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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Active Control of Jets in Cross-Flow for Film Cooling Applications

Jets in cross-flow have applications in film cooling of gas turbine vanes, blades and combustor liners. Their cooling effectiveness depends on the extent to which the cool jet-fluid adheres to the cooled component surface. Lift-off of the cooling jet flow or other mechanisms promoting mixing, cause loss of cooling effectiveness as they allow the hot "free-stream" fluid to come in contact with the component surface. The premise of this project is that cooling effectiveness can be improved by actively controlling (e.9. forcing, pulsing) the jet flow. Active control can be applied to prevent/delay lift-off and suppress mixing. Furthermore, an actively controlled film-cooling system coupled with appropriate sensory input (e.g. temperature or heat flux) can adapt to spatial and temporal variations of the hot-gas path. Thus, it is conceivable that the efficiency of film-cooling systems can be improved, resulting in coolant fluid economy. It is envisioned that Micro Electro-Mechanical Systems (MEMS) will play a role in the realization of such systems. As a first step, a feasibility study will be conducted to evaluate the concept, identify actuation and sensory elements and develop a control strategy. Part of this study will be the design of a proof-of-concept experiment and collection of necessary data.

Nikitopoulos, Dimitris E.↗
NASA NTRS1978

Round jet in a cross flow - Influence of injection angle on vortex properties

A model is developed to infer the properties of a pair of diffuse contrarotating vortices for perpendicular jet injection into the cross flow. Attention is given to pressure distribution on the surface where the jet exhausts, especially in terms of V/STOL applications. A V/STOL wind tunnel experiment is described, whereby a round jet of air (10.16 cm dia) was discharged through a horizontal flat plate into the cross flow of the wind tunnel test section at angles of 45, 60, 75, and 90 deg. Results indicate that the effective vortex strength for both velocity ratios is highest near the jet orifice, and decreases as the vortices are swept downstream, at which point the effective vortex spacing increases. In addition, the core radius of the vortex exhibits properties similar to those of the effective vortex spacing

Krausche, D.↗
NASA NTRS1972

Cross flow in a starved EHD contact

An analysis of lubrication cross flow effects under starved elastohydrodynamic conditions is presented. Starvation is defined as any operating condition such that an increase in oil available to the contact will result in an increase in film thickness. Starved EHD behavior is considered in several situations: (1) when no new oil enters the contact, and (2) when a step change in one of the rolling parameters is introduced at an equilibrium contact. Based on the fact that important oil flow within the Hertz zone is across the rolling contact direction, it is possible to formulate a simple theory which explains quantitatively some aspects of starved ball bearing behavior.

Kingsburg, E. P.↗
NASA NTRS1992

Analysis of penetration and mixing of gas jets in supersonic cross flow

The JETPEN analysis for gas jets in a supersonic cross flow developed earlier at APL/JHU has been extended in several important ways. First, the treatment of cases with injection at angles other than 90 deg has been redone. Next, the second of the three regions formerly treated has been eliminated. Third, the region downstream of the Mach disk for underexpanded cases has been reformulated such that turbulent entrainment of main stream fluid into the plume is modeled, and the equations of motion are solved marching downstream. These changes now permit prediction of the variation in composition, mixing area growth and all other flow variables along the plume. The analysis has been verified by comparison of predictions and experiment over a wide range of conditions. The result is an analysis capable of reliable predictions of the major flowfield variables that can be run on a PC.

Billig, F. S.↗
NASA NTRS2003

Prediction of Bubble Diameter at Detachment from a Wall Orifice in Liquid Cross Flow Under Reduced and Normal Gravity Conditions

Bubble formation and detachment is an integral part of the two-phase flow science. The objective of the present work is to theoretically investigate the effects of liquid cross-flow velocity, gas flow rate embodied in the momentum flux force, and orifice diameter on bubble formation in a wall-bubble injection configuration. A two-dimensional one-stage theoretical model based on a global force balance on the bubble evolving from a wall orifice in a cross liquid flow is presented in this work. In this model, relevant forces acting on the evolving bubble are expressed in terms of the bubble center of mass coordinates and solved simultaneously. Relevant forces in low gravity included the momentum flux, shear-lift, surface tension, drag and inertia forces. Under normal gravity conditions, the buoyancy force, which is dominant under such conditions, can be added to the force balance. Two detachment criteria were applicable depending on the gas to liquid momentum force ratio. For low ratios, the time when the bubble acceleration in the direction of the detachment angle is greater or equal to zero is calculated from the bubble x and y coordinates. This time is taken as the time at which all the detaching forces that are acting on the bubble are greater or equal to the attaching forces. For high gas to liquid momentum force ratios, the time at which the y coordinate less the bubble radius equals zero is calculated. The bubble diameter is evaluated at this time as the diameter at detachment from the fact that the bubble volume is simply given by the product of the gas flow rate and time elapsed. Comparison of the model s predictions was also made with predictions from a two-dimensional normal gravity model based on Kumar-Kuloor formulation and such a comparison is presented in this work.

Nahra, Henry K.↗
NASA NTRS1993

Experimental study of cross flow mixing in cylindrical and rectangular ducts

An experimental investigation of non-reacting cross flow jet injection and mixing in cylindrical and rectangular ducts has been conducted with application to a low emissions combustor. Quantitative measurement of injectant concentration distributions perpendicular to the duct axis were obtained by planar digital imaging of the Mie-scattered light from an aerosol seed mixed with the injectant. The flowfield unmixedness was evaluated using (1) a mixing parameter derived from the ratio of the jet concentration fluctuations to the fully mixed concentration, and (2) probability density functions of the concentration distributions. Mixing rate was measured for 45 degree slant slot and round orifice injectors.

