Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “INCOMPRESSIBLE FLOW”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Vorticity-streamfunction formulation of unsteady incompressible flow past a cylinder - Sensitivity of the computed flow field to the location of the outflow boundary

The influence of the location of the outflow computational boundary on the unsteady incompressible flow past a circular cylinder at Reynolds number 100 is examined. The vorticity-streamfunction formulation of the Navier-Stokes equations is used in all computations. Two types of outflow boundary conditions are subjected to a series of tests in which the domain length is gradually reduced. The traction-free condition performs well in most cases and allows the outflow boundary to be located as close as 6.5 cylinder diameters from the body. The other boundary condition type is not as forgiving, but has the advantage of being simpler to implement and can still provide reasonably accurate solutions. It is also observed that both condition types can influence the flow field strongly and globally when the boundary is brought closer than 2.5 diameters from the body. In such cases the temporal periodicity of the solution is lost.

Behr, M.↗
NASA NTRS2010

Reduced Order Modeling Incompressible Flows

The details: a) Need stable numerical methods; b) Round off error can be considerable; c) Not convinced modes are correct for incompressible flow. Nonetheless, can derive compact and accurate reduced-order models. Can be used to generate actuator models or full flow-field models

Helenbrook, B. T.↗
NASA NTRS1990

Unsteady incompressible flow computations with quadrilateral elements

A comparative investigation, based on a series of numerical tests, of various velocity-pressure elements used for incompressible flow computations is presented. These elements are implemented in conjunction with one-step and multi-step temporal integration of unsteady Navier-Stokes equations. The test cases chosen are the standing vortex problem, the lid-driven cavity flow, and flow past a circular cylinder.

Tezduyar, T. E.↗
NASA NTRS1986

A computer code for three-dimensional incompressible flows using nonorthogonal body-fitted coordinate systems

In this report, a numerical method for solving the equations of motion of three-dimensional incompressible flows in nonorthogonal body-fitted coordinate (BFC) systems has been developed. The equations of motion are transformed to a generalized curvilinear coordinate system from which the transformed equations are discretized using finite difference approximations in the transformed domain. The hybrid scheme is used to approximate the convection terms in the governing equations. Solutions of the finite difference equations are obtained iteratively by using a pressure-velocity correction algorithm (SIMPLE-C). Numerical examples of two- and three-dimensional, laminar and turbulent flow problems are employed to evaluate the accuracy and efficiency of the present computer code. The user's guide and computer program listing of the present code are also included.

Chen, Y. S.↗
NASA NTRS1990

Solution techniques for the vorticity-streamfunction formulation of two-dimensional unsteady incompressible flows

A review of the solution techniques of Tezduyar et al. (1988 and 1989) for the vorticity-streamfunction formulation of two-dimensional incompressible flows is presented. While both the viscous and inviscid cases are considered, the derivation of the proper finite-element formulations for multiply connected domains is emphasized. In all formulations associated with the vorticity transport equation, the streamline upwind/Petrov-Galerkin method is used. The adaptive implicit-explicit and grouped element-by-element solution strategies are employed to maximize the computational efficiency. The solutions obtained in all test cases compare well with solutions from previously published investigations. The convergence and benchmark studies performed in this paper show that the solution techniques presented are accurate, reliable, and efficient.

Tezduyar, T. E.↗
NASA NTRS1986

A numerical method for three-dimensional incompressible flows using nonorthogonal body-fitted coordinate systems

In the present paper, a numerical method for solving the equations of motion of three-dimensional incompressible flows in nonorthogonal body-fitted coordinate (BEC) systems has been developed and evaluated. The equations of motion are transformed to a generalized curvilinear coordinate system from which the transformed equations are discretized using finite difference approximations in the transformed domain. The hybrid scheme and a central differencing plus artificial dissipation scheme are used to approximate the convection terms in the governing equations. Effects of these two schemes on the accuracy of numerical predictions are studied. Solutions of the finite difference equations are obtained iteratively by using a pressure-velocity correction algorithm, SIMPLE-C. Numerical examples of two- and three-dimensional, laminar and turbulent flow problems are employed to evaluate the accuracy and efficiency of the present numerical method.

Chen, Y. S.↗
NASA NTRS1984

Penalty function finite element analysis of steady viscous incompressible flow in rotating coordinates

Finite element methods for incompressible viscous flow in turbomachines have not been presented in the literature previously. This paper develops a penalty function primitive variable method including Coriolis and centrifugal force terms for steady flow in a rotating coordinate system. Simplex elements are used with the result of solution times comparable to equivalent finite different solutions. Example cases considered are Couette flow, Poiseuile flow, flow over a step and flow in a rotating channel. Both laminar and turbulent flows are discussed. The accuracy of computed solutions compares well with theoretical solutions and experimenal measurements.

Rosen, M. C.↗
NASA NTRS1956

Theoretical analysis of incompressible flow through a radial-inlet centrifugal impeller at various weight flows

A method for the solution of the incompressible nonviscous flow through a centrifugal impeller, including the inlet region, is presented. Several numerical solutions are obtained for four weight flows through an impeller at one operating speed. These solutions are refined in the leading-edge region. The results are presented in a series of figures showing streamlines and relative velocity contours. A comparison is made with the results obtained by using a rapid approximate method of analysis.

Kramer, James J↗
NASA NTRS1986

Helmholtz decomposition revisited: Vorticity generation and trailing edge condition. I - Incompressible flows

Using the decomposition for the infinite-space, the issue of the nonuniqueness of the Helmholtz decomposition for the problem of the three-dimensional unsteady incompressible flow around a body is considered. A representation for the velocity that is valid for both the fluid region and the region inside the boundary surface is employed, and the motion of the boundary is described as the limiting case of a sequence of impulsive accelerations. At each instant of velocity discontinuity, vorticity is shown to be generated by the boundary condition on the normal component of the velocity, for both inviscid and viscous flows. In viscous flows, the vorticity is shown to diffuse into the surroundings, and the no-slip conditions are automatically satisfied. A trailing edge condition must be satisfied for the solution to the Euler equations to be the limit of the solution of the Navier-Stokes equations.

