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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

An extended Lagrangian method for subsonic flows

It is well known that fluid motion can be specified by either the Eulerian of Lagrangian description. Most of Computational Fluid Dynamics (CFD) developments over the last three decades have been based on the Eulerian description and considerable progress has been made. In particular, the upwind methods, inspired and guided by the work of Gudonov, have met with many successes in dealing with complex flows, especially where discontinuities exist. However, this shock capturing property has proven to be accurate only when the discontinuity is aligned with one of the grid lines since most upwind methods are strictly formulated in 1-D framework and only formally extended to multi-dimensions. Consequently, the attractive property of crisp resolution of these discontinuities is lost and research on genuine multi-dimensional approach has just been undertaken by several leading researchers. Nevertheless they are still based on the Eulerian description.

Liou, Meng-Sing↗
NASA NTRS1997

Effective Control of Computationally Simulated Wing Rock in Subsonic Flow

The unsteady compressible, full Navier-Stokes (NS) equations and the Euler equations of rigid-body dynamics are sequentially solved to simulate the delta wing rock phenomenon. The NS equations are solved time accurately, using the implicit, upwind, Roe flux-difference splitting, finite-volume scheme. The rigid-body dynamics equations are solved using a four-stage Runge-Kutta scheme. Once the wing reaches the limit-cycle response, an active control model using a mass injection system is applied from the wing surface to suppress the limit-cycle oscillation. The active control model is based on state feedback and the control law is established using pole placement techniques. The control law is based on the feedback of two states: the roll-angle and roll velocity. The primary model of the computational applications consists of a 80 deg swept, sharp edged, delta wing at 30 deg angle of attack in a freestream of Mach number 0.1 and Reynolds number of 0.4 x 10(exp 6). With a limit-cycle roll amplitude of 41.1 deg, the control model is applied, and the results show that within one and one half cycles of oscillation, the wing roll amplitude and velocity are brought to zero.

Kandil, Osama A.↗
NASA NTRS2000

Non-Intrusive, Laser-Based Imaging of Jet-A Fuel Injection and Combustion Species in High Pressure, Subsonic Flows

The emphasis of combustion research efforts at NASA Glenn Research Center (GRC) is on collaborating with industry to design and test gas-turbine combustors and subcomponents for both sub- and supersonic applications. These next-generation aircraft combustors are required to meet strict international environmental restrictions limiting emissions. To meet these goals, innovative combustor concepts require operation at temperatures and pressures far exceeding those of current designs. New and innovative diagnostic tools are necessary to characterize these flow streams since existing methods are inadequate. The combustion diagnostics team at GRC has implemented a suite of highly sensitive, nonintrusive optical imaging methods to diagnose the flowfields of these new engine concepts. By using optically accessible combustors and flame-tubes, imaging of fuel and intermediate combustion species via planar laser-induced fluorescence (PLIF) at realistic pressures are now possible. Direct imaging of the fuel injection process through both planar Mie scattering and PLIF methods is also performed. Additionally, a novel combination of planar fuel fluorescence imaging and computational analysis allows a 3-D examination of the flowfield, resulting in spatially and temporally resolved fuel/air volume distribution maps. These maps provide detailed insight into the fuel injection process at actual conditions, thereby greatly enhancing the evaluation of fuel injector performance and other combustion phenomena. Stable species such as CO2, O2, N2, H2O, and hydrocarbons are also investigated by a newly demonstrated 1-D, spontaneous Raman spectroscopic method. This visible wavelength Raman technique allows the acquisition of quantitative, stable species concentration measurements from the flow.