Liscinsky, D. S.↗
NASA NTRS1997

A Numerical Simulation of a Normal Sonic Jet into a Hypersonic Cross-Flow

This study involves numerical modeling of a normal sonic jet injection into a hypersonic cross-flow. The numerical code used for simulation is GASP (General Aerodynamic Simulation Program.) First the numerical predictions are compared with well established solutions for compressible laminar flow. Then comparisons are made with non-injection test case measurements of surface pressure distributions. Good agreement with the measurements is observed. Currently comparisons are underway with the injection case. All the experimental data were generated at the Southampton University Light Piston Isentropic Compression Tube.

Jeffries, Damon K.↗
NASA NTRS2004

Cross Flow Effects on Glaze Ice Roughness Formation

The present study examines the impact of large-scale cross flow on the creation of ice roughness elements on the leading edge of a swept wing under glaze icing conditions. A three-dimensional triple-deck structure is developed to describe the local interaction of a 3 D air boundary layer with ice sheets and liquid films. A linear stability analysis is presented here. It is found that, as the sweep angle increases, the local icing instabilities enhance and the most linearly unstable modes are strictly three dimensional.

Tsao, Jen-Ching↗
NASA NTRS1993

Experiments on the ground vortex formed by an impinging jet in cross flow

An inclined jet impinging on the ground creates a wall flow that spreads radially from the point of impingement. If a cross-flow is introduced, the upstream component of the wall flow will separate from the ground and create what has been termed the 'ground vortex.' The ground vortex has been shown to have a significant impact on aircraft aerodynamics and is one of the major contributors to hot gas ingestion. The paper discusses a recent study which included a generic wing-body configuration for assessing the impact of the ground vortex on configuration aerodynamics. Wind tunnel tests using fixed ground boards, moving ground belts, and moving model tests are discussed. The emphasis of the data is macroscopic, i.e. forward location of the vortex, effects of ground height, etc.

Blake, William B.↗
NASA NTRS1984

Dilution jets in accelerated cross flows

Results of flow visualization experiments and measurements of the temperature field produced by a single jet and a row of dilution jets issued into a reverse flow combustor are presented. The flow in such combustors is typified by transverse and longitudinal acceleration during the passage through its bending section. The flow visualization experiments are designed to examine the separate effects of longitudinal and transverse acceleration on the jet trajectory and spreading rate. A model describing a dense single jet in a lighter accelerating cross flow is developed. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flows. It uses a modified entrainment correlation obtained from previous experiments of a jet in a cross stream. The flow visualization results are compared with the model calculations in terms of trajectories and spreading rates. Each experiment is typified by a set of three parameters: momentum ratio, density ratio and the densimetric Froude number.

Lipshitz, A.↗
NASA NTRS1984

Dilution Jets in Accelerated Cross Flows

Results of flow visualization experiments and measurements of the temperature field produced by a single jet and a row of dilution jets issued into a reverse flow combustor are presented. The flow in such combustors is typified by transverse and longitudinal acceleration during the passage through its bending section. The flow visualization experiments were designed to examine the separate effects of longitudinal and transverse acceleration on the jet trajectory and spreading rate. A model describing a dense single jet in a lighter accelerating cross flow is developed. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flows. It uses a modified entrainment correlation obtained from previous experiments of a jet in a cross stream. The flow visualization results are compared with the model calculations in terms of trajectories and spreading rates. Each experiment is typified by a set of three parameters: momentum ratio, density ratio, and the densimetric Froude number. When injection velocities are large or densities are small, the Froude number becomes very large and hence, unimportant. Therefore, the Froude number is generally significant in describing liquid experiments but is unimportant for the gas experiments in the combustor. Agreement between test and calculated results is encouraging but tends to become poorer with increasing momentum ratio. The temperature measurements are presented primarily in the form of consecutive normalized temperature profiles. Some interpolated isothermal contours are also shown. The single jet trajectories are consistently found to be swept towards the inner wall of the bend, whether injection is from the outer or the inner wall. This behavior is explained by a drifting effect which consists of a transverse velocity component across the combustor due to the developing nature of the flow along it. Plots of lateral temperature distributions of the jet indicate that under longitudinal acceleration conditions the thermal spreading of the jet may be completely suppressed. Comparison between combustor experimental results and model calculations shows poor agreement due to the drifting effect which is not taken into consideration in the model calculations. The row of jets experiments are characterized by two additional parameters: spacing ratio and confinement parameter. The results are shown in the form of consecutive normalized temperature profiles. The confinement parameter appears to become increasingly important with decreasing spacing ratio, in particular when its effect is enhanced by the drifting phenomenon and associated pressure field. A tightly spaced row of jets injected from the inner wall, prior to the bend, is surprisingly kept attached to the inner wall in spite of the strong turning. A similar attachment for a jet injected from the outer wall is not observed.

Lipshitz, Abraham↗
NASA NTRS1973

Analysis of the injection of a heated turbulent jet into a cross flow

The development of a theoretical model is investigated of the incompressible jet injection process. The discharge of a turbulent jet into a cross flow was mathematically modeled by using an integral method which accounts for natural fluid mechanisms such as turbulence, entrainment, buoyancy, and heat transfer. The analytical results are supported by experimental data and demonstrate the usefulness of the theory for estimating the trajectory and flow properties of the jet for a variety of injection conditions. The capability of predicting jet flow properties, as well as two- and three-dimensional jet paths, was enhanced by obtaining the jet cross-sectional area during the solution of the conservation equations. Realistic estimates of temperature in the jet fluid were acquired by accounting for heat losses in the jet flow due to forced convection and to entrainment of free-stream fluid into the jet.

Campbell, J. F.↗