Morino, L.↗
NASA NTRS1989

Oscillating aerodynamics and flutter of an aerodynamically detuned cascade in an incompressible flow

A mathematical model is developed and utilized to demonstrate the enhanced torsion mode stability associated with alternate blade circumferential aerodynamic detuning of a rotor operating in an incompressible flow field. The oscillating cascade aerodynamics, including steady loading effects, are determined by developing a complete first order unsteady aerodynamic analysis. An unsteady aerodynamic influence coefficient technique is then utilized, thereby enabling the stability of both conventional uniformly spaced rotors and detuned nonuniform circumferentially spaced rotors to be determined. To demonstrate the enhanced flutter aeroelastic stability associated with this aerodynamic detuning mechanism, this model is applied to a baseline unstable rotor with a Gostelow flow geometry.

Chiang, Hsiao-Wei D.↗
NASA NTRS1990

Combination Of Techniques For Computing Incompressible Flow

Pseudocompressibility, upwind differencing, and other techniques used to solve Navier-Stokes equations. Scheme for finite-difference numerical solution of two-dimensional Navier-Stokes equations of incompressible flow combines several recently developed methods, each developed to increase speed and/or accuracy of computations of this kind.

Kwak, D.↗
NASA NTRS1990

Incompressible flow computations based on the vorticity-stream function and velocity-pressure formulations

Finite element procedures and computations based on the velocity-pressure and vorticity-stream function formulations of incompressible flows are presented. Two new multistep velocity-pressure formulations are proposed and compared with the vorticity-stream function and one-step formulations. The example problems chosen are the standing vortex problem and flow past a circular cylinder. Benchmark quality computations are performed for the cylinder problem. The numerical results indicate that the vorticity-stream function formulation and one of the two new multistep formulations involve much less numerical dissipation than the one-step formulation.

Tezduyar, T. E.↗
NASA NTRS1991

Time-accurate incompressible flow computations with quadrilateral velocity-pressure elements

Quadrilateral velocity-pressure elements with constant and linear pressure interpolations are examined in the context of time-accurate finite element computation of unsteady incompressible flows. These elements involve streamline-upwind/Petrov-Galerkin stabilization and are implemented in conjunction with the one-step and multi-step temporal integration of the Navier-Stokes equations. The two test cases chosen for the performance evaluation of the formulations are the standing vortex problem and flow past a circular cylinder at Reynolds number 100.

Tezduyar, T. E.↗
NASA NTRS1985

Incompressible flow in stepped labyrinth seals

A steped labyrinth seal was experimentally investigated to determine the effects of pressure ratio, shaft speed, number of teeth, and tooth/step location upon the leakage through the seal for incompressible flow. The dependence of the flow coefficient upon the number of throttles and pressure ratio are similar to those for straight-through labyrinth seals. It can be noted that the axial location of the throttle with respect to the step had a special effect upon the flow coefficient. That is, the dependency of the flow coefficient upon rotation rate and the number of throttles changes with axial location. It was found that the minimum flow coefficient was obtained when the seal teeth were centered on the step surface. Axial pressure distribution measurements show that when the teeth are centered on the step, the pressure drop from cavity to cavity is almost uniform. It is speculated that the obtaining of this uniform pressure gradient is the cause for the enhanced performance of the stepped labyrinth seal when operated in that configuration.

Morrison, G. L.↗
NASA NTRS1988

Numerical analysis of laminar and turbulent incompressible flows using the finite element Fluid Dynamics Analysis Package (FIDAP)

The purpose of the study is the evaluation of the numerical accuracy of FIDAP (Fluid Dynamics Analysis Package). Accordingly, four test problems in laminar and turbulent incompressible flows are selected and the computational results of these problems compared with other numerical solutions and/or experimental data. These problems include: (1) 2-D laminar flow inside a wall-driven cavity; (2) 2-D laminar flow over a backward-facing step; (3) 2-D turbulent flow over a backward-facing step; and (4) 2-D turbulent flow through a turn-around duct.

Sohn, Jeong L.↗
NASA NTRS1991

Flutter control of incompressible flow turbomachine blade rows by splitter blades

Splitter blades as a passive flutter control technique is investigated by developing a mathematical model to predict the stability of an aerodynamically loaded splittered-rotor operating in an incompressible flow field. The splitter blades, positioned circumferentially in the flow passage between two principal blades, introduce aerodynamic and/or combined aerodynamic-structural detuning into the rotor. The two-dimensional oscillating cascade unsteady aerodynamics, including steady loading effects, are determined by developing a complete first-order unsteady aerodynamic analysis together with an unsteady aerodynamic influence coefficient technique. The torsion mode flutter of both uniformly spaced tuned rotors and detuned rotors are predicted by incorporating the unsteady aerodyamic influence coefficients into a single-degree-of-freedom aeroelastic model. This model is then utilized to demonstrate that incorporating splitters into unstable rotor configurations results in stable splittered-rotor configurations.

Chiang, Hsiao-Wei D.↗
NASA NTRS1991

On the downstream boundary conditions for the vorticity-stream function formulation of two-dimensional incompressible flows

Downstream boundary conditions equivalent to the homogeneous form of the natural boundary conditions associated with the velocity-pressure formulation of the Navier-Stokes equations are derived for the vorticity-stream function formulation of two-dimensional incompressible flows. Of particular interest are the zero normal and shear stress conditions at a downstream boundary.

Tezduyar, T. E.↗