Locke, R. J.↗
NASA NTRS2001

Non-Intrusive, Laser-Based Imaging of Jet-A Fuel Injection and Combustion Species in High Pressure, Subsonic Flows

The emphasis of combustion research efforts at NASA Glenn Research Center (GRC) is on collaborating with industry to design and test gas-turbine combustors and subcomponents for both sub- and supersonic applications. These next-generation aircraft combustors are required to meet strict international environmental restrictions limiting emissions. To meet these goals, innovative combustor concepts require operation at temperatures and pressures far exceeding those of cur-rent designs. New and innovative diagnostic tools are necessary to characterize these flow streams since existing methods are inadequate. The combustion diagnostics team at GRC has implemented a suite of highly sensitive, nonintrusive optical imaging methods to diagnose the flowfields of these new engine concepts. By using optically accessible combustors and flametubes, imaging of fuel and intermediate combustion species via planar laser-induced fluorescence (PLIF) at realistic pressures are now possible. Direct imaging of the fuel injection process through both planar Mie scattering and PLIF methods is also performed. Additionally, a novel combination of planar fuel fluorescence imaging and computational analysis allows a 3-D examination of the flowfield, resulting in spatially and temporally resolved fuel/air volume distribution maps. These maps provide detailed insight into the fuel injection process at actual conditions, thereby greatly enhancing the evaluation of fuel injector performance and other combustion phenomena. Stable species such as CO2, O2, N2O. and hydrocarbons are also investigated by a newly demonstrated 1-D, spontaneous Raman spectroscopic method. This visible wavelength Raman technique allows the acquisition of quantitative. stable species concentration measurements from the flow.

Locke, Randy J.↗
NASA NTRS2000

An Efficient Inverse Aerodynamic Design Method For Subsonic Flows

Computational Fluid Dynamics based design methods are maturing to the point that they are beginning to be used in the aircraft design process. Many design methods however have demonstrated deficiencies in the leading edge region of airfoil sections. The objective of the present research is to develop an efficient inverse design method which is valid in the leading edge region. The new design method is a streamline curvature method, and a new technique is presented for modeling the variation of the streamline curvature normal to the surface. The new design method allows the surface coordinates to move normal to the surface, and has been incorporated into the Constrained Direct Iterative Surface Curvature (CDISC) design method. The accuracy and efficiency of the design method is demonstrated using both two-dimensional and three-dimensional design cases.

Milholen, William E., II↗
NASA NTRS1975

Introduction to the aerodynamics of flight

General concepts of the aerodynamics of flight are discussed. Topics considered include: the atmosphere; fluid flow; subsonic flow effects; transonic flow; supersonic flow; aircraft performance; and stability and control.

Talay, T. A.↗
NASA NTRS2004

Probabilistic Aeroelastic Analysis of Turbomachinery Components

A probabilistic approach is described for aeroelastic analysis of turbomachinery blade rows. Blade rows with subsonic flow and blade rows with supersonic flow with subsonic leading edge are considered. To demonstrate the probabilistic approach, the flutter frequency, damping and forced response of a blade row representing a compressor geometry is considered. The analysis accounts for uncertainties in structural and aerodynamic design variables. The results are presented in the form of probabilistic density function (PDF) and sensitivity factors. For subsonic flow cascade, comparisons are also made with different probabilistic distributions, probabilistic methods, and Monte-Carlo simulation. The approach shows that the probabilistic approach provides a more realistic and systematic way to assess the effect of uncertainties in design variables on the aeroelastic instabilities and response.

Reddy, T. S. R.↗
NASA NTRS1992

A comparison of predicted and measured inlet distortion flows in a subsonic axial inlet flow compressor rotor

Detailed flow measurements were taken inside an isolated axial compressor rotor operating subsonically near peak efficiency. These Laser Anemometer measurements were made with two inlet velocity profiles. One profile consisted of an unmodified baseline flow, and the second profile was distorted by placing axisymmetric screens on the hub and shroud well upstream of the rotor. A detailed comparison in the rotor relative reference frame between a Navier-Stokes solver and the measured experimental results showed good agreement between the predicted and measured flows. A primary flow is defined in the rotor and deviations and the computed predictions is made to assess the development of a passage vortex due to the distortion of the inlet flow. Computer predictions indicate that a distorted inlet profile has a minimal effect on the development of the flow in the rotor passage and the resulting passage vortex.

