turbulent boundary layer. The results show that the ratio of the boundary layer thickness to the duct width is the critical parameter in determining the separation structure.

Yang, Wei-Li↗

NASA NTRS1941

Cooling Tests of an Airplane Equipped with an NACA Cowling and a Wing-duct Cooling System

Cooling tests were made of a Northrop A-17A attack airplane successively equipped with a conventional.NACA cowling and with a wing-duct cooling system. The method of cooling the engine by admitting air from the propeller slipstream into wing ducts, passing it first through the accessory compartment and then over the engine from rear to front, appeared to offer possibilities for improved engine cooling, increased cooling of the accessories, and better fairing of the power-plant installation. The results showed that ground cooling for the wing duct system without cowl flap was better than for the NACA cowling with flap; ground cooling was appreciably improved by installing a cowl flap. Satisfactory temperatures were maintained in both climb and high-speed flight, but, with the use of conventional baffles, a greater quantity of cooling air appeared to be required for the wing duct system.

Turner, L I , Jr↗

NASA NTRS1941

Experimental investigations on freely exposed ducted radiators

This report deals with the relation between the open areas, the drag, and the air flow as observed on freely exposed, ducted radiators - the air conductivity being modified from zero to one unit. In conjunction with theoretical results, the individual components of the drag of ducted radiators are discussed and general rules established for low-loss ducts. The influence of the wall thickness of the ducts, of the length ratio of the exit, and the effects of sonic velocity on diffusers are dealt with by special measurement.

Linke, W↗

NASA NTRS1994

Mixing characteristics of directly opposed rows of jets injected normal to a crossflow in a rectangular duct

An experimental investigation of the mixing of nonreacting opposed rows of inline jets injected perpendicular to a uniform crossflow has been conducted in a rectangular duct. Planar Mie-scattering was used to measure the time-average concentration distribution of the jet fluid in planes perpendicular to the duct axis. Orifice configurations with geometric blockages ranging from 0.59 to 0.89 had similar mixing performance when compared at one-half duct height downstream of injection. Blockage was varied by changing the orifice aspect ratio from 1-to-1 to 1-to-1.5 while maintaining orifice spacing-to-duct height (S/H) at 0.425, jet-to-mainstream mass flow ratio (MR) at 2.0, and jet-to-mainstream momentum-flux ratio (J) at 48. The result indicates that the design correlating expression (at MR = 2) for optimum in line mixing of 2.5 approximately equal to (S/H)(square root of J) is independent of the Webb between adjacent orifices and therefore independent of orifice width. Experimental and numerical results for an orifice aspect ratio 1-to-1 case were in good agreement. The results of a comparison of inline 45 degrees slanted slot and round orifice configuration indicate that in order to obtain equivalent mean concentration distributions at the same J it is necessary to use a smaller S/H for the round orifice configuration. Conclusions about the performance of various orifice shapes can only be obtained from comparison of optimized configurations. Inline jets with different momentum-flux ratios on opposite sides were compared at a constant mass flow ratio. The orifice spacing chosen was previously found to be an optimum configuration when opposing values of J were equal and also an optimum for single side injection. Experimental and empirical results were in good agreement.

Liscinsky, D. S.↗

NASA NTRS1996

Periodic Time-Domain Nonlocal Nonreflecting Boundary Conditions for Duct Acoustics

Periodic time-domain boundary conditions are formulated for direct numerical simulation of acoustic waves in ducts without flow. Well-developed frequency-domain boundary conditions are transformed into the time domain. The formulation is presented here in one space dimension and time; however, this formulation has an advantage in that its extension to variable-area, higher dimensional, and acoustically treated ducts is rigorous and straightforward. The boundary condition simulates a nonreflecting wave field in an infinite uniform duct and is implemented by impulse-response operators that are applied at the boundary of the computational domain. These operators are generated by convolution integrals of the corresponding frequency-domain operators. The acoustic solution is obtained by advancing the Euler equations to a periodic state with the MacCormack scheme. The MacCormack scheme utilizes the boundary condition to limit the computational space and preserve the radiation boundary condition. The success of the boundary condition is attributed to the fact that it is nonreflecting to periodic acoustic waves. In addition, transient waves can pass rapidly out of the solution domain. The boundary condition is tested for a pure tone and a multitone source in a linear setting. The effects of various initial conditions are assessed. Computational solutions with the boundary condition are consistent with the known solutions for nonreflecting wave fields in an infinite uniform duct.

Watson, Willie R.↗