Buoyancy Effects on Flow Structure and Instability of Low-Density Gas Jets

NASA Technical Reports Server (NTRS)

Pasumarthi, Kasyap Sriramachandra

2004-01-01

Reynolds number was varied from 200 to 1500 and jet Richardson number was varied from 0.72 to 0.002. Power spectra plots generated from Fast Fourier Transform (FFT) analysis of angular deflection data acquired at a temporal resolution of 1000Hz reveal substantial damping of the oscillation amplitude in microgravity at low Richardson numbers (0.002). Quantitative concentration data in the form of spatial and temporal evolutions of the instability data in Earth gravity and microgravity reveal significant variations in the jet flow structure upon removal of buoyancy forces. Radial variation of the frequency spectra and time traces of helium concentration revealed the importance of gravitational effects in the jet shear layer region. Linear temporal and spatio-temporal stability analyses of a low-density round gas jet injected into a high-density ambient gas were performed by assuming hyper-tan mean velocity and density profiles. The flow was assumed to be non parallel. Viscous and diffusive effects were ignored. The mean flow parameters were represented as the sum of the mean value and a small normal-mode fluctuation. A second order differential equation governing the pressure disturbance amplitude was derived from the basic conservation equations. The effects of the inhomogeneous shear layer and the Froude number (signifying the effects of gravity) on the temporal and spatio-temporal results were delineated. A decrease in the density ratio (ratio of the density of the jet to the density of the ambient gas) resulted in an increase in the temporal amplification rate of the disturbances. The temporal growth rate of the disturbances increased as the Froude number was reduced. The spatio-temporal analysis performed to determine the absolute instability characteristics of the jet yield positive absolute temporal growth rates at all Fr and different axial locations. As buoyancy was removed (Fr . 8), the previously existing absolute instability disappeared at all locations

Influence of gas flow and applied voltage on interaction of jets in a cross-field helium plasma jet array

NASA Astrophysics Data System (ADS)

Wan, Meng; Liu, Feng; Fang, Zhi; Zhang, Bo; Wan, Hui

2017-09-01

Atmospheric Pressure Plasma Jet arrays can greatly enhance the treatment area to fulfill the need for large-scale surface processing, while the spatial uniformity of the plasma jet array is closely related to the interactions of the adjacent jets. In this paper, a three-tube one-dimensional (1D) He plasma jet array with a cross-field needle-ring electrode structure is used to investigate the influences of the gas flow rate and applied voltage on the interactions of the adjacent jets through electrical, optical, and fluid measurements. The repulsion of the adjacent plume channels is observed using an intensified charge-coupled device (ICCD) and the influence of the gas flow rate and applied voltage on the electrostatic repulsion force, Coulomb force, is discussed. It is found that electrical coupling, mainly electrostatic repulsion force, exists among the jets in the array, which causes both the divergence of the lateral plumes and the nonlinear changes of the discharge power and the transport charge. The deflection angle of the lateral plumes with respect to the central plume in the optical images increases with the increase of applied voltage and decreases with the increase of gas flow rate. The deflection angle of the lateral plumes in the optical images is obviously larger than that of the lateral gas streams in the Schlieren images under the same experimental conditions, and the unconformity of the deflection angles is mainly attributed to the electrostatic repulsion force in adjacent plasma plume channels. The experimental results can help understand the interaction mechanisms of jets in the array and design controllable and scalable plasma jet arrays.

Numerical Investigation of the Interaction of Counterflowing Jets and Supersonic Capsule Flows

NASA Technical Reports Server (NTRS)

Venkatachari, Balaji Shankar; Ito, Yasushi; Cheng, Gary; Chang, Chau-Lyan

2011-01-01

Use of counterflowing jets ejected into supersonic freestreams as a flow control concept to modify the external flowfield has gained renewed interest with regards to potential retropropulsion applications pertinent to entry, descent, and landing investigations. This study describes numerical computations of such a concept for a scaled wind-tunnel capsule model by employing the space-time conservation element solution element viscous flow solver with unstructured meshes. Both steady-state and time-accurate computations are performed for several configurations with different counterflowing jet Mach numbers. Axisymmetric computations exploring the effect of the jet flow rate and jet Mach number on the flow stability, jet interaction with the bow shock and its subsequent impact on the aerodynamic and aerothermal loads on the capsule body are carried out. Similar to previous experimental findings, both long and short penetration modes exist at a windtunnel Mach number of 3.48. It was found that both modes exhibit non-stationary behavior and the former is much more unstable than the latter. It was also found that the unstable long penetration mode only exists in a relatively small range of the jet mass flow rate. Solution-based mesh refinement procedures are used to improve solution accuracy and provide guidelines for a more effective mesh generation procedure for parametric studies. Details of the computed flowfields also serve as a means to broaden the knowledge base for future retropropulsion design studies.

Investigation of Impact Jets Flow in Heat Sink Device of Closed-Circuit Cooling Systems

NASA Astrophysics Data System (ADS)

Tokarev, D. A.; Yenivatov, V. V.; Sokolov, S. S.; Erofeev, V. L.

2018-03-01

The flow simulations of impact jets in the heat sink device of the closed-circuit cooling systems are presented. The analysis of the rate of fluid flow in the heat sink device with the jet supply coolant is given.

Flow Channel Influence of a Collision-Based Piezoelectric Jetting Dispenser on Jet Performance

PubMed Central

Deng, Guiling; Li, Junhui; Duan, Ji’an

2018-01-01

To improve the jet performance of a bi-piezoelectric jet dispenser, mathematical and simulation models were established according to the operating principle. In order to improve the accuracy and reliability of the simulation calculation, a viscosity model of the fluid was fitted to a fifth-order function with shear rate based on rheological test data, and the needle displacement model was fitted to a nine-order function with time based on real-time displacement test data. The results show that jet performance is related to the diameter of the nozzle outlet and the cone angle of the nozzle, and the impacts of the flow channel structure were confirmed. The approach of numerical simulation is confirmed by the testing results of droplet volume. It will provide a reliable simulation platform for mechanical collision-based jet dispensing and a theoretical basis for micro jet valve design and improvement. PMID:29677140

The noise and flow characteristics of inverted-profile coannular jets

NASA Technical Reports Server (NTRS)

Tanna, H. K.; Tester, B. J.; Lau, J. C.

1979-01-01

A basic understanding of the noise reduction mechanisms in shock-free inverted-velocity-profile coannular jets was studied. Acoustic measurements are first conducted in an anechoic facility to isolate the effects of inverted velocity and inverted temperature for coannular jets having constant total thrust, mass flow rate and exit area. To obtain physical explanations of the measured noise changes, several types of experiments are conducted. These include (1) source location experiments using the polar correlation technique, (2) mean flow surveys using a combination pressure/temperature probe, and (3) detailed mean flow and turbulence measurements using a two-point four-channel laser velocimeter. The results from these experiments are presented and discussed in detail. Finally, the measured variations of coannular jet mixing noise with fan-to-primary velocity ratio and static temperature ratio are interpreted by utilizing the results from the various experimental phases in conjunction with the existing Lockheed single jet noise prediction model.

Synthetic Jet Flow Field Database for CFD Validation

NASA Technical Reports Server (NTRS)

Yao, Chung-Sheng; Chen, Fang Jenq; Neuhart, Dan; Harris, Jerome

2004-01-01

An oscillatory zero net mass flow jet was generated by a cavity-pumping device, namely a synthetic jet actuator. This basic oscillating jet flow field was selected as the first of the three test cases for the Langley workshop on CFD Validation of Synthetic Jets and Turbulent Separation Control. The purpose of this workshop was to assess the current CFD capabilities to predict unsteady flow fields of synthetic jets and separation control. This paper describes the characteristics and flow field database of a synthetic jet in a quiescent fluid. In this experiment, Particle Image Velocimetry (PIV), Laser Doppler Velocimetry (LDV), and hot-wire anemometry were used to measure the jet velocity field. In addition, the actuator operating parameters including diaphragm displacement, internal cavity pressure, and internal cavity temperature were also documented to provide boundary conditions for CFD modeling.

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

NASA Technical Reports Server (NTRS)

Simon, F. F.; Ciancone, M. L.

1985-01-01

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 configutations 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.

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

NASA Technical Reports Server (NTRS)

Simon, Frederick F.; Ciancone, Michael L.

1987-01-01

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.

Flow control in axial fan inlet guide vanes by synthetic jets

NASA Astrophysics Data System (ADS)

Cyrus, V.; Trávníček, Z.; Wurst, P.; Kordík, J.

2013-04-01

Tested high pressure axial flow fan with hub/tip ratio of 0.70 and external diameter of 600 mm consisted of inlet guide vanes (IGV), rotor and stator blade rows. Fan peripheral velocity was 47 m/s. Air volume flow rate was changed by turning of rear part of the inlet guide vanes. At turning of 20 deg the flow was separated on the IGV profiles. The synthetic jets were introduced through radial holes in machine casing in the location before flow separation origin. Synthetic jet actuator was designed with the use of a speaker by UT AVCR. Its membrane had diameter of 63 mm. Excitation frequency was chosen in the range of 500 Hz - 700 Hz. Synthetic jets favourably influenced separated flow on the vane profiles in the distance of (5 - 12) mm from the casing surface. The reduction of flow separation area caused in the region near the casing the decrease of the profile loss coefficient approximately by 20%.

Pitched and Yawed Circular Jets in Cross-Flow

NASA Technical Reports Server (NTRS)

Milanovic, Ivana M.; Zaman, K. B. M. Q.; Reddy, D. R. (Technical Monitor)

2002-01-01

Results from an experimental investigation of flow field generated by pitched and yawed jets discharging from a flat plate into a cross-flow are presented. The circular jet was pitched at alpha = 20 degrees and 45 degrees and yawed between beta = 0 degrees and 90 degrees in increments of 15 degrees. The measurements were performed with two X-wires providing all three components of velocity and turbulence intensity. These data were obtained at downstream locations of x = 3, 5, 10 and 20, where the distance x normalized by the jet diameter, is measured from the center of the orifice. Data for all configurations were acquired at a momentum-flux ratio J = 8. Additionally, for selected angles and locations, surveys were conducted for J = 1.5, 4, and 20. As expected, the jet penetration is found to be higher at larger alpha. With increasing beta the jet spreads more. The rate of reduction of peak streamwise vorticity, with the downstream distance is significantly lessened at higher alpha but is found to be practically independent of alpha. Thus, at the farthest measurement station x = 20, omega(sub xmax) is about five times larger for beta = 0 degrees compared to the levels at beta = 0 degrees. Streamwise velocity within the jet-vortex structure is found to depend on the parameter J. At J = 1.5 and 4, 'wake-like' velocity profiles are observed. In comparison, a 'jet-like' overshoot is present at higher J.

Effect of jet-mainstream velocity ratio on flow characteristics and heat transfer enhancement of jet on flat plate flow

NASA Astrophysics Data System (ADS)

Puzu, N.; Prasertsan, S.; Nuntadusit, C.

2017-09-01

The aim of this research was to study the effect of jet-mainstream velocity ratio on flow and heat transfer characteristics of jet on flat plate flow. The jet from pipe nozzle with inner diameter of D=14 mm was injected perpendicularly to mainstream on flat plate. The flat plate was blown by mainstream with uniform velocity profile at 10 m/s. The velocity ratio (jet to mainstream velociy) was varied at VR=0.25 and 3.5 by adjusting velocity of jet flow. For heat transfer measurement, a thin foil technique was used to evaluate the heat transfer coefficient by measuring temperature distributions on heat transfer surface with constant heat flux by using infrared camera. Flow characteristics were simulated by using a computational fluid dynamics (CFD) with commercial software ANSYS Fluent (Ver.15.0). The results showed that the enhancement of heat transfer along downstream direction for the case of VR=0.25 was from the effect of jet stream whereas for the case of VR=3.5 was from the effect of mainstream.

Simulation of Sweep-Jet Flow Control, Single Jet and Full Vertical Tail

NASA Technical Reports Server (NTRS)

Childs, Robert E.; Stremel, Paul M.; Garcia, Joseph A.; Heineck, James T.; Kushner, Laura K.; Storms, Bruce L.

2016-01-01

This work is a simulation technology demonstrator, of sweep jet flow control used to suppress boundary layer separation and increase the maximum achievable load coefficients. A sweep jet is a discrete Coanda jet that oscillates in the plane parallel to an aerodynamic surface. It injects mass and momentum in the approximate streamwise direction. It also generates turbulent eddies at the oscillation frequency, which are typically large relative to the scales of boundary layer turbulence, and which augment mixing across the boundary layer to attack flow separation. Simulations of a fluidic oscillator, the sweep jet emerging from a nozzle downstream of the oscillator, and an array of sweep jets which suppresses boundary layer separation are performed. Simulation results are compared to data from a dedicated validation experiment of a single oscillator and its sweep jet, and from a wind tunnel test of a full-scale Boeing 757 vertical tail augmented with an array of sweep jets. A critical step in the work is the development of realistic time-dependent sweep jet inflow boundary conditions, derived from the results of the single-oscillator simulations, which create the sweep jets in the full-tail simulations. Simulations were performed using the computational fluid dynamics (CFD) solver Overow, with high-order spatial discretization and a range of turbulence modeling. Good results were obtained for all flows simulated, when suitable turbulence modeling was used.

Numerical models of jet disruption in cluster cooling flows

NASA Technical Reports Server (NTRS)

Loken, Chris; Burns, Jack O.; Roettiger, Kurt; Norman, Mike

1993-01-01

We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow.

Flow Separation Control Over a Ramp Using Sweeping Jet Actuators

NASA Technical Reports Server (NTRS)

Koklu, Mehti; Owens, Lewis R.

2014-01-01

Flow separation control on an adverse-pressure-gradient ramp model was investigated using various flow-control methods in the NASA Langley 15-Inch Wind Tunnel. The primary flow-control method studied used a sweeping jet actuator system to compare with more classic flow-control techniques such as micro-vortex generators, steady blowing, and steady- and unsteady-vortex generating jets. Surface pressure measurements and a new oilflow visualization technique were used to characterize the effects of these flow-control actuators. The sweeping jet actuators were run in three different modes to produce steady-straight, steady-angled, and unsteady-oscillating jets. It was observed that all of these flow-control methods are effective in controlling the separated flows on the ramp model. The steady-straight jet energizes the boundary layer by momentum addition and was found to be the least effective method for a fixed momentum coefficient. The steady-angled jets achieved better performance than the steady-straight jets because they generate streamwise vortices that energize the boundary layer by mixing high-momentum fluid with near wall low-momentum fluid. The unsteady-oscillating jets achieved the best performance by increasing the pressure recovery and reducing the downstream flow separation. Surface flow visualizations indicated that two out-of-phase counter-rotating vortices are generated per sweeping jet actuator, while one vortex is generated per vortex-generating jets. The extra vortex resulted in increased coverage, more pressure recovery, and reduced flow separation.

Fluid dynamic aspects of jet noise generation. [noise measurement of jet blast effects from supersonic jet flow in convergent-divergent nozzles

NASA Technical Reports Server (NTRS)

Barra, V.; Panunzio, S.

1976-01-01

Jet engine noise generation and noise propagation was investigated by studying supersonic nozzle flow of various nozzle configurations in an experimental test facility. The experimental facility was constructed to provide a coaxial axisymmetric jet flow of unheated air. In the test setup, an inner primary flow exhausted from a 7 in. exit diameter convergent--divergent nozzle at Mach 2, while a secondary flow had a 10 in. outside diameter and was sonic at the exit. The large dimensions of the jets permitted probes to be placed inside the jet core without significantly disturbing the flow. Static pressure fluctuations were measured for the flows. The nozzles were designed for shock free (balanced) flow at Mach 2. Data processing techniques and experimental procedures were developed in order to study induced disturbances at the edge of the supersonic flows, and the propagation of those disturbances throughout the flows. Equipment used (specifications are given) to record acoustic levels (far field noise) is described. Results and conclusions are presented and discussed. Diagrams of the jet flow fields are included along with photographs of the test stand.

Unsteady jet flow computation towards noise prediction

NASA Technical Reports Server (NTRS)

Soh, Woo-Yung

1994-01-01

An attempt has been made to combine a wave solution method and an unsteady flow computation to produce an integrated aeroacoustic code to predict far-field jet noise. An axisymmetric subsonic jet is considered for this purpose. A fourth order space accurate Pade compact scheme is used for the unsteady Navier-Stokes solution. A Kirchhoff surface integral for the wave equation is employed through the use of an imaginary surface which is a circular cylinder enclosing the jet at a distance. Information such as pressure and its time and normal derivatives is provided on the surface. The sound prediction is performed side by side with the jet flow computation. Retarded time is also taken into consideration since the cylinder body is not acoustically compact. The far-field sound pressure has the directivity and spectra show that low frequency peaks shift toward higher frequency region as the observation angle increases from the jet flow axis.

Flowing of supersonic underexpanded micro-jets in the range of moderate Reynolds numbers

NASA Astrophysics Data System (ADS)

Mironov, S. G.; Aniskin, V. M.; Maslov, A. A.

2017-10-01

The paper presents new experimental results on the simulation of supersonic underexpanded micro-jets by macro-jet in the range of moderate Reynolds numbers of air outflow from the nozzle. A correlation is shown between the variations in the Pitot pressure in the model micro-jet with variations in the length of the supersonic core of real the micro-jets. The results of experiments on the effect of humidity on the pulsation of mass flow rate in a micro-jet are presented.

Noise from Supersonic Coaxial Jets. Part 1; Mean Flow Predictions

NASA Technical Reports Server (NTRS)

Dahl, Milo D.; Morris, Philip J.

1997-01-01

Recent theories for supersonic jet noise have used an instability wave noise generation model to predict radiated noise. This model requires a known mean flow that has typically been described by simple analytic functions for single jet mean flows. The mean flow of supersonic coaxial jets is not described easily in terms of analytic functions. To provide these profiles at all axial locations, a numerical scheme is developed to calculate the mean flow properties of a coaxial jet. The Reynolds-averaged, compressible, parabolic boundary layer equations are solved using a mixing length turbulence model. Empirical correlations are developed to account for the effects of velocity and temperature ratios and Mach number on the shear layer spreading. Both normal velocity profile and inverted velocity profile coaxial jets are considered. The mixing length model is modified in each case to obtain reasonable results when the two stream jet merges into a single fully developed jet. The mean flow calculations show both good qualitative and quantitative agreement with measurements in single and coaxial jet flows.

Estimation of Flow Channel Parameters for Flowing Gas Mixed with Air in Atmospheric-pressure Plasma Jets

NASA Astrophysics Data System (ADS)

Yambe, Kiyoyuki; Saito, Hidetoshi

2017-12-01

When the working gas of an atmospheric-pressure non-equilibrium (cold) plasma flows into free space, the diameter of the resulting flow channel changes continuously. The shape of the channel is observed through the light emitted by the working gas of the atmospheric-pressure plasma. When the plasma jet forms a conical shape, the diameter of the cylindrical shape, which approximates the conical shape, defines the diameter of the flow channel. When the working gas flows into the atmosphere from the inside of a quartz tube, the gas mixes with air. The molar ratio of the working gas and air is estimated from the corresponding volume ratio through the relationship between the diameter of the cylindrical plasma channel and the inner diameter of the quartz tube. The Reynolds number is calculated from the kinematic viscosity of the mixed gas and the molar ratio. The gas flow rates for the upper limit of laminar flow and the lower limit of turbulent flow are determined by the corresponding Reynolds numbers estimated from the molar ratio. It is confirmed that the plasma jet length and the internal plasma length associated with strong light emission increase with the increasing gas flow rate until the rate for the upper limit of laminar flow and the lower limit of turbulent flow, respectively. Thus, we are able to explain the increasing trend in the plasma lengths with the diameter of the flow channel and the molar ratio by using the cylindrical approximation.

Flow visualization of lateral jet injection into swirling crossflow

NASA Technical Reports Server (NTRS)

Ferrell, G. B.; Aoki, K.; Lilley, D. G.

1985-01-01

Flow visualization experiments have been conducted to characterize the time-mean flowfield of a deflected turbulent jet in a confining cylindrical crossflow. Jet-to-crossflow velocity ratios of 2, 4, and 6 were investigated, under crossflow inlet swirler vane angles of 0 (swirler removed), 45 and 70 degrees. Smoke, neutrally-buoyant helium-filled soap bubbles, and multi-spark flow visualization were employed to highlight interesting features of the deflected jet, as well as the trajectory and spread pattern of the jet. Gross flowfield characterization was obtained for a range of lateral jet-to-crossflow velocity ratios and a range of inlet swirl strengths in the main flow. The flow visualization results agree well with the measurements obtained elsewhere with the six-orientation single hot-wire method.

Experimental parametric study of jet vortex generators for flow separation control

NASA Technical Reports Server (NTRS)

Selby, Gregory

1991-01-01

A parametric wind-tunnel study was performed with jet vortex generators to determine their effectiveness in controlling flow separation associated with low-speed turbulence flow over a two-dimensional rearward-facing ramp. Results indicate that flow-separation control can be accomplished, with the level of control achieved being a function of jet speed, jet orientation (with respect to the free-stream direction), and orifice pattern (double row of jets vs. single row). Compared to slot blowing, jet vortex generators can provide an equivalent level of flow control over a larger spanwise region (for constant jet flow area and speed). Dye flow visualization tests in a water tunnel indicated that the most effective jet vortex generator configurations produced streamwise co-rotating vortices.

Flow Coupling Effects in Jet-in-Crossflow Flowfields

NASA Technical Reports Server (NTRS)

Bain, D. B.; Smith, C. E.; Liscinsky, D. S.; Holdeman, J. D.

1996-01-01

The combustor designer is typically required to design liner orifices that effectively mix air jets with crossflow effluent. CFD combustor analysis is typically used in the design process; however the jets are usually assumed to enter the combustor with a uniform velocity and turbulence profile. The jet-mainstream flow coupling is usually neglected because of the computational expense. This CFD study was performed to understand the effect of jet-mainstream flow coupling, and to assess the accuracy of jet boundary conditions that are commonly used in combustor internal calculations. A case representative of a plenum-fed quick-mix section of a Rich Burn/Quick Mix/Lean Burn combustor (i.e. a jet-mainstream mass-flow ratio of about 3 and a jet-mainstream momentum-flux ratio of about 30) was investigated. This case showed that the jet velocity entering the combustor was very non-uniform, with a low normal velocity at the leading edge of the orifice and a high normal velocity at the trailing edge of the orifice. Three different combustor-only cases were analyzed with uniform inlet jet profile. None of the cases matched the plenum-fed calculations. To assess liner thickness effects, a thin-walled case was also analyzed. The CFD analysis showed the thin-walled jets had more penetration than the thick-walled jets.

Numerical Analysis of Pelton Nozzle Jet Flow Behavior Considering Elbow Pipe

NASA Astrophysics Data System (ADS)

Chongji, Zeng; Yexiang, Xiao; Wei, Xu; Tao, Wu; Jin, Zhang; Zhengwei, Wang; Yongyao, Luo

2016-11-01

In Pelton turbine, the dispersion of cylindrical jet have a great influence on the energy interaction of jet and buckets. This paper simulated the internal flow of nozzle and the downstream free jet flow at 3 different needle strokes. The nozzle model consists of the elbow pipe and the needle rod which supported by 4 ribs. Homogenous model and SST k-ω model were adopted to simulate the unsteady two-phase jet flow. The development of free flow, including a contraction process followed by an expansion process, was analysed detailed as well as the influence of the nozzle geometry on the jet flow pattern. The increase of nozzle opening results in a more dispersion jet, which means a higher hydraulic loss. Upstream bend and ribs induce the secondary flow in the jet and decrease the jet concentration.

Optimal Micro-Jet Flow Control for Compact Air Vehicle Inlets

NASA Technical Reports Server (NTRS)

Anderson, Bernhard H.; Miller, Daniel N.; Addington, Gregory A.; Agrell, Johan

2004-01-01

The purpose of this study on micro-jet secondary flow control is to demonstrate the viability and economy of Response Surface Methodology (RSM) to optimally design micro-jet secondary flow control arrays, and to establish that the aeromechanical effects of engine face distortion can also be included in the design and optimization process. These statistical design concepts were used to investigate the design characteristics of "low mass" micro-jet array designs. The term "low mass" micro-jet may refers to fluidic jets with total (integrated) mass flow ratios between 0.10 and 1.0 percent of the engine face mass flow. Therefore, this report examines optimal micro-jet array designs for compact inlets through a Response Surface Methodology.

Flow cytometer jet monitor system

DOEpatents

Van den Engh, Ger

1997-01-01

A direct jet monitor illuminates the jet of a flow cytometer in a monitor wavelength band which is substantially separate from the substance wavelength band. When a laser is used to cause fluorescence of the substance, it may be appropriate to use an infrared source to illuminate the jet and thus optically monitor the conditions within the jet through a CCD camera or the like. This optical monitoring may be provided to some type of controller or feedback system which automatically changes either the horizontal location of the jet, the point at which droplet separation occurs, or some other condition within the jet in order to maintain optimum conditions. The direct jet monitor may be operated simultaneously with the substance property sensing and analysis system so that continuous monitoring may be achieved without interfering with the substance data gathering and may be configured so as to allow the front of the analysis or free fall area to be unobstructed during processing.

Jet-Surface Interaction Test: Flow Measurements Results

NASA Technical Reports Server (NTRS)

Brown, Cliff; Wernet, Mark

2014-01-01

Modern aircraft design often puts the engine exhaust in close proximity to the airframe surfaces. Aircraft noise prediction tools must continue to develop in order to meet the challenges these aircraft present. The Jet-Surface Interaction Tests have been conducted to provide a comprehensive quality set of experimental data suitable for development and validation of these exhaust noise prediction methods. Flow measurements have been acquired using streamwise and cross-stream particle image velocimetry (PIV) and fluctuating surface pressure data acquired using flush mounted pressure transducers near the surface trailing edge. These data combined with previously reported far-field and phased array noise measurements represent the first step toward the experimental data base. These flow data are particularly applicable to development of noise prediction methods which rely on computational fluid dynamics to uncover the flow physics. A representative sample of the large flow data set acquired is presented here to show how a surface near a jet affects the turbulent kinetic energy in the plume, the spatial relationship between the jet plume and surface needed to generate surface trailing-edge noise, and differences between heated and unheated jet flows with respect to surfaces.

Transition to turbulence and noise radiation in heated coaxial jet flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gloor, Michael, E-mail: gloor@ifd.mavt.ethz.ch; Bühler, Stefan; Kleiser, Leonhard

2016-04-15

Laminar-turbulent transition and noise radiation of a parametrized set of subsonic coaxial jet flows with a hot primary (core) stream are investigated numerically by Large-Eddy Simulation (LES) and direct noise computation. This study extends our previous research on local linear stability of heated coaxial jet flows by analyzing the nonlinear evolution of initially laminar flows disturbed by a superposition of small-amplitude unstable eigenmodes. First, a baseline configuration is studied to shed light on the flow dynamics of coaxial jet flows. Subsequently, LESs are performed for a range of Mach and Reynolds numbers to systematically analyze the influences of the temperaturemore » and the velocity ratios between the primary and the secondary (bypass) stream. The results provide a basis for a detailed analysis of fundamental flow-acoustic phenomena in the considered heated coaxial jet flows. Increasing the primary-jet temperature leads to an increase of fluctuation levels and to an amplification of far-field noise, especially at low frequencies. Strong mixing between the cold bypass stream and the hot primary stream as well as the intermittent character of the flow field at the end of the potential core lead to a pronounced noise radiation at an aft angle of approximately 35{sup ∘}. The velocity ratio strongly affects the shear-layer development and therefore also the noise generation mechanisms. Increasing the secondary-stream velocity amplifies the dominance of outer shear-layer perturbations while the disturbance growth rates in the inner shear layer decrease. Already for r{sub mic} > 40R{sub 1}, where r{sub mic} is the distance from the end of the potential core and R{sub 1} is the core-jet radius, a perfect 1/r{sub mic} decay of the sound pressure amplitudes is observed. The potential-core length increases for higher secondary-stream velocities which leads to a shift of the center of the dominant acoustic radiation in the downstream direction.« less

Mass-loss rates, ionization fractions, shock velocities, and magnetic fields of stellar jets

NASA Technical Reports Server (NTRS)

Hartigan, Patrick; Morse, Jon A.; Raymond, John

1994-01-01

In this paper we calculate emission-line ratios from a series of planar radiative shock models that cover a wide range of shock velocities, preshock densities, and magnetic fields. The models cover the initial conditions relevant to stellar jets, and we show how to estimate the ionization fractions and shock velocities in jets directly from observations of the strong emission lines in these flows. The ionization fractions in the HH 34, HH 47, and HH 111 jets are approximately 2%, considerably smaller than previous estimates, and the shock velocities are approximately 30 km/s. For each jet the ionization fractions were found from five different line ratios, and the estimates agree to within a factor of approximately 2. The scatter in the estimates of the shock velocities is also small (+/- 4 km/s). The low ionization fractions of stellar jets imply that the observed electron densities are much lower than the total densities, so the mass-loss rates in these flows are correspondingly higher (approximately greater than 2 x 10(exp -7) solar mass/yr). The mass-loss rates in jets are a significant fraction (1%-10%) of the disk accretion rates onto young stellar objects that drive the outflows. The momentum and energy supplied by the visible portion of a typical stellar jet are sufficient to drive a weak molecular outflow. Magnetic fields in stellar jets are difficult to measure because the line ratios from a radiative shock with a magnetic field resemble those of a lower velocity shock without a field. The observed line fluxes can in principle indicate the strength of the field if the geometry of the shocks in the jet is well known.

The flow structure of jets from transient sources and implications for modeling short-duration explosive volcanic eruptions

NASA Astrophysics Data System (ADS)

Chojnicki, K. N.; Clarke, A. B.; Adrian, R. J.; Phillips, J. C.

2014-12-01

We used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum, a condition that defines plumes from discrete Vulcanian and Strombolian-style eruptions. We simultaneously measured the analog-jet discharge rate (the supply rate of momentum) and the analog-jet internal velocity distribution (a consequence of momentum transport and dilution). Then, we examined the changes in the analog-jet velocity distribution over time to assess the impact of the supply-rate variations on the momentum-driven rise dynamics. We found that the analog-jet velocity distribution changes significantly and quickly as the supply rate varied, such that the whole-field distribution at any instant differed considerably from the time average. We also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0.93 in an individual unsteady jet. Consequently, we conclude that supply-rate variations exert first-order control over jet dynamics, and therefore cannot be neglected in models without compromising their capability to predict large-scale eruption behavior. These findings emphasize the fundamental differences between unsteady and steady jet dynamics, and show clearly that: (i) variations in source momentum flux directly control the dynamics of the resulting flow; (ii) impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi-steady flow models. New modeling approaches capable of describing the time-dependent properties of transient volcanic eruption plumes are needed before their trajectory, dilution, and stability can be reliably computed for hazards management.

DBD Actuated Flow Control of Wall-Jet and Cross-Flow Interaction for Film Cooling Applications

NASA Astrophysics Data System (ADS)

Tirumala, Rakshit; Benard, Nicolas; Moreau, Eric; Fenot, Matthieu; Lalizel, Gildas; Dorignac, Eva

2014-11-01

In this work, we use surface DBD actuators to control the interaction between a wall jet and mainstream flow in film cooling applications. The intention of the study is to improve the contact of the jet with the wall and enhance the convective heat transfer coefficient downstream of the jet exit. A 2D wall jet (10 mm height) is injected into the mainstream flow at an angle of 30°. With an injected jet velocity (Ui) of 5 m/s, two blowing ratios M (=ρi Ui / ρ∞U∞) of 1.0 and 0.5 are studied corresponding to the mainstream flow velocity (U∞) of 5 m/s and 10 m/s respectively. Different configurations of the DBD actuator are studied, positioned both inside the jet and on the downstream side. PIV measurements are conducted to investigate the flow field of the interaction between the jet and cross flow. Streamwise velocity profiles at different downstream locations are compared to analyze the efficacy of the plasma actuator in improving the contact between the injected jet stream and the wall surface. Reynolds shear stress measurements are also conducted to study the mixing regions in the plasma-jet-mainstream flow interaction. Work was partially funded by the French government program ``Investissements d'avenir'' (LABEX INTERACTIFS, reference ANR-11-LABX-0017-01).

Asymptotic Spreading Rate of Initially Compressible Jets-Experiment and Analysis

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

1998-01-01

Experimental results for the spreading and centerline velocity decay rates for round, compressible jets, from a convergent and a convergent-divergent nozzle, are presented. The spreading rate is determined from the variation of streamwise mass flux obtained from Pitot probe surveys. Results for the far asymptotic region show that both spreading and centerline velocity decay rates, when nondimensionalized by parameters at the nozzle exit, decrease with increasing "jet Mach number" M(sub j). Dimensional analysis with the assumption of momentum conservation, together with compressible flow calculations for the conditions at the nozzle exit, predict this Mach number dependence well. The analysis also demonstrates that an increase in the "potential core length" of the jet occurring with increasing M(sub j), a commonly observed trend, is largely accounted for simply by the variations in the density and static pressure at the nozzle exit. The effect of decreasing mixing efficiency with increasing compressibility is inferred to contribute only partially to the latter trend.

The ground vortex flow field associated with a jet in a cross flow impinging on a ground plane for uniform and annular turbulent axisymmetric jets. M.S. Thesis

NASA Technical Reports Server (NTRS)

Cavage, William M.; Kuhlman, John M.

1993-01-01

An experimental study was conducted of the impingement of a single circular jet on a ground plane in a cross flow. This geometry is a simplified model of the interaction of propulsive jet exhaust from a V/STOL aircraft with the ground in forward flight. Jets were oriented normal to the cross flow and ground plane. Jet size, cross flow-to-jet velocity ratio, ground plane-to-jet board spacing, and jet exit turbulence level and mean velocity profile shape were all varied to determine their effects on the size of the ground vortex interaction region which forms on the ground plane, using smoke injection into the jet. Three component laser Doppler velocimeter measurements were made with a commercial three color system for the case of a uniform jet with exit spacing equal to 5.5 diameters and cross flow-to-jet velocity ratio equal to 0.11. The flow visualization data compared well for equivalent runs of the same nondimensional jet exit spacing and the same velocity ratio for different diameter nozzles, except at very low velocity ratios and for the larger nozzle, where tunnel blockage became significant. Variation of observed ground vortex size with cross flow-to-jet velocity ratio was consistent with previous studies. Observed effects of jet size and ground plane-to-jet board spacing were relatively small. Jet exit turbulence level effects were also small. However, an annular jet with a low velocity central core was found to have a significantly smaller ground vortex than an equivalent uniform jet at the same values of cross flow-to-jet velocity ratio and jet exit-to-ground plane spacing. This may suggest a means of altering ground vortex behavior somewhat, and points out the importance of proper simulation of jet exit velocity conditions. LV data indicated unsteady turbulence levels in the ground vortex in excess of 70 percent.

Micrometer-thickness liquid sheet jets flowing in vacuum

NASA Astrophysics Data System (ADS)

Galinis, Gediminas; Strucka, Jergus; Barnard, Jonathan C. T.; Braun, Avi; Smith, Roland A.; Marangos, Jon P.

2017-08-01

Thin liquid sheet jet flows in vacuum provide a new platform for performing experiments in the liquid phase, for example X-ray spectroscopy. Micrometer thickness, high stability, and optical flatness are the key characteristics required for successful exploitation of these targets. A novel strategy for generating sheet jets in vacuum is presented in this article. Precision nozzles were designed and fabricated using high resolution (0.2 μm) 2-photon 3D printing and generated 1.49 ± 0.04 μm thickness, stable, and <λ /20-flat jets in isopropanol under normal atmosphere and under vacuum at 5 × 10-1 mbar. The thin sheet technology also holds great promise for advancing the fields of high harmonic generation in liquids, laser acceleration of ions as well as other fields requiring precision and high repetition rate targets.

Coronal Jet Collimation by Nonlinear Induced Flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vasheghani Farahani, S.; Hejazi, S. M.

2017-08-01

Our objective is to study the collimation of solar jets by nonlinear forces corresponding to torsional Alfvén waves together with external forces. We consider a straight, initially non-rotating, untwisted magnetic cylinder embedded in a plasma with a straight magnetic field, where a shear between the internal and external flows exists. By implementing magnetohydrodynamic theory and taking into account the second-order thin flux tube approximation, the balance between the internal nonlinear forces is visualized. The nonlinear differential equation containing the ponderomotive, magnetic tension, and centrifugal forces in the presence of the shear flow is obtained. The solution presents the scale ofmore » influence of the propagating torsional Alfvén wave on compressive perturbations. Explicit expressions for the compressive perturbations caused by the forces connected to the torsional Alfvén wave show that, in the presence of a shear flow, the magnetic tension and centrifugal forces do not cancel each other’s effects as they did in its absence. This shear flow plays in favor of the magnetic tension force, resulting in a more efficient collimation. Regarding the ponderomotive force, the shear flow has no effect. The phase relations highlight the interplay of the shear flow and the plasma- β . As the shear flow and plasma- β increase, compressive perturbation amplitudes emerge. We conclude that the jet collimation due to the torsional Alfvén wave highly depends on the location of the jet. The shear flow tightens the collimation as the jet elevates up to the solar corona.« less

Coronal Jet Collimation by Nonlinear Induced Flows

NASA Astrophysics Data System (ADS)

Vasheghani Farahani, S.; Hejazi, S. M.

2017-08-01

Our objective is to study the collimation of solar jets by nonlinear forces corresponding to torsional Alfvén waves together with external forces. We consider a straight, initially non-rotating, untwisted magnetic cylinder embedded in a plasma with a straight magnetic field, where a shear between the internal and external flows exists. By implementing magnetohydrodynamic theory and taking into account the second-order thin flux tube approximation, the balance between the internal nonlinear forces is visualized. The nonlinear differential equation containing the ponderomotive, magnetic tension, and centrifugal forces in the presence of the shear flow is obtained. The solution presents the scale of influence of the propagating torsional Alfvén wave on compressive perturbations. Explicit expressions for the compressive perturbations caused by the forces connected to the torsional Alfvén wave show that, in the presence of a shear flow, the magnetic tension and centrifugal forces do not cancel each other’s effects as they did in its absence. This shear flow plays in favor of the magnetic tension force, resulting in a more efficient collimation. Regarding the ponderomotive force, the shear flow has no effect. The phase relations highlight the interplay of the shear flow and the plasma-β. As the shear flow and plasma-β increase, compressive perturbation amplitudes emerge. We conclude that the jet collimation due to the torsional Alfvén wave highly depends on the location of the jet. The shear flow tightens the collimation as the jet elevates up to the solar corona.

