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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 163 records · Page 9
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NASA NTRS1985

Numerical calculation of subsonic jets in crossflow with reduced numerical diffusion

A series of calculations are reported for two, subsonic jet in crossflow geometries. The parametric variation examined are the lateral spacing of a row of jets. The first series of calculations corresponds to a widely space jet geometry, S/D = 4, and the second series corresponds to closely spaced jets, S/D = 2. The calculations are done with alternate differencing schemes to illustrate the impact of numerical diffusion. The calculated jet trajectories agreed well with experimental data in the widely spaced jet geometry, but not in the closely spaced geometry.

Claus, R. W.↗
NASA NTRS1985

Effects of non-uniform velocity profiles on dual jets in a crossflow

The interaction between engine exhaust jets and the freestream affects the aerodynamic and stability characteristics of VTOL aircraft during the transition from hover to forward flight. This interaction is often modeled as a simple uniform jet issuing from a flat plate into a subsonic crossflow. The distribution of pressures induced by the jet on the surface of the plate can be used to predict the lift loss and pitching moment for a full-scale aircraft. The uniform jet model has limitations because an actual turbofan engine generates a rather nonuniform exit velocity profile. The purpose of this work is to study the effect of a nonuniform velocity profile on the surface pressure distribution. The mutual interaction of dual jets also is investigated in side-by-side and tandem configurations. Detailed pressure distributions are presented for two jet-to-freestream velocity ratios of 2.2 and 4.0. One important finding is that a nonuniform jet with a high velocity periphery and a low velocity core has a higher effective velocity ratio than a uniform jet with the same mass flow.

Moore, C. L.↗
NASA NTRS1986

Dual rectangular jets from a flat plate in a crossflow

Wind tunnel tests were carried out in order to study the single and dual rectangular crossflow jets injected from a flat plate perpendicular to a free stream. The length-to-width ratio of the jets was 3.97, and the spacing between the center lines was 4.7 times the width of a single jet. Surface pressure distributions were obtained for jet-to-freestream velocity ratios of 2.2 and 4, respectively. The following conclusions are offered on the basis of the experimental results: (1) the downstream extension of the negative pressures is extended to the dual jets in comparison to the single jet; (2) by increasing the jet-to-freestream velocity ratio the downstream extension of negative pressures is reduced, but negative upstream pressures become larger; (3) very high peak negative pressures occur at the front side edges of the rectangular jets compared to round jets. Velocity vector plots in the flowfield of the dual jets are given.

Kavsaoglu, M.↗
NASA NTRS1986

Computation of turbulent supersonic flows around pointed bodies having crossflow separation

The numerical method developed by Schiff and Sturek (1980) on the basis of the thin-layer parabolized Navier-Stokes equations of Schiff and Steger (1980) is extended to the case of turbulent supersonic flows on pointed bodies at high angles of attack. The governing equations, the numerical scheme, and modifications to the algebraic eddy-viscosity turbulence model are described; and results for three cones and one ogive-cylinder body (obtained using grids of 50 nonuniformly spaced points in the radial direction between the body and the outer boundary) are presented graphically and compared with published experimental data. The grids employed are found to provide sufficient spatial resolution of the leeward-side vortices; when combined with the modified turbulence model, they are shown to permit accurate treatment of flows with large regions of crossflow separation.

Degani, D.↗
NASA NTRS1987

Three-dimensional nearfield characterization of a VSTOL jet in turbulent crossflow

This paper documents the measurement and prediction of the near-field evolution of the steady, subsonic, turbulent three-dimensional external aerodynamic flow-field associated with a high speed jet issued from an orifice perpendicular to an imposed crossflow velocity field. A parabolic Navier-Stokes CFD solver is employed, utilizing a Kappa-epsilon closure system with algebraic Reynolds stress equation, in concert with suitably defined porous far-field boundary conditions and a virtual source initial condition procedure. The CFD results correlate well with NASA generated near-field LDA experimental data on mean velocity and rms fluctuation velocity (interpolated to turbulent kinetic energy) distributions. The numerical results in the farther field predict the vortex roll-up and jet deflection/entrainment characterization verified by pitot-static mean velocity experimental data. Detailed results are presented for a circular jet for velocity ratios ranging 4 to 8.

Baker, A. J.↗
NASA NTRS1987

Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

Simon, Frederick F.↗
NASA NTRS1988

A jet in a crossflow

In the transition from hover to wingborn flight, V/STOL aircraft rely on the direct thrust of lift jets to supplement wing generated lift. The lifting jets interact with the flow over the aerodynamic surface to produce a complex flow around the aircraft. The simplest configuration which retains the essential characteristics of the jet/aerodynamic-surface interaction problem is a subsonic round jet exhausting perpendicularly through a large flat plate into a uniform crossflow. This configuration was studied extensively, both by experiment and by analysis. As a result, a fairly complete experiment data base exists for comparison with the numerical calculations. Research publications and presentations in this area are included. Each citation is followed by an abstract of the work.