Owen, Albert K.↗
NASA NTRS1981

Finite element analysis of inviscid subsonic boattail flow

A finite element code for analysis of inviscid subsonic flows over arbitrary nonlifting planar or axisymmetric bodies is described. The code solves a novel primitive variable formulation of the coupled irrotationality and compressible continuity equations. Results for flow over a cylinder, a sphere, and a NACA 0012 airfoil verify the code. Computed subcritical flows over an axisymmetric boattailed afterbody compare well with finite difference results and experimental data. Interative coupling with an integral turbulent boundary layer code shows strong viscous effects on the inviscid flow. Improvements in code efficiency and extensions to transonic flows are discussed.

Chima, R. V.↗
NASA NTRS1981

Finite element analysis of inviscid subsonic boattail flow

A finite element code for analysis of inviscid subsonic flows over arbitrary nonlifting planar or axisymmetric bodies is described. The code solves a novel primitive variable formulation of the coupled irrotationality and compressible continuity equations. Results for flows over a cylinder, a sphere, and a NACA 0012 airfoil verify the code. Computed subcritical flows over an axisymmetric boattailed afterbody compare well with finite difference results and experimental data. Iterative coupling with an integral turbulent boundary layer code shows strong viscous effects on the inviscid flow. Improvements in code efficiency and extensions to transonic flows are discussed.

Chima, R. V.↗
NASA NTRS1983

A computational method for subsonic compressible flow in diffusers

Integral methods are used to model subsonic flow in planar diffusers operating with or without stall. Turbulent boundary layers are computed with a lag-entrainment method employing new correlations for shape factor and skin friction, which are based on a Coles-Van Driest velocity profile. The inviscid flow is modeled as one dimensional and is easily coupled with the boundary layer method to yield equations that can be solved by integrating in the downstream direction. Analysis of the equations describing flow in a diffuser shows that the boundary layer separation singularity may not be eliminated by viscous-inviscid interaction; a modified interaction scheme is used to guarantee a non-singular equation set. The nature of this singularity offers an explanation for the apparent universality of asymmetric stall in planar diffusers. Results for several flows demonstrate the accuracy and range of applicability of the method.

Childs, R. E.↗
NASA NTRS1982

Phenomenological study of subsonic turbulent flow over a swept rearward-facing step

The phenomenology of turbulent, subsonic flow over a swept, rearward-facing step was studied. Effects of variations in step height, sweep angle, base geometry, and end conditions on the 3-D separated flow were examined. The separated flow was visualized using smoke wire, oil drop, and surface tuft techniques. Measurements include surface pressure, reattachment distance and swirl angle. Results indicate: (1) model/test section coupling affects the structure of the separated flow, but spanwise end conditions do not; (2) the independence principle is evidently valid for sweep angles up to 38 deg; (3) a sweep angle/swirl angle correlation exists; and (4) base modifications can significantly reduce the reattachment distance.

Selby, G. V.↗
NASA NTRS1983

Laser-induced fluorescence technique for velocity field measurements in subsonic gas flows

A nonintrusive optical technique is reported for multiple-point velocity measurements in subsonic flows. The technique is based on the detection of fluorescence from a Doppler-shifted absorption line of seeded iodine molecules excited at a laser frequency fixed in the wing of the line. Counterpropagating laser sheets are used to illuminate the flow, in the present case a nitrogen round jet, thereby eliminating the need for an unshifted reference signal. The fluorescence is detected simultaneously at 10,000 points in a plane of the flow using a 100 x 100 element photodiode-array camera. The velocity at each point is computed from four successive camera frames, each recorded with a different beam direction. The measured mean velocities between 5 and 50 m/sec agree well with data from the literature.

Hiller, B.↗