Multiphase flow of miscible liquids: jets and drops

NASA Astrophysics Data System (ADS)

Walker, Travis W.; Logia, Alison N.; Fuller, Gerald G.

2015-05-01

Drops and jets of liquids that are miscible with the surrounding bulk liquid are present in many processes from cleaning surfaces with the aid of liquid soaps to the creation of biocompatible implants for drug delivery. Although the interactions of immiscible drops and jets show similarities to miscible systems, the small, transient interfacial tension associated with miscible systems create distinct outcomes such as intricate droplet shapes and breakup resistant jets. Experiments have been conducted to understand several basic multiphase flow problems involving miscible liquids. Using high-speed imaging of the morphological evolution of the flows, we have been able to show that these processes are controlled by interfacial tensions. Further multiphase flows include investigating miscible jets, which allow the creation of fibers from inelastic materials that are otherwise difficult to process due to capillary breakup. This work shows that stabilization from the diminishing interfacial tensions of the miscible jets allows various elongated morphologies to be formed.

An experimental investigation of gas jets in confined swirling air flow

NASA Technical Reports Server (NTRS)

Mongia, H.; Ahmed, S. A.; Mongia, H. C.

1984-01-01

The fluid dynamics of jets in confined swirling flows which is of importance to designers of turbine combustors and solid fuel ramjets used to power missiles fired from cannons were examined. The fluid dynamics of gas jets of different densities in confined swirling flows were investigated. Mean velocity and turbulence measurements are made with a one color, one component laser velocimeter operating in the forward scatter mode. It is shown that jets in confined flow with large area ratio are highly dissipative which results in both air and helium/air jet centerline velocity decays. For air jets, the jet like behavior in the tube center disappears at about 20 diameters downstream of the jet exit. This phenomenon is independent of the initial jet velocity. The turbulence field at this point also decays to that of the background swirling flow. A jet like behavior in the tube center is noticed even at 40 diameters for the helium/air jets. The subsequent flow and turbulence field depend highly on the initial jet velocity. The jets are fully turbulent, and the cause of this difference in behavior is attributed to the combined action swirl and density difference. This observation can have significant impact on the design of turbine combustors and solid fuel ramjets subject to spin.

Propulsive jet simulation with air and helium in launcher wake flows

NASA Astrophysics Data System (ADS)

Stephan, Sören; Radespiel, Rolf

2017-06-01

The influence on the turbulent wake of a generic space launcher model due to the presence of an under-expanded jet is investigated experimentally. Wake flow phenomena represent a significant source of uncertainties in the design of a space launcher. Especially critical are dynamic loads on the structure. The wake flow is investigated at supersonic (M=2.9) and hypersonic (M=5.9) flow regimes. The jet flow is simulated using air and helium as working gas. Due to the lower molar mass of helium, higher jet velocities are realized, and therefore, velocity ratios similar to space launchers can be simulated. The degree of under-expansion of the jet is moderate for the supersonic case (p_e/p_∞ ≈ 5) and high for the hypersonic case (p_e/p_∞ ≈ 90). The flow topology is described by Schlieren visualization and mean-pressure measurements. Unsteady pressure measurements are performed to describe the dynamic wake flow. The influences of the under-expanded jet and different jet velocities are reported. On the base fluctuations at a Strouhal number, around St_D ≈ 0.25 dominate for supersonic free-stream flows. With air jet, a fluctuation-level increase on the base is observed for Strouhal numbers above St_D ≈ 0.75 in hypersonic flow regime. With helium jet, distinct peaks at higher frequencies are found. This is attributed to the interactions of wake flow and jet.

Mixing and NO(x) Emission Calculations of Confined Reacting Jet Flows in a Cylindrical Duct

NASA Technical Reports Server (NTRS)

Holdeman, James D. (Technical Monitor); Oechsle, Victor L.

2003-01-01

Rapid mixing of cold lateral jets with hot cross-stream flows in confined configurations is of practical interest in gas turbine combustors as it strongly affects combustor exit temperature quality, and gaseous emissions in for example rich-lean combustion. It is therefore important to further improve our fundamental understanding of the important processes of dilution jet mixing especially when the injected jet mass flow rate exceeds that of the cross-stream. The results reported in this report describe some of the main flow characteristics which develop in the mixing process in a cylindrical duct. A 3-dimensional tool has been used to predict the mixing flow field characteristics and NOx emission in a quench section of an RQL combustor, Eighteen configurations have been analyzed in a circular geometry in a fully reacting environment simulating the operating condition of an actual RQL gas turbine combustion liner. The evaluation matrix was constructed by varying three parameters: 1) jet-to-mainstream momentum-flux ratio (J), 2) orifice shape or orifice aspect ratio, and 3) slot slant angle. The results indicate that the mixing flow field significantly varies with the value of the jet penetration and subsequently, slanting elongated slots generally improve the mixing uniformity at high J conditions. Round orifices produce more uniform mixing and low NO(x) emissions at low J due to the strong and adequate jet penetration. No significant correlation was found between the NO(x) production rates and the mixing deviation parameters, however, strong correlation was found between NO(x) formation and jet penetration. In the computational results, most of the NO(x) formation occurred behind the orifice starting at the orifice wake region. Additional NO(x) is formed upstream of the orifice in certain configurations with high J conditions due to the upstream recirculation.

Computation of inlet reference plane flow-field for a subscale free-jet forebody/inlet model and comparison to experimental data

NASA Astrophysics Data System (ADS)

McClure, M. D.; Sirbaugh, J. R.

1991-02-01

The computational fluid dynamics (CFD) computer code PARC3D was used to predict the inlet reference plane (IRP) flow field for a side-mounted inlet and forebody simulator in a free jet for five different flow conditions. The calculations were performed for free-jet conditions, mass flow rates, and inlet configurations that matched the free-jet test conditions. In addition, viscous terms were included in the main flow so that the viscous free-jet shear layers emanating from the free-jet nozzle exit were modeled. A measure of the predicted accuracy was determined as a function of free-stream Mach number, angle-of-attack, and sideslip angle.

Flow behaviour of negatively buoyant jets in immiscible ambient fluid

NASA Astrophysics Data System (ADS)

Geyer, A.; Phillips, J. C.; Mier-Torrecilla, M.; Idelsohn, S. R.; Oñate, E.

2012-01-01

In this paper we investigate experimentally the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid. Experiments are carried out by injecting a jet of dyed fresh water through a nozzle in the base of a cylindrical tank containing rapeseed oil. The fountain inlet flow rate and nozzle diameter were varied to cover a wide range of Richardson Ri (8 × 10-4 < Ri < 1.98), Reynolds Re (467 < Re < 5,928) and Weber We (2.40 < We < 308.56) numbers. Based on the Re, Ri and We values for the experiments, we have determined a regime map to define how these values may control the occurrence of the observed flow types. Whereas Ri plays a stronger role when determining the maximum penetration height, the effect of the Reynolds number is stronger predicting the flow behaviour for a specific nozzle diameter and injection velocity.

Characteristics of inhomogeneous jets in confined swirling air flows

NASA Technical Reports Server (NTRS)

So, R. M. C.; Ahmed, S. A.

1984-01-01

An experimental program to study the characteristics of inhomogeneous jets in confined swirling flows to obtain detailed and accurate data for the evaluation and improvement of turbulent transport modeling for combustor flows is discussed. The work was also motivated by the need to investigate and quantify the influence of confinement and swirl on the characteristics of inhomogeneous jets. The flow facility was constructed in a simple way which allows easy interchange of different swirlers and the freedom to vary the jet Reynolds number. The velocity measurements were taken with a one color, one component DISA Model 55L laser-Doppler anemometer employing the forward scatter mode. Standard statistical methods are used to evaluate the various moments of the signals to give the flow characteristics. The present work was directed at the understanding of the velocity field. Therefore, only velocity and turbulence data of the axial and circumferential components are reported for inhomogeneous jets in confined swirling air flows.

Numerical analysis of exhaust jet secondary combustion in hypersonic flow field

NASA Astrophysics Data System (ADS)

Yang, Tian-Peng; Wang, Jiang-Feng; Zhao, Fa-Ming; Fan, Xiao-Feng; Wang, Yu-Han

2018-05-01

The interaction effect between jet and control surface in supersonic and hypersonic flow is one of the key problems for advanced flight control system. The flow properties of exhaust jet secondary combustion in a hypersonic compression ramp flow field were studied numerically by solving the Navier-Stokes equations with multi-species and combustion reaction effects. The analysis was focused on the flow field structure and the force amplification factor under different jet conditions. Numerical results show that a series of different secondary combustion makes the flow field structure change regularly, and the temperature increases rapidly near the jet exit.

Synthetic Jet Interactions with Flows of Varying Separation Severity and Spanwise Flow Magnitude

NASA Astrophysics Data System (ADS)

Monastero, Marianne; Lindstrom, Annika; Amitay, Michael

2017-11-01

Flow physics associated with the interactions of synthetic jet actuators with a highly three-dimensional separated flow over a flapped airfoil were investigated experimentally and analyzed using stereo particle image velocimetry (SPIV) and surface pressure data. Increased understanding of active flow control devices in flows which are representative of airplane wings or tails can lead to actuator placement (i.e., chordwise location, spanwise spacing) with the greatest beneficial effect on performance. An array of discrete synthetic jets was located just upstream of the control surface hingeline and operated at a blowing ratio of 1 and non-dimensional frequency of 48. Detailed flowfield measurements over the control surface were conducted, where the airfoil's sweep angle and the control surface deflection angle were fixed at 20°. Focus was placed on the local and global flowfields as spanwise actuator spacing was varied. Moreover, surface pressure measurement for several sweep angles, control surface deflection angles, and angles of attack were also performed. Actuation resulted in an overall separation reduction and a dependence of local flowfield details (i.e. separation severity, spanwise flow magnitude, flow structures, and jet trajectory) on spanwise jet spacing. The Boeing Company.

Experimental Study of Impinging Jets Flow-Fields

DTIC Science & Technology

2016-07-27

1 Grant # N000141410830 Experimental Study of Impinging Jet Flow-Fields Final Report for Period: Jun 15, 2014 – Jun 14, 2016 PI: Dennis K...impinging jet model in the absence of any jet heating. The results of the computations had been compared with the experimental data produced in the...of the validity of the computations, and also of the experimental approach. Figure 12a. Initial single

Development of an Empirical Methods for Predicting Jet Mixing Noise of Cold Flow Rectangular Jets

NASA Technical Reports Server (NTRS)

Russell, James W.

1999-01-01

This report presents an empirical method for predicting the jet mixing noise levels of cold flow rectangular jets. The report presents a detailed analysis of the methodology used in development of the prediction method. The empirical correlations used are based on narrow band acoustic data for cold flow rectangular model nozzle tests conducted in the NASA Langley Jet Noise Laboratory. There were 20 separate nozzle test operating conditions. For each operating condition 60 Hz bandwidth microphone measurements were made over a frequency range from 0 to 60,000 Hz. Measurements were performed at 16 polar directivity angles ranging from 45 degrees to 157.5 degrees. At each polar directivity angle, measurements were made at 9 azimuth directivity angles. The report shows the methods employed to remove screech tones and shock noise from the data in order to obtain the jet mixing noise component. The jet mixing noise was defined in terms of one third octave band spectral content, polar and azimuth directivity, and overall power level. Empirical correlations were performed over the range of test conditions to define each of these jet mixing noise parameters as a function of aspect ratio, jet velocity, and polar and azimuth directivity angles. The report presents the method for predicting the overall power level, the average polar directivity, the azimuth directivity and the location and shape of the spectra for jet mixing noise of cold flow rectangular jets.

Time-dependent jet flow and noise computations

NASA Technical Reports Server (NTRS)

Berman, C. H.; Ramos, J. I.; Karniadakis, G. E.; Orszag, S. A.

1990-01-01

Methods for computing jet turbulence noise based on the time-dependent solution of Lighthill's (1952) differential equation are demonstrated. A key element in this approach is a flow code for solving the time-dependent Navier-Stokes equations at relatively high Reynolds numbers. Jet flow results at Re = 10,000 are presented here. This code combines a computationally efficient spectral element technique and a new self-consistent turbulence subgrid model to supply values for Lighthill's turbulence noise source tensor.

Jet flow issuing from an axisymmetric pipe-cavity-orifice nozzle

NASA Astrophysics Data System (ADS)

Broučková, Zuzana; Pušková, Pavlína; Trávníček, Zdeněk; Šafařík, Pavel

2016-03-01

An axisymmetric air jet flow is experimentally investigated under passive flow control. The jet issues from a pipe of the inner diameter and length of 10 mm and 150 mm which is equipped with an axisymmetric cavity at the pipe end. The cavity operates as a resonator creating self-sustained acoustic excitations of the jet flow. A mechanism of excitations is rather complex - in comparison with a common Helmholtz resonator. The experiments were performed using flow visualization, microphone measurements and time-mean velocity measurements by the Pitot probe. The power spectral density (PSD) and the sound pressure level (SPL) were evaluated from microphone measurements. The jet Reynolds number ranged Re = 1600-18 000. Distinguishable peaks in PSD indicated a function of the resonator. Because the most effective acoustic response was found at higher Re, a majority of experiments focused on higher Re regime. The results demonstrate effects of the passive control on the jet behavior. Fluid mixing and velocity decay along the axis is intensified. It causes shortening of the jet transition region. On the other hand, an inverse proportionality of the velocity decay (u ~ 1/x) in the fully developed region is not changed. The momentum and kinetic energy fluxes decrease more intensively in the controlled jets in comparison with common jets.

The gas jet behavior in submerged Laval nozzle flow

NASA Astrophysics Data System (ADS)

Gong, Zhao-xin; Lu, Chuan-jing; Li, Jie; Cao, Jia-yi

2017-12-01

The behavior of the combustion gas jet in a Laval nozzle flow is studied by numerical simulations. The Laval nozzle is installed in an engine and the combustion gas comes out of the engine through the nozzle and then injects into the surrounding environment. First, the jet injection into the air is simulated and the results are verified by the theoretical solutions of the 1-D isentropic flow. Then the behavior of the gas jet in a submerged Laval nozzle flow is simulated for various water depths. The stability of the jet and the jet evolution with a series of expansion waves and compression waves are analyzed, as well as the mechanism of the jet in a deep water depth. Finally, the numerical results are compared with existing experimental data and it is shown that the characteristics of the water blockage and the average values of the engine thrust are in good agreement and the unfixed engine in the experiment is the cause of the differences of the frequency and the amplitude of the oscillation.

Landau-Squire jet as a versatile probe to measure flow rate through individual nanochannel and nanotubes

NASA Astrophysics Data System (ADS)

Secchi, Eleonora; Marbach, Sophie; Siria, Alessandro; Bocquet, Lyderic

2015-11-01

Over the last decade, nanometric sized channels have been intensively investigated since new model of fluid transport are expected due to the flow confinement at the nanometric scale. Nanoconfinement generates new phenomena, such as superfast flows in carbon nanotubes and slippage over smooth surfaces. However, a major challenge of nanofluidics lies in fabricating nanoscale fluidic devices and developing new velocimetry techniques able to measure flow rates down to femtoL/s. In this work we report the experimental study of the velocity fields generated by pressure driven flow from glass nanochannel with a diameter ranging from 1 μm to 100nm. The flow emerging from these channels can be described by the classical Landau-Squire solution of the Navier-Stokes equation for a point jet. We show that due to the peculiarity of this flow, it can be used as an efficient probe to characterize the permeability of nanochannels. Velocity field is measured experimentally seeding the fluid in the reservoir with 500 nm Polystyrene particles and measuring the velocity with a standard PIV algorithm. Predictions are tested for nanochannels of several dimensions and supported by ionic current measurement. This demonstrates that this technique is a powerful tool to characterize the flow through nanochannels. We finally apply this method to the measurement of the flow emerging from a single carbon nanotube inserted in the nanochannels and present first data of permeability measurement through a single nanotube.

Boundary Conditions for Jet Flow Computations

NASA Technical Reports Server (NTRS)

Hayder, M. E.; Turkel, E.

1994-01-01

Ongoing activities are focused on capturing the sound source in a supersonic jet through careful large eddy simulation (LES). One issue that is addressed is the effect of the boundary conditions, both inflow and outflow, on the predicted flow fluctuations, which represent the sound source. In this study, we examine the accuracy of several boundary conditions to determine their suitability for computations of time-dependent flows. Various boundary conditions are used to compute the flow field of a laminar axisymmetric jet excited at the inflow by a disturbance given by the corresponding eigenfunction of the linearized stability equations. We solve the full time dependent Navier-Stokes equations by a high order numerical scheme. For very small excitations, the computed growth of the modes closely corresponds to that predicted by the linear theory. We then vary the excitation level to see the effect of the boundary conditions in the nonlinear flow regime.

Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

NASA Technical Reports Server (NTRS)

Yep, Tze-Wing; Agrawal, Ajay K.; Griffin, DeVon; Salzman, Jack (Technical Monitor)

2001-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet flow was significantly influenced by the gravity. The jet in microgravity was up to 70 percent wider than that in Earth gravity. The jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes a change in gravity in the drop tower.

Evaluation of Turbulence-Model Performance in Jet Flows

NASA Technical Reports Server (NTRS)

Woodruff, S. L.; Seiner, J. M.; Hussaini, M. Y.; Erlebacher, G.

2001-01-01

The importance of reducing jet noise in both commercial and military aircraft applications has made jet acoustics a significant area of research. A technique for jet noise prediction commonly employed in practice is the MGB approach, based on the Lighthill acoustic analogy. This technique requires as aerodynamic input mean flow quantities and turbulence quantities like the kinetic energy and the dissipation. The purpose of the present paper is to assess existing capabilities for predicting these aerodynamic inputs. Two modern Navier-Stokes flow solvers, coupled with several modern turbulence models, are evaluated by comparison with experiment for their ability to predict mean flow properties in a supersonic jet plume. Potential weaknesses are identified for further investigation. Another comparison with similar intent is discussed by Barber et al. The ultimate goal of this research is to develop a reliable flow solver applicable to the low-noise, propulsion-efficient, nozzle exhaust systems being developed in NASA focused programs. These programs address a broad range of complex nozzle geometries operating in high temperature, compressible, flows. Seiner et al. previously discussed the jet configuration examined here. This convergent-divergent nozzle with an exit diameter of 3.6 inches was designed for an exhaust Mach number of 2.0 and a total temperature of 1680 F. The acoustic and aerodynamic data reported by Seiner et al. covered a range of jet total temperatures from 104 F to 2200 F at the fully-expanded nozzle pressure ratio. The aerodynamic data included centerline mean velocity and total temperature profiles. Computations were performed independently with two computational fluid dynamics (CFD) codes, ISAAC and PAB3D. Turbulence models employed include the k-epsilon model, the Gatski-Speziale algebraic-stress model and the Girimaji model, with and without the Sarkar compressibility correction. Centerline values of mean velocity and mean temperature are

Flow Field and Acoustic Predictions for Three-Stream Jets

NASA Technical Reports Server (NTRS)

Simmons, Shaun Patrick; Henderson, Brenda S.; Khavaran, Abbas

2014-01-01

Computational fluid dynamics was used to analyze a three-stream nozzle parametric design space. The study varied bypass-to-core area ratio, tertiary-to-core area ratio and jet operating conditions. The flowfield solutions from the Reynolds-Averaged Navier-Stokes (RANS) code Overflow 2.2e were used to pre-screen experimental models for a future test in the Aero-Acoustic Propulsion Laboratory (AAPL) at the NASA Glenn Research Center (GRC). Flowfield solutions were considered in conjunction with the jet-noise-prediction code JeNo to screen the design concepts. A two-stream versus three-stream computation based on equal mass flow rates showed a reduction in peak turbulent kinetic energy (TKE) for the three-stream jet relative to that for the two-stream jet which resulted in reduced acoustic emission. Additional three-stream solutions were analyzed for salient flowfield features expected to impact farfield noise. As tertiary power settings were increased there was a corresponding near nozzle increase in shear rate that resulted in an increase in high frequency noise and a reduction in peak TKE. As tertiary-to-core area ratio was increased the tertiary potential core elongated and the peak TKE was reduced. The most noticeable change occurred as secondary-to-core area ratio was increased thickening the secondary potential core, elongating the primary potential core and reducing peak TKE. As forward flight Mach number was increased the jet plume region decreased and reduced peak TKE.

Gravitational Effects on Flow Instability and Transition in Low Density Jets

NASA Technical Reports Server (NTRS)

Agrawal A. K.; Parthasarathy, K.; Pasumarthi, K.; Griffin, D. W.

2000-01-01

Recent experiments have shown that low-density gas jets injected into a high-density ambient gas undergo an instability mode, leading to highly-periodic oscillations in the flow-field for certain conditions. The transition from laminar to turbulent flow in these jets is abrupt, without the gradual change in scales. Even the fine scale turbulent structure repeats itself with extreme regularity from cycle to cycle. Similar observations were obtained in buoyancy-dominated and momentum-dominated jets characterized by the Richardson numbers, Ri = [gD(rho(sub a)-rho(sub j))/rho(sub j)U(sub j)(exp 2) ] where g is the gravitational acceleration, D is the jet diameter, rho(sub a) and rho(sub a) are, respectively, the free-stream and jet densities, and U(sub j) is the mean jet exit velocity. At high Richardson numbers, the instability is presumably caused by buoyancy since the flow-oscillation frequency (f) or the Strouhal number, St = [fD/U(sub j)] scales with Ri. In momentum-dominated jets, however, the Strouhal number of the oscillating flow is relatively independent of the Ri. In this case, a local absolute instability is predicted in the potential core of low-density jets with S [= rho(sub j)/rho(sub a)] < 0.7, which agrees qualitatively with experiments. Although the instability in gas jets of high Richardson numbers is attributed to buoyancy, direct physical evidence has not been acquired in experiments. If the instability is indeed caused by buoyancy, the near-field flow structure of the jet will change significantly when the buoyancy is removed, for example, in the microgravity environment. Thus, quantitative data on the spatial and temporal evolutions of the instability, length and time scale of the oscillating mode and its effects on the mean flow and breakdown of the potential core are needed in normal and microgravity to delineate gravitational effects in buoyant jets. In momentum dominated low-density jets, the instability is speculated to originate in the

SIMULATION AND MOCKUP OF SNS JET-FLOW TARGET WITH WALL JET FOR CAVITATION DAMAGE MITIGATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wendel, Mark W; Geoghegan, Patrick J; Felde, David K

2014-01-01

Pressure waves created in liquid mercury pulsed spallation targets at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory induce cavitation damage on the stainless steel target container. The cavitation damage is thought to limit the lifetime of the target for power levels at and above 1 MW. Severe through-wall cavitation damage on an internal wall near the beam entrance window has been observed in spent-targets. Surprisingly though, there is very little damage on the walls that bound an annular mercury channel that wraps around the front and outside of the target. The mercury flow through this channel ismore » characterized by smooth, attached streamlines. One theory to explain this lack of damage is that the uni-directional flow biases the direction of the collapsing cavitation bubble, reducing the impact pressure and subsequent damage. The theory has been reinforced by in-beam separate effects data. For this reason, a second-generation SNS mercury target has been designed with an internal wall jet configuration intended to protect the concave wall where damage has been observed. The wall jet mimics the annular flow channel streamlines, but since the jet is bounded on only one side, the momentum is gradually diffused by the bulk flow interactions as it progresses around the cicular path of the target nose. Numerical simulations of the flow through this jet-flow target have been completed, and a water loop has been assembled with a transparent test target in order to visualize and measure the flow field. This paper presents the wall jet simulation results, as well as early experimental data from the test loop.« less

Analysis of multiple jets in a cross-flow

NASA Astrophysics Data System (ADS)

Isaac, K. M.; Schetz, J. A.

1982-12-01

The analysis of Campbell and Schetz (1973) is extended to the study of multiple jets in a cross flow, where the interaction of two jets is taken into account by a modification of the drag coefficient that is sensed by each jet. Results show that the rear jet trajectory is significantly modified by the presence of the front one even when the jets are spaced far apart. The analysis is applicable to such phenomena as the exhaust of chimney stack smoke into a wind and the lift jets of a V/STOL aircraft during takeoff or landing in strong winds.

High-Flow Jet Exit Rig Designed and Fabricated

NASA Technical Reports Server (NTRS)

Buehrle, Robert J.; Trimarchi, Paul A.

2003-01-01

The High-Flow Jet Exit Rig at the NASA Glenn Research Center is designed to test single flow jet nozzles and to measure the appropriate thrust and noise levels. The rig has been designed for the maximum hot condition of 16 lbm/sec of combustion air at 1960 R (maximum) and to produce a maximum thrust of 2000 lb. It was designed for cold flow of 29.1 lbm/sec of air at 530 R. In addition, it can test dual-flow nozzles (nozzles with bypass flow in addition to core flow) with independent control of each flow. The High- Flow Jet Exit Rig was successfully fabricated in late 2001 and is being readied for checkout tests. The rig will be installed in Glenn's Aeroacoustic Propulsion Laboratory. The High-Flow Jet Exit Rig consists of the following major components: a single component force balance, the natural-gas-fueled J-79 combustor assembly, the plenum and manifold assembly, an acoustic/instrumentation/seeding (A/I/S) section, a table, and the research nozzles. The rig will be unique in that it is designed to operate uncooled. The structure survives the 1960 R test condition because it uses carefully selected high temperature alloy materials such as Hastelloy-X. The lower plenum assembly was designed to operate at pressures to 450 psig at 1960 R, in accordance with the ASME B31.3 piping code. The natural gas-fueled combustor fires directly into the lower manifold. The hot air is directed through eight 1-1/2-in. supply pipes that supply the upper plenum. The flow is conditioned in the upper plenum prior to flowing to the research nozzle. The 1-1/2-in. supply lines are arranged in a U-shaped design to provide for a flexible piping system. The combustor assembly checkout was successfully conducted in Glenn's Engine Component Research Laboratory in the spring of 2001. The combustor is a low-smoke version of the J79 combustor used to power the F4 Phantom military aircraft. The natural gas-fueled combustor demonstrated high-efficiency combustion over a wide range of operating

Survey of Turbulence Models for the Computation of Turbulent Jet Flow and Noise

NASA Technical Reports Server (NTRS)

Nallasamy, N.

1999-01-01

The report presents an overview of jet noise computation utilizing the computational fluid dynamic solution of the turbulent jet flow field. The jet flow solution obtained with an appropriate turbulence model provides the turbulence characteristics needed for the computation of jet mixing noise. A brief account of turbulence models that are relevant for the jet noise computation is presented. The jet flow solutions that have been directly used to calculate jet noise are first reviewed. Then, the turbulent jet flow studies that compute the turbulence characteristics that may be used for noise calculations are summarized. In particular, flow solutions obtained with the k-e model, algebraic Reynolds stress model, and Reynolds stress transport equation model are reviewed. Since, the small scale jet mixing noise predictions can be improved by utilizing anisotropic turbulence characteristics, turbulence models that can provide the Reynolds stress components must now be considered for jet flow computations. In this regard, algebraic stress models and Reynolds stress transport models are good candidates. Reynolds stress transport models involve more modeling and computational effort and time compared to algebraic stress models. Hence, it is recommended that an algebraic Reynolds stress model (ASM) be implemented in flow solvers to compute the Reynolds stress components.

A computational model for three-dimensional incompressible wall jets with large cross flow

NASA Technical Reports Server (NTRS)

Murphy, W. D.; Shankar, V.; Malmuth, N. D.

1979-01-01

A computational model for the flow field of three dimensional incompressible wall jets prototypic of thrust augmenting ejectors with large cross flow is presented. The formulation employs boundary layer equations in an orthogonal curvilinear coordinate system. Simulation of laminar as well as turbulen wall jets is reported. Quantification of jet spreading, jet growth, nominal separation, and jet shrink effects due to corss flow are discussed.

Low Dimensional Study of a Supersonic Multi-Stream Jet Flow

NASA Astrophysics Data System (ADS)

Tenney, Andrew; Berry, Matthew; Aycock-Rizzo, Halley; Glauser, Mark; Lewalle, Jacques

2017-11-01

In this study, the near field of a two stream supersonic jet flow is examined using low dimensional tools. The flow issues from a multi-stream nozzle as described in A near-field investigation of a supersonic, multi-stream jet: locating turbulence mechanisms through velocity and density measurements by Magstadt et al., with the bulk flow Mach number, M1, being 1.6, and the second stream Mach number, M2, reaching the sonic condition. The flow field is visualized using Particle Image Velocimetry (PIV), with frames captured at a rate of 4Hz. Time-resolved pressure measurements are made just aft of the nozzle exit, as well as in the far-field, 86.6 nozzle hydraulic diameters away from the exit plane. The methodologies used in the analysis of this flow include Proper Orthogonal Decomposition (POD), and the continuous wavelet transform. The results from this ``no deck'' case are then compared to those found in the study conducted by Berry et al. From this comparison, we draw conclusions about the effects of the presence of an aft deck on the low dimensional flow description, and near field spectral content. Supported by AFOSR Grant FA9550-15-1-0435, and AFRL, through an SBIR Grant with Spectral Energies, LLC.

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

NASA Technical Reports Server (NTRS)

Campbell, J. F.; Schetz, J. A.

1973-01-01

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.

Swirl effect on flow structure and mixing in a turbulent jet

NASA Astrophysics Data System (ADS)

Kravtsov, Z. D.; Sharaborin, D. K.; Dulin, V. M.

2018-03-01

The paper reports on experimental study of turbulent transport in the initial region of swirling turbulent jets. The particle image velocimetry and planar laser-induced fluorescence techniques are used to investigate the flow structure and passive scalar concentration, respectively, in free air jet with acetone vapor. Three flow cases are considered, viz., non-swirling jets and swirling jets with and without vortex breakdown and central recirculation zone. Without vortex breakdown, the swirl is shown to promote jet mixing with surrounding air and to decrease the jet core length. The vortex core breakdown further enhances mixing as the jet core disintegrates at the nozzle exit.

The Existence of Steady Compressible Subsonic Impinging Jet Flows

NASA Astrophysics Data System (ADS)

Cheng, Jianfeng; Du, Lili; Wang, Yongfu

2018-03-01

In this paper, we investigate the compressible subsonic impinging jet flows through a semi-infinitely long nozzle and impacting on a solid wall. Firstly, it is shown that given a two-dimensional semi-infinitely long nozzle and a wall behind the nozzle, and an appropriate atmospheric pressure, then there exists a smooth global subsonic compressible impinging jet flow with two asymptotic directions. The subsonic impinging jet develops two free streamlines, which initiate smoothly at the end points of the semi-infinitely long nozzles. In particular, there exists a smooth curve which separates the fluids which go to different places downstream. Moreover, under some suitable asymptotic assumptions of the nozzle, the asymptotic behaviors of the compressible subsonic impinging jet flows in the inlet and the downstream are obtained by means of a blow-up argument. On the other hand, the non-existence of compressible subsonic impinging jet flows with only one asymptotic direction is also established. This main result in this paper solves the open problem (4) in Chapter 16.3 proposed by uc(Friedman) in his famous survey (uc(Friedman) in Mathematics in industrial problems, II, I.M.A. volumes in mathematics and its applications, vol 24, Springer, New York, 1989).

Refraction of high frequency noise in an arbitrary jet flow

NASA Technical Reports Server (NTRS)

Khavaran, Abbas; Krejsa, Eugene A.

1994-01-01

Refraction of high frequency noise by mean flow gradients in a jet is studied using the ray-tracing methods of geometrical acoustics. Both the two-dimensional (2D) and three-dimensional (3D) formulations are considered. In the former case, the mean flow is assumed parallel and the governing propagation equations are described by a system of four first order ordinary differential equations. The 3D formulation, on the other hand, accounts for the jet spreading as well as the axial flow development. In this case, a system of six first order differential equations are solved to trace a ray from its source location to an observer in the far field. For subsonic jets with a small spreading angle both methods lead to similar results outside the zone of silence. However, with increasing jet speed the two prediction models diverge to the point where the parallel flow assumption is no longer justified. The Doppler factor of supersonic jets as influenced by the refraction effects is discussed and compared with the conventional modified Doppler factor.

Gravitational Effects on Near Field Flow Structure of Low Density Gas Jets

NASA Technical Reports Server (NTRS)

Griffin, D. W.; Yep, T. W.; Agrawal, A. K.

2005-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2- second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of site measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and helium mole percentage obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low density jet was buoyancy induced. The paper provides quantitative details of temporal flow evolution as the experiment undergoes change in gravity in the drop tower.

Velocity field of a round jet in a cross flow for various jet injection angles and velocity ratios. [Langley V/STOL tunnel

NASA Technical Reports Server (NTRS)

Fearn, R. L.; Weston, R. P.

1979-01-01

A subsonic round jet injected from a flat plate into a subsonic crosswind of the same temperature was investigated. Velocity and pressure measurements in planes perpendicular to the path of the jet were made for nominal jet injection angles of 45 deg, 60 deg, 75 deg, 90 deg, and 105 deg and for jet/cross flow velocity ratios of four and eight. The velocity measurements were obtained to infer the properties of the vortex pair associated with a jet in a cross flow. Jet centerline and vortex trajectories were determined and fit with an empirical equation that includes the effects of jet injection angle, jet core length, and jet/cross flow velocity ratios.

Jet array impingement flow distributions and heat transfer characteristics. Effects of initial crossflow and nonuniform array geometry. [gas turbine engine component cooling

NASA Technical Reports Server (NTRS)

Florschuetz, L. W.; Metzger, D. E.; Su, C. C.; Isoda, Y.; Tseng, H. H.

1982-01-01

Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. The configurations considered are intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The effects of an initial crossflow which approaches the array through an upstream extension of the channel are considered. Flow distributions as well as heat transfer coefficients and adiabatic wall temperatures resolved to one streamwise hole spacing were measured as a function of the initial crossflow rate and temperature relative to the jet flow rate and temperature. Both Nusselt number profiles and dimensionless adiabatic wall temperature (effectiveness) profiles are presented and discussed. Special test results which show a significant reduction of jet orifice discharge coefficients owing to the effect of a confined crossflow are also presented, along with a flow distribution model which incorporates those effects. A nonuniform array flow distribution model is developed and validated.

Vortex flows with suspended separation regions and long-range untwisted central jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abramovich, G.N.; Trofimov, R.S.

1988-05-01

A study is made of possible physicoaerodynamic configurations of vortical flow with suspended separation regions and untwisted central jets. Such flows are encountered in power plants (heat exchangers, combustion chambers, and chemical reactors) and in nature (tornadoes). The basic configurations of several flows of this type are described, including the structure of a flow formed by coaxial cocurrent twisted jets, the flow in a conical swirl chamber with the formation of an untwisted long-range axial jet, the flow pattern in a gas turbine engine chamber, and some considerations regarding the aerodynamics of a tornado.

Quasi-radial wall jets as a new concept in boundary layer flow control

NASA Astrophysics Data System (ADS)

Javadi, Khodayar; Hajipour, Majid

2018-01-01

This work aims to introduce a novel concept of wall jets wherein the flow is radially injected into a medium through a sector of a cylinder, called quasi-radial (QR) wall jets. The results revealed that fluid dynamics of the QR wall jet flow differs from that of conventional wall jets. Indeed, lateral and normal propagations of a conventional three-dimensional wall jet are via shear stresses. While, lateral propagation of a QR wall jet is due to mean lateral component of the velocity field. Moreover, discharged Arrays of conventional three-dimensional wall jets in quiescent air lead to formation of a combined wall jet at large distant from the nozzles, while QR wall jet immediately spread in lateral direction, meet each other and merge together very quickly in a short distance downstream of the jet nozzles. Furthermore, in discharging the conventional jets into an external flow, there is no strong interaction between them as they are moving parallel. While, in QR wall jets the lateral components of the velocity field strongly interact with boundary layer of the external flow and create strong helical vortices acting as vortex generators.

Numerical investigation of cylinder wake flow with a rear stagnation jet

NASA Astrophysics Data System (ADS)

Mo, J. D.; Duke, M. R., Jr.

1994-05-01

Upon visualization of the flow past a cylinder with a rear stagnation jet (RSJ), the flow appears fully attached as conventional inviscid flow does. Therefore, at first glance, it would be suspected that the form drag on the cylinder has been reduced to zero as predicted by inviscid flow theory. However, a detailed numerical simulation reveals that the form drag coefficient increases as the jet velocity increases. The mechanics of the increasing form drag are addressed. The following conclusions were drawn: (1) flow behind a cylinder can be effectively influenced by a RSJ; (2) the unsymmetric wake flow becomes symmetric when the RSI is in operation with a velocity ratio as low as 1; the size of the symmetric recirculation region becomes smaller as the jet speed increases; (3) a RSJ forces a symmetrical wake flow pattern, thus eliminating the lateral force; (4) the pressure on the cylinder surface decreases over the entire surface, but significantly more on the downstream side of the cylinder, as the jet velocity increases, causing an increase in form drag as jet velocity ratio increases; and (5) the RSJ to significantly increase form drag on a bluff body has direct applications in aerodynamic controls of reentry or fligths at high angles of attack.

Flow-field characteristics of high-temperature annular buoyant jets and their development laws influenced by ventilation system.

PubMed

Wang, Yi; Huang, Yanqiu; Liu, Jiaping; Wang, Hai; Liu, Qiuhan

2013-01-01

The flow-field characteristics of high-temperature annular buoyant jets as well as the development laws influenced by ventilation system were studied using numerical methods to eliminate the pollutants effectively in this paper. The development laws of high-temperature annular buoyant jets were analyzed and compared with previous studies, including radial velocity distribution, axial velocity and temperature decay, reattachment position, cross-section diameter, volumetric flow rate, and velocity field characteristics with different pressures at the exhaust hood inlet. The results showed that when the ratio of outer diameter to inner diameter of the annulus was smaller than 5/2, the flow-field characteristics had significant difference compared to circular buoyant jets with the same outer diameter. For similar diameter ratios, reattachment in this paper occurred further downstream in contrast to previous study. Besides, the development laws of volumetric flow rate and cross-section diameter were given with different initial parameters. In addition, through analyzing air distribution characteristics under the coupling effect of high-temperature annular buoyant jets and ventilation system, it could be found that the position where maximum axial velocity occurred was changing gradually when the pressure at the exhaust hood inlet changed from 0 Pa to -5 Pa.