Fearn, Richard L.↗
NASA NTRS1988

Modeling of liquid jets injected transversely into a supersonic crossflow

Analytical/numerical modeling of the behavior of a single nonreacting liquid jet in compressible (high subsonic and supersonic) crossflows is described here. Inviscid, compressible flow about the elliptical cross-section of the jet is solved numerically, using a procedure modeled after that of Godunov. External boundary layer analysis along the surface of the elliptical cross-section allows determination of an effective drag associated with the jet, which balances centripetal forces resulting from jet deflection. Mass and momentum balances performed along the jet, with and without the inclusion of mass loss due to droplet shedding, are then incorporated so that liquid jet trajectories and bow shock penetration may be calculated. Comparisons of the predictions are made with experimental results.

Heister, S. D.↗
NASA NTRS1988

Numerical investigation of a jet in ground effect with a crossflow

One of the flows inherent in V/STOL operations, the jet in ground effect with a crossflow, is studied using the Fortified Navier-Stokes (FNS) scheme. Through comparison of the simulation results and the experimental data, and through the variation of the flow parameters (in the simulation) a number of interesting characteristics of the flow have been observed. For example, it appears that the forward penetration of the ground vortex is a strong inverse function of the level of mixing in the ground vortex. An effort has also been made to isolate issues which require additional work in order to improve the numerical simulation of the jet in ground effect flow. The FNS approach simplifies the simulation of a single jet in ground effect, but will be even more effective in applications to more complex topologies.

Van Dalsem, W. R.↗
NASA NTRS1989

Numerical solution of a two-dimensional jet in a supersonic crossflow using an upwind relaxation scheme

A numerical scheme for predicting complex two-dimensional viscous flow fields is presented. The algorithm uses Roe's method for defining the inviscid fluxes and a line relaxation scheme to solve the resulting discrete approximation. The effects of turbulence are modelled using an algebraic eddy viscosity model. An adaptive grid scheme is employed to improve the resolution of complex flow field phenomena. The algorithm is applied to the solution of a sonic jet in a supersonic crossflow. Numerical results are compared with experimental data to validate the numerical approach.

Thompson, D. S.↗
NASA NTRS1989

The gaseous jet in supersonic crossflow

An analytical/numerical model for the deflection and mixing of a single gaseous jet in a supersonic crossflow is presented. The jet cross-section is described in terms of the compressible vortex pair resulting from viscous and impulsive forces acting at the jet periphery, and the vortex pair data are combined with data for the mass and momentum balance along the jet axis in order to model the trajectory and mixing of the injected fluid. A numerical technique is employed to solve for the inviscid outer flow and the position of the bow shock which envelopes the jet. The model is shown to be capable of predicting overall jet penetration (for perfectly or slightly underexpanded jets) to within 10 percent of experimental findings, while requiring only a few seconds of computer time.

Heister, S. D.↗
NASA NTRS1989

Rectangular jets in a crossflow

Rectangular jets injected from a flat plate into a crossflow at large angles have been studied. Results were obtained as surface pressure distributions, mean velocity vector plots, turbulence intensities, and Reynolds stresses in the jet plume. The length-to-width ratio of the jets was 4, and the jets were aligned streamwise as single and side-by-side dual jets. The jet injection angles were 90 and 60 deg. Surface pressure distribution results were obtained for jet-to-freestream velocity ratios of 2.2, 4, and 8. Mean flow and turbulence flowfield data were obtained for the side-by-side dual jets, mainly for the jet-to-freestream velocity ratio of 4. The jets featured strong negative pressure peaks near the front nozzle corners. The 60-deg jets produced lower magnitude negative pressures, which are distributed over a lesser area when compared to the 90-deg jets.