Flow-Field Characteristics of High-Temperature Annular Buoyant Jets and Their Development Laws Influenced by Ventilation System

PubMed Central

Liu, Jiaping; Wang, Hai; Liu, Qiuhan

2013-01-01

The flow-field characteristics of high-temperature annular buoyant jets as well as the development laws influenced by ventilation system were studied using numerical methods to eliminate the pollutants effectively in this paper. The development laws of high-temperature annular buoyant jets were analyzed and compared with previous studies, including radial velocity distribution, axial velocity and temperature decay, reattachment position, cross-section diameter, volumetric flow rate, and velocity field characteristics with different pressures at the exhaust hood inlet. The results showed that when the ratio of outer diameter to inner diameter of the annulus was smaller than 5/2, the flow-field characteristics had significant difference compared to circular buoyant jets with the same outer diameter. For similar diameter ratios, reattachment in this paper occurred further downstream in contrast to previous study. Besides, the development laws of volumetric flow rate and cross-section diameter were given with different initial parameters. In addition, through analyzing air distribution characteristics under the coupling effect of high-temperature annular buoyant jets and ventilation system, it could be found that the position where maximum axial velocity occurred was changing gradually when the pressure at the exhaust hood inlet changed from 0 Pa to −5 Pa. PMID:24000278

Device specific analysis of neonatal aortic outflow cannula jet flows for improved cardiopulmonary bypass hemodynamics

NASA Astrophysics Data System (ADS)

Menon, Prahlad; Sotiropoulos, Fotis; Undar, Akif; Pekkan, Kerem

2011-11-01

Hemodynamically efficient aortic outflow cannulae can provide high blood volume flow rates at low exit force during extracorporeal circulation in pediatric or neonatal cardiopulmonary bypass repairs. Furthermore, optimal hemolytic aortic insertion configurations can significantly reduce risk of post-surgical neurological complications and developmental defects in the young patient. The methodology and results presented in this study serve as a baseline for design of superior aortic outflow cannulae based on a novel paradigm of characterizing jet-flows at different flow regimes. In-silico evaluations of multiple cannula tips were used to delineate baseline hemodynamic performance of the popular pediatric cannula tips in an experimental cuboidal test-rig, using PIV. High resolution CFD jet-flow simulations performed for various cannula tips in the cuboidal test-rig as well as in-vivo insertion configurations have suggested the existence of optimal surgically relevant characteristics such as cannula outflow angle and insertion depth for improved hemodynamic performance during surgery. Improved cannula tips were designed with internal flow-control features for decreased blood damage and increased permissible flow rates.

The Effects of Sweeping Jet Actuator Parameters on Flow Separation Control

NASA Technical Reports Server (NTRS)

Koklu, Mehti

2015-01-01

A parametric experimental study was performed with sweeping jet actuators (fluidic oscillators) to determine their effectiveness in controlling flow separation on an adverse pressure gradient ramp. Actuator parameters that were investigated include blowing coefficients, operation mode, pitch and spreading angles, streamwise location, aspect ratio, and scale. Surface pressure measurements and surface oil flow visualization were used to characterize the effects of these parameters on the actuator performance. 2D Particle Image Velocimetry measurements of the flow field over the ramp and hot-wire measurements of the actuator's jet flow were also obtained for selective cases. In addition, the sweeping jet actuators were compared to other well-known flow control techniques such as micro-vortex generators, steady blowing, and steady vortex-generating jets. The results confirm that the sweeping jet actuators are more effective than steady blowing and steady vortex-generating jets. The results also suggest that an actuator with a larger spreading angle placed closer to the location where the flow separates provides better performance. For the cases tested, an actuator with an aspect ratio, which is the width/depth of the actuator throat, of 2 was found to be optimal. For a fixed momentum coefficient, decreasing the aspect ratio to 1 produced weaker vortices while increasing the aspect ratio to 4 reduced coverage area. Although scaling down the actuator (based on the throat dimensions) from 0.25 inch x 0.125 inch to 0.15 inch x 0.075 inch resulted in similar flow control performance, scaling down the actuator further to 0.075 inch x 0.0375 inch reduced the actuator efficiency by reducing the coverage area and the amount of mixing in the near-wall region. The results of this study provide insight that can be used to design and select the optimal sweeping jet actuator configuration for flow control applications.

Characteristics of transverse hydrogen jet in presence of multi air jets within scramjet combustor

NASA Astrophysics Data System (ADS)

Barzegar Gerdroodbary, M.; Fallah, Keivan; Pourmirzaagha, H.

2017-03-01

In this article, three-dimensional simulation is performed to investigate the effects of micro air jets on mixing performances of cascaded hydrogen jets within a scramjet combustor. In order to compare the efficiency of this technique, constant total fuel rate is injected through one, four, eight and sixteen arrays of portholes in a Mach 4.0 crossflow with a fuel global equivalence ratio of 0.5. In this method, micro air jets are released within fuel portholes to augment the penetration in upward direction. Extensive studies were performed by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Numerical studies on various air and fuel arrangements are done and the mixing rate and penetration are comprehensively investigated. Also, the flow feature of the fuel and air jets for different configuration is revealed. According to the obtained results, the influence of the micro air jets is significant and the presence of micro air jets increases the mixing rate about 116%, 77%, 56% and 41% for single, 4, 8 and 16 multi fuel jets, respectively. The maximum mixing rate of the hydrogen jet is obtained when the air jets are injected within the sixteen multi fuel jets. According to the circulation analysis of the flow for different air and fuel arrangements, it was found that the effects of air jets on flow structure are varied in various conditions and the presence of the micro jet highly intensifies the circulation in the case of 8 and 16 multi fuel jets.

An Investigation of Transonic Flow Fields Surrounding Hot and Cold Sonic Jets

NASA Technical Reports Server (NTRS)

Lee, George

1961-01-01

An investigation at free-stream Mach numbers of 0.90 t o 1.10 was made to determine (1) the jet boundaries and the flow fields around hot and cold jets, and (2) whether a cold-gas jet could adequately simulate the boundary and flow field of hot-gas jet. Schlieren photographs and static-pressure surveys were taken in the vacinity of a sonic jet which was operated over a range of jet pressure ratios of 1 to 6, specific heat ratios at the nozzle exit of 1.29 and 1.40, and jet temperatures up to 2600 R.

Two-, three-, and four-poster jets in cross flow

NASA Technical Reports Server (NTRS)

Vukits, Thomas J.; Sullivan, John P.; Murthy, S. N. B.

1993-01-01

In connection with the problems of the ingestion of hot exhaust gases in engines of V/STOL and STOVL aircraft in ground effect, a series of studies have been undertaken. Ground impinging, two- and three-poster jets operating in the presence of cross flow were studied. The current paper is divided into two parts. The first part is a comparison of the low speed, two-, three-, and four-poster jet cases, with respect to the flowfield in the region of interaction between the forward and the jet flows. These include cases with mass balanced inlet suction. An analysis of the inlet entry plane of the low speed two- and three-poster jet cases is also given. In the second part, high speed results for a two jet configuration without inlet suction are given. The results are based on quantitative, marker concentration distributions obtained by digitizing video images.

Dilution Jet Behavior in the Turn Section of a Reverse Flow Combuster

NASA Technical Reports Server (NTRS)

Riddlebaugh, S. M.; Lipshitz, A.; Greber, I.

1982-01-01

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 temperature measurements are presented in the form of consecutive normalized temperature profiles, and jet trajectories. Single jet trajectories were swept toward the inner wall of the turn, whether injection was from the inner or outer wall. This behavior is explained by the radially inward velocity component necessary to support irrotational flow through the turn. Comparison between experimental results and model calculations showed poor agreement due to the model's not including the radial velocity component. A widely spaced row of jets produced trajectories similar to single jets at similar test conditions, but as spacing ratio was reduced, penetration was reduced to the point where the dilution jet flow attached to the wall.

Effects of rotating flows on combustion and jet noise.

NASA Technical Reports Server (NTRS)

Schwartz, I. R.

1972-01-01

Experimental investigations of combustion in rotating (swirling) flow have shown that the mixing and combustion processes were accelerated, flame length and noise levels significantly decreased, and flame stability increased relative to that obtained without rotation. Unsteady burning accompanied by a pulsating flame, violent fluctuating jet, and intense noise present in straight flow burning were not present in rotating flow burning. Correlations between theory and experiment show good agreement. Such effects due to rotating flows could lead to suppressing jet noise, improving combustion, reducing pollution, and decreasing aircraft engine size. Quantitative analysis of the aero-acoustic relationship and noise source characteristics are needed.-

Relationship Between Ureteral Jet Flow, Visual Analogue Scale, and Ureteral Stone Size.

PubMed

Ongun, Sakir; Teken, Abdurrazak; Yılmaz, Orkun; Süleyman, Sakir

2017-06-01

To contribute to the diagnosis and treatment of ureteral stones by investigating the relationship between the ureteral jet flow measurements of patients with ureteral stones and the size of the stones and the patients' pain scores. The sample consisted of patients who presented acute renal colic between December 2014 and 2015 and from a noncontrast computed tomography were found to have a urinary stone. The ureteral jet flow velocities were determined using Doppler ultrasonography. The patients were all assessed in terms of stone size, localization and area, anteroposterior pelvis (AP) diameter, and visual analogue scale (VAS) scores. A total of 102 patients were included in the study. As the VAS score decreased, the peak jet flow velocity on the stone side increased, whereas the flow velocity on the other side, AP diameter, and stone area were reduced (P < .05). As the stone size increased, the peak jet flow velocity was reduced and the AP diameter increased significantly (P < .05). Ureteral jet flow was not observed in 17 patients on the stone side. A statistically significant difference was found between these patients and the remaining patients in terms of all parameters (P < .05). For patients, in whom the peak flow velocity of ureteral jet is low and with a severe level of pain or the peak flow velocity of ureteral jet cannot be measured, there is a low possibility of spontaneous passage and a high possibility of a large stone, and therefore the treatment should be started immediately. Copyright © 2017 Elsevier Inc. All rights reserved.

Structure of hydrogen-rich transverse jets in a vitiated turbulent flow

DOE PAGES

Lyra, Sgouria; Wilde, Benjamin; Kolla, Hemanth; ...

2014-11-24

Our paper reports the results of a joint experimental and numerical study of the flow characteristics and flame structure of a hydrogen rich jet injected normal to a turbulent, vitiated crossflow of lean methane combustion products. Simultaneous high-speed stereoscopic PIV and OH PLIF measurements were obtained and analyzed alongside three-dimensional direct numerical simulations of inert and reacting JICF with detailed H2/COH2/CO chemistry. Both the experiment and the simulation reveal that, contrary to most previous studies of reacting JICF stabilized in low-to-moderate temperature air crossflow, the present conditions lead to a burner-attached flame that initiates uniformly around the burner edge. Significantmore » asymmetry is observed, however, between the reaction zones located on the windward and leeward sides of the jet, due to the substantially different scalar dissipation rates. The windward reaction zone is much thinner in the near field, while also exhibiting significantly higher local and global heat release than the much broader reaction zone found on the leeward side of the jet. The unsteady dynamics of the windward shear layer, which largely control the important jet/crossflow mixing processes in that region, are explored in order to elucidate the important flow stability implications arising in the inert and reacting JICF. The paper concludes with an analysis of the ignition, flame characteristics, and global structure of the burner-attached flame. FurthermoreChemical explosive mode analysis (CEMA) shows that the entire windward shear layer, and a large region on the leeward side of the jet, are highly explosive prior to ignition and are dominated by non-premixed flame structures after ignition. The predominantly mixing limited nature of the flow after ignition is examined by computing the Takeno flame index, which shows that ~70% of the heat release occurs in non-premixed regions.« less

Fluid-flow of a row of jets in crossflow - A numerical study

NASA Technical Reports Server (NTRS)

Kim, S.-W.; Benson, T. J.

1992-01-01

A detailed computer-visualized flow field of a row of jets in a confined crossflow is presented. The Reynolds averaged Navier-Stokes equations are solved using a finite volume method that incorporates a partial differential equation for incremental pressure to obtain a divergence-free flow field. The turbulence is described by a multiple-time-scale turbulence model. The computational domain includes the upstream region of the circular jet so that the interaction between the jet and the crossflow is simulated accurately. It is shown that the row of jets in the crossflow is characterized by a highly complex flow field that includes a horse-shoe vortex and two helical vortices whose secondary velocity components are co-rotating in space. It is also shown that the horse-shoe vortex is a ring of reversed flows located along the circumference of the jet exit.

Numerical Investigation of Flow Around Rectangular Cylinders with and Without Jets

NASA Technical Reports Server (NTRS)

Tiwari, S. N .; Pidugu, S. B.

1999-01-01

The problem of flow past bluff bodies was studied extensively in the past. The problem of drag reduction is very important in many high speed flow applications. Considerable work has been done in this subject area in case of circular cylinders. The present study attempts to investigate the feasibility of drag reduction on a rectangular cylinder by flow injection by flow injection from the rear stagnation region. The physical problem is modeled as two-dimensional body and numerical analysis is carried out with and without trailing jets. A commercial code is used for this purpose. Unsteady computation is performed in case of rectangular cylinders with no trailing jets where as steady state computation is performed when jet is introduced. It is found that drag can be reduced by introducing jets with small intensity in rear stagnation region of the rectangular cylinders.

Experiments and modeling of dilution jet flow fields

NASA Technical Reports Server (NTRS)

Holdeman, James D.

1986-01-01

Experimental and analytical results of the mixing of single, double, and opposed rows of jets with an isothermal or variable-temperature main stream in a straight duct are presented. This study was performed to investigate flow and geometric variations typical of the complex, three-dimensional flow field in the dilution zone of gas-turbine-engine combustion chambers. The principal results, shown experimentally and analytically, were the following: (1) variations in orifice size and spacing can have a significant effect on the temperature profiles; (2) similar distributions can be obtained, independent of orifice diameter, if momentum-flux ratio and orifice spacing are coupled; (3) a first-order approximation of the mixing of jets with a variable-temperature main stream can be obtained by superimposing the main-stream and jets-in-an-isothermal-crossflow profiles; (4) the penetration of jets issuing mixing is slower and is asymmetric with respect to the jet centerplanes, which shift laterally with increasing downstream distance; (5) double rows of jets give temperature distributions similar to those from a single row of equally spaced, equal-area circular holes; (6) for opposed rows of jets, with the orifice centerlines in line, the optimum ratio of orifice spacing to duct height is one-half the optimum value for single-side injection at the same momentum-flux ratiol and (7) for opposed rows of jets, with the orifice centerlines staggered, the optimum ratio of orifice spacing to duct height is twice the optimum value for single-side injection at the same momentum-flux ratio.

Growth rate measurement in free jet experiments

NASA Astrophysics Data System (ADS)

Charpentier, Jean-Baptiste; Renoult, Marie-Charlotte; Crumeyrolle, Olivier; Mutabazi, Innocent

2017-07-01

An experimental method was developed to measure the growth rate of the capillary instability for free liquid jets. The method uses a standard shadow-graph imaging technique to visualize a jet, produced by extruding a liquid through a circular orifice, and a statistical analysis of the entire jet. The analysis relies on the computation of the standard deviation of a set of jet profiles, obtained in the same experimental conditions. The principle and robustness of the method are illustrated with a set of emulated jet profiles. The method is also applied to free falling jet experiments conducted for various Weber numbers and two low-viscosity solutions: a Newtonian and a viscoelastic one. Growth rate measurements are found in good agreement with linear stability theory in the Rayleigh's regime, as expected from previous studies. In addition, the standard deviation curve is used to obtain an indirect measurement of the initial perturbation amplitude and to identify beads on a string structure on the jet. This last result serves to demonstrate the capability of the present technique to explore in the future the dynamics of viscoelastic liquid jets.

Mean flow characteristics for the oblique impingement of an axisymmetric jet

NASA Technical Reports Server (NTRS)

Foss, J. F.; Kleis, S. J.

1975-01-01

The oblique impingement of an axisymmetric jet has been investigated. A summary of the data and the analytical interpretations of the dominant mechanisms which influence the flow are reported. The major characteristics of the shallow angle oblique jet impingement flow field are: (1) minimal dynamic spreading as revealed by the surface pressure field, (2) pronounced kinematic spreading as revealed by the jet flow velocity field, (3) a pronounced upstream shift of the stagnation point from the maximum pressure point, (4) the production of streamwise vorticity by the impingement process.

Effect of Secondary Jet-flow Angle on Performance of Turbine Inter-guide-vane Burner Based on Jet-vortex Flow

NASA Astrophysics Data System (ADS)

Zheng, Haifei; Tang, Hao; Xu, Xingya; Li, Ming

2014-08-01

Four different secondary airflow angles for the turbine inter-guide-vane burners with trapped vortex cavity were designed. Comparative analysis between combustion performances influenced by the variation of secondary airflow angle was carried out by using numerical simulation method. The turbulence was modeled using the Scale-Adaptive Simulation (SAS) turbulence model. Four cases with different secondary jet-flow angles (-45°, 0°, 30°, 60°) were studied. It was observed that the case with secondary jet-flows at 60° angle directed upwards (1) has good mixing effect; (2) mixing effect is the best although the flow field distributions inside both of the cavity and the main flow passage for the four models are very similar; (3) has complete combustion and symmetric temperature distribution on the exit section of guide vane (X = 70 mm), with uniform temperature distribution, less temperature gradient, and shrank local high temperature regions in the notch located on the guide vane.

Jet Engine Exhaust Nozzle Flow Effector

NASA Technical Reports Server (NTRS)

Turner, Travis L. (Inventor); Cano, Roberto J. (Inventor); Silox, Richard J. (Inventor); Buehrle, Ralph D. (Inventor); Cagle, Christopher M. (Inventor); Cabell, Randolph H. (Inventor); Hilton, George C. (Inventor)

2014-01-01

A jet engine exhaust nozzle flow effector is a chevron formed with a radius of curvature with surfaces of the flow effector being defined and opposing one another. At least one shape memory alloy (SMA) member is embedded in the chevron closer to one of the chevron's opposing surfaces and substantially spanning from at least a portion of the chevron's root to the chevron's tip.

Jet Engine Exhaust Nozzle Flow Effector

NASA Technical Reports Server (NTRS)

Turner, Travis L. (Inventor); Buehrle, Ralph D. (Inventor); Silcox, Richard J. (Inventor); Cagle, Christopher M. (Inventor); Cabell, Randolph H. (Inventor); Hilton, George C. (Inventor); Cano, Roberto J. (Inventor)

2011-01-01

A jet engine exhaust nozzle flow effector is a chevron formed with a radius of curvature with surfaces of the flow effector being defined and opposing one another. At least one shape memory alloy (SMA) member is embedded in the chevron closer to one of the chevron's opposing surfaces and substantially spanning from at least a portion of the chevron's root to the chevron's tip.

Effects of the shear layer growth rate on the supersonic jet noise

NASA Astrophysics Data System (ADS)

Ozawa, Yuta; Nonomura, Taku; Oyama, Akira; Mamori, Hiroya; Fukushima, Naoya; Yamamoto, Makoto

2017-11-01

Strong acoustic waves emitted from rocket plume might damage to rocket payloads because their payloads consist of fragile structure. Therefore, understanding and prediction of acoustic wave generation are of importance not only in science, but also in engineering. The present study makes experiments of a supersonic jet flow at the Mach number of 2.0 and investigates a relationship between growth rate of a shear layer and noise generation of the supersonic jet. We conducted particle image velocimetry (PIV) and acoustic measurements for three different shaped nozzles. These nozzles were employed to control the condition of a shear layer of the supersonic jet flow. We applied single-pixel ensemble correlation method (Westerweel et al., 2004) for the PIV images to obtain high-resolution averaged velocity profiles. This correlation method enabled us to obtain detailed data of the shear layer. For all cases, acoustic measurements clearly shows the noise source position at the end of a potential core of the jet. In the case where laminar to turbulent transition occurred in the shear layer, the sound pressure level increased by 4 dB at the maximum. This research is partially supported by Presto, JST (JPMJPR1678) and KAKENHI (25709009 and 17H03473).

Gravitational Effects on Flow Instability and Transition in Low Density Jets

NASA Technical Reports Server (NTRS)

Agrawal, Ajay K.; Parthasarathy, Ramkumar

2004-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique suited for the microgravity environment. The flow structure was characterized by distributions of helium mole fraction obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. Experiments reveal that the global flow oscillations observed in Earth gravity are absent in microgravity. The report provides quantitative details of flow evolution as the experiment undergoes change in gravity in the drop tower.

Turbulent Deflagrated Flame Interaction with a Fluidic Jet Flow for Deflagration-to-Detonation Flame Acceleration

NASA Astrophysics Data System (ADS)

Chambers, Jessica; McGarry, Joseph; Ahmed, Kareem

2015-11-01

Detonation is a high energetic mode of pressure gain combustion. Detonation combustion exploits the pressure rise to augment high flow momentum and thermodynamic cycle efficiencies. The driving mechanism of deflagrated flame acceleration to detonation is turbulence generation and induction. A fluidic jet is an innovative method for the production of turbulence intensities and flame acceleration. Compared to traditional obstacles, the jet reduces the pressure losses and heat soak effects while providing turbulence generation control. The investigation characterizes the turbulent flame-flow interactions. The focus of the study is on classifying the turbulent flame dynamics and the temporal evolution of turbulent flame regime. The turbulent flame-flow interactions are experimentally studied using a LEGO Detonation facility. Advanced high-speed laser diagnostics, particle image velocimetry (PIV), planar laser induced florescence (PLIF), and Schlieren imaging are used in analyzing the physics of the interaction and flame acceleration. Higher turbulence induction is observed within the turbulent flame after contact with the jet, leading to increased flame burning rates. The interaction with the fluidic jet results in turbulent flame transition from the thin reaction zones to the broken reaction regime.

Flow instabilities in non-uniformly heated helium jet arrays used for divertor PFCs

DOE PAGES

Youchison, Dennis L.

2015-07-30

In this study, due to a lack of prototypical experimental data, little is known about the off-normal behavior of recently proposed divertor jet cooling concepts. This article describes a computational fluid dynamics (CFD) study on two jet array designs to investigate their susceptibility to parallel flow instabilities induced by non-uniform heating and large increases in the helium outlet temperature. The study compared a single 25-jet helium-cooled modular divertor (HEMJ) thimble and a micro-jet array with 116 jets. Both have pure tungsten armor and a total mass flow rate of 10 g/s at a 600 °C inlet temperature. We investigated flowmore » perturbations caused by a 30 MW/m 2 off-normal heat flux applied over a 25 mm 2 area in addition to the nominal 5 MW/m 2 applied over a 75 mm 2 portion of the face. The micro-jet array exhibited lower temperatures and a more uniform surface temperature distribution than the HEMJ thimble. We also investigated the response of a manifolded nine-finger HEMJ assembly using the nominal heat flux and a 274 mm 2 heated area. For the 30 MW/m2 case, the micro-jet array absorbed 750 W in the helium with a maximum armor surface temperature of 1280 °C and a fluid/solid interface temperature of 801 °C. The HEMJ absorbed 750 W with a maximum armor surface temperature of 1411 °C and a fluid/solid interface temperature of 844 °C. For comparison, both the single HEMJ finger and the micro-jet array used 5-mm-thick tungsten armor. The ratio of maximum to average temperature and variations in the local heat transfer coefficient were lower for the micro-jet array compared to the HEMJ device. Although high heat flux testing is required to validate the results obtained in these simulations, the results provide important guidance in jet design and manifolding to increase heat removal while providing more even temperature distribution and minimizing non-uniformity in the gas flow and thermal stresses at the armor joint.« less

Effects of the electrical parameters and gas flow rate on the generation of reactive species in liquids exposed to atmospheric pressure plasma jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baek, Eun Jeong; Joh, Hea Min; Kim, Sun Ja

2016-07-15

In this work, an atmospheric pressure plasma jet was fabricated and studied for plasma–liquid interactions. The plasma jet consists of a quartz-covered pin electrode and outer quartz tube with a tapered nozzle. Using the current–voltage (I-V) and optical emission characteristics of the plasma jet, the plasma density and the speed of the plume were investigated. The optical emission spectra clearly indicated the excited NO, O, OH, N{sub 2}, and N{sub 2}{sup +} in the plasma plumes. Then the plasma jets were applied to the deionized water. We investigated the effects of the operating parameters such as applied voltage, pulse frequency,more » and gas flow rate on the generation of reactive species in the gas and liquid phases. The densities of reactive species including OH radicals were obtained at the plasma–liquid surface and inside the plasma-treated liquids using ultraviolet absorption spectroscopy and chemical probe method. The nitrite concentration was detected by Griess assay. The data are very suggestive that there is a strong correlation among the production of reactive oxygen and nitrogen species (RONS) in the plasmas and liquids.« less

A CFD study of gas-solid jet in a CFB riser flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Tingwen; Guenther, Chris

2012-03-01

Three-dimensional high-resolution numerical simulations of a gas–solid jet in a high-density riser flow were conducted. The impact of gas–solid injection on the riser flow hydrodynamics was investigated with respect to voidage, tracer mass fractions, and solids velocity distribution. The behaviors of a gas–solid jet in the riser crossflow were studied through the unsteady numerical simulations. Substantial separation of the jetting gas and solids in the riser crossflow was observed. Mixing of the injected gas and solids with the riser flow was investigated and backmixing of gas and solids was evaluated. In the current numerical study, both the overall hydrodynamics ofmore » riser flow and the characteristics of gas–solid jet were reasonably predicted compared with the experimental measurements made at NETL.« less

Investigation on Plasma Jet Flow Phenomena During DC Air Arc Motion in Bridge-Type Contacts

NASA Astrophysics Data System (ADS)

Zhai, Guofu; Bo, Kai; Chen, Mo; Zhou, Xue; Qiao, Xinlei

2016-05-01

Arc plasma jet flow in the air was investigated under a bridge-type contacts in a DC 270 V resistive circuit. We characterized the arc plasma jet flow appearance at different currents by using high-speed photography, and two polished contacts were used to search for the relationship between roughness and plasma jet flow. Then, to make the nature of arc plasma jet flow phenomena clear, a simplified model based on magnetohydrodynamic (MHD) theory was established and calculated. The simulated DC arc plasma was presented with the temperature distribution and the current density distribution. Furthermore, the calculated arc flow velocity field showed that the circular vortex was an embodiment of the arc plasma jet flow progress. The combined action of volume force and contact surface was the main reason of the arc jet flow. supported by National Natural Science Foundation of China (Nos. 51307030, 51277038)

Arc Jet Facility Test Condition Predictions Using the ADSI Code

NASA Technical Reports Server (NTRS)

Palmer, Grant; Prabhu, Dinesh; Terrazas-Salinas, Imelda

2015-01-01

The Aerothermal Design Space Interpolation (ADSI) tool is used to interpolate databases of previously computed computational fluid dynamic solutions for test articles in a NASA Ames arc jet facility. The arc jet databases are generated using an Navier-Stokes flow solver using previously determined best practices. The arc jet mass flow rates and arc currents used to discretize the database are chosen to span the operating conditions possible in the arc jet, and are based on previous arc jet experimental conditions where possible. The ADSI code is a database interpolation, manipulation, and examination tool that can be used to estimate the stagnation point pressure and heating rate for user-specified values of arc jet mass flow rate and arc current. The interpolation is performed in the other direction (predicting mass flow and current to achieve a desired stagnation point pressure and heating rate). ADSI is also used to generate 2-D response surfaces of stagnation point pressure and heating rate as a function of mass flow rate and arc current (or vice versa). Arc jet test data is used to assess the predictive capability of the ADSI code.

LAUNCHING AND QUENCHING OF BLACK HOLE RELATIVISTIC JETS AT LOW ACCRETION RATE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pu, Hung-Yi; Chang, Hsiang-Kuang; Hirotani, Kouichi

2012-10-20

Relativistic jets are launched from black hole (BH) X-ray binaries and active galactic nuclei when the disk accretion rate is below a certain limit (i.e., when the ratio of the accretion rate to the Eddingtion accretion rate, m-dot , is below about 0.01) but quenched when above. We propose a new paradigm to explain this observed coupling between the jet and the accretion disk by investigating the extraction of the rotational energy of a BH when it is surrounded by different types of accretion disk. At low accretion rates (e.g., when m-dot {approx}<0.1), the accretion near the event horizon ismore » quasi-spherical. The accreting plasmas fall onto the event horizon in a wide range of latitudes, breaking down the force-free approximation near the horizon. To incorporate the plasma inertia effect, we consider the magnetohydrodynamical (MHD) extraction of the rotational energy from BHs by the accreting MHD fluid, as described by the MHD Penrose process. It is found that the energy extraction operates, and hence a relativistic jet is launched, preferentially when the accretion disk consists of an outer Shakura-Sunyaev disk (SSD) and an inner advection-dominated accretion flow. When the entire accretion disk type changes into an SSD, the jet is quenched because the plasmas bring more rest-mass energy than what is extracted from the hole electromagnetically to stop the extraction. Several other issues related to observed BH disk-jet couplings, such as why the radio luminosity increases with increasing X-ray luminosity until the radio emission drops, are also explained.« less

Flow Characterization Studies of the 10-MW TP3 Arc-Jet Facility: Probe Sweeps

NASA Technical Reports Server (NTRS)

Goekcen, Tahir; Alunni, Antonella I.

2016-01-01

This paper reports computational simulations and analysis in support of calibration and flow characterization tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted in the NASA Ames 10-MW TP3 facility using flat-faced stagnation calorimeters at six conditions corresponding to the steps of a simulated flight heating profile. Data were obtained using a conical nozzle test configuration in which the models were placed in a free jet downstream of the nozzle. Experimental surveys of arc-jet test flow with pitot pressure and heat flux probes were also performed at these arc-heater conditions, providing assessment of the flow uniformity and valuable data for the flow characterization. Two different sets of pitot pressure and heat probes were used: 9.1-mm sphere-cone probes (nose radius of 4.57 mm or 0.18 in) with null-point heat flux gages, and 15.9-mm (0.625 in) diameter hemisphere probes with Gardon gages. The probe survey data clearly show that the test flow in the TP3 facility is not uniform at most conditions (not even axisymmetric at some conditions), and the extent of non-uniformity is highly dependent on various arc-jet parameters such as arc current, mass flow rate, and the amount of cold-gas injection at the arc-heater plenum. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzle and test box, including the models tested. Comparisons of computations with the experimental measurements show reasonably good agreement except at the extreme low pressure conditions of the facility envelope.

Mixing liquid-liquid stratified flows using transverse jets in cross flows

NASA Astrophysics Data System (ADS)

Wright, Stuart; Matar, Omar K.; Markides, Christos N.

2017-11-01

Low pipeline velocities in horizontal liquid-liquid flows lead to gravitationally-induced stratification. This results in flow situations that have no point where average properties can be measured. Inline mixing limits the stratification effect by forming unstable liquid-liquid dispersions. An experimental system is used to measure the mixing performance of various jet-in-cross-flow (JICF) configurations as examples of active inline mixers. The test section consists of a 8.5-m long ETFE pipe with a 50-mm diameter, which is refractive index-matched to both a 10 cSt silicone oil and a 51 wt% glycerol solution. This practice allows advanced laser-based optical techniques, namely PLIF and PIV/PTV, to be applied to these flows in order to measure the phase fractions and velocity fields, respectively. A volume of a fluid (VOF) CFD code is then used to simulate simple jet geometries and to demonstrate the breakup and dispersion capabilities of JICFs in stratified pipeline flows by predicting their mixing efficiency. These simulation results are contrasted with the experimental results to examine the effectiveness of these simulations in predicting the dispersion and breakup. Funding from Cameron/Schlumberger, and the TMF Consortium gratefully acknowledged.

Fluctuating pressures in flow fields of jets

NASA Technical Reports Server (NTRS)

Schroeder, J. C.; Haviland, J. K.

1976-01-01

The powered lift configurations under present development for STOL aircraft are the externally blown flap (EBF), involving direct jet impingement on the aircraft flaps, and the upper surface blown (USB), where the jet flow is attached on the upper surface of the wing and directed downwards. Towards the goal of developing scaling laws to predict unsteady loads imposed on the structural components of these STOL aircraft from small model tests, the near field fluctuating pressure behavior for the simplified cases of a round free cold jet and the same jet impinging on a flat plate was investigated. Examples are given of coherences, phase lags (giving convection velocities), and overall fluctuating pressure levels measured. The fluctuating pressure levels measured on the flat plate are compared to surface fluctuating pressure levels measured on full-scale powered-lift configuration models.

Buoyancy Effects on Flow Transition in Low-Density Inertial Gas Jets

NASA Technical Reports Server (NTRS)

Pasumarthi, Kasyap S.; Agrawal, Ajay K.

2005-01-01

Effects of buoyancy on transition from laminar to turbulent flow are presented for momentum-dominated helium jet injected into ambient air. The buoyancy was varied in a 2.2-sec drop tower facility without affecting the remaining operating parameters. The jet flow in Earth gravity and microgravity was visualized using the rainbow schlieren deflectometry apparatus. Results show significant changes in the flow structure and transition behavior in the absence of buoyancy.

Dripping and jetting regimes in co-flowing capillary jets: unforced measurements and response to driving

NASA Astrophysics Data System (ADS)

Baroud, Charles; Cordero, Maria-Luisa; Gallaire, Francois

2011-11-01

We study the breakup of drops in a co-flowing jet, within the confinement of a microfluidic channel. The breakup can occur right after the nozzle (dripping) or through the generation of a liquid jet that breaks up a long distance from the nozzle (jetting). Traditionally, these two regimes have been considered to reflect an absolutely unstable jet or a convectively unstable jet, respectively. We first provide measurements of the frequency of oscillation and breakup of the liquid jet; the dispersion relation thus obtained compares well with existing theories for convective instabilities in the case of the jetting regime. However, the theories in the absolutely unstable mode fail to predict the evolution of the frequency and drop size in the dripping regime. We also test the jet response to an external forcing, using a focused laser to locally heat the jet. The dripping regime is found to be insensitive to the perturbation and the frequency of drop formation remains unaltered. In contrast, the jetting regime locks to the external frequency, which translates into a modification of the drop size in agreement with the dispersion relations. This confirms the convective nature of the jetting regime. Permanent address: Universidad de Chile.

Numerical Simulation of a High Mach Number Jet Flow

NASA Technical Reports Server (NTRS)

Hayder, M. Ehtesham; Turkel, Eli; Mankbadi, Reda R.

1993-01-01

The recent efforts to develop accurate numerical schemes for transition and turbulent flows are motivated, among other factors, by the need for accurate prediction of flow noise. The success of developing high speed civil transport plane (HSCT) is contingent upon our understanding and suppression of the jet exhaust noise. The radiated sound can be directly obtained by solving the full (time-dependent) compressible Navier-Stokes equations. However, this requires computational storage that is beyond currently available machines. This difficulty can be overcome by limiting the solution domain to the near field where the jet is nonlinear and then use acoustic analogy (e.g., Lighthill) to relate the far-field noise to the near-field sources. The later requires obtaining the time-dependent flow field. The other difficulty in aeroacoustics computations is that at high Reynolds numbers the turbulent flow has a large range of scales. Direct numerical simulations (DNS) cannot obtain all the scales of motion at high Reynolds number of technological interest. However, it is believed that the large scale structure is more efficient than the small-scale structure in radiating noise. Thus, one can model the small scales and calculate the acoustically active scales. The large scale structure in the noise-producing initial region of the jet can be viewed as a wavelike nature, the net radiated sound is the net cancellation after integration over space. As such, aeroacoustics computations are highly sensitive to errors in computing the sound sources. It is therefore essential to use a high-order numerical scheme to predict the flow field. The present paper presents the first step in a ongoing effort to predict jet noise. The emphasis here is in accurate prediction of the unsteady flow field. We solve the full time-dependent Navier-Stokes equations by a high order finite difference method. Time accurate spatial simulations of both plane and axisymmetric jet are presented. Jet Mach

Rethinking the process of detrainment: jets in obstructed natural flows

NASA Astrophysics Data System (ADS)

Mossa, Michele; de Serio, Francesca

2016-12-01

A thorough understanding of the mixing and diffusion of turbulent jets released in porous obstructions is still lacking in literature. This issue is undoubtedly of interest because it is not strictly limited to vegetated flows, but also includes outflows which come from different sources and which spread among oyster or wind farms, as well as aerial pesticide treatments sprayed onto orchards. The aim of the present research is to analyze this process from a theoretical point of view. Specifically, by examining the entrainment coefficient, it is deduced that the presence of a canopy prevents a momentum jet from having an entrainment process, but rather promotes its detrainment. In nature, detrainment is usually associated with buoyancy-driven flows, such as plumes or density currents flowing in a stratified environment. The present study proves that detrainment occurs also when a momentum-driven jet is issued in a not-stratified obstructed current, such as a vegetated flow.

Flow field topology of submerged jets with fractal generated turbulence

NASA Astrophysics Data System (ADS)

Cafiero, Gioacchino; Discetti, Stefano; Astarita, Tommaso

2015-11-01

Fractal grids (FGs) have been recently an object of numerous investigations due to the interesting capability of generating turbulence at multiple scales, thus paving the way to tune mixing and scalar transport. The flow field topology of a turbulent air jet equipped with a square FG is investigated by means of planar and volumetric particle image velocimetry. The comparison with the well-known features of a round jet without turbulence generators is also presented. The Reynolds number based on the nozzle exit section diameter for all the experiments is set to about 15 000. It is demonstrated that the presence of the grid enhances the entrainment rate and, as a consequence, the scalar transfer of the jet. Moreover, due to the effect of the jet external shear layer on the wake shed by the grid bars, the turbulence production region past the grid is significantly shortened with respect to the documented behavior of fractal grids in free-shear conditions. The organization of the large coherent structures in the FG case is also analyzed and discussed. Differently from the well-known generation of toroidal vortices due to the growth of azimuthal disturbances within the jet shear layer, the fractal grid introduces cross-wise disturbs which produce streamwise vortices; these structures, although characterized by a lower energy content, have a deeper streamwise penetration than the ring vortices, thus enhancing the entrainment process.

Flow-structure interaction effects on a jet emanating from a flexible nozzle

PubMed Central

Murugappan, S.; Gutmark, E. J.; Lakhamraju, R. R.; Khosla, S.

2008-01-01

In recent years, a wide variety of applications have been found for the use of pulsed jets in the area of flow control. The goal of the current study was to identify the flow field and mixing characteristics associated with an incompressible elongated jet emitted from a flexible nozzle. The shape of the nozzle was that of a high aspect ratio jet deforming from a fully opened to a completely closed configuration. The jet was characterized by a pulsatile flow that was self-excited by the motion of the flexible tube. The frequency of excitation was found to be between 150 and 175 Hz and the Strouhal number (nondimensional frequency) varied from 0.17 to 0.45. The jet flow was dominated by vortices that were shed from the nozzle with an axis parallel to the major axis. The vortices in the near field were quasi-two-dimensional so that measurements performed at the center plane represented the dynamics of the entire vortex. The nozzle excited two different modes depending on the tension applied to the flexible nozzle and the volumetric flow through it. The first was a flapping mode, which was associated with alternate shedding of vortices. This caused strong steering of the jet to one side or the other. The second mode was a symmetric mode that was associated with the formation of counter-rotating vortex pairs. Turbulence and jet spread in the measured planes were much larger in the first mode than the second one. PMID:19547723

Transient Characteristics of a Fluidic Device for Circulatory Jet Flow.

PubMed

Phan, Hoa Thanh; Dinh, Thien Xuan; Bui, Phong Nhu; Dau, Van Thanh

2018-03-13

In this paper, we report on the design, simulation, and experimental analysis of a miniaturized device that can generate multiple circulated jet flows. The device is actuated by a lead zirconate titanate (PZT) diaphragm. The flows in the device were studied using three-dimensional transient numerical simulation with the programmable open source OpenFOAM and was comparable to the experimental result. Each flow is verified by two hotwires mounted at two positions inside each consisting chamber. The experiment confirmed that the flow was successfully created, and it demonstrated good agreement with the simulation. In addition, a prospective application of the device as an angular rate sensor is also demonstrated. The device is robust, is minimal in size, and can contribute to the development of multi-axis fluidic inertial sensors, fluidic amplifiers, gas mixing, coupling, and analysis.

Transient Characteristics of a Fluidic Device for Circulatory Jet Flow

PubMed Central

Phan, Hoa Thanh; Dinh, Thien Xuan; Bui, Phong Nhu

2018-01-01

In this paper, we report on the design, simulation, and experimental analysis of a miniaturized device that can generate multiple circulated jet flows. The device is actuated by a lead zirconate titanate (PZT) diaphragm. The flows in the device were studied using three-dimensional transient numerical simulation with the programmable open source OpenFOAM and was comparable to the experimental result. Each flow is verified by two hotwires mounted at two positions inside each consisting chamber. The experiment confirmed that the flow was successfully created, and it demonstrated good agreement with the simulation. In addition, a prospective application of the device as an angular rate sensor is also demonstrated. The device is robust, is minimal in size, and can contribute to the development of multi-axis fluidic inertial sensors, fluidic amplifiers, gas mixing, coupling, and analysis. PMID:29534014

An experimental study of the flow field surrounding a subsonic jet in a cross flow. M.S. Thesis

NASA Technical Reports Server (NTRS)

Dennis, Robert Foster

1993-01-01

An experimental investigation of the flow interaction of a 5.08 cm (2.00 in.) diameter round subsonic jet exhausting perpendicularly to a flat plate in a subsonic cross flow was conducted in the NASA Ames 7x1O ft. Wind Tunnel Number One. Flat plate surface pressures were measured at 400 locations in a 30.48 cm (12.0 in.) concentric circular array surrounding the jet exit. Results from these measurements are provided in tabular and graphical form for jet-to-crossflow velocity ratios ranging from 4 to 12, and for jet exit Mach numbers ranging from 0.50 to 0.93. Laser doppler velocimeter (LDV) three component velocity measurements were made in selected regions in the developed jet plume and near the flat plate surface, at a jet Mach number of 0.50 and jet-to-crossflow velocity ratios of 6 and 8. The results of both pressure and LDV measurements are compared with the results of previous experiments. In addition, pictures of the jet plume shape at jet velocity ratios ranging from 4 to 12 were obtained using schleiren photography. The LDV measurements are consistent with previous work, but more extensive measurements will be necessary to provide a detailed picture of the flow field. The surface pressure results compare closely with previous work and provide a useful characterization of jet induced surface pressures. The results demonstrate the primary influence of jet velocity ratio and the secondary influence of jet Mach number in determining such surface pressures.

Study of the propagation of a plane turbulent jet in flow-through chamber workings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laigna, K.Yu.; Potter, E.A.

1988-05-01

The purpose of this study was to determine experimentally the parameters of microstructures of confined planar jets and to investigate the specific features of turbulent diffusion of impurities in such flows for problems of mine ventilation and pollution abatement in underground workings. A confined planar jet flowing from a slot coaxially into the model of a chamber working of rectangular transverse cross section was studied. The averaged and pulsating characteristics of the jet were measured by a thermoanemometer. Transient and channel zones were identified and the movement of the jet within them was described. Results demonstrated that the turbulent diffusionmore » coefficient in the jet-affected zone was greater by two or three orders of magnitude than in the remainder of the flow and that it is therefore incorrect to use turbulent diffusion coefficients of confined flows for evaluations of the jet diffusion of impurities.« less

High-Speed Rainbow Schlieren Deflectometry Analysis of Helium Jets Flowing into Air for Microgravity Applications

NASA Technical Reports Server (NTRS)

Leptuch, Peter A.

2002-01-01

The flow phenomena of buoyant jets have been analyzed by many researchers in recent years. Few, however have studied jets in microgravity conditions, and the exact nature of the flow under these conditions has until recently been unknown. This study seeks to extend the work done by researchers at the university of Oklahoma in examining and documenting the behavior of helium jets in micro-gravity conditions. Quantitative rainbow schlieren deflectometry data have been obtained for helium jets discharging vertically into quiescent ambient air from tubes of several diameters at various flow rates using a high-speed digital camera. These data have obtained before, during and after the onset of microgravity conditions. High-speed rainbow schlieren deflectometry has been developed for this study with the installation and use of a high-speed digital camera and modifications to the optical setup. Higher temporal resolution of the transitional phase between terrestrial and micro-gravity conditions has been obtained which has reduced the averaging effect of longer exposure times used in all previous schlieren studies. Results include color schlieren images, color time-space images (temporal evolution images), frequency analyses, contour plots of hue and contour plots of helium mole fraction. The results, which focus primarily on the periods before and during the onset of microgravity conditions, show that the pulsation of the jets normally found in terrestrial gravity ("earth"-gravity) conditions cease, and the gradients in helium diminish to produce a widening of the jet in micro-gravity conditions. In addition, the results show that the disturbance propagate upstream from a downstream source.

Prediction of Turbulent Jet Mixing Noise Reduction by Water Injection

NASA Technical Reports Server (NTRS)

Kandula, Max

2008-01-01

A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum and energy for the confrol volume, and introduces the concept of effective jet parameters (jet temperature, jet velocity and jet Mach number). It is shown that the water to jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated, and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach number and jet Reynolds number. Predictions from the model show satisfactory comparison with available test data on perfectly expanded hot supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios.

Post-stenotic plug-like jet with a vortex ring demonstrated by 4D flow MRI.

PubMed

Kim, Guk Bae; Ha, Hojin; Kweon, Jihoon; Lee, Sang Joon; Kim, Young-Hak; Yang, Dong Hyun; Kim, Namkug

2016-05-01

To investigate the details of the flow structure of a plug-like jet that had a vortex ring in pulsatile stenotic phantoms using 4D flow MRI. Pulsatile Newtonian flows in two stenotic phantoms with 50% and 75% reductions in area were scanned by 4D flow MRI. Blood analog working fluid was circulated via the stenotic phantom using a pulsatile pump at a constant pulsating frequency of 1Hz. The velocity and vorticity fields of the plug-like jet with a vortex ring were quantitatively analyzed in the spatial and temporal domains. Pulsatile stenotic flow showed a plug-like jet at the specific stenotic degree of 50% in our pulsatile waveform design. This plug-like jet was found at the decelerating period in the post-stenotic region of 26.4mm (1.2 D). It revealed a vortex ring structure with vorticity strength in the range of ±100s(-1). We observed a plug-like jet with a vortex ring in pulsatile stenotic flow by in vitro visualization using 4D flow MRI. In this plug-like jet, the local fastest flow region occurred at the post-systole phase in the post-stenotic region, which was distinguishable from a typical stenotic jet flow at systole phase. Copyright © 2015 Elsevier Inc. All rights reserved.

The silent base flow and the sound sources in a laminar jet.

PubMed

Sinayoko, Samuel; Agarwal, Anurag

2012-03-01

An algorithm to compute the silent base flow sources of sound in a jet is introduced. The algorithm is based on spatiotemporal filtering of the flow field and is applicable to multifrequency sources. It is applied to an axisymmetric laminar jet and the resulting sources are validated successfully. The sources are compared to those obtained from two classical acoustic analogies, based on quiescent and time-averaged base flows. The comparison demonstrates how the silent base flow sources shed light on the sound generation process. It is shown that the dominant source mechanism in the axisymmetric laminar jet is "shear-noise," which is a linear mechanism. The algorithm presented here could be applied to fully turbulent flows to understand the aerodynamic noise-generation mechanism. © 2012 Acoustical Society of America

Nozzle Free Jet Flows Within the Strong Curved Shock Regime

NASA Technical Reports Server (NTRS)

Shih, Tso-Shin

1975-01-01

A study based on inviscid analysis was conducted to examine the flow field produced from a convergent-divergent nozzle when a strong curved shock occurs. It was found that a certain constraint is imposed on the flow solution of the problem which is the unique feature of the flow within this flow regime, and provides the reason why the inverse method of calculation cannot be employed for these problems. An approximate method was developed to calculate the flow field, and results were obtained for two-dimensional flows. Analysis and calculations were performed for flows with axial symmetry. It is shown that under certain conditions, the vorticity generated at the jet boundary may become infinite and the viscous effect becomes important. Under other conditions, the asymptotic free jet height as well as the corresponding shock geometry were determined.

Flow and Acoustic Properties of Low Reynolds Number Underexpanded Supersonic Jets. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hu, Tieh-Feng

1981-01-01

Jet noise on underexpanded supersonic jets are studied with emphasis on determining the role played by large scale organized flow fluctuations in the flow and acoustic processes. The experimental conditions of the study were chosen as low Reynolds number (Re=8,000) Mach 1.4 and 2.1, and moderate Reynolds number (Re=68,000) Mach 1.6 underexpanded supersonic jets exhausting from convergent nozzles. At these chosen conditions, detailed experimental measurements were performed to improve the understanding of the flow and acoustic properties of underexpanded supersonic jets.

Free compressible jet investigation

NASA Astrophysics Data System (ADS)

De Gregorio, Fabrizio

2014-03-01

The nozzle pressure ratio (NPR) effect on a supersonic turbulent jet was investigated. A dedicated convergent/divergent nozzle together with a flow feeding system was designed and manufactured. A nozzle Mach exit of M j = 1.5 was selected in order to obtain a convective Mach number of M c = 0.6. The flow was investigated for over-expanded, correctly expanded and under-expanded jet conditions. Mach number, total temperature and flow velocity measurements were carried out in order to characterise the jet behaviour. The inlet conditions of the jet flow were monitored in order to calculate the nozzle exit speed of sound and evaluate the mean Mach number distribution starting from the flow velocity data. A detailed analysis of the Mach results obtained by a static Pitot probe and by a particle image velocimetry measurement system was carried out. The mean flow velocity was investigated, and the axial Mach decay and the spreading rate were associated with the flow structures and with the compressibility effects. Aerodynamics of the different jet conditions was evaluated, and the shock cells structures were detected and discussed correlating the jet structure to the flow fluctuation and local turbulence. The longitudinal and radial distribution of the total temperature was investigated, and the temperature profiles were analysed and discussed. The total temperature behaviour was correlated to the turbulent phenomena and to the NPR jet conditions. Self-similarity condition was encountered and discussed for the over-expanded jet. Compressibility effects on the local turbulence, on the turbulent kinetic energy and on the Reynolds tensor were discussed.

A study of the round jet/plane wall flow field

NASA Technical Reports Server (NTRS)

Foss, J. F.; Kleis, S. J.

1971-01-01

Impingement angles, between the axisymmetric jet axis and the plane wall, from zero to 15 degrees have been examined for nozzle heights of 0.75, 1.0, 1.5 and 2.0 diameters and for: (1) a fully developed pipe flow, and (2) a relatively uniform exit velocity condition. Velocity measurements have been used to define isotach contours and to determine mass, momentum and energy flux values for the near field (within five diameters) of the jet. Surface pressure measurements have been used to define surface pressure forces and jet centerline trajectories. The geometric and flow conditions examined and the interpretation of the results have been motivated by the externally blown flap STOL aircraft application.

A Turbulence model taking into account the longitudinal flow inhomogeneity in mixing layers and jets

NASA Astrophysics Data System (ADS)

Troshin, A. I.

2017-06-01

The problem of potential core length overestimation of subsonic free jets by Reynolds-averaged Navier-Stokes (RANS) based turbulence models is addressed. It is shown that the issue is due to the incorrect velocity profile modeling of the jet mixing layers. An additional source term in ω equation is proposed which takes into account the effect of longitudinal flow inhomogeneity on turbulence in mixing layers. Computations confirm that the modified Speziale-Sarkar-Gatski/Launder- Reece-Rodi-omega (SSG/LRR-ω) turbulence model correctly predicts the mean velocity profiles in both initial and far-field regions of subsonic free plane jet as well as the centerline velocity decay rate.

Schlieren Measurements of Buoyancy Effects on Flow Transition in Low-Density Gas Jets

NASA Technical Reports Server (NTRS)

Pasumarthi, Kasyap S.; Agrawal, Ajay K.

2005-01-01

The transition from laminar to turbulent flow in helium jets discharged into air was studied using Rainbow Schlieren Deflectometry technique. In particular, the effects of buoyancy on jet oscillations and flow transition length were considered. Experiments to simulate microgravity were conducted in the 2.2s drop tower at NASA Glenn Research Center. The jet Reynolds numbers varied from 800 to1200 and the jet Richardson numbers ranged between 0.01 and 0.004. Schlieren images revealed substantial variations in the flow structure during the drop. Fast Fourier Transform (FFT) analysis of the data obtained in Earth gravity experiments revealed the existence of a discrete oscillating frequency in the transition region, which matched the frequency in the upstream laminar regime. In microgravity, the transition occurred farther downstream indicating laminarization of the jet in the absence of buoyancy. The amplitude of jet oscillations was reduced by up to an order of magnitude in microgravity. Results suggest that jet oscillations were buoyancy induced and that the brief microgravity period may not be sufficient for the oscillations to completely subside.

Can Ureteral Jet Flow Measurement Predict Spontaneous Passage of Distal Ureteral Stones?

PubMed

Ongun, Sakir; Teken, Abdurrazak; Yılmaz, Orkun; Süleyman, Sakir

2018-06-27

The study aimed to investigate the relationship between the spontaneous passage of distal ureteral stones and ureteral jet flow measurement. The study included 74 patients with acute renal colic between June 2015 and June 2016, and distal ureteral stones of 10 mm or less in a non-contrast CT were comprised in a prospective study. The ureteral jet was measured by Doppler ultrasonography. At the fourth week follow-up, kidney-ureter-bladder radiography was taken and the patients who no longer had a stone were considered to have spontaneously passed it. The average stone size of the patients was 5.6 ± 2.0 mm. After 4 weeks of follow-up, 55 patients (74.3%) had passed the stone spontaneously whereas 19 (25.6%) had not. The patients in the former group were found to have a higher peak flow velocity of ureteral jet on the stone side than those in the latter group. In regression analysis ureteral jet on the stone side was independently associated with spontaneous passage (p = 0.027). For the spontaneous passage, a ureteral jet flow peak velocity above 15.25 cm/s had an 85.4% sensitivity and 63.1% specificity. Measurement of the ureteral jet flow peak velocity can be beneficial in predicting the potential spontaneous passage of distal ureteral stones. © 2018 S. Karger AG, Basel.

Experimental and Numerical Investigation of Flow Properties of Supersonic Helium-Air Jets

NASA Technical Reports Server (NTRS)

Miller, Steven A. E.; Veltin, Jeremy

2010-01-01

Heated high speed subsonic and supersonic jets operating on- or off-design are a source of noise that is not yet fully understood. Helium-air mixtures can be used in the correct ratio to simulate the total temperature ratio of heated air jets and hence have the potential to provide inexpensive and reliable flow and acoustic measurements. This study presents a combination of flow measurements of helium-air high speed jets and numerical simulations of similar helium-air mixture and heated air jets. Jets issuing from axisymmetric convergent and convergent-divergent nozzles are investigated, and the results show very strong similarity with heated air jet measurements found in the literature. This demonstrates the validity of simulating heated high speed jets with helium-air in the laboratory, together with the excellent agreement obtained in the presented data between the numerical predictions and the experiments. The very close match between the numerical and experimental data also validates the frozen chemistry model used in the numerical simulation.

Predicting the stability of a compressible periodic parallel jet flow

NASA Technical Reports Server (NTRS)

Miles, Jeffrey H.

1996-01-01

It is known that mixing enhancement in compressible free shear layer flows with high convective Mach numbers is difficult. One design strategy to get around this is to use multiple nozzles. Extrapolating this design concept in a one dimensional manner, one arrives at an array of parallel rectangular nozzles where the smaller dimension is omega and the longer dimension, b, is taken to be infinite. In this paper, the feasibility of predicting the stability of this type of compressible periodic parallel jet flow is discussed. The problem is treated using Floquet-Bloch theory. Numerical solutions to this eigenvalue problem are presented. For the case presented, the interjet spacing, s, was selected so that s/omega =2.23. Typical plots of the eigenvalue and stability curves are presented. Results obtained for a range of convective Mach numbers from 3 to 5 show growth rates omega(sub i)=kc(sub i)/2 range from 0.25 to 0.29. These results indicate that coherent two-dimensional structures can occur without difficulty in multiple parallel periodic jet nozzles and that shear layer mixing should occur with this type of nozzle design.

Three dimensional flow field measurements of a 4:1 aspect ratio subsonic jet

NASA Technical Reports Server (NTRS)

Morrison, G. L.; Swan, D. H.

1989-01-01

Flow field measurements for a subsonic rectangular cold air jet with an aspect ratio of 4:1 (12.7 x 50.8 mm) at a Mach number of 0.09 and Re of 100,000 have been carried out using a three-dimensional laser Doppler anemometer system. Mean velocity measurements show that the jet width spreads more rapidly along the minor axis than along the major axis. The outward velocities, however, are not significantly different for the two axes, indicating the presence of enhanced mixing along the minor axis. The jet slowly changes from a rectangular jet to a circular jet as the flow progresses downstream.

Flow Physics of Synthetic Jet Interactions on a Sweptback Model with a Control Surface

NASA Astrophysics Data System (ADS)

Monastero, Marianne; Amitay, Michael

2016-11-01

Active flow control using synthetic jets can be used on aerodynamic surfaces to improve performance and increase fuel efficiency. The flowfield resulting from the interaction of the jets with a separated crossflow with a spanwise component must be understood to determine actuator spacing for aircraft integration. The current and previous work showed adjacent synthetic jets located upstream of a control surface hingeline on a sweptback model interact with each other under certain conditions. Whether these interactions are constructive or destructive is dependent on the spanwise spacing of the jets, the severity of separation over the control surface, and the magnitude of the spanwise flow. Measuring and understanding the detailed flow physics of the flow structures emanating from the synthetic jet orifices and their interactions with adjacent jets of varying spacings is the focus of this work. Wind tunnel experiments were conducted at the Rensselaer Polytechnic Institute Subsonic Wind Tunnel using stereo particle image velocimetry (SPIV) and pressure measurements to study the effect that varying the spanwise spacing has on the overall performance. Initial SPIV data gave insight into defining and understanding the mechanisms behind the beneficial or detrimental jets interactions.

Buoyancy Effects on Flow Transition in Hydrogen Gas Jet Diffusion Flames

NASA Technical Reports Server (NTRS)

Albers, Burt W.; Agrawal, Ajay K.; Griffin, DeVon (Technical Monitor)

2000-01-01

Experiments were performed in earth-gravity to determine how buoyancy affected transition from laminar to turbulent flow in hydrogen gas jet diffusion flames. The jet exit Froude number characterizing buoyancy in the flame was varied from 1.65 x 10(exp 5) to 1.14 x 10(exp 8) by varying the operating pressure and/or burner inside diameter. Laminar fuel jet was discharged vertically into ambient air flowing through a combustion chamber. Flame characteristics were observed using rainbow schlieren deflectometry, a line-of-site optical diagnostic technique. Results show that the breakpoint length for a given jet exit Reynolds number increased with increasing Froude number. Data suggest that buoyant transitional flames might become laminar in the absence of gravity. The schlieren technique was shown as effective in quantifying the flame characteristics.

Sweeping Jet Actuator in a Quiescent Environment

NASA Technical Reports Server (NTRS)

Koklu, Mehti; Melton, Latunia P.

2013-01-01

This study presents a detailed analysis of a sweeping jet (fluidic oscillator) actuator. The sweeping jet actuator promises to be a viable flow control actuator candidate due to its simple, no moving part structure and its high momentum, spatially oscillating flow output. Hot-wire anemometer and particle image velocimetry measurements were carried out with an emphasis on understanding the actuator flow field in a quiescent environment. The time averaged, fluctuating, and instantaneous velocity measurements are provided. A modified actuator concept that incorporates high-speed solenoid valves to control the frequency of oscillation enabled phase averaged measurements of the oscillating jet. These measurements reveal that in a given oscillation cycle, the oscillating jet spends more time on each of the Coanda surfaces. In addition, the modified actuator generates four different types of flow fields, namely: a non oscillating downward jet, a non oscillating upward jet, a non oscillating straight jet, and an oscillating jet. The switching from an upward jet to a downward jet is accomplished by providing a single pulse from the solenoid valve. Once the flow is switched, the flow stays there until another pulse is received. The oscillating jet is compared with a non oscillating straight jet, which is a typical planar turbulent jet. The results indicate that the oscillating jet has a higher (5 times) spreading rate, more flow entrainment, and higher velocity fluctuations (equal to the mean velocity).

Comparison of Turbulence Models for Nozzle-Afterbody Flows with Propulsive Jets

NASA Technical Reports Server (NTRS)

Compton, William B., III

1996-01-01

A numerical investigation was conducted to assess the accuracy of two turbulence models when computing non-axisymmetric nozzle-afterbody flows with propulsive jets. Navier-Stokes solutions were obtained for a Convergent-divergent non-axisymmetric nozzle-afterbody and its associated jet exhaust plume at free-stream Mach numbers of 0.600 and 0.938 at an angle of attack of 0 deg. The Reynolds number based on model length was approximately 20 x 10(exp 6). Turbulent dissipation was modeled by the algebraic Baldwin-Lomax turbulence model with the Degani-Schiff modification and by the standard Jones-Launder kappa-epsilon turbulence model. At flow conditions without strong shocks and with little or no separation, both turbulence models predicted the pressures on the surfaces of the nozzle very well. When strong shocks and massive separation existed, both turbulence models were unable to predict the flow accurately. Mixing of the jet exhaust plume and the external flow was underpredicted. The differences in drag coefficients for the two turbulence models illustrate that substantial development is still required for computing very complex flows before nozzle performance can be predicted accurately for all external flow conditions.

Implications of Upwells as Hydrodynamic Jets in a Pulse Jet Mixed System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pease, Leonard F.; Bamberger, Judith A.; Minette, Michael J.

2015-08-01

upwell satisfies these criteria when vigorous breakthrough is achieved, not all available data follow the free jet profile for the central upwell, particularly at lower nozzle velocities. Alternative flow regimes are considered and new models for cloud height, “cavern height,” and the rate of jet penetration (jet celerity) are benchmarked against data to anchor scaling analyses. This analytical modeling effort to provide a technical basis for scaling PJM mixed vessels has significant implications for vessel mixing, because jet physics underlies “cavern” height, cloud height, and the volume of mixing considerations. A new four-parameter cloud height model compares favorably to experimental results. This model is predictive of breakthrough in 8 ft vessel tests with the two-part simulant. Analysis of the upwell in the presence of yield stresses finds evidence of expanding turbulent jets, confined turbulent jets, and confined laminar flows. For each, the critical elevation at which jet momentum depletes is predicted, which compare favorably to experimental cavern height data. Partially coupled momentum and energy balances suggest that these are limiting cases of a gradual transition from a turbulent expanding flow to a confined laminar flow. This analysis of the central upwell alone lays essential groundwork for complete analysis of mode three mixing (i.e., breakthrough with slow peripheral mixing). Consideration of jet celerity shows that the rate of jet penetration is a governing consideration in breakthrough to the surface. Estimates of the volume of mixing are presented. This analysis shows that flow along the vessel wall is sluggish such that the central upwell governs the volume of mixing. This analysis of the central upwell alone lays essential groundwork for complete analysis of mode three mixing and estimates of hydrogen release rates from first principles.« less

Fluidic Vectoring of a Planar Incompressible Jet Flow

NASA Astrophysics Data System (ADS)

Mendez, Miguel Alfonso; Scelzo, Maria Teresa; Enache, Adriana; Buchlin, Jean-Marie

2018-06-01

This paper presents an experimental, a numerical and a theoretical analysis of the performances of a fluidic vectoring device for controlling the direction of a turbulent, bi-dimensional and low Mach number (incompressible) jet flow. The investigated design is the co-flow secondary injection with Coanda surface, which allows for vectoring angles up to 25° with no need of moving mechanical parts. A simple empirical model of the vectoring process is presented and validated via experimental and numerical data. The experiments consist of flow visualization and image processing for the automatic detection of the jet centerline; the numerical simulations are carried out solving the Unsteady Reynolds Average Navier- Stokes (URANS) closed with the k - ω SST turbulence model, using the PisoFoam solver from OpenFOAM. The experimental validation on three different geometrical configurations has shown that the model is capable of providing a fast and reliable evaluation of the device performance as a function of the operating conditions.

Ejector Noise Suppression with Auxiliary Jet Injection

NASA Technical Reports Server (NTRS)

Berman, Charles H.; Andersen, Otto P., Jr.

1997-01-01

An experimental program to reduce aircraft jet turbulence noise investigated the interaction of small auxiliary jets with a larger main jet. Significant reductions in the far field jet noise were obtained over a range of auxiliary jet pressures and flow rates when used in conjunction with an acoustically lined ejector. While the concept is similar to that of conventional ejector suppressors that use mechanical mixing devices, the present approach should improve thrust and lead to lower weight and less complex noise suppression systems since no hardware needs to be located in the main jet flow. A variety of auxiliary jet and ejector configurations and operating conditions were studied. The best conditions tested produced peak to peak noise reductions ranging from 11 to 16 dB, depending on measurement angle, for auxiliary jet mass flows that were 6.6% of the main jet flow with ejectors that were 8 times the main jet diameter in length. Much larger reductions in noise were found at the original peak frequencies of the unsuppressed jet over a range of far field measurement angles.

A Very Stable High Throughput Taylor Cone-jet in Electrohydrodynamics

PubMed Central

Morad, M. R.; Rajabi, A.; Razavi, M.; Sereshkeh, S. R. Pejman

2016-01-01

A stable capillary liquid jet formed by an electric field is an important physical phenomenon for formation of controllable small droplets, power generation and chemical reactions, printing and patterning, and chemical-biological investigations. In electrohydrodynamics, the well-known Taylor cone-jet has a stability margin within a certain range of the liquid flow rate (Q) and the applied voltage (V). Here, we introduce a simple mechanism to greatly extend the Taylor cone-jet stability margin and produce a very high throughput. For an ethanol cone-jet emitting from a simple nozzle, the stability margin is obtained within 1 kV for low flow rates, decaying with flow rate up to 2 ml/h. By installing a hemispherical cap above the nozzle, we demonstrate that the stability margin could increase to 5 kV for low flow rates, decaying to zero for a maximum flow rate of 65 ml/h. The governing borders of stability margins are discussed and obtained for three other liquids: methanol, 1-propanol and 1-butanol. For a gravity-directed nozzle, the produced cone-jet is more stable against perturbations and the axis of the spray remains in the same direction through the whole stability margin, unlike the cone-jet of conventional simple nozzles. PMID:27917956

High-frequency counter-flow plasma synthetic jet actuator and its application in suppression of supersonic flow separation

NASA Astrophysics Data System (ADS)

Wang, Hongyu; Li, Jun; Jin, Di; Tang, Mengxiao; Wu, Yun; Xiao, Lianghua

2018-01-01

We come up with a control strategy for suppression of supersonic flow separation based on high-frequency Counter-flow Plasma Synthetic Jet Actuator (CPSJA). The main purpose of this investigation is to verify if its control authority can be enhanced by the jet/shock interaction. We use a blunt nose to generate a bow shock, a step on a flat plate to introduce a massive separation in a Mach 2 wind tunnel, and the CPSJA to generate Plasma Synthetic Jet (PSJ). In this study, pulsed capacitive discharge is provided for an array of CPSJAs, which makes the actuation (discharge) frequency f1 = 1 kHz, f2 = 2 kHz and f3 = 3 kHz. We use the high-speed schlieren imaging and fast response pressure transducers as well as a numerical simulation to investigate the quiescent PSJ properties, the interaction between the jet and bow shock, and its disturbance effect on the downstream separated region. The schlieren images show that PSJ is characterized by a succession of vortex rings; the jet strength weakens with the increase of frequency. A 4.5 mN jet thrust is found for all the frequencies. The simulation results show that jet/shock interaction produces vorticity in the vortex ring of the jet, enhancing turbulent mixing in PSJ so that a great deal of momentum is produced into the flow. We found the downstream flow is significantly disturbed by the enhanced actuation. Actuation with frequency of f2, f3 which is close to the natural frequency fn of the separation bubble suppresses the separation with the upstream laminar boundary layer being periodically attenuated, which has a better control effect than f1. The control effect is sensitive to the position where PSJ interacts with the shear layer, but the amount of energy deposited in one pulse is not crucial in a separation reduction in the experiment.

A study of flow past an airfoil with a jet issuing from its lower surface

NASA Technical Reports Server (NTRS)

Krothapalli, A.; Leopold, D.

1984-01-01

The aerodynamics of a NACA 0018 airfoil with a rectangular jet of finite aspect ratio exiting from its lower surface at 90 deg to the chord were investigated. The jet was located at 50% of the wing chord. Measurements include static pressures on the airfoil surface, total pressures in the near wake, and local velocity vectors in different planes of the wake. The effects of jet cross flow interaction on the aerodynamics of the airfoil are studied. It is indicated that at all values of momentum coefficients, the jet cross flow interaction produces a strong contra-rotating vortex structure in the near wake. The flow behind the jet forms a closed recirculation region which extends up to a chord length down stream of the trailing edge which results in the flow field to become highly three dimensional. The various aerodynamic force coefficients vary significantly along the span of the wing. The results are compared with a jet flap configuration.

Sonic environment of aircraft structure immersed in a supersonic jet flow stream

NASA Technical Reports Server (NTRS)

Guinn, W. A.; Balena, F. J.; Soovere, J.

1976-01-01

Test methods for determining the sonic environment of aircraft structure that is immersed in the flow stream of a high velocity jet or that is subjected to the noise field surrounding the jet, were investigated. Sonic environment test data measured on a SCAT 15-F model in the flow field of Mach 1.5 and 2.5 jets were processed. Narrow band, lateral cross correlation and noise contour plots are presented. Data acquisition and reduction methods are depicted. A computer program for scaling the model data is given that accounts for model size, jet velocity, transducer size, and jet density. Comparisons of scaled model data and full size aircraft data are made for the L-1011, S-3A, and a V/STOL lower surface blowing concept. Sonic environment predictions are made for an engine-over-the-wing SST configuration.

Viscous-inviscid calculations of jet entrainment effects on the subsonic flow over nozzle afterbodies

NASA Technical Reports Server (NTRS)

Wilmoth, R. G.

1980-01-01

A viscous-inviscid interaction model was developed to account for jet entrainment effects in the prediction of the subsonic flow over nozzle afterbodies. The model is based on the concept of a weakly interacting shear layer in which the local streamline deflections due to entrainment are accounted for by a displacement-thickness type of correction to the inviscid plume boundary. The entire flow field is solved in an iterative manner to account for the effects on the inviscid external flow of the turbulent boundary layer, turbulent mixing and chemical reactions in the shear layer, and the inviscid jet exhaust flow. The components of the computational model are described, and numerical results are presented to illustrate the interactive effects of entrainment on the overall flow structure. The validity of the model is assessed by comparisons with data obtained form flow-field measurements on cold-air jet exhausts. Numerical results and experimental data are also given to show the entrainment effects on nozzle boattail drag under various jet exhaust and free-stream flow conditions.

Linearized unsteady jet analysis

NASA Technical Reports Server (NTRS)

Viets, H.; Piatt, M.

1979-01-01

The introduction of a time dependency into a jet flow to change the rate at which it mixes with a coflowing stream or ambient condition is investigated. The advantages and disadvantages of the unsteady flow are discussed in terms of steady state mass and momentum transfer. A linear system which is not limited by frequency constraints and evolves through a simplification of the equations of motion is presented for the analysis of the unsteady flow field generated by the time dependent jet.

Active flow control of subsonic flow in an adverse pressure gradient using synthetic jets and passive micro flow control devices

NASA Astrophysics Data System (ADS)

Denn, Michael E.

Several recent studies have shown the advantages of active and/or passive flow control devices for boundary layer flow modification. Many current and future proposed air vehicles have very short or offset diffusers in order to save vehicle weight and create more optimal vehicle/engine integration. Such short coupled diffusers generally result in boundary layer separation and loss of pressure recovery which reduces engine performance and in some cases may cause engine stall. Deployment of flow control devices can alleviate this problem to a large extent; however, almost all active flow control devices have some energy penalty associated with their inclusion. One potential low penalty approach for enhancing the diffuser performance is to combine the passive flow control elements such as micro-ramps with active flow control devices such as synthetic jets to achieve higher control authority. The goal of this dissertation is twofold. The first objective is to assess the ability of CFD with URANS turbulence models to accurately capture the effects of the synthetic jets and micro-ramps on boundary layer flow. This is accomplished by performing numerical simulations replicating several experimental test cases conducted at Georgia Institute of Technology under the NASA funded Inlet Flow Control and Prediction Technologies Program, and comparing the simulation results with experimental data. The second objective is to run an expanded CFD matrix of numerical simulations by varying various geometric and other flow control parameters of micro-ramps and synthetic jets to determine how passive and active control devices interact with each other in increasing and/or decreasing the control authority and determine their influence on modification of boundary layer flow. The boundary layer shape factor is used as a figure of merit for determining the boundary layer flow quality/modification and its tendency towards separation. It is found by a large number of numerical experiments and

Experimental study of vorticity-strain rate interaction in turbulent partially-premixed jet flames using tomographic particle image velocimetry

DOE PAGES

Coriton, Bruno; Frank, Jonathan H.

2016-02-16

In turbulent flows, the interaction between vorticity, ω, and strain rate, s, is considered a primary mechanism for the transfer of energy from large to small scales through vortex stretching. The ω-s coupling in turbulent jet flames is investigated using tomographic particle image velocimetry (TPIV). TPIV provides a direct measurement of the three-dimensional velocity field from which ω and s are determined. The effects of combustion and mean shear on the ω-s interaction are investigated in turbulent partially premixed methane/air jet flames with high and low probabilities of localized extinction as well as in a non-reacting isothermal air jet withmore » Reynolds number of approximately 13,000. Results show that combustion causes structures of high vorticity and strain rate to agglomerate in highly correlated, elongated layers that span the height of the probe volume. In the non-reacting jet, these structures have a more varied morphology, greater fragmentation, and are not as well correlated. The enhanced spatiotemporal correlation of vorticity and strain rate in the stable flame results in stronger ω-s interaction characterized by increased enstrophy and strain-rate production rates via vortex stretching and straining, respectively. The probability of preferential local alignment between ω and the eigenvector of the intermediate principal strain rate, s 2, which is intrinsic to the ω-s coupling in turbulent flows, is larger in the flames and increases with the flame stability. The larger mean shear in the flame imposes a preferential orientation of ω and s 2 tangential to the shear layer. The extensive and compressive principal strain rates, s 1 and s 3, respectively, are preferentially oriented at approximately 45° with respect to the jet axis. As a result, the production rates of strain and vorticity tend to be dominated by instances in which ω is parallel to the s 1¯-s 2¯ plane and orthogonal to s 3¯.« less

Letter: Transient interaction between plasma jet and supersonic compression ramp flow

NASA Astrophysics Data System (ADS)

Huang, He-Xia; Tan, Hui-Jun; Sun, Shu; Zhang, Yu-Chao; Cheng, Lin

2018-04-01

The rapid flow evolution between a plasma jet and a 20° compression ramp flow is captured by a high-speed schlieren system at Mach 2.0. Several interesting flow phenomena are observed for the first time. The pulsed jet, which generates strong perturbations, forces the crossflow boundary layer to separate and forms a forward moving shock. A typical shock-on-shock interaction occurs when the precursor shock intersects with the original shock. The interaction is initially regular, and then it transforms into an irregular one with a Mach stem connecting the precursor shock and original ramp shock.

Iso-thermal flow characteristics of rotationally symmetric jets generating a swirl within a cylindrical chamber

NASA Astrophysics Data System (ADS)

Long, Shen; Lau, Timothy C. W.; Chinnici, Alfonso; Tian, Zhao Feng; Dally, Bassam B.; Nathan, Graham J.

2018-05-01

We present a systematic experimental study of the interaction between four rotationally symmetric jets within a cylindrical chamber, under conditions relevant to a wide range of engineering applications, including the technology of a Hybrid Solar Receiver Combustor (HSRC). The HSRC geometry is simplified here to a cylindrical cavity with four inlet jets (representing four burners) which are configured in an annular arrangement and aligned at an inclination angle to the axis with a tangential component (azimuthal angle) to generate a swirl in the chamber. In this study, the jet inclination angle (αj) was varied over the range of 25°-45°, while the jet azimuthal angle (θj) was varied from 5° to 15°. The inlet Reynolds number for each injected jet and the number of jets were fixed at ReD = 10 500 and 4, respectively. Measurements obtained with Particle Image Velocimetry were used to characterise the large-scale flow field within selected configurations. The results reveal a significant dependence of the mean and root-mean-square flow-fields on the jet azimuthal angle (θj) and the jet inclination angle (αj). Three different flow regimes with distinctive flow characteristics were identified within the configurations investigated here. It was also found that θj can significantly influence (a) the position and strength of an external recirculation zone and a central recirculation zone, (b) the extent of turbulence fluctuation, and (c) the flow unsteadiness. Importantly, the effect of αj on the flow characteristics was found to depend strongly on the value of θj.