Kavsaoglu, M. S.↗
NASA NTRS1989

On the interaction of stationary crossflow vortices and Tollmien-Schlichting waves in the boundary layer on a rotating disc

There are many fluid flows where the onset of transition can be caused by different instability mechanisms which compete among themselves. The interaction is considered of two types of instability mode (at an asymptotically large Reynolds number) which can occur in the flow above a rotating disc. In particular, the interaction is examined between lower branch Tollmien-Schlichting (TS) waves and the upper branch, stationary, inviscid crossflow vortex whose asymptotic structure has been described by Hall (1986). This problem is studied in the context of investigating the effect of the vortex on the stability characteristics of a small TS wave. Essentially, it is found that the primary effect is felt through the modification to the mean flow induced by the presence of the vortex. Initially, the TS wave is taken to be linear in character and it is shown (for the cases of both a linear and a nonlinear stationary vortex) that the vortex can exhibit both stabilizing and destabilizing effects on the TS wave and the nature of this influence is wholly dependent upon the orientation of this latter instability. Further, the problem is examined with a larger TS wave, whose size is chosen so as to ensure that this mode is nonlinear in its own right. An amplitude equation for the evolution of the TS wave is derived which admits solutions corresponding to finite amplitude, stable, traveling waves.

Bassom, Andrew P.↗
NASA NTRS1989

Navier-Stokes simulation of the crossflow instability in swept-wing flows

The computational modeling of the transition process characteristic of flows over swept wings are described. Specifically, the crossflow instability and crossflow/T-S wave interactions are analyzed through the numerical solution of the full three-dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiments. The leading edge region of a swept wing is considered in a three-dimensional spatial simulation with random disturbances as the initial conditions. The work has been closely coordinated with the experimental program of Professor William Saric, examining the same problem. Comparisons with NASA flight test data and the experiments at Arizona State University were a necessary and an important integral part of this work.

Reed, Helen L.↗
NASA NTRS1990

Calculation of 3D turbulent jets in crossflow with a multigrid method and a second-moment closure model

A multigrid method is presented for calculating turbulent jets in crossflow. Fairly rapid convergence is obtained with the k-epsilon turbulence model, but computations with a full Reynolds stress turbulence model (RSM) are not yet very efficient. Grid dependency tests show that there are slight differences between results obtained on the two finest grid levels. Computations using the RSM are significantly different from those with k-epsilon model and compare better to experimental data. Some work is still required to improve the efficiency of the computations with the RSM.

Demuren, A. O.↗
NASA NTRS1990

Multigrid Calculations of a Jet in Crossflow

A series of numerical calculations are made of a jet in crossflow using progressive mesh refinement up to 2.4 million grid points. A solution algorithm that combined the features of a point-coupled solution of the momentum and continuity equations with multigrid acceleration demonstrated efficient convergence of the governing equations. In comparisons with experimental data, some features of the jet flow field were found to be predicted reasonably well, but the results still remain affected by numerical diffusion.

Claus, R. W.↗
NASA NTRS1990

Three-dimensional compressible jet-in-crossflow calculations using improved viscosity models and adapted grid

Previous calculations of jet-in-crossflow problems have been sensitive to the turbulence and artificial viscosity models and to the grid. Consequently, the eddy viscosity model in the PARC3D code was modified to consider the turbulent jet by switching from the Baldwin-Lomax (1978) model to an axisymmetric jet model. A modified artificial viscosity model has been utilized and evaluated in this study as well. The new model includes cell size scaling and a directional dependence in the coefficients. Computational results from PARC3D demonstrate the effects of the viscosity models on the pressure distribution fore and aft of the jet and the ability of the adaptive grid scheme to adjust to the three-dimensional gradients around the jet.

Lytle, John K.↗
NASA NTRS1991

Mixing of multiple jets with a confined subsonic crossflow. Summary of NASA-supported experiments and modeling

Experimental and computational results on the mixing of single, double, and opposed rows of jets with an isothermal or variable temperature mainstream in a confined subsonic crossflow are summarized. The studies were performed to investigate flow and geometric variations typical of the complex 3-D flowfield in the dilution zone of combustion chambers in gas turbine engines. The principal observations from the experiments were that the momentum-flux ratio was the most significant flow variable, and that temperature distributions were similar (independent of orifice diameter) when the orifice spacing and the square-root of the momentum-flux ratio were inversely proportional. The experiments and empirical model for the mixing of a single row of jets from round holes were extended to include several variations typical of gas turbine combustors. Combinations of flow and geometry that gave optimum mixing were identified from the experimental results. Based on results of calculations made with a 3-D numerical model, the empirical model was further extended to model the effects of curvature and convergence. The principle conclusions from this study were that the orifice spacing and momentum-flux relationships were the same as observed previously in a straight duct, but the jet structure was significantly different for jets injected from the inner wall wall of a turn than for those injected from the outer wall. Also, curvature in the axial direction caused a drift of the jet trajectories toward the inner wall, but the mixing in a turning and converging channel did not seem to be inhibited by the convergence, independent of whether the convergence was radial or circumferential. The calculated jet penetration and mixing in an annulus were similar to those in a rectangular duct when the orifice spacing was specified at the radius dividing the annulus into equal areas.

Holdeman, James D.↗