Mixing augmentation of transverse hydrogen jet by injection of micro air jets in supersonic crossflow

NASA Astrophysics Data System (ADS)

Anazadehsayed, A.; Barzegar Gerdroodbary, M.; Amini, Y.; Moradi, R.

2017-08-01

In this study, the influences of the micro air jet on the mixing of the sonic transverse hydrogen through micro-jets subjected to a supersonic crossflow are investigated. A three-dimensional numerical study has been performed to reveal the affects of micro air jet on mixing of the hydrogen jet in a Mach 4.0 crossflow with a global equivalence ratio of 0.5. Parametric studies were conducted on the various air jet conditions by using the Reynolds-averaged Navier-Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. Complex jet interactions were found in the downstream region with a variety of flow features depending upon the angle of micro air jet. These flow features were found to have subtle effects on the mixing of hydrogen jets. Results indicate a different flow structure as air jet is presented in the downstream of the fuel jet. According to the results, without air, mixing occurs at a low rate. When the air jet is presented in the downstream of fuel jet, significant increase (up to 300%) occurs in the mixing performance of the hydrogen jet at downstream. In multi fuel jets, the mixing performance of the fuel jet is increased more than 200% when the micro air jet is injected. Consequently, an enhanced mixing zone occurs downstream of the injection slots which leads to flame-holding.

Characteristics of strongly-forced turbulent jets and non-premixed jet flames

NASA Astrophysics Data System (ADS)

Lakshminarasimhan, K.; Clemens, N. T.; Ezekoye, O. A.

2006-10-01

Previous researchers have demonstrated that strong pulsations of the fuel flow rate can significantly reduce the flame length and luminosity of laminar/transitional non-premixed jet flames. The physical mechanisms responsible for these changes are investigated experimentally in acoustically-forced jet flows where the peak velocity fluctuations are up to eight times the mean flow velocity. Both reacting and non-reacting flows were studied and Reynolds numbers, based on the mean flow properties, ranged from 800 to 10,000 (corresponding to peak Reynolds numbers of 1,450-23,000), and forcing frequencies ranged from 290 to 1,140 Hz. Both the first and second organ-pipe resonance modes of the fuel delivery tube were excited to obtain these frequencies. An analysis of the acoustic forcing characteristics within the resonance tube is provided in order to understand the source of the high amplitude forcing. Flow visualization of jets with first resonant forcing confirms the presence of large-scale coherent vortices and strong reverse flow near the exit of the fuel tube. With second-resonant forcing, however, vortices are not emitted from the tube as they are drawn back into the fuel tube before they can fully form. Increased fine-scale turbulence is associated with both resonant cases, but particularly at second resonance. The power spectra of the velocity fluctuations for a resonantly pulsed jet show the presence of an inertial subrange indicating that the flow becomes fully turbulent even for mean-Reynolds-number jets that are nominally laminar. It is shown that these pulsed jet flows exhibit strong similarities to synthetic jets and that the Strouhal number, based on the maximum velocity at the fuel tube exit, is the dominant parameter for scaling these flows. The Strouhal number determines the downstream location where the coherent vortices breakdown, and is found to provide better collapse of flame length data (both current and previous) than other parameters that have

Propagation of atmospheric pressure helium plasma jet into ambient air at laminar gas flow

NASA Astrophysics Data System (ADS)

Pinchuk, M.; Stepanova, O.; Kurakina, N.; Spodobin, V.

2017-05-01

The formation of an atmospheric pressure plasma jet (APPJ) in a gas flow passing through the discharge gap depends on both gas-dynamic properties and electrophysical parameters of the plasma jet generator. The paper presents the results of experimental and numerical study of the propagation of the APPJ in a laminar flow of helium. A dielectric-barrier discharge (DBD) generated inside a quartz tube equipped with a coaxial electrode system, which provided gas passing through it, served as a plasma source. The transition of the laminar regime of gas flow into turbulent one was controlled by the photography of a formed plasma jet. The corresponding gas outlet velocity and Reynolds numbers were revealed experimentally and were used to simulate gas dynamics with OpenFOAM software. The data of the numerical simulation suggest that the length of plasma jet at the unvarying electrophysical parameters of DBD strongly depends on the mole fraction of ambient air in a helium flow, which is established along the direction of gas flow.

On the self-preservation of turbulent jet flows with variable viscosity

NASA Astrophysics Data System (ADS)

Danaila, Luminita; Gauding, Michael; Varea, Emilien; Turbulence; mixing Team

2017-11-01

The concept of self-preservation has played an important role in shaping the understanding of turbulent flows. The assumption of complete self-preservation imposes certain constrains on the dynamics of the flow, allowing to express one-point or two-point statistics by choosing an appropriate unique length scale. Determining this length scale and its scaling is of high relevance for modeling. In this work, we study turbulent jet flows with variable viscosity from the self-preservation perspective. Turbulent flows encountered in engineering and environmental applications are often characterized by fluctuations of viscosity resulting for instance from variations of temperature or species composition. Starting from the transport equation for the moments of the mixture fraction increment, constraints for self-preservation are derived. The analysis is based on direct numerical simulations of turbulent jet flows where the viscosity between host and jet fluid differs. It is shown that fluctuations of viscosity do not affect the decay exponents of the turbulent energy or the dissipation but modify the scaling of two-point statistics in the dissipative range. Moreover, the analysis reveals that complete self-preservation in turbulent flows with variable viscosity cannot be achieved. Financial support from Labex EMC3 and FEDER is gratefully acknowledged.

Determination of the alpha(s) using jet rates at LEP

NASA Astrophysics Data System (ADS)

Donkers, Michael A.

Jets are produced in any high energy collision of particles in which quarks are produced in the final state. Using the OPAL detector to measure particles produced in e+e- collisions at the LEP accelerator, the rate of jet formation has been measured at 91 GeV as well as each of the LEP2 energies, ranging from 161 GeV to 207 GeV. The jet rate observables, in particular the differential 2-jet rate and the average jet rate can be used to determine a value of the strong coupling constant, alphas, by fitting to various theoretical predictions. The value of alphas has been determined using data at 91 GeV and a combined sample comprising all of the LEP2 energies with a luminosity weighted centre-of-mass energy of 195.8 GeV for 10 theoretical predictions and two jet clustering algorithms. A fit of the 91 GeV and LEP2 values of alphas determined using the ln R matching prediction is also performed on the D2 and distributions to the 3-loop alphas prediction to produce 4 values of alphas(MZ 0).

Enhancement of convective heat transfer in internal flows using an electrically-induced corona jet

NASA Astrophysics Data System (ADS)

Baghaei Lakeh, Reza

The enhancement of heat transfer by active and passive methods has been the subject of many academic and industrial research studies. Internal flows play a major role in many applications and different methods have been utilized to augment the heat transfer to internal flows. Secondary flows consume part of the kinetic energy of the flow and disturb the boundary layer. Inducing secondary flows is known as mechanism for heat transfer enhancement. Secondary flows may be generated by corona discharge and ion-driven flows. When a high electric potential is applied to a conductor, a high electric field will be generated. The high electric field may exceed the partial break-down of the neutral molecules of surrounding gas (air) and generate a low-temperature plasma in the vicinity of the conductor. The generated plasma acts as a source of ions that accelerate under the influence of the electric field and escape beyond the plasma region and move toward the grounded electrode. The accelerating ions collide with neutral particles of the surrounding gas and impose a dragging effect which is interpreted as a body-force to the air particles. The shape and configuration of the emitting and receiving electrodes has a significant impact on the distribution of the electric body-force and the resulting electrically-induced flow field. It turned out that the certain configurations of longitudinal electrodes may cause a jet-like secondary flow field on the cross section of the flow passage in internal flows. The impingement effect of the corona jet on the walls of the channel disturbs the boundary layer, enhances the convective heat transfer, and generates targeted cooling along the centerline of the jet. The results of the current study show that the concentric configuration of a suspended wire-electrode in a circular tube leads to a hydrostatic condition and do not develop any electrically-induced secondary flow; however, the eccentric wire-electrode configuration generates a

Direct numerical simulations of two-phase laminar jet flows with different cross-section injection geometries

NASA Astrophysics Data System (ADS)

Abdel-Hameed, H.; Bellan, J.

2002-10-01

Direct numerical simulations are performed of spatial, three-dimensional, laminar jets of different inlet geometric configurations for the purpose of quantifying the characteristics of the flows; both single-phase (SP) and two-phase (TP) free jets are considered. The TP jets consist of gas laden with liquid drops randomly injected at the inlet. Drop evaporation ensues both due to the gaseous flow being initially unvitiated by the vapor species corresponding to the liquid drops, and to drop heating as the initial drop temperature is lower than that of the carrier gas. The conservation equations for the TP flow include complete couplings of mass, momentum, and energy based on thermodynamically self-consistent specification of the vapor enthalpy, internal energy, and latent heat of vaporization. Inlet geometries investigated are circular, elliptic, rectangular, square, and triangular. The results focus both on the different spreading achieved according to the inlet geometry, as well as on the considerable change in the flow field due to the presence of the drops. The most important consequence of the drop interaction with the flow is the production of streamwise vorticity that alters entrainment and species mixing according to the inlet geometry. Similar to their SP equivalent, TP jets are shown to reach steady-state entrainment; examination of the flows at this time station shows that the potential cores of TP jets are shorter by an order of magnitude than their SP counterpart. Moreover, whereas the TP circular jet exhibits a symmetric entrainment pattern well past the streamwise location of the potential core, noncircular jets display at the same location strong departures from symmetry. Furthermore, the SP-jet phenomenon of axis switching is no longer present in TP jets. The distributions of drop-number density, liquid mass, and evaporated species are compared for different inlet cross sections and recommendations are made regarding the optimal choice for different

Multi-specie isothermal flow calculations of widely-spaced co-axial jets in a confined sudden expansion, with the central jet dominant

NASA Astrophysics Data System (ADS)

Sturgess, G. J.; Syed, S. A.

1982-06-01

A numerical simulation is made of the flow in the Wright Aeronautical Propulsion Laboratory diffusion flame research combustor operating with a strong central jet of carbon dioxide in a weak and removed co-axial jet of air. The simulation is based on a finite difference solution of the time-average, steady-state, elliptic form of the Reynolds equations. Closure for these equations is provided by a two-equation turbulence model. Comparisons between measurements and predictions are made for centerline axial velocities and radial profiles of CO2 concentration. Earlier findings for a single specie, constant density, single jet flow that a large expansion ratio confined jet behaves initially as if it were unconfined, are confirmed for the multiple-specie, variable density, multiple-jet system. The lack of universality in the turbulence model constants and the turbulent Schmidt/Prandtl number is discussed.

CFD Assessment of Orifice Aspect Ratio and Mass Flow Ratio on Jet Mixing in Rectangular Ducts

NASA Technical Reports Server (NTRS)

Bain, D. B.; Smith, C. E.; Holdeman, J. D.

1994-01-01

Isothermal CFD analysis was performed on axially opposed rows of jets mixing with cross flow in a rectangular duct. Laterally, the jets' centerlines were aligned with each other on the top and bottom walls. The focus of this study was to characterize the effects of orifice aspect ratio and jet-to-mainstream mass flow ratio on jet penetration and mixing. Orifice aspect ratios (L/W) of 4-to-1, 2-to-1, and 1-to-1, along with circular holes, were parametrically analyzed. Likewise, jet-to-mainstream mass flow ratios (MR) of 2.0, 0.5, and 0.25 were systematically investigated. The jet-to-mainstream momentum-flux ratio (J) was maintained at 36 for all cases, and the orifice spacing-to-duct height (S/H) was varied until optimum mixing was attained for each configuration. The numerical results showed that orifice aspect ratio (and likewise orifice blockage) had little effect on jet penetration and mixing. Based on mixing characteristics alone, the 4-to-1 slot was comparable to the circular orifice. The 4-to-1 slot has a smaller jet wake which may be advantageous for reducing emissions. However, the axial length of a 4-to-1 slot may be prohibitively long for practical application, especially for MR of 2.0. The jet-to-mainstream mass flow ratio had a more significant effect on jet penetration and mixing. For a 4-to-1 aspect ratio orifice, the design correlating parameter for optimum mixing (C = (S/H)(sq. root J)) varied from 2.25 for a mass flow ratio of 2.0 to 1.5 for a mass flow ratio of 0.25.

Parametric Study of Synthetic-Jet-Based Flow Control on a Vertical Tail Model

NASA Astrophysics Data System (ADS)

Monastero, Marianne; Lindstrom, Annika; Beyar, Michael; Amitay, Michael

2015-11-01

Separation control over the rudder of the vertical tail of a commercial airplane using synthetic-jet-based flow control can lead to a reduction in tail size, with an associated decrease in drag and increase in fuel savings. A parametric, experimental study was undertaken using an array of finite span synthetic jets to investigate the sensitivity of the enhanced vertical tail side force to jet parameters, such as jet spanwise spacing and jet momentum coefficient. A generic wind tunnel model was designed and fabricated to fundamentally study the effects of the jet parameters at varying rudder deflection and model sideslip angles. Wind tunnel results obtained from pressure measurements and tuft flow visualization in the Rensselaer Polytechnic Subsonic Wind Tunnel show a decrease in separation severity and increase in model performance in comparison to the baseline, non-actuated case. The sensitivity to various parameters will be presented.

Rapid Confined Mixing Using Transverse Jets Part 2: Multiple Jets

NASA Astrophysics Data System (ADS)

Forliti, David; Salazar, David

2012-11-01

An experimental study has been conducted at the Air Force Research Laboratory at Edwards Air Force Base to investigate the properties of confined mixing devices that employ transverse jets. The experiment considers the mixing of water with a mixture of water and fluorescein, and planar laser induced fluorescence was used to measure instantaneous mixture fraction distributions in the cross section view. Part one of this study presents the scaling law development and results for a single confined transverse jet. Part two will describe the results of configurations including multiple transverse jets. The different regimes of mixing behavior, ranging from under to overpenetration of the transverse jets, are characterized in terms of a new scaling law parameter presented in part one. The level of unmixedness, a primary metric for mixing device performance, is quantified for different jet diameters, number of jets, and relative flow rates. It is apparent that the addition of a second transverse jet provides enhanced scalar uniformity in the main pipe flow cross section compared to a single jet. Three and six jet configurations also provide highly uniform scalar distributions. Turbulent scalar fluctuation intensities, spectral features, and spatial eigenfunctions using the proper orthogonal decomposition will be presented. Distribution A: Public Release, Public Affairs Clearance Number: 12656.

Numerical experiment on the flow field properties of a blunted body with a counterflowing jet in supersonic flows

NASA Astrophysics Data System (ADS)

Huang, Wei; Zhang, Rui-Rui; Yan, Li; Ou, Min; Moradi, R.

2018-06-01

The prediction of the drag and heat flux reduction characteristics is a very important issue in the conceptual design phase of the hypersonic vehicle. In this paper, the flow field properties around a blunted body with a counterflowing jet in the supersonic flow with the freestream Mach number being 3.98 were investigated numerically, and they are obtained by means of the two-dimensional axisymmetric Reynolds-averaged Navier-Stokes (RANS) equations coupled with the two equation standard k-ε turbulence model. The surface Stanton number distributions, as well as the surface static pressures, were extracted from the flow field structures in order to evaluate the drag and heat flux reduction characteristics. Further, the influences of the jet pressure ratio and the jet Mach number on the drag and heat flux reduction were analyzed based on the detailed code validation and grid independency analysis process. The obtained results show that the flow cell Reynolds number has a great impact on the heat flux prediction, and its best value is 5.0 for the case studied in the current study. However, the flow cell Reynolds number and the grid scale both have only a slight impact on the prediction of the surface static pressure distribution, as well as the turbulence model. The larger jet pressure ratio is beneficial for the drag and heat flux reduction, and the smaller jet Mach number is beneficial for the heat flux reduction. Further, the long penetration mode is beneficial for the drag reduction, but it is not beneficial for the heat flux reduction.

Transient survey rates for orphan afterglows from compact merger jets

NASA Astrophysics Data System (ADS)

Lamb, Gavin P.; Tanaka, Masaomi; Kobayashi, Shiho

2018-06-01

Orphan afterglows from short γ-ray bursts (GRBs) are potential candidates for electromagnetic (EM) counterpart searches to gravitational wave (GW) detected neutron star or neutron star black hole mergers. Various jet dynamical and structure models have been proposed that can be tested by the detection of a large sample of GW-EM counterparts. We make predictions for the expected rate of optical transients from these jet models for future survey telescopes, without a GW or GRB trigger. A sample of merger jets is generated in the redshift limits 0 ≤ z ≤ 3.0, and the expected peak r-band flux and time-scale above the Large Synoptic Survey Telescope (LSST) or Zwicky Transient Factory (ZTF) detection threshold, mr = 24.5 and 20.4, respectively, is calculated. General all-sky rates are shown for mr ≤ 26.0 and mr ≤ 21.0. The detected orphan and GRB afterglow rate depends on jet model, typically 16≲ R≲ 76 yr-1 for the LSST, and 2≲ R ≲ 8 yr-1 for ZTF. An excess in the rate of orphan afterglows for a survey to a depth of mr ≤ 26 would indicate that merger jets have a dominant low-Lorentz factor population, or the jets exhibit intrinsic jet structure. Careful filtering of transients is required to successfully identify orphan afterglows from either short- or long-GRB progenitors.

Spike-Nosed Bodies and Forward Injected Jets in Supersonic Flow

NASA Technical Reports Server (NTRS)

Gilinsky, M.; Washington, C.; Blankson, I. M.; Shvets, A. I.

2002-01-01

The paper contains new numerical simulation and experimental test results of blunt body drag reduction using thin spikes mounted in front of a body and one- or two-phase jets injected against a supersonic flow. Numerical simulations utilizing the NASA CFL3D code were conducted at the Hampton University Fluid Mechanics and Acoustics Laboratory (FM&AL) and experimental tests were conducted using the facilities of the IM/MSU Aeromechanics and Gas Dynamics Laboratory. Previous results were presented at the 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. Those results were based on some experimental and numerical simulation tests for supersonic flow around spike-nosed or shell-nosed bodies, and numerical simulations were conducted only for a single spike-nosed or shell-nosed body at zero attack angle, alpha=0. In this paper, experimental test results of gas, liquid and solid particle jet injection against a supersonic flow are presented. In addition, numerical simulation results for supersonic flow around a multiple spike-nosed body with non-zero attack angles and with a gas and solid particle forward jet injection are included. Aerodynamic coefficients: drag, C(sub D), lift, C(sub L), and longitudinal momentum, M(sub z), obtained by numerical simulation and experimental tests are compared and show good agreement.

Spike-Nosed Bodies and Forward Injected Jets in Supersonic Flow

NASA Technical Reports Server (NTRS)

Gilinsky, M.; Washington, C.; Blankson, I. M.; Shvets, A. I.

2002-01-01

The paper contains new numerical simulation and experimental test results of blunt body drag reduction using thin spikes mounted in front of a body and one- or two-phase jets injected against a supersonic flow. Numerical simulations utilizing the NASA CFL3D code were conducted at the Hampton University Fluid Mechanics and Acoustics Laboratory (FM&AL) and experimental tests were conducted using the facilities of the IM/MSU Aeromechanics and Gas Dynamics Laboratory. Previous results were presented at the 37th AIAA/ASME/SAE/ASEE Joint Propulsion Conference. Those results were based on some experimental and numerical simulation tests for supersonic flow around spike-nosed or shell-nosed bodies, and numerical simulations were conducted only for a single spike-nosed or shell-nosed body at zero attack angle, alpha = 0 degrees. In this paper, experimental test results of gas, liquid and solid particle jet injection against a supersonic flow are presented. In addition, numerical simulation results for supersonic flow around a multiple spike-nosed body with non-zero attack angles and with a gas and solid particle forward jet injection are included. Aerodynamic coefficients: drag, C (sub D), lift, C(sub L), and longitudinal momentum, M(sub z), obtained by numerical simulation and experimental tests are compared and show good agreement.

Global Artificial Boundary Conditions for Computation of External Flow Problems with Propulsive Jets

NASA Technical Reports Server (NTRS)

Tsynkov, Semyon; Abarbanel, Saul; Nordstrom, Jan; Ryabenkii, Viktor; Vatsa, Veer

1998-01-01

We propose new global artificial boundary conditions (ABC's) for computation of flows with propulsive jets. The algorithm is based on application of the difference potentials method (DPM). Previously, similar boundary conditions have been implemented for calculation of external compressible viscous flows around finite bodies. The proposed modification substantially extends the applicability range of the DPM-based algorithm. In the paper, we present the general formulation of the problem, describe our numerical methodology, and discuss the corresponding computational results. The particular configuration that we analyze is a slender three-dimensional body with boat-tail geometry and supersonic jet exhaust in a subsonic external flow under zero angle of attack. Similarly to the results obtained earlier for the flows around airfoils and wings, current results for the jet flow case corroborate the superiority of the DPM-based ABC's over standard local methodologies from the standpoints of accuracy, overall numerical performance, and robustness.

Production of microbubbles from axisymmetric flow focusing in the jetting regime for moderate Reynolds numbers.

PubMed

Vega, E J; Acero, A J; Montanero, J M; Herrada, M A; Gañán-Calvo, A M

2014-06-01

We analyze both experimentally and numerically the formation of microbubbles in the jetting regime reached when a moderately viscous liquid stream focuses a gaseous meniscus inside a converging micronozzle. If the total (stagnation) pressure of the injected gas current is fixed upstream, then there are certain conditions on which a quasisteady gas meniscus forms. The meniscus tip is sharpened by the liquid stream down to the gas molecular scale. On the other side, monodisperse collections of microbubbles can be steadily produced in the jetting regime if the feeding capillary is appropriately located inside the nozzle. In this case, the microbubble size depends on the feeding capillary position. The numerical simulations for an imposed gas flow rate show that a recirculation cell appears in the gaseous meniscus for low enough values of that parameter. The experiments allow one to conclude that the bubble pinch-off comprises two phases: (i) a stretching motion of the precursor jet where the neck radius versus the time before the pinch essentially follows a potential law, and (ii) a final stage where a very thin and slender gaseous thread forms and eventually breaks apart into a number of micron-sized bubbles. Because of the difference between the free surface and core velocities, the gaseous jet breakage differs substantially from that of liquid capillary jets and gives rise to bubbles with diameters much larger than those expected from the Rayleigh-type capillary instability. The dependency of the bubble diameter upon the flow-rate ratio agrees with the scaling law derived by A. M. Gañán-Calvo [Phys. Rev. E 69, 027301 (2004)], although a slight influence of the Reynolds number can be observed in our experiments.

Dynamics of coherent flow structures of a pulsating unsteady glottal jet in human phonation.

NASA Astrophysics Data System (ADS)

Neubauer, Juergen; Miraghaie, Reza; Berry, David

2004-11-01

The primary sound source for human voice is oscillation of the vocal folds in the larynx. Phonation is the self-sustained oscillation of the viscoelastic vocal fold tissue driven by the air flow from the lung. It is due to the flow-induced Hopf instability of the biomechanical-aerodynamic system of vocal folds coupled to the aeroacoustic driving air flow. The aim of this study is to provide insight to the aero-acoustic part of the primary sound source of human voice. A physical rubber model of vocal folds with air flow conditions typical for human phonation was used. This model exhibits self-sustained oscillations similar to those in human phonation. The oscillating physical model can be regarded as a dynamic slit-like orifice that discharges a pulsating unsteady jet. A left-right flapping of the glottal jet axis was detected using hotwire anemometer measurements of the unsteady glottal jet. Flow visualization experiments revealed the detachment of the glottal jet from the physical model folds during the accelerating and decelerating phase of the jet pulsation. Roll-up of large-scale vortex rings as well as secondary vortex shedding in the form of Von Karman street due to shear layer instability were found downstream of the physical model.

Prediction of recirculation zones in isothermal coaxial jet flows relevant to combustors

NASA Technical Reports Server (NTRS)

Nallasamy, M.

1987-01-01

The characteristics of the recirculation zones in confined coaxial turbulent jets are investigated numerically employing the kappa - epsilon turbulence model. The geometrical arrangement corresponds to the experimental study of Owen (AIAA J. 1976) and the investigation is undertaken to provide information for isothermal flow relevant to combustor flows. For the first time, the shape, size, and location of the recirculation zones for the above experimental configuration are correctly predicted. The processes leading to the observed results are explained. Detailed comparisons of the prediction with measurements are made. It is shown that the recirculation zones are very sensitive to the central jet exit configuration and the velocity ratio of the jets.

Investigation of a reacting jet injected into vitiated crossflow using CARS, high repetition rate OH-PLIF, and high repetition rate PIV

NASA Astrophysics Data System (ADS)

Roa, Mario

The proposed PhD thesis research program will be carried out in a staged combustion test rig developed with funding from Siemens Power Generation Inc. and the United States Department of Energy. This research program will study the reacting flow field created by an injector that is axially distributed along the combustor with use the laser diagnostics methods: Coherent Anti-Stokes Raman Spectroscopy (CARS), high repetition rate OH Planar Laser Induced Florescence (OHPLIF), and high repetition rate Particle Image Velocimetry (PIV), to determine why certain conditions result in low NOx emissions. This data will be used to validated the development of more precise computer models. These laser diagnostic techniques will be applied to the reacting jet produced using an extended, premixed 10 mm injector using both natural gas (NG) and hydrogen (H2) as fuels. The objective of this thesis research is to use advance laser diagnostics to gain insight into the reacting flow field resulting form transverse injection into a vitiated cross flow. The advance laser diagnostics will also provide insight into pollution formation mechanisms and will be used for validating CFD models of the transverse jet injection. The following measurements will be performed: (1) dual pump nitrogen/hydrogen (H2/ N2) CARS at the midplane of the extended 10 mm nozzle, (2) high repetition rate OH-PLIF and emission sampling for the same extended nozzle using NG and H2 as secondary fuel, (3) and combing both high repetition OH-PLIF and high repetition rate PIV for extended 10 mm nozzle for both NG and H2 secondary fuel. The PIV measurements will be combined with OH-PLIF in a simultaneous manner, with the OH fluorescence centered between the two PIV laser pulses. The dual pump H2/N2 CARS system will be used to measure both temperature of the reacting jet and the species concentration ratio of H2/ N2. The high repetition rate OH-PLIF, conducted with a 5 kHz, dual cavity Nd:YAG laser that optically pumps a

Flow topologies and turbulence scales in a jet-in-cross-flow

DOE PAGES

Oefelein, Joseph C.; Ruiz, Anthony M.; Lacaze, Guilhem

2015-04-03

This study presents a detailed analysis of the flow topologies and turbulence scales in the jet-in-cross-flow experiment of [Su and Mungal JFM 2004]. The analysis is performed using the Large Eddy Simulation (LES) technique with a highly resolved grid and time-step and well controlled boundary conditions. This enables quantitative agreement with the first and second moments of turbulence statistics measured in the experiment. LES is used to perform the analysis since experimental measurements of time-resolved 3D fields are still in their infancy and because sampling periods are generally limited with direct numerical simulation. A major focal point is the comprehensivemore » characterization of the turbulence scales and their evolution. Time-resolved probes are used with long sampling periods to obtain maps of the integral scales, Taylor microscales, and turbulent kinetic energy spectra. Scalar-fluctuation scales are also quantified. In the near-field, coherent structures are clearly identified, both in physical and spectral space. Along the jet centerline, turbulence scales grow according to a classical one-third power law. However, the derived maps of turbulence scales reveal strong inhomogeneities in the flow. From the modeling perspective, these insights are useful to design optimized grids and improve numerical predictions in similar configurations.« less

Flow Control Under Low-Pressure Turbine Conditions Using Pulsed Jets

NASA Technical Reports Server (NTRS)

Volino, Ralph J.; Ibrahim, Mounir B.

2012-01-01

This publication is the final report of research performed under an NRA/Cooperative Interagency Agreement, and includes a supplemental CD-ROM with detailed data. It is complemented by NASA/CR-2012-217416 and NASA/CR-2012-217417 which include a Ph.D. Dissertation and an M.S. thesis respectively, performed under this contract. In this study the effects of unsteady wakes and flow control using vortex generator jets (VGJs) were studied experimentally and computationally on the flow over the L1A low pressure turbine (LPT) airfoil. The experimental facility was a six passage linear cascade in a low speed wind tunnel at the U.S. Naval Academy. In parallel, computational work using the commercial code FLUENT (ANSYS, Inc.) was performed at Cleveland State University, using Unsteady Reynolds Averaged Navier Stokes (URANS) and Large Eddy Simulations (LES) methods. In the first phase of the work, the baseline flow was documented under steady inflow conditions without flow control. URANS calculations were done using a variety of turbulence models. In the second phase of the work, flow control was added using steady and pulsed vortex generator jets. The VGJs successfully suppressed separation and reduced aerodynamic losses. Pulsed operation was more effective and mass flow requirements are very low. Numerical simulations of the VGJs cases showed that URANS failed to capture the effect of the jets. LES results were generally better. In the third phase, effects of unsteady wakes were studied. Computations with URANS and LES captured the wake effect and generally predicted separation and reattachment to match the experiments. Quantitatively the results were mixed. In the final phase of the study, wakes and VGJs were combined and synchronized using various timing schemes. The timing of the jets with respect to the wakes had some effect, but in general once the disturbance frequency was high enough to control separation, the timing was not very important.

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

NASA Technical Reports Server (NTRS)

Nikitopoulos, Dimitris E.

2003-01-01

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.

Computational Analysis of the Flow and Acoustic Effects of Jet-Pylon Interaction

NASA Technical Reports Server (NTRS)

Hunter, Craig A.; Thomas, Russell H.; Abdol-Hamid, K. S.; Pao, S. Paul; Elmiligui, Alaa A.; Massey, Steven J.

2005-01-01

Computational simulation and prediction tools were used to understand the jet-pylon interaction effect in a set of bypass-ratio five core/fan nozzles. Results suggest that the pylon acts as a large scale mixing vane that perturbs the jet flow and jump starts the jet mixing process. The enhanced mixing and associated secondary flows from the pylon result in a net increase of noise in the first 10 diameters of the jet s development, but there is a sustained reduction in noise from that point downstream. This is likely the reason the pylon nozzle is quieter overall than the baseline round nozzle in this case. The present work suggests that focused pylon design could lead to advanced pylon shapes and nozzle configurations that take advantage of propulsion-airframe integration to provide additional noise reduction capabilities.

Effective Jet Properties for the Prediction of Turbulent Mixing Noise Reduction by Water Injection

NASA Technical Reports Server (NTRS)

Kandula, Max; Lonergan, Michael J.

2007-01-01

A one-dimensional control volume formulation is developed for the determination of jet mixing noise reduction due to water injection. The analysis starts from the conservation of mass, momentum and energy for the control volume, and introduces the concept of effective jet parameters (jet temperature, jet velocity and jet Mach number). It is shown that the water to jet mass flow rate ratio is an important parameter characterizing the jet noise reduction on account of gas-to-droplet momentum and heat transfer. Two independent dimensionless invariant groups are postulated, and provide the necessary relations for the droplet size and droplet Reynolds number. Results are presented illustrating the effect of mass flow rate ratio on the jet mixing noise reduction for a range of jet Mach number and jet Reynolds number. Predictions from the model show satisfactory comparison with available test data on supersonic jets. The results suggest that significant noise reductions can be achieved at increased flow rate ratios.

Supersonic plasma jets in experiments for radiophysical testing of bodies flow

NASA Astrophysics Data System (ADS)

Balakirev, B. A.; Bityurin, V. A.; Bocharov, A. N.; Brovkin, V. G.; Vedenin, P. V.; Lashkov, V. A.; Mashek, I. Ch; Pashchina, A. S.; Petrovskiy, V. P.; Khoronzhuk, R. S.; Dobrovolskaya, A. S.

2018-01-01

The action of differently oriented magnetic fields on the parameters of bow shock created in the vicinity of aerodynamic bodies placed into the supersonic gas-plasma flows is studied. For these experiments two types of the high speed plasma jet sources are used—magneto-plasma compressor (MPC) and powerful pulse capillary type discharge. MPC allows to create the plasma jets with gas flow velocity of 10 ± 2 km/s, lifetime 30-50 μs, temperature Te ≈ 3 ± 0.5 eV, electron density about ne ˜ 1016cm-3 and temperature Te ≈ 3 ± 0.5 eV. The jet source based on powerful capillary discharge creates the flows with lifetime 1-20 ms, Mach numbers 3-8, plasma flow velocity 3-10 km/s, vibration and rotation temperatures 9000-14000 and 3800-6000 K respectively. The results of our first experiments show the possibility of using gas-plasma sources based on MPC and powerful capillary discharge for aerodynamic and radiophysical experiments. Comparatively small magnetic field B = 0.23-0.5 T, applied to the obtained bow shocks, essentially modify them. This can lead to a change in shape and an increase in the distance between the detached shock wave and the streamlined body surface if B is parallel to the jet velocity or to decrease this parameter if B is orthogonal to the oncoming flow. Probably, the first case can be useful for reducing the thermal load and aerodynamic drug of streamlined body and the second case can be used to control the radio-transparency of the plasma layer and solving the blackout problem.

The entrainment rate for a row of turbulent jets. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Gordon, Eliott B.; Greber, Isaac

1990-01-01

Entrainment rates for a row of isothermal circular air jets issuing into a quiescent environment are found by integrating velocity distributions measured by a linearized hot-wire anemometer. Jet spacing to jet diameter ratios of 2.5, 5, 10, and 20 are studied at jet Reynold's numbers ranging from 5110 to 12070. Velocity distributions are determined at regular downstream intervals at axial distances equal to 16.4 to 164 jet diameters from the jet source. The entrainment rates for the four spacing configurations vary monotonically with increasing spacing/diameter between the limiting case of the slot jet entrainment rate (where the jet spacing to diameter ratio is zero) and the circular jet entrainment rate (in which the spacing to diameter ratio is infinity).

Effect of Oscillating Tabs on a Jet-in-Cross-Flow

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

2003-01-01

A novel technique for active control of a jet-in-cross-flow is explored in this study. Two triangular tabs are placed at the 90 degree and 270 degree edges of the jet orifice, relative to the direction of the cross-flow. A slight asymmetry in the placement of the two tabs is reversed periodically. This causes a profound oscillation of the flow field that persists as far downstream as the measurements were permitted by the facility (100 orifice diameters). Parametric dependence of the unsteadiness and its impact on the flowfield has been investigated preliminarily. It is found that the effect becomes increasingly pronounced with increasing value of the momentum flux ratio (J). However, there is little or no effect at low values of J in the range, J less than 15. The effective frequencies of oscillation are low - more than an order of magnitude lower than that found with oscillatory blowing technique in previous studies. The flow mechanism apparently involves a direct perturbation of the counter-rotating streamwise vortex pair of the flow.

Mixing and NOx Emission Calculations of Confined Reacting Jet Flows in Cylindrical and Annular Ducts

NASA Technical Reports Server (NTRS)

Oechsle, Victor L.; Connor, Christopher H.; Holdeman, James D. (Technical Monitor)

2000-01-01

Rapid mixing of cold lateral jets with hot cross-stream flows in confined configurations is of practical interest in gas turbine combustors as it strongly affects combustor exit temperature quality, and gaseous emissions in for example rich-lean combustion. It is therefore important to further improve our fundamental understanding of the important processes of dilution jet mixing especially when the injected jet mass flow rate exceeds that of the cross-stream. The results reported in this report describe some of the main flow characteristics which develop in the mixing process in a cylindrical duct. A three-dimensional computational fluid dynamics (CFD) code has been used to predict the mixing flow field characteristics and NOx emission in a quench section of a rich-burn/quick-mix/lean-burn (RQL) combustor. Sixty configurations have been analyzed in both circular and annular geometries in a fully reacting environment simulating the operating condition of an actual RQL gas turbine combustion liner. The evaluation matrix was constructed by varying the number of orifices per row and orifice shape. Other parameters such as J (momentum-flux ratio), MR (mass flowrate ratio), DR (density ratio), and mixer sector orifice ACd (effective orifice area) were maintained constant throughout the entire study. The results indicate that the mixing flow field can be correlated with the NOx production if they are referenced with the stoichiometric equivalence ratio value and not the equilibrium value. The mixing flowfields in both circular and annular mixers are different. The penetration of equal jets in both annular and circular geometries is vastly different which significantly affects the performance of the mixing section. In the computational results with the circular mixer, most of the NOx formation occurred behind the orifice starting at the orifice wake region. General trends have been observed in the NOx production as the number of orifices is changed and this appears to be

Plasma action on helium flow in cold atmospheric pressure plasma jet experiments

NASA Astrophysics Data System (ADS)

Darny, T.; Pouvesle, J.-M.; Fontane, J.; Joly, L.; Dozias, S.; Robert, E.

2017-10-01

In this work, helium flow modifications, visualized by schlieren imaging, induced by the plasma generated in a plasma jet have been studied in conditions used for biomedical treatments (jet being directed downwards with a low helium flow rate). It has been shown that the plasma action can shift up to few centimeters downstream the effects of buoyancy, which allows to the helium flow to reach a target below in conditions for which it is not the case when the plasma is off. This study reveals the critical role of large and long lifetime negative ions during repetitive operations in the kHz regime, inducing strong modifications in the gas propagation. The cumulative added streamwise momentum transferred to ambient air surrounding molecules resulting from a series of applied voltage pulses induces a gradual built up of a helium channel on tens of millisecond timescale. In some conditions, a remarkable stable cylindrical helium channel can be generated to the target with plasma supplied by negative polarity voltage pulses whereas a disturbed flow results from positive polarity operation. This has a direct effect on air penetration in the helium channel and then on the reactive species production over the target which is of great importance for biomedical applications. It has also been shown that with an appropriate combination of negative and positive polarity pulses, it is possible to benefit from both polarity features in order to optimize the plasma plume propagation and plasma delivery to a target.

Jet stability and wall impingement flow field in a thermal striping experiment

DOE PAGES

Lomperski, S.; Obabko, A.; Merzari, E.; ...

2017-08-10

We present velocity and temperature field measurements for a 0.9 x 0.9 x 1.7 m glass tank in which two air jets at Re=10000 mix and impinge upon the lid at ambient temperature and pressure. Flow patterns are characterized across a 350 x 200 mm plane located 3 mm below the lid for two inlet geometries: 1) “extended”, in which inlet channels protrude above the tank base, and 2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid flow field, appearing as three stagnant regions for the extended case and only one formore » flush. The dichotomy is attributed to system stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 oC and jets near Re=10000. A 50 m-long fiber optic distributed temperature sensor positioned 2 mm below the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping.« less

Jet stability and wall impingement flow field in a thermal striping experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lomperski, S.; Obabko, A.; Merzari, E.

We present velocity and temperature field measurements for a 0.9 x 0.9 x 1.7 m glass tank in which two air jets at Re=10000 mix and impinge upon the lid at ambient temperature and pressure. Flow patterns are characterized across a 350 x 200 mm plane located 3 mm below the lid for two inlet geometries: 1) “extended”, in which inlet channels protrude above the tank base, and 2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid flow field, appearing as three stagnant regions for the extended case and only one formore » flush. The dichotomy is attributed to system stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 oC and jets near Re=10000. A 50 m-long fiber optic distributed temperature sensor positioned 2 mm below the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping.« less

Active Flow Control Using Sweeping Jet Actuators on a Semi-Span Wing Model

NASA Technical Reports Server (NTRS)

Melton, LaTunia Pack; Koklu, Mehti

2016-01-01

Wind tunnel experiments were performed using active flow control on an unswept semispan wing model with a 30% chord trailing edge flap to aid in the selection of actuators for a planned high Reynolds number experiment. Two sweeping jet actuator sizes were investigated to determine the influence of actuator size on the active flow control system efficiency. Sweeping jet actuators with orifice sizes of 1 mm x 2 mm and 2 mm x 4 mm were selected because of the differences in actuator jet sweep angle. The parameters that were varied include actuator momentum, freestream velocity, and trailing edge flap deflection angle. Steady and unsteady pressure data, Particle Image Velocimetry data, and force and moment data were acquired to assess the performance of the two actuators. In addition to the wind tunnel experiments, benchtop studies of the actuators were performed to characterize the jets produced by each actuator. Benchtop investigations of the smaller actuator reveal that the jet exiting the actuator has a reduced sweep angle compared to published data for larger versions of this type of actuator. The larger actuator produces an oscillating jet that attaches to the external di?user walls at low supply pressures and produces the expected sweep angles. The AFC results using the smaller actuators show that while the actuators can control flow separation, the selected spacing of 3.3 cm may be too large due to the reduced sweep angle. In comparison, the spacing for the larger actuators, 6.6 cm, appears to be optimal for the Mach numbers investigated. Particle Image Velocimetry results are presented and show how the wall jets produced by the actuators cause the flow to attach to the flap surface.

Jet and Vortex Projectile Flows in Shock/bubble-on-wall Configuration

NASA Astrophysics Data System (ADS)

Peng, Gaozhu; Zabusky, Norman

2001-11-01

We observe intense coaxial upstream and radial flow structures from a shock in air interacting with a SF6 half-bubble placed against an ideally reflecting wall. Our axisymmetric numerical simulations were done with PPM and models a spherical bubble struck symmetrically by two identical approaching shocks . A "dual" vorticity deposition arises at early time and a coaxial upstream moving primary jet and radial vortex ring flow appears. A coherent vortex ring or vortex projectile (VP), with entrained shocklets originates from the vortex layer produced at the Mach stem (which arises from the primary reflected shock). This VP moves ahead of the jet. The original transmitted wave and other trapped waves in the expanding axial jet causes a collapsing and expanding cavity and other instabilities on the complex bubble interface. We present and analyze our results with different diagnostics: vorticity, density, divergence of velocity, and numerical shadowgraph patterns; global quantification of circulation, enstrophy and r-integrated vorticity; etc. We also discuss data projection and filtering for quantifying and validating complex flows.

Application of Synthetic Jets to Reduce Stator Flow Separation in a Low Speed Axial Compressor

NASA Technical Reports Server (NTRS)

Braunscheidel, Edward P.; Culley, Dennis E.; Zaman, Khairul B.M.Q.

2008-01-01

Flow control using synthetic jet injection has been applied in a low speed axial compressor. The synthetic jets were applied from the suction surface of a stator vane via a span-wise row of slots pitched in the streamwise direction. Actuation was provided externally from acoustic drivers coupled to the vane tip via flexible tubing. The acoustic resonance characteristics of the system, and the resultant jet velocities were obtained. The effects on the separated flow field for various jet velocities and frequencies were explored. Total pressure loss reductions across the vane passage were measured. The effect of synthetic jet injection was shown to be comparable to that of pulsatory injection with mass addition for stator vanes which had separated flow. While only a weak dependence of the beneficial effect was noted based on the excitation frequency, a strong dependence on the amplitude was observed at all frequencies.

Wing shielding of high velocity jet and shock-associated noise with cold and hot flow jets

NASA Technical Reports Server (NTRS)

Vonglahn, U.; Groesbeck, D.; Wagner, J.

1976-01-01

Jet exhaust noise shielding data are presented for cold and hot flows (ambient to 1,100 K) and pressure ratios from 1.7 to 2.75. A nominal 9.5-cm diameter conical nozzle was used with simple shielding surfaces that were varied in length from 28.8 to 114.3 cm. The nozzle was located 8.8 cm above the surfaces. The acoustic data with the various sheilding lengths are compared to each other and to that for the nozzle alone. In general, short shielding surfaces that provided shielding for subsonic jets did not provide as much shielding for jets with shock noise, however, long shielding surfaces did shield shock noise effectively.

Dilution jet configurations in a reverse flow combustor. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Zizelman, J.

1985-01-01

Results of measurements of both temperature and velocity fields within a reverse flow combustor are presented. Flow within the combustor is acted upon by perpendicularly injected cooling jets introduced at three different locations along the inner and outer walls of the combustor. Each experiment is typified by a group of parameters: density ratio, momentum ratio, spacing ratio, and confinement parameter. Measurements of both temperature and velocity are presented in terms of normalized profiles at azimuthal positions through the turn section of the combustion chamber. Jet trajectories defined by minimum temperature and maximum velocity give a qualitative indication of the location of the jet within the cross flow. Results of a model from a previous temperature study are presented in some of the plots of data from this work.

Jet reconstruction and performance using particle flow with the ATLAS Detector.

PubMed

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Zhou, N; Zhu, C G; Zhu, H; Zhu, J; Zhu, Y; Zhuang, X; Zhukov, K; Zibell, A; Zieminska, D; Zimine, N I; Zimmermann, C; Zimmermann, S; Zinonos, Z; Zinser, M; Ziolkowski, M; Živković, L; Zobernig, G; Zoccoli, A; Zou, R; Nedden, M Zur; Zwalinski, L

2017-01-01

This paper describes the implementation and performance of a particle flow algorithm applied to 20.2 fb[Formula: see text] of ATLAS data from 8 TeV proton-proton collisions in Run 1 of the LHC. The algorithm removes calorimeter energy deposits due to charged hadrons from consideration during jet reconstruction, instead using measurements of their momenta from the inner tracker. This improves the accuracy of the charged-hadron measurement, while retaining the calorimeter measurements of neutral-particle energies. The paper places emphasis on how this is achieved, while minimising double-counting of charged-hadron signals between the inner tracker and calorimeter. The performance of particle flow jets, formed from the ensemble of signals from the calorimeter and the inner tracker, is compared to that of jets reconstructed from calorimeter energy deposits alone, demonstrating improvements in resolution and pile-up stability.

Jet reconstruction and performance using particle flow with the ATLAS Detector

NASA Astrophysics Data System (ADS)

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M.; Schaefer, D.; Schaefer, L.; Schaefer, R.; Schaeffer, J.; Schaepe, S.; Schaetzel, S.; Schäfer, U.; Schaffer, A. C.; Schaile, D.; Schamberger, R. D.; Scharf, V.; Schegelsky, V. A.; Scheirich, D.; Schernau, M.; Schiavi, C.; Schier, S.; Schildgen, L. K.; Schillo, C.; Schioppa, M.; Schlenker, S.; Schmidt-Sommerfeld, K. R.; Schmieden, K.; Schmitt, C.; Schmitt, S.; Schmitz, S.; Schnoor, U.; Schoeffel, L.; Schoening, A.; Schoenrock, B. D.; Schopf, E.; Schott, M.; Schouwenberg, J. F. P.; Schovancova, J.; Schramm, S.; Schuh, N.; Schulte, A.; Schultens, M. J.; Schultz-Coulon, H.-C.; Schulz, H.; Schumacher, M.; Schumm, B. A.; Schune, Ph.; Schwartzman, A.; Schwarz, T. A.; Schweiger, H.; Schwemling, Ph.; Schwienhorst, R.; Schwindling, J.; Schwindt, T.; Sciandra, A.; Sciolla, G.; Scuri, F.; Scutti, F.; Searcy, J.; Seema, P.; Seidel, S. C.; Seiden, A.; Seixas, J. M.; Sekhniaidze, G.; Sekhon, K.; Sekula, S. J.; Semprini-Cesari, N.; Serfon, C.; Serin, L.; Serkin, L.; Sessa, M.; Seuster, R.; Severini, H.; Sfiligoj, T.; Sforza, F.; Sfyrla, A.; Shabalina, E.; Shaikh, N. W.; Shan, L. Y.; Shang, R.; Shank, J. T.; Shapiro, M.; Shatalov, P. B.; Shaw, K.; Shaw, S. M.; Shcherbakova, A.; Shehu, C. Y.; Shen, Y.; Sherwood, P.; Shi, L.; Shimizu, S.; Shimmin, C. O.; Shimojima, M.; Shirabe, S.; Shiyakova, M.; Shlomi, J.; Shmeleva, A.; Saadi, D. Shoaleh; Shochet, M. J.; Shojaii, S.; Shope, D. R.; Shrestha, S.; Shulga, E.; Shupe, M. A.; Sicho, P.; Sickles, A. M.; Sidebo, P. E.; Haddad, E. Sideras; Sidiropoulou, O.; Sidorov, D.; Sidoti, A.; Siegert, F.; Sijacki, Dj.; Silva, J.; Silverstein, S. B.; Simak, V.; Simic, Lj.; Simion, S.; Simioni, E.; Simmons, B.; Simon, M.; Sinervo, P.; Sinev, N. B.; Sioli, M.; Siragusa, G.; Siral, I.; Sivoklokov, S. Yu.; Sjölin, J.; Skinner, M. B.; Skubic, P.; Slater, M.; Slavicek, T.; Slawinska, M.; Sliwa, K.; Slovak, R.; Smakhtin, V.; Smart, B. H.; Smiesko, J.; Smirnov, N.; Smirnov, S. Yu.; Smirnov, Y.; Smirnova, L. N.; Smirnova, O.; Smith, J. W.; Smith, M. N. K.; Smith, R. W.; Smizanska, M.; Smolek, K.; Snesarev, A. A.; Snyder, I. M.; Snyder, S.; Sobie, R.; Socher, F.; Soffer, A.; Soh, D. A.; Sokhrannyi, G.; Sanchez, C. A. Solans; Solar, M.; Soldatov, E. Yu.; Soldevila, U.; Solodkov, A. A.; Soloshenko, A.; Solovyanov, O. V.; Solovyev, V.; Sommer, P.; Son, H.; Song, H. Y.; Sopczak, A.; Sorin, V.; Sosa, D.; Sotiropoulou, C. L.; Soualah, R.; Soukharev, A. M.; South, D.; Sowden, B. C.; Spagnolo, S.; Spalla, M.; Spangenberg, M.; Spanò, F.; Sperlich, D.; Spettel, F.; Spieker, T. M.; Spighi, R.; Spigo, G.; Spiller, L. A.; Spousta, M.; Denis, R. D. St.; Stabile, A.; Stamen, R.; Stamm, S.; Stanecka, E.; Stanek, R. W.; Stanescu, C.; Stanitzki, M. M.; Stapnes, S.; Starchenko, E. A.; Stark, G. H.; Stark, J.; Stark, S. H.; Staroba, P.; Starovoitov, P.; Stärz, S.; Staszewski, R.; Steinberg, P.; Stelzer, B.; Stelzer, H. J.; Stelzer-Chilton, O.; Stenzel, H.; Stewart, G. A.; Stillings, J. A.; Stockton, M. C.; Stoebe, M.; Stoicea, G.; Stolte, P.; Stonjek, S.; Stradling, A. R.; Straessner, A.; Stramaglia, M. E.; Strandberg, J.; Strandberg, S.; Strandlie, A.; Strauss, M.; Strizenec, P.; Ströhmer, R.; Strom, D. M.; Stroynowski, R.; Strubig, A.; Stucci, S. A.; Stugu, B.; Styles, N. A.; Su, D.; Su, J.; Suchek, S.; Sugaya, Y.; Suk, M.; Sulin, V. V.; Sultansoy, S.; Sumida, T.; Sun, S.; Sun, X.; Suruliz, K.; Suster, C. J. E.; Sutton, M. R.; Suzuki, S.; Svatos, M.; Swiatlowski, M.; Swift, S. P.; Sykora, I.; Sykora, T.; Ta, D.; Tackmann, K.; Taenzer, J.; Taffard, A.; Tafirout, R.; Taiblum, N.; Takai, H.; Takashima, R.; Takeshita, T.; Takubo, Y.; Talby, M.; Talyshev, A. A.; Tanaka, J.; Tanaka, M.; Tanaka, R.; Tanaka, S.; Tanioka, R.; Tannenwald, B. B.; Araya, S. Tapia; Tapprogge, S.; Tarem, S.; Tartarelli, G. F.; Tas, P.; Tasevsky, M.; Tashiro, T.; Tassi, E.; Delgado, A. Tavares; Tayalati, Y.; Taylor, A. C.; Taylor, G. N.; Taylor, P. T. E.; Taylor, W.; Teixeira-Dias, P.; Temple, D.; Kate, H. Ten; Teng, P. K.; Teoh, J. J.; Tepel, F.; Terada, S.; Terashi, K.; Terron, J.; Terzo, S.; Testa, M.; Teuscher, R. J.; Theveneaux-Pelzer, T.; Thomas, J. P.; Thomas-Wilsker, J.; Thompson, P. D.; Thompson, A. S.; Thomsen, L. A.; Thomson, E.; Tibbetts, M. J.; Torres, R. E. Ticse; Tikhomirov, V. O.; Tikhonov, Yu. A.; Timoshenko, S.; Tipton, P.; Tisserant, S.; Todome, K.; Todorova-Nova, S.; Tojo, J.; Tokár, S.; Tokushuku, K.; Tolley, E.; Tomlinson, L.; Tomoto, M.; Tompkins, L.; Toms, K.; Tong, B.; Tornambe, P.; Torrence, E.; Torres, H.; Pastor, E. Torró; Toth, J.; Touchard, F.; Tovey, D. R.; Treado, C. J.; Trefzger, T.; Tresoldi, F.; Tricoli, A.; Trigger, I. M.; Trincaz-Duvoid, S.; Tripiana, M. F.; Trischuk, W.; Trocmé, B.; Trofymov, A.; Troncon, C.; Trottier-McDonald, M.; Trovatelli, M.; Truong, L.; Trzebinski, M.; Trzupek, A.; Tsang, K. W.; Tseng, J. C.-L.; Tsiareshka, P. V.; Tsipolitis, G.; Tsirintanis, N.; Tsiskaridze, S.; Tsiskaridze, V.; Tskhadadze, E. G.; Tsui, K. M.; Tsukerman, I. I.; Tsulaia, V.; Tsuno, S.; Tsybychev, D.; Tu, Y.; Tudorache, A.; Tudorache, V.; Tulbure, T. T.; Tuna, A. N.; Tupputi, S. A.; Turchikhin, S.; Turgeman, D.; Cakir, I. Turk; Turra, R.; Tuts, P. M.; Ucchielli, G.; Ueda, I.; Ughetto, M.; Ukegawa, F.; Unal, G.; Undrus, A.; Unel, G.; Ungaro, F. C.; Unno, Y.; Unverdorben, C.; Urban, J.; Urquijo, P.; Urrejola, P.; Usai, G.; Usui, J.; Vacavant, L.; Vacek, V.; Vachon, B.; Valderanis, C.; Santurio, E. Valdes; Valencic, N.; Valentinetti, S.; Valero, A.; Valéry, L.; Valkar, S.; Vallier, A.; Ferrer, J. A. Valls; Van Den Wollenberg, W.; van der Graaf, H.; van Eldik, N.; van Gemmeren, P.; Van Nieuwkoop, J.; van Vulpen, I.; van Woerden, M. C.; Vanadia, M.; Vandelli, W.; Vanguri, R.; Vaniachine, A.; Vankov, P.; Vardanyan, G.; Vari, R.; Varnes, E. W.; Varni, C.; Varol, T.; Varouchas, D.; Vartapetian, A.; Varvell, K. E.; Vasquez, J. G.; Vasquez, G. A.; Vazeille, F.; Schroeder, T. Vazquez; Veatch, J.; Veeraraghavan, V.; Veloce, L. M.; Veloso, F.; Velz, T.; Veneziano, S.; Ventura, A.; Venturi, M.; Venturi, N.; Venturini, A.; Vercesi, V.; Verducci, M.; Verkerke, W.; Vermeulen, J. C.; Vetterli, M. C.; Maira, N. Viaux; Viazlo, O.; Vichou, I.; Vickey, T.; Boeriu, O. E. Vickey; Viehhauser, G. H. A.; Viel, S.; Vigani, L.; Villa, M.; Perez, M. Villaplana; Vilucchi, E.; Vincter, M. G.; Vinogradov, V. B.; Vishwakarma, A.; Vittori, C.; Vivarelli, I.; Vlachos, S.; Vlasak, M.; Vogel, M.; Vokac, P.; Volpi, G.; von der Schmitt, H.; von Toerne, E.; Vorobel, V.; Vorobev, K.; Vos, M.; Voss, R.; Vossebeld, J. H.; Vranjes, N.; Milosavljevic, M. Vranjes; Vrba, V.; Vreeswijk, M.; Vuillermet, R.; Vukotic, I.; Wagner, P.; Wagner, W.; Wagner-Kuhr, J.; Wahlberg, H.; Wahrmund, S.; Wakabayashi, J.; Walder, J.; Walker, R.; Walkowiak, W.; Wallangen, V.; Wang, C.; Wang, C.; Wang, F.; Wang, H.; Wang, H.; Wang, J.; Wang, J.; Wang, Q.; Wang, R.; Wang, S. M.; Wang, T.; Wang, W.; Wang, W.; Wang, Z.; Wanotayaroj, C.; Warburton, A.; Ward, C. P.; Wardrope, D. R.; Washbrook, A.; Watkins, P. M.; Watson, A. T.; Watson, M. F.; Watts, G.; Watts, S.; Waugh, B. M.; Webb, A. F.; Webb, S.; Weber, M. S.; Weber, S. W.; Weber, S. A.; Webster, J. S.; Weidberg, A. R.; Weinert, B.; Weingarten, J.; Weiser, C.; Weits, H.; Wells, P. S.; Wenaus, T.; Wengler, T.; Wenig, S.; Wermes, N.; Werner, M. D.; Werner, P.; Wessels, M.; Whalen, K.; Whallon, N. L.; Wharton, A. M.; White, A.; White, M. J.; White, R.; Whiteson, D.; Wickens, F. J.; Wiedenmann, W.; Wielers, M.; Wiglesworth, C.; Wiik-Fuchs, L. A. M.; Wildauer, A.; Wilk, F.; Wilkens, H. G.; Williams, H. H.; Williams, S.; Willis, C.; Willocq, S.; Wilson, J. A.; Wingerter-Seez, I.; Winklmeier, F.; Winston, O. J.; Winter, B. T.; Wittgen, M.; Wobisch, M.; Wolf, T. M. H.; Wolff, R.; Wolter, M. W.; Wolters, H.; Worm, S. D.; Wosiek, B. K.; Wotschack, J.; Woudstra, M. J.; Wozniak, K. W.; Wu, M.; Wu, S. L.; Wu, X.; Wu, Y.; Wyatt, T. R.; Wynne, B. M.; Xella, S.; Xi, Z.; Xia, L.; Xu, D.; Xu, L.; Yabsley, B.; Yacoob, S.; Yamaguchi, D.; Yamaguchi, Y.; Yamamoto, A.; Yamamoto, S.; Yamanaka, T.; Yamauchi, K.; Yamazaki, Y.; Yan, Z.; Yang, H.; Yang, H.; Yang, Y.; Yang, Z.; Yao, W.-M.; Yap, Y. C.; Yasu, Y.; Yatsenko, E.; Wong, K. H. Yau; Ye, J.; Ye, S.; Yeletskikh, I.; Yigitbasi, E.; Yildirim, E.; Yorita, K.; Yoshihara, K.; Young, C.; Young, C. J. S.; Youssef, S.; Yu, D. R.; Yu, J.; Yu, J.; Yuan, L.; Yuen, S. P. Y.; Yusuff, I.; Zabinski, B.; Zacharis, G.; Zaidan, R.; Zaitsev, A. M.; Zakharchuk, N.; Zalieckas, J.; Zaman, A.; Zambito, S.; Zanzi, D.; Zeitnitz, C.; Zeman, M.; Zemla, A.; Zeng, J. C.; Zeng, Q.; Zenin, O.; Ženiš, T.; Zerwas, D.; Zhang, D.; Zhang, F.; Zhang, G.; Zhang, H.; Zhang, J.; Zhang, L.; Zhang, L.; Zhang, M.; Zhang, R.; Zhang, R.; Zhang, X.; Zhang, Y.; Zhang, Z.; Zhao, X.; Zhao, Y.; Zhao, Z.; Zhemchugov, A.; Zhong, J.; Zhou, B.; Zhou, C.; Zhou, L.; Zhou, M.; Zhou, M.; Zhou, N.; Zhu, C. G.; Zhu, H.; Zhu, J.; Zhu, Y.; Zhuang, X.; Zhukov, K.; Zibell, A.; Zieminska, D.; Zimine, N. I.; Zimmermann, C.; Zimmermann, S.; Zinonos, Z.; Zinser, M.; Ziolkowski, M.; Živković, L.; Zobernig, G.; Zoccoli, A.; Zou, R.; Nedden, M. zur; Zwalinski, L.

2017-07-01

This paper describes the implementation and performance of a particle flow algorithm applied to 20.2 fb^{-1} of ATLAS data from 8 TeV proton-proton collisions in Run 1 of the LHC. The algorithm removes calorimeter energy deposits due to charged hadrons from consideration during jet reconstruction, instead using measurements of their momenta from the inner tracker. This improves the accuracy of the charged-hadron measurement, while retaining the calorimeter measurements of neutral-particle energies. The paper places emphasis on how this is achieved, while minimising double-counting of charged-hadron signals between the inner tracker and calorimeter. The performance of particle flow jets, formed from the ensemble of signals from the calorimeter and the inner tracker, is compared to that of jets reconstructed from calorimeter energy deposits alone, demonstrating improvements in resolution and pile-up stability.

Interaction of a Rectangular Jet with a Flat-Plate Placed Parallel to the Flow

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Brown, C. A.; Bridges, J. A.

2013-01-01

An experimental study is carried out addressing the flowfield and radiated noise from the interaction of a large aspect ratio rectangular jet with a flat plate placed parallel to but away from the direct path of the jet. Sound pressure level spectra exhibit an increase in the noise levels for both the 'reflected' and 'shielded' sides of the plate relative to the free-jet case. Detailed cross-sectional distributions of flowfield properties obtained by hot-wire anemometry are documented for a low subsonic condition. Corresponding mean Mach number distributions obtained by Pitot-probe surveys are presented for high subsonic conditions. In the latter flow regime and for certain relative locations of the plate, a flow resonance accompanied by audible tones is encountered. Under the resonant condition the jet cross-section experiences an 'axis-switching' and flow visualization indicates the presence of an organized 'vortex street'. The trends of the resonant frequency variation with flow parameters exhibit some similarities to, but also marked differences with, corresponding trends of the well-known edgetone phenomenon.

Background noise measurements from jet exit vanes designed to reduced flow pulsations in an open-jet wind tunnel

NASA Technical Reports Server (NTRS)

Hoad, D. R.; Martin, R. M.

1985-01-01

Many open jet wind tunnels experience pulsations of the flow which are typically characterized by periodic low frequency velocity and pressure variations. One method of reducing these fluctuations is to install vanes around the perimeter of the jet exit to protrude into the flow. Although these vanes were shown to be effective in reducing the fluctuation content, they can also increase the test section background noise level. The results of an experimental acoustic program in the Langley 4- by 7-Meter Tunnel is presented which evaluates the effect on tunnel background noise of such modifications to the jet exit nozzle. Noise levels for the baseline tunnel configuration are compared with those for three jet exit nozzle modifications, including an enhanced noise reduction configuration that minimizes the effect of the vanes on the background noise. Although the noise levels for this modified vane configuration were comparable to baseline tunnel background noise levels in this facility, installation of these modified vanes in an acoustic tunnel may be of concern because the noise levels for the vanes could be well above background noise levels in a quiet facility.

Prediction of Drag Reduction in Supersonic and Hypersonic Flows with Counterflow Jets

NASA Technical Reports Server (NTRS)

Daso, Endwell O.; Beaulieu, Warren; Hager, James O.; Turner, James E. (Technical Monitor)

2002-01-01

Computational fluid dynamics solutions of the flowfield of a truncated cone-cylinder with and without counterflow jets have been obtained for the short penetration mode (SPM) and long penetration mode (LPM) of the freestream-counterflow jet interaction flowfield. For the case without the counterflow jet, the comparison of the normalized surface pressures showed very good agreement with experimental data. For the case with the SPM jet, the predicted surface pressures did not compare as well with the experimental data upstream of the expansion corner, while aft of the expansion corner, the comparison of the solution and the data is seen to give much better agreement. The difference in the prediction and the data could be due to the transient character of the jet penetration modes, possible effects of the plasma physics that are not accounted for here, or even the less likely effect of flow turbulence, etc. For the LPM jet computations, one-dimensional isentropic relations were used to derived the jet exit conditions in order to obtain the LPM solutions. The solution for the jet exit Mach number of 3 shows a jet penetration several times longer than that of the SPM, and therefore much weaker bow shock, with an attendant reduction in wave drag. The LPM jet is, in essence, seen to be a "pencil" of fluid, with much higher dynamic pressure, embedded in the oncoming supersonic or hypersonic freestream. The methodology for determining the conditions for the LPM jet could enable a practical approach for the design and application of counterflow LPM jets for the reduction of wave drag and heat flux, thus significantly enhancing the aerodynamic characteristics and aerothermal performance of supersonic and hypersonic vehicles. The solutions show that the qualitative flow structure is very well captured. The obtained results, therefore, suggest that counterflowing jets are viable candidate technology concepts that can be employed to give significant reductions in wave drag, heat

On the Surface Breakup of a Non-turbulent Round Liquid Jet in Cross-flow

NASA Astrophysics Data System (ADS)

Behzad, Mohsen; Ashgriz, Nasser

2011-11-01

The atomization of a non-turbulent liquid jet injected into a subsonic cross-flow consists of two parts: (1) primary breakup and (2) secondary breakup. Two distinct regimes for the liquid jet primary breakup have been recognized; the so called column breakup and surface breakup. In the column breakup mode, the entire liquid jet undergoes disintegration into large liquid lumps. Quiet differently in the surface breakup regime, liquid fragments with various sizes and shapes are separated from the surface of the jet. Despite many experimental studies the mechanisms of jet surface breakup is not fully understood. Thus this study aims at providing useful observations regarding the underlying physics involving the surface breakup mechanism of a liquid jet in cross-flow, using detailed numerical simulations. The results show that a two-stage mechanism can be responsible for surface breakup. In the first stage, a sheet-like structure extrudes towards the downstream, and in the second stage it disintegrates into ligaments and droplets due to aerodynamic instability.

Development of Computational Aeroacoustics Code for Jet Noise and Flow Prediction

NASA Astrophysics Data System (ADS)

Keith, Theo G., Jr.; Hixon, Duane R.

2002-07-01

Accurate prediction of jet fan and exhaust plume flow and noise generation and propagation is very important in developing advanced aircraft engines that will pass current and future noise regulations. In jet fan flows as well as exhaust plumes, two major sources of noise are present: large-scale, coherent instabilities and small-scale turbulent eddies. In previous work for the NASA Glenn Research Center, three strategies have been explored in an effort to computationally predict the noise radiation from supersonic jet exhaust plumes. In order from the least expensive computationally to the most expensive computationally, these are: 1) Linearized Euler equations (LEE). 2) Very Large Eddy Simulations (VLES). 3) Large Eddy Simulations (LES). The first method solves the linearized Euler equations (LEE). These equations are obtained by linearizing about a given mean flow and the neglecting viscous effects. In this way, the noise from large-scale instabilities can be found for a given mean flow. The linearized Euler equations are computationally inexpensive, and have produced good noise results for supersonic jets where the large-scale instability noise dominates, as well as for the tone noise from a jet engine blade row. However, these linear equations do not predict the absolute magnitude of the noise; instead, only the relative magnitude is predicted. Also, the predicted disturbances do not modify the mean flow, removing a physical mechanism by which the amplitude of the disturbance may be controlled. Recent research for isolated airfoils' indicates that this may not affect the solution greatly at low frequencies. The second method addresses some of the concerns raised by the LEE method. In this approach, called Very Large Eddy Simulation (VLES), the unsteady Reynolds averaged Navier-Stokes equations are solved directly using a high-accuracy computational aeroacoustics numerical scheme. With the addition of a two-equation turbulence model and the use of a relatively

Cold atmospheric pressure air plasma jet for medical applications

NASA Astrophysics Data System (ADS)

Kolb, J. F.; Mohamed, A.-A. H.; Price, R. O.; Swanson, R. J.; Bowman, A.; Chiavarini, R. L.; Stacey, M.; Schoenbach, K. H.

2008-06-01

By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.

The Effects of Surfaces on the Aerodynamics and Acoustics of Jet Flows

NASA Technical Reports Server (NTRS)

Smith, Matthew J.; Miller, Steven A. E.

2013-01-01

Aircraft noise mitigation is an ongoing challenge for the aeronautics research community. In response to this challenge, low-noise aircraft concepts have been developed that exhibit situations where the jet exhaust interacts with an airframe surface. Jet flows interacting with nearby surfaces manifest a complex behavior in which acoustic and aerodynamic characteristics are altered. In this paper, the variation of the aerodynamics, acoustic source, and far-field acoustic intensity are examined as a large at plate is positioned relative to the nozzle exit. Steady Reynolds-Averaged Navier-Stokes solutions are examined to study the aerodynamic changes in the field-variables and turbulence statistics. The mixing noise model of Tam and Auriault is used to predict the noise produced by the jet. To validate both the aerodynamic and the noise prediction models, results are compared with Particle Image Velocimetry (PIV) and free-field acoustic data respectively. The variation of the aerodynamic quantities and noise source are examined by comparing predictions from various jet and at plate configurations with an isolated jet. To quantify the propulsion airframe aeroacoustic installation effects on the aerodynamic noise source, a non-dimensional number is formed that contains the flow-conditions and airframe installation parameters.

Computational Fluid Dynamic Simulation of Flow in Abrasive Water Jet Machining

NASA Astrophysics Data System (ADS)

Venugopal, S.; Sathish, S.; Jothi Prakash, V. M.; Gopalakrishnan, T.

2017-03-01

Abrasive water jet cutting is one of the most recently developed non-traditional manufacturing technologies. In this machining, the abrasives are mixed with suspended liquid to form semi liquid mixture. The general nature of flow through the machining, results in fleeting wear of the nozzle which decrease the cutting performance. The inlet pressure of the abrasive water suspension has main effect on the major destruction characteristics of the inner surface of the nozzle. The aim of the project is to analyze the effect of inlet pressure on wall shear and exit kinetic energy. The analysis could be carried out by changing the taper angle of the nozzle, so as to obtain optimized process parameters for minimum nozzle wear. The two phase flow analysis would be carried by using computational fluid dynamics tool CFX. It is also used to analyze the flow characteristics of abrasive water jet machining on the inner surface of the nozzle. The availability of optimized process parameters of abrasive water jet machining (AWJM) is limited to water and experimental test can be cost prohibitive. In this case, Computational fluid dynamics analysis would provide better results.

Penetration Characteristics of Air, Carbon Dioxide and Helium Transverse Sonic Jets in Mach 5 Cross Flow.

PubMed

Erdem, Erinc; Kontis, Konstantinos; Saravanan, Selvaraj

2014-12-08

An experimental investigation of sonic air, CO 2 and Helium transverse jets in Mach 5 cross flow was carried out over a flat plate. The jet to freestream momentum flux ratio, J, was kept the same for all gases. The unsteady flow topology was examined using high speed schlieren visualisation and PIV. Schlieren visualisation provided information regarding oscillating jet shear layer structures and bow shock, Mach disc and barrel shocks. Two-component PIV measurements at the centreline, provided information regarding jet penetration trajectories. Barrel shocks and Mach disc forming the jet boundary were visualised/quantified also jet penetration boundaries were determined. Even though J is kept the same for all gases, the penetration patterns were found to be remarkably different both at the nearfield and the farfield. Air and CO 2 jet resulted similar nearfield and farfield penetration pattern whereas Helium jet spread minimal in the nearfield.

Penetration Characteristics of Air, Carbon Dioxide and Helium Transverse Sonic Jets in Mach 5 Cross Flow

PubMed Central

Erdem, Erinc; Kontis, Konstantinos; Saravanan, Selvaraj

2014-01-01

An experimental investigation of sonic air, CO2 and Helium transverse jets in Mach 5 cross flow was carried out over a flat plate. The jet to freestream momentum flux ratio, J, was kept the same for all gases. The unsteady flow topology was examined using high speed schlieren visualisation and PIV. Schlieren visualisation provided information regarding oscillating jet shear layer structures and bow shock, Mach disc and barrel shocks. Two-component PIV measurements at the centreline, provided information regarding jet penetration trajectories. Barrel shocks and Mach disc forming the jet boundary were visualised/quantified also jet penetration boundaries were determined. Even though J is kept the same for all gases, the penetration patterns were found to be remarkably different both at the nearfield and the farfield. Air and CO2 jet resulted similar nearfield and farfield penetration pattern whereas Helium jet spread minimal in the nearfield. PMID:25494348

Supersonic Injection of Aerated Liquid Jet

NASA Astrophysics Data System (ADS)

Choudhari, Abhijit; Sallam, Khaled

2016-11-01

A computational study of the exit flow of an aerated two-dimensional jet from an under-expanded supersonic nozzle is presented. The liquid sheet is operating within the annular flow regime and the study is motivated by the application of supersonic nozzles in air-breathing propulsion systems, e.g. scramjet engines, ramjet engines and afterburners. The simulation was conducted using VOF model and SST k- ω turbulence model. The test conditions included: jet exit of 1 mm and mass flow rate of 1.8 kg/s. The results show that air reaches transonic condition at the injector exit due to the Fanno flow effects in the injector passage. The aerated liquid jet is alternately expanded by Prandtl-Meyer expansion fan and compressed by oblique shock waves due to the difference between the back (chamber) pressure and the flow pressure. The process then repeats itself and shock (Mach) diamonds are formed at downstream of injector exit similar to those typical of exhaust plumes of propulsion system. The present results, however, indicate that the flow field of supersonic aerated liquid jet is different from supersonic gas jets due to the effects of water evaporation from the liquid sheet. The contours of the Mach number, static pressure of both cases are compared to the theory of gas dynamics.

Stretched Inertial Jets

NASA Astrophysics Data System (ADS)

Ghabache, Elisabeth; Antkowiak, Arnaud; Seon, Thomas; Villermaux, Emmanuel

2015-11-01

Liquid jets often arise as short-lived bursting liquid flows. Cavitation or impact-driven jets, bursting champagne bubbles, shaped-charge jets, ballistospores or drop-on-demand inkjet printing are a few examples where liquid jets are suddenly released. The trademark of all these discharge jets is the property of being stretched, due to the quenching injection. the present theoretical and experimental investigation, the structure of the jet flow field will be unraveled experimentally for a few emblematic occurrences of discharge jets. Though the injection markedly depends on each flow configuration, the jet velocity field will be shown to be systematically and rapidly attracted to the universal stretching flow z/t. The emergence of this inertial attractor actually only relies on simple kinematic ingredients, and as such is fairly generic. The universality of the jet velocity structure will be discussed.

High-repetition-rate interferometric Rayleigh scattering for flow-velocity measurements

NASA Astrophysics Data System (ADS)

Estevadeordal, Jordi; Jiang, Naibo; Cutler, Andrew D.; Felver, Josef J.; Slipchenko, Mikhail N.; Danehy, Paul M.; Gord, James R.; Roy, Sukesh

2018-03-01

High-repetition-rate interferometric-Rayleigh-scattering (IRS) velocimetry is demonstrated for non-intrusive, high-speed flow-velocity measurements. High temporal resolution is obtained with a quasi-continuous burst-mode laser that is capable of operating at 10-100 kHz, providing 10-ms bursts with pulse widths of 5-1000 ns and pulse energy > 100 mJ at 532 nm. Coupled with a high-speed camera system, the IRS method is based on imaging the flow field through an etalon with 8-GHz free spectral range and capturing the Doppler shift of the Rayleigh-scattered light from the flow at multiple points having constructive interference. The seed-laser linewidth permits a laser linewidth of < 150 MHz at 532 nm. The technique is demonstrated in a high-speed jet, and high-repetition-rate image sequences are shown.

Nasal Jet-CPAP (variable flow) versus Bubble-CPAP in preterm infants with respiratory distress: an open label, randomized controlled trial.

PubMed

Bhatti, A; Khan, J; Murki, S; Sundaram, V; Saini, S S; Kumar, P

2015-11-01

To compare the failure rates between Jet continuous positive airway pressure device (J-CPAP-variable flow) and Bubble continuous positive airway device (B-CPAP) in preterm infants with respiratory distress. Preterm newborns <34 weeks gestation with onset of respiratory distress within 6 h of life were randomized to receive J-CPAP (a variable flow device) or B-CPAP (continuous flow device). A standardized protocol was followed for titration, weaning and removal of CPAP. Pressure was monitored close to the nares in both the devices every 6 hours and settings were adjusted to provide desired CPAP. The primary outcome was CPAP failure rate within 72 h of life. Secondary outcomes were CPAP failure within 7 days of life, need for surfactant post-randomization, time to CPAP failure, duration of CPAP and complications of prematurity. An intention to treat analysis was done. One-hundred seventy neonates were randomized, 80 to J-CPAP and 90 to B-CPAP. CPAP failure rates within 72 h were similar in infants who received J-CPAP and in those who received B-CPAP (29 versus 21%; relative risks 1.4 (0.8 to 2.3), P=0.25). Mean (95% confidence intervals) time to CPAP failure was 59 h (54 to 64) in the Jet CPAP group in comparison with 65 h (62 to 68) in the Bubble CPAP group (log rank P=0.19). All other secondary outcomes were similar between the two groups. In preterm infants with respiratory distress starting within 6 h of life, CPAP failure rates were similar with Jet CPAP and Bubble CPAP.

Jet mixing into a heated cross flow in a cylindrical duct: Influence of geometry and flow variations

NASA Technical Reports Server (NTRS)

Hatch, M. S.; Sowa, W. A.; Samuelsen, G. S.; Holdeman, J. D.

1992-01-01

To examine the mixing characteristics of jets in an axi-symmetric can geometry, temperature measurements were obtained downstream of a row of cold jets injected into a heated cross stream. Parametric, non-reacting experiments were conducted to determine the influence of geometry and flow variations on mixing patterns in a cylindrical configuration. Results show that jet to mainstream momentum flux ratio and orifice geometry significantly impact the mixing characteristics of jets in a can geometry. For a fixed number of orifices, the coupling between momentum flux ratio and injector determines (1) the degree of jet penetration at the injection plane, and (2) the extent of circumferential mixing downstream of the injection plane. The results also show that, at a fixed momentum flux ratio, jet penetration decreases with (1) an increase in slanted slot aspect ratio, and (2) an increase in the angle of the slots with respect to the mainstream direction.

Measurements of air entrainment by vertical plunging liquid jets

NASA Astrophysics Data System (ADS)

El Hammoumi, M.; Achard, J. L.; Davoust, L.

2002-06-01

This paper addresses the issue of the air-entrainment process by a vertical plunging liquid jet. A non-dimensional physical analysis, inspired by the literature on the stability of free jets submitted to an aerodynamic interaction, was developed and yielded two correlation equations for the laminar and the turbulent plunging jets. These correlation equations allow the volumetric flow rate of the air carryunder represented by the Weber number of entrainment We n to be predicted. The plunging jets under consideration issued from circular tubes long enough to achieve a fully developed flow at the outlet. A sensitive technique based on a rising soap meniscus was developed to measure directly the volumetric flow rate of the air carryunder. Our data are compared with other experimental data available in the literature; they also stand as a possible database for future theoretical modelling.

Stability of a jet in confined pressure-driven biphasic flows at low reynolds numbers.

PubMed

Guillot, Pierre; Colin, Annie; Utada, Andrew S; Ajdari, Armand

2007-09-07

Motivated by its importance for microfluidic applications, we study the stability of jets formed by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes confinement and Poiseuille flow profiles. We experimentally evidence a transition between situations where the flow takes the form of a jet and regimes where drops are produced. We describe this as the transition from convective to absolute instability, within a simple linear analysis using lubrication theory for flows at low Reynolds number, and reach remarkable agreement with the data.

Numerical Analysis of Flow Evolution in a Helium Jet Injected into Ambient Air

NASA Technical Reports Server (NTRS)

Satti, Rajani P.; Agrawal, Ajay K.

2005-01-01

A computational model to study the stability characteristics of an evolving buoyant helium gas jet in ambient air environment is presented. Numerical formulation incorporates a segregated approach to solve for the transport equations of helium mass fraction coupled with the conservation equations of mixture mass and momentum using a staggered grid method. The operating parameters correspond to the Reynolds number varying from 30 to 300 to demarcate the flow dynamics in oscillating and non-oscillating regimes. Computed velocity and concentration fields were used to analyze the flow structure in the evolving jet. For Re=300 case, results showed that an instability mode that sets in during the evolution process in Earth gravity is absent in zero gravity, signifying the importance of buoyancy. Though buoyancy initiates the instability, below a certain jet exit velocity, diffusion dominates the entrainment process to make the jet non-oscillatory as observed for the Re=30 case. Initiation of the instability was found to be dependent on the interaction of buoyancy and momentum forces along the jet shear layer.

Aeroacoustic Characteristics of Model Jet Test Facility Flow Conditioners

NASA Technical Reports Server (NTRS)

Kinzie, Kevin W.; Henderson, Brenda S.; Haskin, Harry H.

2005-01-01

An experimental investigation of flow conditioning devices used to suppress internal rig noise in high speed, high temperature experimental jet facilities is discussed. The aerodynamic and acoustic characteristics of a number of devices including pressure loss and extraneous noise generation are measured. Both aerodynamic and acoustic characteristics are strongly dependent on the porosity of the flow conditioner and the closure ratio of the duct system. For unchoked flow conditioners, the pressure loss follows conventional incompressible flow models. However, for choked flow conditioners, a compressible flow model where the duct and flow conditioner system is modeled as a convergent-divergent nozzle can be used to estimate pressure loss. Choked flow conditioners generate significantly more noise than unchoked conditioners. In addition, flow conditioners with small hole diameters or sintered metal felt material generate less self-noise noise compared to flow conditioners with larger holes.

Characteristics of a Strongly-Pulsed Non-Premixed Jet Flame in Cross-flow

NASA Astrophysics Data System (ADS)

Gamba, Mirko; Clemens, Noel T.; Ezekoye, Ofodike A.

2006-11-01

The effects of large-amplitude, high-frequency harmonic forcing of turbulent nonpremixed hydrogen/methane jet flames in cross-flow (JFICF) are investigated experimentally. Flame lengths, penetration lengths, and mixing characteristics are studied using flame luminosity imaging, planar laser Mie scattering visualization and particle image velocimetry. Mean jet Reynolds numbers of 1,600 and 3,250 (peak Re ˜2,500--6,500) with corresponding mean momentum flux ratios, r, of 1.9 and 3.7 (peak r ˜2.6--8.3) are considered. Forcing frequencies of 100 Hz and 300 Hz with amplitudes of ˜60%--300% are investigated. Consistent with previous work, a drastic decrease in flame length and soot emission, an increase in flame penetration and an improved jet fuel/cross-flow air mixing are observed for the larger forcing amplitude cases. Partial pre-mixing induced by near-field reverse flow, near-field vortex/vortex interaction and large-scale stirring, rendered stronger by large forcing amplitudes and frequencies, are thought to play a key role on the observed effects.

Numerical mixing calculations of confined reacting jet flows in a cylindrical duct

NASA Technical Reports Server (NTRS)

Oechsle, Victor L.; Holdeman, J. D.

1995-01-01

The results reported in this paper describe some of the main flow characteristics and NOx production results which develop in the mixing process in a constant cross-sectional cylindrical duct. A 3-dimensional numerical model has been used to predict the mixing flow field and NOx characteristics in a mixing section of an RQL combustor. Eighteen configurations have been analyzed in a circular geometry in a fully reacting environment simulating the operating condition of an actual RQL gas turbine combustion liner. The evaluation matrix was constructed by varying three parameter: (1) jet-to-mainstream momentum-flux ration (J), (2) orifice shape or orifice aspect ratio, and (3) slot slant angle. The results indicate that the mixing flow field and NOx production significantly vary with the value of the jet penetration and subsequently, slanting elongated slots generally improve the NOx production at high J conditions. Round orifices produce low NOx at low J due to the strong jet penetration. The NOx production trends do not correlate with the mixing non-uniformity parameters described herein.

Analysis of turbulent free-jet hydrogen-air diffusion flames with finite chemical reaction rates

NASA Technical Reports Server (NTRS)

Sislian, J. P.; Glass, I. I.; Evans, J. S.

1979-01-01

A numerical analysis is presented of the nonequilibrium flow field resulting from the turbulent mixing and combustion of an axisymmetric hydrogen jet in a supersonic parallel ambient air stream. The effective turbulent transport properties are determined by means of a two-equation model of turbulence. The finite-rate chemistry model considers eight elementary reactions among six chemical species: H, O, H2O, OH, O2 and H2. The governing set of nonlinear partial differential equations was solved by using an implicit finite-difference procedure. Radial distributions were obtained at two downstream locations for some important variables affecting the flow development, such as the turbulent kinetic energy and its dissipation rate. The results show that these variables attain their peak values on the axis of symmetry. The computed distribution of velocity, temperature, and mass fractions of the chemical species gives a complete description of the flow field. The numerical predictions were compared with two sets of experimental data. Good qualitative agreement was obtained.

Study of parameters and entrainment of a jet in cross-flow arrangement with transition at two low Reynolds numbers

NASA Astrophysics Data System (ADS)

Cárdenas, Camilo; Denev, Jordan A.; Suntz, Rainer; Bockhorn, Henning

2012-10-01

Investigation of the mixing process is one of the main issues in chemical engineering and combustion and the configuration of a jet into a cross-flow (JCF) is often employed for this purpose. Experimental data are gained for the symmetry plane in a JCF-arrangement of an air flow using a combination of particle image velocimetry (PIV) with laser-induced fluorescence (LIF). The experimental data with thoroughly measured boundary conditions are complemented with direct numerical simulations, which are based on idealized boundary conditions. Two similar cases are studied with a fixed jet-to-cross-flow velocity ratio of 3.5 and variable cross-flow Reynolds numbers equal to 4,120 and 8,240; in both cases the jet issues from the pipe at laminar conditions. This leads to a laminar-to-turbulent transition, which depends on the Reynolds number and occurs quicker for the case with higher Reynolds number in both experiments and simulations as well. It was found that the Reynolds number only slightly affects the jet trajectory, which in the case with the higher Reynolds number is slightly deeper. It is attributed to the changed boundary layer shape of the cross-flow. Leeward streamlines bend toward the jet and are responsible for the strong entrainment of cross-flow fluid into the jet. Velocity components are compared for the two Reynolds numbers at the leeward side at positions where strongest entrainment is present and a pressure minimum near the jet trajectory is found. The numerical simulations showed that entrainment is higher for the case with the higher Reynolds number. The latter is attributed to the earlier transition in this case. Fluid entrainment of the jet in cross-flow is more than twice stronger than for a similar flow of a jet issuing into a co-flowing stream. This comparison is made along the trajectory of the two jets at a distance of 5.5 jet diameters downstream and is based on the results from the direct numerical simulations and recently published

Submerged jet mixing in nuclear waste tanks: a correlation for jet velocity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daas, M.; Srivastava, R.; Roelant, D.

2007-07-01

Experimental studies were carried out in jet-stirred slurry tanks to correlate the influence of nozzle diameter, initial jet flow velocity, submerged depth of jet, tank diameter and slurry properties on the jet axial velocity. The tanks used in the experimental work had diameters of 0.3 m (1-ft) and 2.13 m (7-ft). The fluids emerged from nozzles of 0.003 m and 0.01 m in diameter, 1/8-inch and 3/8-inch respectively. The examined slurries were non-Newtonian and contained 5 weight percent total insoluble solids. The axial velocities along the centerline of a submerged jet stream were measured at different jet flow rates andmore » at various distances from the nozzle orifice (16 to 200 nozzle diameters) utilizing electromagnetic velocity meter. A new simplified correlation was developed to describe the jet axial velocity in submerged jet stirred tanks utilizing more than 350 data points. The Buckingham Pi theorem and non-linear regression method of multivariate approximation, in conjunction with the Gauss-Jordan elimination method, were used to develop the new correlation. The new correlation agreed well with the experimental data obtained from the current study. Good agreement was also possible with literature data except at large distances from the nozzle as the model slightly overestimated the jet axial velocity. The proposed correlation incorporates the contributions of system geometry, fluid properties, and external forces. Furthermore, it provides reasonable estimates of jet axial velocity. (authors)« less

Three-dimensional flow over a conical afterbody containing a centered propulsive jet: A numerical simulation

NASA Technical Reports Server (NTRS)

Deiwert, G. S.; Rothmund, H.

1984-01-01

The supersonic flow field over a body of revolution incident to the free stream is simulated numerically on a large, array processor (the CDC CYBER 205). The configuration is composed of a cone-cylinder forebody followed by a conical afterbody from which emanates a centered, supersonic propulsive jet. The free-stream Mach number is 2, the jet-exist Mach number is 2.5, and the jet-to-free-stream static pressure ratio is 3. Both the external flow and the exhaust are ideal air at a common total temperature.

Liquid Jet Cavitation via Molecular Dynamics

NASA Astrophysics Data System (ADS)

Ashurst, W. T.

1997-11-01

A two-dimensional molecular dynamics simulation of a liquid jet is used to investigate cavitation in a diesel-like fuel injector. A channel with a length four times its width has been examined at various system sizes (widths of 20 to 160 σ, where σ is the zero energy location in the Lennard-Jones potential). The wall boundary condition is Maxwell's diffuse reflection, similar to the work by Sun & Ebner (Phys. Rev A 46, 4813, 1992). Currently, the jet exhausts into a vacuum, but a second, low density gas will be incorporated to represent the compressed air in a diesel chamber. Four different flow rates are examined. With ρ U equal to √mɛ/σ^2 (the largest flow rate) the static pressure decreases by a factor of twenty between the channel entrance and exit. The largest flow rate has a parabolic velocity profile with almost constant density across the channel. The smallest flow rate has the same velocity profile but the density exhibits a large variation, with the minimum value in the channel center. Thus, the product ρ U is nearly constant across the channel at this flow rate. The discharge coefficient CD has a small variation with flow rate, but the velocity coefficient CV varies with the amount of two-phase fluid within the channel. The ratio of CV to CD varies from 1.3 (largest flow rate) to 2.0 (the smallest flow rate, which is one-eighth of the largest).

Interfacial Stability of Spherically Converging Plasma Jets for Magnetized Target Fusion

NASA Technical Reports Server (NTRS)

Thio, Y. C. Francis; Cassibry, Jason; Wu, S. T.; Eskridge, Richard; Smith, James; Lee, Michael; Rodgers, Stephen L. (Technical Monitor)

2000-01-01

A fusion propulsion scheme has been proposed that makes use of the merging of a spherical distribution of plasma jets to dynamically form a gaseous liner to implode a magnetized target to produce the fusion reaction. In this paper, a study is made of the interfacial stability of the interaction of these jets. Specifically, the Orr-Sommerfeld equation is integrated to obtain the growth rate of a perturbation to the primary flow at the interface between the colliding jets. The results lead to an estimate on the tolerances on the relative flow velocities of the merging plasma jets to form a stable, imploding liner. The results show that the maximum temporal growth rate of the perturbed flow at the jet interface is very small in comparison with the time to full compression of the liner. These data suggest that, as far as the stability of the interface between the merging jets is concerned, the formation of the gaseous liner can withstand velocity variation of the order of 10% between the neighboring jets over the density and temperature ranges investigated.

Advanced high performance vertical hybrid synthetic jet actuator

NASA Technical Reports Server (NTRS)

Xu, Tian-Bing (Inventor); Jiang, Xiaoning (Inventor); Su, Ji (Inventor)

2011-01-01

The present invention comprises a high performance, vertical, zero-net mass-flux, synthetic jet actuator for active control of viscous, separated flow on subsonic and supersonic vehicles. The present invention is a vertical piezoelectric hybrid zero-net mass-flux actuator, in which all the walls of the chamber are electrically controlled synergistically to reduce or enlarge the volume of the synthetic jet actuator chamber in three dimensions simultaneously and to reduce or enlarge the diameter of orifice of the synthetic jet actuator simultaneously with the reduction or enlargement of the volume of the chamber. The jet velocity and mass flow rate for the present invention will be several times higher than conventional piezoelectric synthetic jet actuators.

An Experimental Investigation of the Flow Structure of Supersonic Impinging Jets

NASA Technical Reports Server (NTRS)

Henderson, Brenda; Bridges, James; Wernet, Mark

2002-01-01

An experimental investigation into the jet structure associated with sound production by a supersonic impinging jet is presented. Large plate impinging tones are investigated for a nozzle pressure ratio (NPR) of 4 and nozzle-to-plate spacings between 1 and 5 nozzle exit diameters, where NPR is equal to the ratio of the stagnation pressure to the pressure at the nozzle lip. Results from phase-locked shadowgraph and phase-averaged digital particle image velocimetry (DPIV) studies indicate that, during the oscillation cycle, the Mach disk oscillates axially, a well defined recirculation zone is created in the subsonic impingement region and moves toward the plate, and the compression and expansion regions in the outer supersonic flow move downstream, Sound appears to be generated in the wall jet at approximately 2.6R from the jet axis, where R is the nozzle exit radius. The oscillatory motion in the wall jet is the result of the periodic fluid motion in the near wall region.

VTOL in ground effect flows for closely spaced jets. [to predict pressure and upwash forces on aircraft structures

NASA Technical Reports Server (NTRS)

Migdal, D.; Hill, W. G., Jr.; Jenkins, R. C.

1979-01-01

Results of a series of in ground effect twin jet tests are presented along with flow models for closely spaced jets to help predict pressure and upwash forces on simulated aircraft surfaces. The isolated twin jet tests revealed unstable fountains over a range of spacings and jet heights, regions of below ambient pressure on the ground, and negative pressure differential in the upwash flow field. A separate computer code was developed for vertically oriented, incompressible jets. This model more accurately reflects fountain behavior without fully formed wall jets, and adequately predicts ground isobars, upwash dynamic pressure decay, and fountain lift force variation with height above ground.

Tickling a high speed round jet

NASA Astrophysics Data System (ADS)

Arakeri, Vijay; Krothapalli, Anjaneyulu; Siddavaram, Vikram; Alkislar, Mehmet

2001-11-01

We have experimentally studied the effect of tickling a Mach 0.9 round jet with a set of microjets.Two dimensional velocity field measurements with PIV show a significant reduction in the turbulent intensities in the developing region of the jet with the activation of the microjets.Quantitatively,the axial and normal turbulence intensities are reduced by about 15respectively;even a larger effect is found on the magnitude of the correlation of axial and normal fluctuation intensities with a reduction of almost 40possible with a mass flow rate of the microjets being only about one percent of the main jet mass flow rate and hence justifying the use of the term `tickling`.The above findings are difficult to explain on the basis of stability considerations since there is very little change in the mean profile.Physically,the observed effect could be due to the alteration of the large eddy structures,which are so natural to a round jet,by the presence of the microjets.Exact nature of this interaction may be clarified with three dimensional PIV studies.It is expected that the tickling of the jet done as presently could have a favourable reflection in the aeroacoustics characteristics of the main jet.

Shear flow control of cold and heated rectangular jets by mechanical tabs. Volume 1: Results and discussion

NASA Technical Reports Server (NTRS)

Brown, W. H.; Ahuja, K. K.

1989-01-01

The effects of mechanical protrusions on the jet mixing characteristics of rectangular nozzles for heated and unheated subsonic and supersonic jet plumes were studied. The characteristics of a rectangular nozzle of aspect ratio 4 without the mechanical protrusions were first investigated. Intrusive probes were used to make the flow measurements. Possible errors introduced by intrusive probes in making shear flow measurements were also examined. Several scaled sizes of mechanical tabs were then tested, configured around the perimeter of the rectangular jet. Both the number and the location of the tabs were varied. From this, the best configuration was selected. The conclusions derived were: (1) intrusive probes can produce significant errors in the measurements of the velocity of jets if they are large in diameter and penetrate beyond the jet center; (2) rectangular jets without tabs, compared to circular jets of the same exit area, provide faster jet mixing; and (3) further mixing enhancement is possible by using mechanical tabs.

Real jet effects on dual jets in a crossflow

NASA Technical Reports Server (NTRS)

Schetz, J. A.

1984-01-01

A 6-ft by 6-ft wind tunnel section was modification to accommodate the 7-ft wide NASA dual-jet flate model in an effort to determine the effects of nonuniform and/or noncircular jet exhaust profiles on the pressure field induced on a nearby surface. Tests completed yield surface pressure measurements for a 90 deg circular injector producing exit profiles representative of turbofan nozzles (such as the TF-34 nozzle). The measurements were obtained for both tandem and side-by-side jet configurations, jet spacing of S/D =2, and velocity ratios of R=2.2 and 4.0. Control tests at the same mass flow rate but with uniform exit velocity profiles were also conducted, for comparison purposes. Plots for 90 deg injection and R=2.2 show that the effects of exit velocity profile nonuniformity are quite significant.

Flow Field Characterization of an Angled Supersonic Jet Near a Bluff Body

NASA Technical Reports Server (NTRS)

Wolter, John D.; Childs, Robert; Wernet, Mark P.; Shestopalov, Andrea; Melton, John E.

2011-01-01

An experiment was performed to acquire data from a hot supersonic jet in cross flow for the purpose of validating computational fluid dynamics (CFD) turbulence modeling relevant to the Orion Launch Abort System. Hot jet conditions were at the highest temperature and pressure that could be acquired in the test facility. The nozzle pressure ratio was 28.5, and the nozzle temperature ratio was 3. These conditions are different from those of the flight vehicle, but sufficiently high to model the observed turbulence features. Stereo Particle Image Velocimetry (SPIV) data and capsule pressure data are presented. Features of the flow field are presented and discussed

Prediction and validation of blowout limits of co-flowing jet diffusion flames -- effect of dilution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karbasi, M.; Wierzba, I.

1996-10-01

The blowout limits of a co-flowing turbulent methane jet diffusion flame with addition of diluent in either jet fuel or surrounding air stream is studied both analytically and experimentally. Helium, nitrogen and carbon dioxide were employed as the diluents. Experiments indicated that an addition of diluents to the jet fuel or surrounding air stream decreased the stability limit of the jet diffusion flames. The strongest effect was observed with carbon dioxide as the diluent followed by nitrogen and then by helium. A model of extinction based on recognized criterion of the mixing time scale to characteristic combustion time scale ratiomore » using experimentally derived correlations is proposed. It is capable of predicting the large reduction of the jet blowout velocity due to a relatively small increase in the co-flow stream velocity along with an increase in the concentration of diluent in either the jet fuel or surrounding air stream. Experiments were carried out to validate the model. The predicted blowout velocities of turbulent jet diffusion flames obtained using this model are in good agreement with the corresponding experimental data.« less

Investigation of the flow-field of two parallel round jets impinging normal to a flat surface

NASA Astrophysics Data System (ADS)

Myers, Leighton M.

The flow-field features of dual jet impingement were investigated through sub-scale model experiments. The experiments were designed to simulate the environment of a Short Takeoff, and Vertical Landing, STOVL, aircraft performing a hover over the ground, at different heights. Two different dual impinging jet models were designed, fabricated, and tested. The Generation 1 Model consisted of two stainless-steel nozzles, in a tandem configuration, each with an exit diameter of approximately 12.7 mm. The front convergent nozzle was operated at the sonic Mach number of 1.0, while the rear C-D nozzle was generally operated supersonically. The nozzles were embedded in a rectangular flat plate, referred to as the lift plate, which represents a generic lifting surface. The lift plate was instrumented with 36 surface pressure taps, which were used to examine the flow entrainment and recirculation patterns caused by varying the stand-off distance from the nozzle exits to a flat ground surface. The stand-off distance was adjusted with a sliding rail frame that the ground plane was mounted to. Typical dimensionless stand-off distances (ground plane separation) were H/DR = 2 to 24. A series of measurements were performed with the Generation 1 model, in the Penn State High Speed Jet Aeroacoustics Laboratory, to characterize the basic flow phenomena associated with dual jet impingement. The regions of interest in the flow-field included the vertical jet plume(s), near impingement/turning region, and wall jet outwash. Other aspects of interest included the loss of lift (suckdown) that occurs as the ground plane separation distance becomes small, and azimuthal variation of the acoustic noise radiation. Various experimental methods and techniques were used to characterize the flow-field, including flow-visualization, pressure rake surveys, surface mounted pressure taps, laser Doppler velocimetry, and acoustic microphone arrays. A second dual impinging jet scale model, Generation 2

Rectangular subsonic jet flow field measurements

NASA Technical Reports Server (NTRS)

Morrison, Gerald L.; Swan, David H.

1990-01-01

Flow field measurements of three subsonic rectangular cold air jets are presented. The three cases had aspect ratios of 1x2, 1x4 at a Mach number of 0.09 and an aspect ratio of 1x2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemometer system. The data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data are presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made.

Magnetic Resonance Velocimetry analysis of an angled impinging jet

NASA Astrophysics Data System (ADS)

Irhoud, Alexandre; Benson, Michael; Verhulst, Claire; van Poppel, Bret; Elkins, Chris; Helmer, David

2016-11-01

Impinging jets are used to achieve high heat transfer rates in applications ranging from gas turbine engines to electronics. Despite the importance and relative simplicity of the geometry, simulations historically fail to accurately predict the flow behavior in the vicinity of the flow impingement. In this work, we present results from a novel experimental technique, Magnetic Resonance Velocimetry (MRV), which measures three-dimensional time-averaged velocity without the need for optical access. The geometry considered in this study is a circular jet angled at 45 degrees and impinging on a flat plate, with a separation of approximately seven jet diameters between the jet exit and the impingement location. Two flow conditions are considered, with Reynolds numbers of roughly 800 and 14,000. Measurements from the MRV experiment are compared to predictions from Reynolds Averaged Navier Stokes (RANS) simulations, thus demonstrating the utility of MRV for validation of numerical analyses of impinging jet flow.

Cryogenic and Simulated Fuel Jet Breakup in Argon, Helium and Nitrogen Gas Flows

NASA Technical Reports Server (NTRS)

Ingebo, Robert D.

1995-01-01

Two-phase flow atomization of liquid nitrogen jets was experimentally investigated. They were co-axially injected into high-velocity gas flows of helium, nitrogen and argon, respectively, and atomized internally inside a two-fluid fuel nozzle. Cryogenic sprays with relatively high specific surface areas were produced, i.e., ratios of surface area to volume were fairly high. This was indicated by values of reciprocal Sauter mean diameters, RSMD's, as measured with a scattered- light scanning instrument developed at NASA Lewis Research Center. Correlating expressions were derived for the three atomizing gases over a gas temperature range of 111 to 422 K. Also, the correlation was extended to include waterjet breakup data that had been previously obtained in simulating fuel jet breakup in sonic velocity gas flow. The final correlating expression included a new dimensionless molecular-scale acceleration group. It was needed to correlate RSMD data, for LN2 and H2O sprays, with the fluid properties of the liquid jets and atomizing gases used in this investigation.

Numerical Study of Rarefied Hypersonic Flow Interacting with a Continuum Jet. Degree awarded by Pennsylvania State Univ., Aug. 1999

NASA Technical Reports Server (NTRS)

Glass, Christopher E.

2000-01-01

An uncoupled Computational Fluid Dynamics-Direct Simulation Monte Carlo (CFD-DSMC) technique is developed and applied to provide solutions for continuum jets interacting with rarefied external flows. The technique is based on a correlation of the appropriate Bird breakdown parameter for a transitional-rarefied condition that defines a surface within which the continuum solution is unaffected by the external flow-jet interaction. The method is applied to two problems to assess and demonstrate its validity; one of a jet interaction in the transitional-rarefied flow regime and the other in the moderately rarefied regime. Results show that the appropriate Bird breakdown surface for uncoupling the continuum and non-continuum solutions is a function of a non-dimensional parameter relating the momentum flux and collisionality between the two interacting flows. The correlation is exploited for the simulation of a jet interaction modeled for an experimental condition in the transitional-rarefied flow regime and the validity of the correlation is demonstrated. The uncoupled technique is also applied to an aerobraking flight condition for the Mars Global Surveyor spacecraft with attitude control system jet interaction. Aerodynamic yawing moment coefficients for cases without and with jet interaction at various angles-of-attack were predicted, and results from the present method compare well with values published previously. The flow field and surface properties are analyzed in some detail to describe the mechanism by which the jet interaction affects the aerodynamics.

Jet launching radius in low-power radio-loud AGNs in advection-dominated accretion flows

NASA Astrophysics Data System (ADS)

Le, Truong; Newman, William; Edge, Brinkley

2018-06-01

Using our theory for the production of relativistic outflows, we estimate the jet launching radius and the inferred mass accretion rate for 52 low-power radio-loud AGNs based on the observed jet powers. Our analysis indicates that (1) a significant fraction of the accreted energy is required to convert the accreted mass to relativistic energy particles for the production of the jets near the event horizon, (2) the jet's launching radius moves radially towards the horizon as the mass accretion rate or jet's power increases, and (3) no jet/outflow formation is possible beyond 44 gravitational radii.

Influence of vortical flow structures on the glottal jet location in the supraglottal region.

PubMed

Kniesburges, Stefan; Hesselmann, Christina; Becker, Stefan; Schlücker, Eberhard; Döllinger, Michael

2013-09-01

Within the fully coupled multiphysics phonation process, the fluid flow plays an important role for sound production. This study addresses phenomena in the flow downstream of synthetic self-oscillating vocal folds. An experimental setup consisting of devices for producing and conditioning the flow including the main test channel was applied. The supraglottal channel was designed to prevent an acoustic coupling to the vocal folds. Hence, the oscillations were aerodynamically driven. The cross-section of the supraglottal channel was systematically varied by increasing the distance between the lateral channel walls. The vocal folds consisted of silicone rubber of homogenous material distribution generating self-sustained oscillations. The airflow was visualized in the immediate supraglottal region using a laser-sheet technique and a digital high-speed camera. Furthermore, the flow was studied by measuring the static pressure distributions on both lateral supraglottal channel walls. The results clearly showed different flow characteristics depending on the supraglottal configuration. In all cases with supraglottal channel, the jet was located asymmetrical and bent in medial-lateral direction. Furthermore, the side to which the jet was deflected changed in between the consecutive cycles showing a bifurcational behavior. Previously, this phenomenon was explained by the Coanda effect. However, the present data suggest that the deflection of the jet was mainly caused by large air vortices in the supraglottal channel produced by the flow field of previous oscillations. In contrast, for the case without supraglottal channel, the air jet was found totally symmetrical stabilized by the constant pressure in the ambient region. The emitted sound signal showed additional subharmonic tonal peaks for the asymmetric flow cases, which are characteristics for diplophonia. Copyright © 2013 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

Rich phenomenology encountered when two jets collide in microgravity

NASA Astrophysics Data System (ADS)

Suñol, Francesc; Gonzalez-Cinca, Ricard

The collision between two impinging liquid jets has been experimentally studied in the low gravity environment provided by the ZARM drop tower. The effects of impact angle and liquid flow rate on the collision between like-doublet jets have been considered. Tests were carried out with distilled water injected through nozzles with an internal diameter of 0.7 mm into a test cell. Impact angle varied between 10(°) and 180(°) (frontal collision), while the liquid flow rate ranged between 20 ml/min and 80 ml/min for each nozzle. Such a large parameter range allowed us to observe different phenomena resulting from the jets collision: oscillating droplets attached to the nozzles, a non-uniform spatial distribution of bouncing droplets, coalescing droplets generating a single central droplet, coalescing jets, bouncing jets, liquid chains and liquid sheets. A map of the different patterns observed has been obtained. We present results on the structure of the jets after collision, the breakup length and the size of the generated droplet. The resulting structure of impinging jets highly depends on the Reynolds and Weber numbers, and the proper alignment of the colliding jets.

Unsteady penetration of a target by a liquid jet

PubMed Central

Uth, Tobias; Deshpande, Vikram S.

2013-01-01

It is widely acknowledged that ceramic armor experiences an unsteady penetration response: an impacting projectile may erode on the surface of a ceramic target without substantial penetration for a significant amount of time and then suddenly start to penetrate the target. Although known for more than four decades, this phenomenon, commonly referred to as dwell, remains largely unexplained. Here, we use scaled analog experiments with a low-speed water jet and a soft, translucent target material to investigate dwell. The transient target response, in terms of depth of penetration and impact force, is captured using a high-speed camera in combination with a piezoelectric force sensor. We observe the phenomenon of dwell using a soft (noncracking) target material. The results show that the penetration rate increases when the flow of the impacting water jet is reversed due to the deformation of the jet–target interface––this reversal is also associated with an increase in the force exerted by the jet on the target. Creep penetration experiments with a constant indentation force did not show an increase in the penetration rate, confirming that flow reversal is the cause of the unsteady penetration rate. Our results suggest that dwell can occur in a ductile noncracking target due to flow reversal. This phenomenon of flow reversal is rather widespread and present in a wide range of impact situations, including water-jet cutting, needleless injection, and deposit removal via a fluid jet. PMID:24277818

Enhanced fuel efficiency on tractor-trailers using synthetic jet-based active flow control

NASA Astrophysics Data System (ADS)

Amitay, Michael; Menicovich, David; Gallardo, Daniele

2016-04-01

The application of piezo-electrically-driven synthetic-jet-based active flow control to reduce drag on tractor-trailers was explored experimentally in wind tunnel testing as well as full-scale road tests. Aerodynamic drag accounts for more than 50% of the usable energy at highway speeds, a problem that applies primarily to trailer trucks. Therefore, a reduction in aerodynamic drag results in large saving of fuel and reduction in CO2 emissions. The active flow control technique that is being used relies on a modular system comprised of distributed, small, highly efficient actuators. These actuators, called synthetic jets, are jets that are synthesized at the edge of an orifice by a periodic motion of a piezoelectric diaphragm(s) mounted on one (or more) walls of a sealed cavity. The synthetic jet is zero net mass flux (ZNMF), but it allows momentum transfer to flow. It is typically driven near diaphragm and/or cavity resonance, and therefore, small electric input [O(10W)] is required. Another advantage of this actuator is that no plumbing is required. The system doesn't require changes to the body of the truck, can be easily reconfigured to various types of vehicles, and consumes small amounts of electrical power from the existing electrical system of the truck. Preliminary wind tunnel results showed up to 18% reduction in fuel consumption, whereas road tests also showed very promising results.

Cell membrane deformation and bioeffects produced by tandem bubble-induced jetting flow

PubMed Central

Yuan, Fang; Yang, Chen; Zhong, Pei

2015-01-01

Cavitation with bubble–bubble interaction is a fundamental feature in therapeutic ultrasound. However, the causal relationships between bubble dynamics, associated flow motion, cell deformation, and resultant bioeffects are not well elucidated. Here, we report an experimental system for tandem bubble (TB; maximum diameter = 50 ± 2 μm) generation, jet formation, and subsequent interaction with single HeLa cells patterned on fibronectin-coated islands (32 × 32 μm) in a microfluidic chip. We have demonstrated that pinpoint membrane poration can be produced at the leading edge of the HeLa cell in standoff distance Sd ≤ 30 μm, driven by the transient shear stress associated with TB-induced jetting flow. The cell membrane deformation associated with a maximum strain rate on the order of 104 s−1 was heterogeneous. The maximum area strain (εA,M) decreased exponentially with Sd (also influenced by adhesion pattern), a feature that allows us to create distinctly different treatment outcome (i.e., necrosis, repairable poration, or nonporation) in individual cells. More importantly, our results suggest that membrane poration and cell survival are better correlated with area strain integral (∫​εA2dt) instead of εA,M, which is characteristic of the response of materials under high strain-rate loadings. For 50% cell survival the corresponding area strain integral was found to vary in the range of 56 ∼ 123 μs with εA,M in the range of 57 ∼ 87%. Finally, significant variations in individual cell’s response were observed at the same Sd, indicating the potential for using this method to probe mechanotransduction at the single cell level. PMID:26663913

Influence of a Large Free Stream Disturbance Level on Dynamics of a Jet in a Cross Flow

NASA Technical Reports Server (NTRS)

Foss, J. J.; Wark, C. E.

1983-01-01

An experiment to study the physical agents that are responsible for the jet turning into the streamwise direction, and the mixing of the jet and the cross stream fluid in the case of a jet in a cross flow is discussed.

A measurement of multi-jet rates in deep-inelastic scattering at HERA

NASA Astrophysics Data System (ADS)

Abt, I.; Ahmed, T.; Andreev, V.; Andrieu, B.; Appuhn, R.-D.; Arpagaus, M.; Babaev, A.; Bärwolff, H.; Bán, J.; Baranov, P.; Barrelet, E.; Bartel, W.; Bassler, U.; Beck, H. P.; Behrend, H.-J.; Belousov, A.; Berger, Ch.; Bergstein, H.; Bernardi, G.; Bernet, R.; Bertrand-Coremans, G.; Besançon, M.; Biddulph, P.; Binder, E.; Bischoff, A.; Bizot, J. C.; Blobel, V.; Borras, K.; Bosetti, P. C.; Boudry, V.; Bourdarios, C.; Brasse, F.; Braun, U.; Braunschweig, W.; Brisson, V.; Bruncko, D.; Büngener, L.; Bürger, J.; Büsser, F. W.; Buniatian, A.; Burke, S.; Buschhorn, G.; Campbell, A. J.; Carli, T.; Charles, F.; Clarke, D.; Clegg, A. B.; Colombo, M.; Coughlan, J. A.; Courau, A.; Coutures, Ch.; Cozzika, G.; Criegee, L.; Cvach, J.; Dagoret, S.; Dainton, J. B.; Danilov, M.; Dann, A. W. E.; Dau, W. D.; David, M.; Deffur, E.; Delcourt, B.; Del Buono, L.; Devel, M.; de Roeck, A.; Dingus, P.; Dollfus, C.; Dowell, J. D.; Dreis, H. B.; Drescher, A.; Duboc, J.; Düllmann, D.; Dünger, O.; Duhm, H.; Ebbinghaus, R.; Eberle, M.; Ebert, J.; Ebert, T. R.; Eckerlin, G.; Efremenko, V.; Egli, S.; Eichenberger, S.; Eichler, R.; Eisele, F.; Eisenhandler, E.; Ellis, N. N.; Ellison, R. J.; Elsen, E.; Erdmann, M.; Evrard, E.; Favart, L.; Fedotov, A.; Feeken, D.; Felst, R.; Feltesse, J.; Fensome, I. F.; Ferencei, J.; Ferrarotto, F.; Flamm, K.; Flauger, W.; Fleischer, M.; Flieser, M.; Flügge, G.; Fomenko, A.; Fominykh, B.; Forbush, M.; Formánek, J.; Foster, J. M.; Franke, G.; Fretwurst, E.; Fuhrmann, P.; Gabathuler, E.; Gamerdinger, K.; Garvey, J.; Gayler, J.; Gellrich, A.; Gennis, M.; Genzel, H.; Gerhards, R.; Godfrey, L.; Goerlach, U.; Goerlich, L.; Gogitidze, N.; Goldberg, M.; Goodall, A. M.; Gorelov, I.; Goritchev, P.; Grab, C.; Grässler, H.; Grässler, R.; Greenshaw, T.; Greif, H.; Grindhammer, G.; Gruber, C.; Haack, J.; Haidt, D.; Hajduk, L.; Hamon, O.; Handschuh, D.; Hanlon, E. M.; Hapke, M.; Harjes, J.; Haydar, R.; Haynes, W. J.; Heatherington, J.; Hedberg, V.; Heinzelmann, G.; Henderson, R. C. W.; Henschel, H.; Herma, R.; Herynek, I.; Hildesheim, W.; Hill, P.; Hilton, C. D.; Hladký, J.; Hoeger, K. C.; Huet, Ph.; Hufnagel, H.; Huot, N.; Ibbotson, M.; Itterbeck, H.; Jabiol, M.-A.; Jacholkowska, A.; Jacobsson, C.; Jaffre, M.; Jansen, T.; Jönsson, L.; Johannsen, K.; Johnson, D. P.; Johnson, L.; Jung, H.; Kalmus, P. I. P.; Kasarian, S.; Kaschowitz, R.; Kasselmann, P.; Kathage, U.; Kaufmann, H. H.; Kenyon, I. R.; Kermiche, S.; Keuker, C.; Kiesling, C.; Klein, M.; Kleinwort, C.; Knies, G.; Ko, W.; Köhler, T.; Kolanoski, H.; Kole, F.; Kolya, S. D.; Korbel, V.; Korn, M.; Kostka, P.; Kotelnikov, S. K.; Krasny, M. W.; Krehbiel, H.; Krücker, D.; Krüger, U.; Kubenka, J. P.; Küster, H.; Kuhlen, M.; Kurča, T.; Kurzhöfer, J.; Kuznik, B.; Lacour, D.; Lamarche, F.; Lander, R.; Landon, M. P. J.; Lange, W.; Langkau, R.; Lanius, P.; Laporte, J. F.; Lebedev, A.; Leuschner, A.; Leverenz, C.; Levonian, S.; Lewin, D.; Ley, Ch.; Lindner, A.; Lindström, G.; Linsel, F.; Lipinski, J.; Loch, P.; Lohmander, H.; Lopez, G. C.; Lüers, D.; Magnussen, N.; Malinovski, E.; Mani, S.; Marage, P.; Marks, J.; Marshall, R.; Martens, J.; Martin, R.; Martyn, H.-U.; Martyniak, J.; Masson, S.; Mavroidis, A.; Maxfield, S. J.; McMahon, S. J.; Mehta, A.; Meier, K.; Mercer, D.; Merz, T.; Meyer, C. A.; Meyer, H.; Meyer, J.; Mikocki, S.; Milone, V.; Monnier, E.; Moreau, F.; Moreels, J.; Morris, J. V.; Müller, K.; Murín, P.; Murray, S. A.; Nagovizin, V.; Naroska, B.; Naumann, Th.; Newman, P. R.; Newton, D.; Neyret, D.; Nguyen, H. K.; Niebergall, F.; Niebuhr, C.; Nisius, R.; Nowak, G.; Noyes, G. W.; Nyberg, M.; Oberlack, H.; Obrock, U.; Olsson, J. E.; Orenstein, S.; Ould-Saada, F.; Pascaud, C.; Patel, G. D.; Peppel, E.; Peters, S.; Phillips, H. T.; Phillips, J. P.; Pichler, Ch.; Pilgram, W.; Pitzl, D.; Prell, S.; Prosi, R.; Rädel, G.; Raupach, F.; Rauschnabel, K.; Reimer, P.; Reinshagen, S.; Ribarics, P.; Riech, V.; Riedlberger, J.; Riess, S.; Rietz, M.; Robertson, S. M.; Robmann, P.; Roosen, R.; Rostovtsev, A.; Royon, C.; Rudowicz, M.; Ruffer, M.; Rusakov, S.; Rybicki, K.; Sahlmann, N.; Sanchez, E.; Sankey, D. P. C.; Savitsky, M.; Schacht, P.; Schleper, P.; von Schlippe, W.; Schmidt, C.; Schmidt, D.; Schmitz, W.; Schöning, A.; Schröder, V.; Schulz, M.; Schwab, B.; Schwind, A.; Scobel, W.; Seehausen, U.; Sell, R.; Semenov, A.; Shekelyan, V.; Sheviakov, I.; Shooshtari, H.; Shtarkov, L. N.; Siegmon, G.; Siewert, U.; Sirois, Y.; Skillicorn, I. O.; Smirnov, P.; Smith, J. R.; Smolik, L.; Soloviev, Y.; Spitzer, H.; Staroba, P.; Steenbock, M.; Steffen, P.; Steinberg, R.; Stella, B.; Stephens, K.; Stier, J.; Stösslein, U.; Strachota, J.; Straumann, U.; Struczinski, W.; Sutton, J. P.; Taylor, R. E.; Tchernyshov, V.; Thiebaux, C.; Thompson, G.; Tichomirov, I.; Truöl, P.; Turnau, J.; Tutas, J.; Urban, L.; Usik, A.; Valkar, S.; Valkarova, A.; Vallée, C.; van Esch, P.; Vartapetian, A.; Vazdik, Y.; Vecko, M.; Verrecchia, P.; Vick, R.; Villet, G.; Vogel, E.; Wacker, K.; Walker, I. W.; Walther, A.; Weber, G.; Wegener, D.; Wegner, A.; Wellisch, H. P.; West, L. R.; Willard, S.; Winde, M.; Winter, G.-G.; Wolff, Th.; Womersley, L. A.; Wright, A. E.; Wulff, N.; Yiou, T. P.; Žáček, J.; Závada, P.; Zeitnitz, C.; Ziaeepour, H.; Zimmer, M.; Zimmermann, W.; Zomer, F.

1994-03-01

Multi-jet production is observed in deep-inelastic electron proton scattering with the H1 detector at HERA. Jet rates for momentum transfers squared up to 500 GeV2 are determined using the JADE jet clustering algorithm. They are found to be in agreement with predictions from QCD based models.

Flow of supersonic jets across flat plates: Implications for ground-level flow from volcanic blasts

NASA Astrophysics Data System (ADS)

Orescanin, Mara M.; Prisco, David; Austin, Joanna M.; Kieffer, Susan W.

2014-04-01

We report on laboratory experiments examining the interaction of a jet from an overpressurized reservoir with a canonical ground surface to simulate lateral blasts at volcanoes such as the 1980 blast at Mount St. Helens. These benchmark experiments test the application of supersonic jet models to simulate the flow of volcanic jets over a lateral topography. The internal shock structure of the free jet is modified such that the Mach disk shock is elevated above the surface. In elevation view, the width of the shock is reduced in comparison with a free jet, while in map view the dimensions are comparable. The distance of the Mach disk shock from the vent is in good agreement with free jet data and can be predicted with existing theory. The internal shock structures can interact with and penetrate the boundary layer. In the shock-boundary layer interaction, an oblique shock foot is present in the schlieren images and a distinctive ground signature is evident in surface measurements. The location of the oblique shock foot and the surface demarcation are closely correlated with the Mach disk shock location during reservoir depletion, and therefore, estimates of a ground signature in a zone devastated by a blast can be based on the calculated shock location from free jet theory. These experiments, combined with scaling arguments, suggest that the imprint of the Mach disk shock on the ground should be within the range of 4-9 km at Mount St. Helens depending on assumed reservoir pressure and vent dimensions.

Particle-laden swirling free jets: Measurements and predictions

NASA Technical Reports Server (NTRS)

Bulzan, D. L.; Shuen, J.-S.; Faeth, G. M.

1987-01-01

A theoretical and experimental investigation of single-phase and particle-laden weakly swirling jets was conducted. The jets were injected vertically downward from a 19 mm diameter tube with swirl numbers ranging from 0 to 0.33. The particle-laden jets had a single loading ratio (0.2) with particles having a SMD of 39 microns. Mean and fluctuating properties of both phases were measured using nonintrusive laser based methods while particle mass flux was measured using an isokinetic sampling probe. The continuous phase was analyzed using both a baseline kappa-epsilon turbulence model and an extended version with modifications based on the flux Richardson number to account for effects of streamline curvature. To highlight effects of interphase transport rates and particle/turbulence interactions, effects of the particles were analyzed as follows: (1) locally homogeneous flow (LHF) analysis, where interphase transport rates are assumed to be infinitely fast; (2) deterministic separated flow (DSF) analysis, where finite interphase transport rates are considered but particle/turbulence interactions are ignored; and (3) stochastic separated flow (SSF) analysis, where both effects are considered using random-walk computations.

Mean Flow and Noise Prediction for a Separate Flow Jet With Chevron Mixers

NASA Technical Reports Server (NTRS)

Koch, L. Danielle; Bridges, James; Khavaran, Abbas

2004-01-01

Experimental and numerical results are presented here for a separate flow nozzle employing chevrons arranged in an alternating pattern on the core nozzle. Comparisons of these results demonstrate that the combination of the WIND/MGBK suite of codes can predict the noise reduction trends measured between separate flow jets with and without chevrons on the core nozzle. Mean flow predictions were validated against Particle Image Velocimetry (PIV), pressure, and temperature data, and noise predictions were validated against acoustic measurements recorded in the NASA Glenn Aeroacoustic Propulsion Lab. Comparisons are also made to results from the CRAFT code. The work presented here is part of an on-going assessment of the WIND/MGBK suite for use in designing the next generation of quiet nozzles for turbofan engines.

Turbine exhaust diffuser with a gas jet producing a coanda effect flow control

DOEpatents

Orosa, John; Montgomery, Matthew

2014-02-11

An exhaust diffuser system and method for a turbine engine includes an inner boundary and an outer boundary with a flow path defined therebetween. The inner boundary is defined at least in part by a hub structure that has an upstream end and a downstream end. The outer boundary may include a region in which the outer boundary extends radially inward toward the hub structure and may direct at least a portion of an exhaust flow in the diffuser toward the hub structure. The hub structure includes at least one jet exit located on the hub structure adjacent to the upstream end of the tail cone. The jet exit discharges a flow of gas substantially tangential to an outer surface of the tail cone to produce a Coanda effect and direct a portion of the exhaust flow in the diffuser toward the inner boundary.

Wedge Shock and Nozzle Exhaust Plume Interaction in a Supersonic Jet Flow

NASA Technical Reports Server (NTRS)

Castner, Raymond; Zaman, Khairul; Fagan, Amy; Heath, Christopher

2014-01-01

Fundamental research for sonic boom reduction is needed to quantify the interaction of shock waves generated from the aircraft wing or tail surfaces with the nozzle exhaust plume. Aft body shock waves that interact with the exhaust plume contribute to the near-field pressure signature of a vehicle. The plume and shock interaction was studied using computational fluid dynamics and compared with experimental data from a coaxial convergent-divergent nozzle flow in an open jet facility. A simple diamond-shaped wedge was used to generate the shock in the outer flow to study its impact on the inner jet flow. Results show that the compression from the wedge deflects the nozzle plume and shocks form on the opposite plume boundary. The sonic boom pressure signature of the nozzle exhaust plume was modified by the presence of the wedge. Both the experimental results and computational predictions show changes in plume deflection.

Flow Control Under Low-Pressure Turbine Conditions Using Pulsed Jets: Experimental Data Archive

NASA Technical Reports Server (NTRS)

Volino, Ralph J.; Ibrahim, Mounir B.

2012-01-01

This publication is the final report of research performed under an NRA/Cooperative Interagency Agreement, and includes a supplemental CD-ROM with detailed data. It is complemented by NASA/CR-2012-217416 and NASA/CR-2012-217417 which include a Ph.D. Dissertation and an M.S. thesis respectively, performed under this contract. In this study the effects of unsteady wakes and flow control using vortex generator jets (VGJs) were studied experimentally and computationally on the flow over the L1A low pressure turbine (LPT) airfoil. The experimental facility was a six passage linear cascade in a low speed wind tunnel at the U.S. Naval Academy. In parallel, computational work using the commercial code FLUENT (ANSYS, Inc.) was performed at Cleveland State University, using Unsteady Reynolds Averaged Navier Stokes (URANS) and Large Eddy Simulations (LES) methods. In the first phase of the work, the baseline flow was documented under steady inflow conditions without flow control. URANS calculations were done using a variety of turbulence models. In the second phase of the work, flow control was added using steady and pulsed vortex generator jets. The VGJs successfully suppressed separation and reduced aerodynamic losses. Pulsed operation was more effective and mass flow requirements are very low. Numerical simulations of the VGJs cases showed that URANS failed to capture the effect of the jets. LES results were generally better. In the third phase, effects of unsteady wakes were studied. Computations with URANS and LES captured the wake effect and generally predicted separation and reattachment to match the experiments. Quantitatively the results were mixed. In the final phase of the study, wakes and VGJs were combined and synchronized using various timing schemes. The timing of the jets with respect to the wakes had some effect, but in general once the disturbance frequency was high enough to control separation, the timing was not very important. This is the supplemental CD-ROM

Studies of the flow and turbulence fields in a turbulent pulsed jet flame using LES/PDF

NASA Astrophysics Data System (ADS)

Zhang, Pei; Masri, Assaad R.; Wang, Haifeng

2017-09-01

A turbulent piloted jet flame subject to a rapid velocity pulse in its fuel jet inflow is proposed as a new benchmark case for the study of turbulent combustion models. In this work, we perform modelling studies of this turbulent pulsed jet flame and focus on the predictions of its flow and turbulence fields. An advanced modelling strategy combining the large eddy simulation (LES) and the probability density function (PDF) methods is employed to model the turbulent pulsed jet flame. Characteristics of the velocity measurements are analysed to produce a time-dependent inflow condition that can be fed into the simulations. The effect of the uncertainty in the inflow turbulence intensity is investigated and is found to be very small. A method of specifying the inflow turbulence boundary condition for the simulations of the pulsed jet flame is assessed. The strategies for validating LES of statistically transient flames are discussed, and a new framework is developed consisting of different averaging strategies and a bootstrap method for constructing confidence intervals. Parametric studies are performed to examine the sensitivity of the predictions of the flow and turbulence fields to model and numerical parameters. A direct comparison of the predicted and measured time series of the axial velocity demonstrates a satisfactory prediction of the flow and turbulence fields of the pulsed jet flame by the employed modelling methods.

Liquid jet pumped by rising gas bubbles

NASA Technical Reports Server (NTRS)

Hussain, N. A.; Siegel, R.

1975-01-01

A two-phase mathematical model is proposed for calculating the induced turbulent vertical liquid flow. Bubbles provide a large buoyancy force and the associated drag on the liquid moves the liquid upward. The liquid pumped upward consists of the bubble wakes and the liquid brought into the jet region by turbulent entrainment. The expansion of the gas bubbles as they rise through the liquid is taken into account. The continuity and momentum equations are solved numerically for an axisymmetric air jet submerged in water. Water pumping rates are obtained as a function of air flow rate and depth of submergence. Comparisons are made with limited experimental information in the literature.

Boundary-layer-ingesting inlet flow control system

NASA Technical Reports Server (NTRS)

Owens, Lewis R. (Inventor); Allan, Brian G. (Inventor)

2010-01-01

A system for reducing distortion at the aerodynamic interface plane of a boundary-layer-ingesting inlet using a combination of active and passive flow control devices is disclosed. Active flow control jets and vortex generating vanes are used in combination to reduce distortion across a range of inlet operating conditions. Together, the vortex generating vanes can reduce most of the inlet distortion and the active flow control jets can be used at a significantly reduced control jet mass flow rate to make sure the inlet distortion stays low as the inlet mass flow rate varies. Overall inlet distortion, measured and described as average SAE circumferential distortion descriptor, was maintained at a value of 0.02 or less. Advantageous arrangements and orientations of the active flow control jets and the vortex generating vanes were developed using computational fluid dynamics simulations and wind tunnel experimentations.

The NASA Subsonic Jet Particle Image Velocimetry (PIV) Dataset

NASA Technical Reports Server (NTRS)

Bridges, James; Wernet, Mark P.

2011-01-01

Many tasks in fluids engineering require prediction of turbulence of jet flows. The present document documents the single-point statistics of velocity, mean and variance, of cold and hot jet flows. The jet velocities ranged from 0.5 to 1.4 times the ambient speed of sound, and temperatures ranged from unheated to static temperature ratio 2.7. Further, the report assesses the accuracies of the data, e.g., establish uncertainties for the data. This paper covers the following five tasks: (1) Document acquisition and processing procedures used to create the particle image velocimetry (PIV) datasets. (2) Compare PIV data with hotwire and laser Doppler velocimetry (LDV) data published in the open literature. (3) Compare different datasets acquired at the same flow conditions in multiple tests to establish uncertainties. (4) Create a consensus dataset for a range of hot jet flows, including uncertainty bands. (5) Analyze this consensus dataset for self-consistency and compare jet characteristics to those of the open literature. The final objective was fulfilled by using the potential core length and the spread rate of the half-velocity radius to collapse of the mean and turbulent velocity fields over the first 20 jet diameters.

Analytical and experimental study of the acoustics and the flow field characteristics of cavitating self-resonating water jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chahine, G.L.; Genoux, P.F.; Johnson, V.E. Jr.

1984-09-01

Waterjet nozzles (STRATOJETS) have been developed which achieve passive structuring of cavitating submerged jets into discrete ring vortices, and which possess cavitation incipient numbers six times higher than obtained with conventional cavitating jet nozzles. In this study we developed analytical and numerical techniques and conducted experimental work to gain an understanding of the basic phenomena involved. The achievements are: (1) a thorough analysis of the acoustic dynamics of the feed pipe to the nozzle; (2) a theory for bubble ring growth and collapse; (3) a numerical model for jet simulation; (4) an experimental observation and analysis of candidate second-generation low-sigmamore » STRATOJETS. From this study we can conclude that intensification of bubble ring collapse and design of highly resonant feed tubes can lead to improved drilling rates. The models here described are excellent tools to analyze the various parameters needed for STRATOJET optimizations. Further analysis is needed to introduce such important factors as viscosity, nozzle-jet interaction, and ring-target interaction, and to develop the jet simulation model to describe the important fine details of the flow field at the nozzle exit.« less

Establishing Consensus Turbulence Statistics for Hot Subsonic Jets

NASA Technical Reports Server (NTRS)

Bridges, James; Werner, Mark P.

2010-01-01

velocimetry (LDV) data published in the open literature. Compare different datasets acquired at roughly the same flow conditions to establish uncertainties. Create a consensus dataset for a range of hot jet flows, including uncertainty bands. Analyze this consensus dataset for self-consistency and compare jet characteristics to those of the open literature. One final objective fulfilled by this work was the demonstration of a universal scaling for the jet flow fields, at least within the region of interest to aeroacoustics. The potential core length and the spread rate of the half-velocity radius were used to collapse of the mean and turbulent velocity fields over the first 20 jet diameters in a highly satisfying manner.

The Isolated Synthetic Jet in Crossflow: A Benchmark for Flow Control Simulation

NASA Technical Reports Server (NTRS)

Schaeffler, Norman W.; Jenkins, Luther N.

2006-01-01

An overview of the data acquisition, reduction, and uncertainty of experimental measurements made of the flowfield created by the interaction of an isolated synthetic jet and a turbulent boundary layer is presented. The experimental measurements were undertaken to serve as the second of three computational fluid dynamics validation databases for Active Flow Control. The validation databases were presented at the NASA Langley Research Center Workshop on CFD Validation of Synthetic Jets and Turbulent Separation Control in March, 2004. Detailed measurements were made to document the boundary conditions for the flow and also for the phase-averaged flowfield itself. Three component Laser-Doppler Velocimetry, 2-D Particle Image Velocimetry, and Stereo Particle Image Velocimetry were utilized to document the phase-averaged velocity field and the turbulent stresses.

The Isolated Synthetic Jet in Crossflow: A Benchmark for Flow Control Simulation

NASA Technical Reports Server (NTRS)

Schaeffler, Norman W.; Jenkins, Luther N.

2004-01-01

An overview of the data acquisition, reduction, and uncertainty of experimental measurements of the flowfield created by the interaction of an isolated synthetic jet and a turbulent boundary layer is presented. The experimental measurements were undertaken to serve as the second of three computational fluid dynamics validation databases for Active Flow Control. The validation databases were presented at the NASA Langley Research Center Workshop on CFD Validation of Synthetic Jets and Turbulent Separation Control in March, 2004. Detailed measurements were made to document the boundary conditions for the flow and also for the phase-averaged flowfield itself. Three component Laser-Doppler Velocimetry, 2-D Particle Image Velocimetry, and Stereo Particle Image Velocimetry were utilized to document the phase averaged velocity field and the turbulent stresses.

Supersonic, Transverse Jet from a Rotating Ogive Cylinder in a Hypersonic Flow.

DTIC Science & Technology

1987-11-01

of the flow are captured by the computation, although there is a slight discrepancy in the projected angle of the bow shock envelope induced by the jet...depicts the comparison of the experimental and computed pitot pressure profiles at three locations downstream of the jet. The shock structure can be...pressure measurements might be traced to the fact that the pitot probe was aligned only in the freestream direction. In the region near the wall, the

Impinging Jets and the Erodibility of Cohesive Sediment

NASA Astrophysics Data System (ADS)

Karamigolbaghi, M.; Bennett, S. J.; Ghaneeizad, S. M.; Atkinson, J. F.

2016-12-01

Defining the erodibility of cohesive sediment remains a critical challenge in Earth surface systems. The primary geomorphic law used in such applications relates erosion rate to an erodibility coefficient and an excess shear stress term. To assess erodibility, an inverse modeling approach can be adopted, wherein a known stress is applied to the cohesive sediment, and the erodibility parameters can be deduced through observation of erosion as a function of time. An impinging jet, as used in the jet erosion test, would appear to be an ideal flow (stress) source for erosion assessment. Recent work, however, has demonstrated that jet hydrodynamics can depart significantly from ideal flow conditions when employed for in situ erosion assessment. Here we will review jet theory and the use of jets for assessing the erodibility of cohesive sediment. Our results show that (1) flow confinement and the generation of secondary circulation can significantly change bed shear stress near and downstream of impingement, (2) the evolving scour hole shape, as conditioned by material characteristics and the erosion process, can significantly alter jet hydrodynamics and bed shear stress magnitudes and distributions near and downstream of impingement, and (3) incidental variations in material characteristics in carefully-executed, long-lived experiments can produce markedly different scour hole shapes and derived erodibility indices. Examples from experimental, numerical, and field observations will be used to illustrate these hydrodynamic and material effects on observed and predicted erosion rates. Because such effects are difficult to anticipate, the uncertainty of in situ cohesive sediment assessments using impinging jets can be quite large.

Boundary-Layer-Ingesting Inlet Flow Control

NASA Technical Reports Server (NTRS)

Owens, Lewis R.; Allan, Brian G.; Gorton, Susan A.

2008-01-01

An experimental study was conducted to provide the first demonstration of an active flow control system for a flush-mounted inlet with significant boundary-layer-ingestion in transonic flow conditions. The effectiveness of the flow control in reducing the circumferential distortion at the engine fan-face location was assessed using a 2.5%-scale model of a boundary-layer-ingesting offset diffusing inlet. The inlet was flush mounted to the tunnel wall and ingested a large boundary layer with a boundary-layer-to-inlet height ratio of 35%. Different jet distribution patterns and jet mass flow rates were used in the inlet to control distortion. A vane configuration was also tested. Finally a hybrid vane/jet configuration was tested leveraging strengths of both types of devices. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow rates through the duct and the flow control actuators. The distortion and pressure recovery were measured at the aerodynamic interface plane. The data show that control jets and vanes reduce circumferential distortion to acceptable levels. The point-design vane configuration produced higher distortion levels at off-design settings. The hybrid vane/jet flow control configuration reduced the off-design distortion levels to acceptable ones and used less than 0.5% of the inlet mass flow to supply the jets.

A Model for the Vortex Pair Associated with a Jet in a Cross Flow

NASA Technical Reports Server (NTRS)

Sellers, William L.

1975-01-01

A model is presented for the contrarotating vortex pair that is formed by a round, turbulent, subsonic jet directed normally into a uniform, subsonic cross flow. The model consists of a set of algebraic equations that describe the properties of the vortex pair as a function of their location in the jet plume. The parameters of the model are physical characteristics of the vortices such as the vortex strength, spacing, and core size. These parameters are determined by velocity measurements at selective points in the jet plume.

Probing the Jet Turnover Frequency Dependence on Mass and Mass Accretion Rate

NASA Astrophysics Data System (ADS)

Hammerstein, Erica; Gültekin, Kayhan; King, Ashley

2018-01-01

We have examined a sample of 15 sub-Eddington supermassive black holes (SMBHs) in a variety of galaxy classifications to further understand the proposed fundamental plane of black hole activity and scaling relations between black hole masses and their radio and X-ray luminosities. This plane describes black holes from stellar-mass to supermassive. The physics probed by these sub-Eddington systems is thought to be a radiatively inefficient, jet-dominated accretion flow. By studying black holes in this regime, we can learn important information on the disk-jet connection for accreting black holes.A key factor in studying the fundamental plane is the turnover frequency — the frequency at which emission transitions from optically thick at lower frequencies to optically thin at higher frequencies. This turnover point can be measured by observing the source in both radio and X-ray. Our project aims to test the dependence of the turnover frequency on mass and mass accretion rate.Radio observations of the sample were obtained using the Karl G. Jansky Very Large Array (VLA) in the range of 5-40 GHz across four different frequency bands in A configuration to give the highest spatial resolution to focus on the core emission. Our carefully chosen sample of SMBHs with dynamically measured masses consists of two sub-samples: those with approximately constant mass accretion rate (LX/LEdd ~ 10‑7) and those with approximately constant mass (MBH ~ 108 Msun). X-ray data were obtained from archival Chandra observations. To find the turnover frequency, we used Markov Chain Monte Carlo methods to fit two power laws to the radio data and the archival X-ray data. The intersection of the radio and X-ray fits is the turnover frequency.We present the results for both subsamples of SMBHs and their relationship between the turnover frequency and X-ray luminosity, which we take to scale with mass accretion rate, and jet power derived from both radio and X-ray properties.

A High-Resolution Capability for Large-Eddy Simulation of Jet Flows

NASA Technical Reports Server (NTRS)

DeBonis, James R.

2011-01-01

A large-eddy simulation (LES) code that utilizes high-resolution numerical schemes is described and applied to a compressible jet flow. The code is written in a general manner such that the accuracy/resolution of the simulation can be selected by the user. Time discretization is performed using a family of low-dispersion Runge-Kutta schemes, selectable from first- to fourth-order. Spatial discretization is performed using central differencing schemes. Both standard schemes, second- to twelfth-order (3 to 13 point stencils) and Dispersion Relation Preserving schemes from 7 to 13 point stencils are available. The code is written in Fortran 90 and uses hybrid MPI/OpenMP parallelization. The code is applied to the simulation of a Mach 0.9 jet flow. Four-stage third-order Runge-Kutta time stepping and the 13 point DRP spatial discretization scheme of Bogey and Bailly are used. The high resolution numerics used allows for the use of relatively sparse grids. Three levels of grid resolution are examined, 3.5, 6.5, and 9.2 million points. Mean flow, first-order turbulent statistics and turbulent spectra are reported. Good agreement with experimental data for mean flow and first-order turbulent statistics is shown.

Rectangular subsonic jet flow field measurements

NASA Technical Reports Server (NTRS)

Morrison, Gerald L.; Swan, David H.

1989-01-01

Flow field measurements are presented of 3 subsonic rectangular cold air jets. The 3 cases presented had aspect ratios of 1 x 2, 1 x 4 at a Mach number of 0.09 and an aspect ratio of 1 x 2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemoneter system. The presented data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data is presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made. All tabular data are available in ASCII format on MS-DOS compatible disks.

Active control of continuous air jet with bifurcated synthetic jets

NASA Astrophysics Data System (ADS)

Dančová, Petra; Vít, Tomáš; Jašíková, Darina; Novosád, Jan

The synthetic jets (SJs) have many significant applications and the number of applications is increasing all the time. In this research the main focus is on the primary flow control which can be used effectively for the heat transfer increasing. This paper deals with the experimental research of the effect of two SJs worked in the bifurcated mode used for control of an axisymmetric air jet. First, the control synthetic jets were measured alone. After an adjustment, the primary axisymmetric jet was added in to the system. For comparison, the primary flow without synthetic jets control was also measured. All experiments were performed using PIV method whereby the synchronization between synthetic jets and PIV system was necessary to do.

Physical and chemical behavior of flowing endothermic jet fuels

NASA Astrophysics Data System (ADS)

Ward, Thomas Arthur

Hydrocarbon fuels have been used as cooling media for aircraft jet engines for decades. However, modern aircraft engines are reaching a practical heat transfer limit beyond which the convective heat transfer provided by fuels is no longer adequate. One solution is to use an endothermic fuel that absorbs heat through a series of pyrolytic chemical reactions. However, many of the physical and chemical processes involved in endothermic fuel degradation are not well understood. The purpose of this dissertation is to study different characteristics of endothermic fuels using experiments and computational models. In the first section, data from three flow experiments using heated Jet-A fuel and additives were analyzed (with the aid of CFD calculations) to study the effects of treated surfaces on surface deposition. Surface deposition is the primary impediment in creating an operational endothermic fuel heat exchanger system, because deposits can obstruct fuel pathways causing a catastrophic system failure. As heated fuel flows through a fuel system, trace species within the fuel react with dissolved O2 to form surface deposits. At relatively higher fuel temperatures, the dissolved O2 is depleted, and pyrolytic chemistry becomes dominant (at temperatures greater than ˜500 °C). In the first experiment, the dissolved O2 consumption of heated fuel was measured on different surface types over a range of temperatures. It is found that use of treated tubes significantly delays oxidation of the fuel. In the second experiment, the treated length of tubing was progressively increased, which varied the characteristics of the thermal-oxidative deposits formed. In the third experiment, pyrolytic surface deposition in either fully treated or untreated tubes is studied. It is found that the treated surface significantly reduced the formation of surface deposits for both thermal oxidative and pyrolytic degradation mechanisms. Moreover, it is found that the chemical reactions resulting

The resonance of twin supersonic jets

NASA Technical Reports Server (NTRS)

Morris, Philip J.

1989-01-01

This paper presents an analytical study of the resonant interaction between twin supersonic jets. An instability wave model is used to describe the large scale coherent structures in the jet mixing layers. A linearized shock cell model is also given for the jets when operating off design. The problem's geometry admits four types of normal modes associated with each azimuthal mode number in the single jet. The stability of these modes is examined for both a vortex sheet model of the jet and a jet flow represented by realistic profiles. The growth rates of each mode number and type are found to vary with jet separation and mixing layer thickness and Strouhal number. Contours of equal pressure level are obtained for each mode. The region close to the symmetry axis is found to have the greatest pressure fluctuation amplitude.

Numerical simulation of flow and mass transfer for large KDP crystal growth via solution-jet method

NASA Astrophysics Data System (ADS)

Yin, Huawei; Li, Mingwei; Hu, Zhitao; Zhou, Chuan; Li, Zhiwei

2018-06-01

A novel technique of growing large crystals of potassium dihydrogen phosphate (KDP) named solution-jet method is proposed. The aim is to increase supersaturation on the pyramidal face, especially for crystal surface regions close to the rotation axis. The fluid flow and surface supersaturation distribution of crystals grown under different conditions were computed using the finite-volume method. Results indicate that the time-averaged supersaturation of the pyramidal face in the proposed method significantly increases and the supersaturation difference from the crystal center to edge clearly decreases compared with the rotating-crystal method. With increased jet velocity, supersaturation on the pyramidal face steadily increases. Rotation rate considerably affects the magnitude and distribution of the prismatic surface supersaturation. With increased crystal size, the mean value of surface supersaturation averaged over the pyramid gradually decreases; conversely, standard deviation increases, which is detrimental to crystal growth. Moreover, the significant roles played by natural and forced convection in the process of mass transport are discussed. Results show that further increased jet velocity to 0.6 m/s renders negligible the effects of natural convection around the pyramid. The simulation for step propagation indicates that solution-jet method can promote a steady step migration and enhance surface morphology stability, which can improve the crystal quality.

Elastomeric Microchip Electrospray Emitter for Stable Cone-Jet Mode Operation in the Nano-Flow Regime

PubMed Central

Kelly, Ryan T.; Tang, Keqi; Irimia, Daniel; Toner, Mehmet; Smith, Richard D.

2009-01-01

Despite widespread interest in combining lab-on-a-chip technologies with mass spectrometry (MS)-based analyses, the coupling of microfluidics to electrospray ionization (ESI)-MS remains challenging. We report a robust, integrated poly(dimethylsiloxane) microchip interface for ESI-MS using simple and widely accessible microfabrication procedures. The interface uses an auxiliary channel to provide electrical contact for the stable cone-jet electrospray without sample loss or dilution. The electric field at the channel terminus is enhanced by two vertical cuts that cause the interface to taper to a line rather than to a point, and the formation of a small Taylor cone at the channel exit ensures sub-nL post-column dead volumes. Cone-jet mode electrospray was demonstrated for up to 90% aqueous solutions and for extended durations. Comparable ESI-MS sensitivities were achieved using both microchip and conventional fused silica capillary emitters, but stable cone-jet mode electrosprays could be established over a far broader range of flow rates (from 50-1000 nL/min) and applied potentials using the microchip emitters. This attribute of the microchip emitter should simplify electrospray optimization and make the stable electrospray more resistant to external perturbations. PMID:18419138

Capillary instability of elliptic liquid jets

NASA Astrophysics Data System (ADS)

Amini, Ghobad; Dolatabadi, Ali

2011-08-01

Instability of a liquid jet issuing from an elliptic nozzle in Rayleigh mode is investigated and its behavior is compared with a circular jet. Mathematical solution of viscous free-surface flow for asymmetric geometry is complicated if 3-D analytical solutions are to be obtained. Hence, one-dimensional Cosserat (directed curve) equations are used which can be assumed as a low order form of Navier-Stokes equations for slender jets. Linear solution is performed using perturbation method. Temporal dispersion equation is derived to find the most unstable wavelength responsible for the jet breakup. The obtained results for a circular jet (i.e., an ellipse with an aspect ratio of one) are compared with the classical results of Rayleigh and Weber for inviscid and viscous cases, respectively. It is shown that in the Rayleigh regime, which is the subject of this research, symmetric perturbations are unstable while asymmetric perturbations are stable. Consequently, spatial analysis is performed and the variation of growth rate under the effect of perturbation frequencies for various jet velocities is demonstrated. Results reveal that in comparison with a circular jet, the elliptic jet is more unstable. Furthermore, among liquid jets with elliptical cross sections, those with larger ellipticities have a larger instability growth rate.

Operating limitations of high speed jet lubricated ball bearings

NASA Technical Reports Server (NTRS)

Zaretsky, E. V.; Signer, H.; Bamberger, E. N.

1975-01-01

A parametric study was performed with 120-mm bore angular-contact ball bearings having a nominal contact angle of 20 degrees. The bearings had either an inner- or an outer-race land riding cage, and lubrication was by recirculating oil jets which had either a single or dual orifice. Thrust load, speed, and lubricant flow rate were varied. Test results were compared with those previously reported and obtained from bearings of the same design which were under-race lubricated but run under the same conditions. Jet lubricated ball bearings were limited to speeds less than 2,500,000 DN, and bearings having inner-race land riding cages produced lower temperatures than bearings with outer-race land riding cages. For a given lubricant flow rate dual orifice jets produced lower bearing temperatures than single orifice jets, but under-race lubrication produced lower bearing temperatures under all conditions of operation with no apparent bearing speed limitation.

Numerical Simulation of Hydrogen Air Supersonic Coaxial Jet

NASA Astrophysics Data System (ADS)

Dharavath, Malsur; Manna, Pulinbehari; Chakraborty, Debasis

2017-10-01

In the present study, the turbulent structure of coaxial supersonic H2-air jet is explored numerically by solving three dimensional RANS equations along with two equation k-ɛ turbulence model. Grid independence of the solution is demonstrated by estimating the error distribution using Grid Convergence Index. Distributions of flow parameters in different planes are analyzed to explain the mixing and combustion characteristics of high speed coaxial jets. The flow field is seen mostly diffusive in nature and hydrogen diffusion is confined to core region of the jet. Both single step laminar finite rate chemistry and turbulent reacting calculation employing EDM combustion model are performed to find the effect of turbulence-chemistry interaction in the flow field. Laminar reaction predicts higher H2 mol fraction compared to turbulent reaction because of lower reaction rate caused by turbulence chemistry interaction. Profiles of major species and temperature match well with experimental data at different axial locations; although, the computed profiles show a narrower shape in the far field region. These results demonstrate that standard two equation class turbulence model with single step kinetics based turbulence chemistry interaction can describe H2-air reaction adequately in high speed flows.

Numerical simulations of mounding and submerging flows of shear-thinning jets impinging in a container

DOE PAGES

Roberts, Scott A.; Rao, Rekha R.

2011-10-01

Continuous jets of non-Newtonian fluids impinging on a fluid surface exhibit instabilities from jet buckling and coiling at low Reynolds numbers to delayed die swell, mounding, and air entrainment at higher Reynolds numbers. Filling containers with complex fluids is an important process for many industries, where the need for high throughput requires operating at high Reynolds numbers. In this regime, air entrainment can produce a visually unappealing product, causing a major quality control issue. Just prior to the onset of air entrainment, however, there exists an ideal filling regime which we term “planar filling,” as it is characterized by amore » relatively flat free surface that maintains its shape over time. In this paper, we create a steady-state, 2-D axisymmetric finite element model to study the transition from planar filling to the onset of air entrainment in a container filling process with generalized-Newtonian fluids. We use this model to explore the operating window for Newtonian and shear-thinning (or, more generally, deformation-rate-thinning) fluids, demonstrating that the flow behavior is characterized by a balance between inertial, viscous, and gravitational forces, as characterized by the Reynolds and Froude numbers. A scaling analysis suggests that the relevant parameters for calculating these dimensionless numbers are located where the jet impacts the liquid surface, and simulations show that the transition from planar filling to air entrainment often occurs when Re ~ O(10). Our study found that the bottom and side surfaces of the container drastically influence this transition to entrainment, stabilizing the flow.« less

Effect of LES models on the entrainment characteristics in a turbulent planar jet

NASA Astrophysics Data System (ADS)

Chambel Lopes, Diogo; da Silva, Carlos; Raman, Venkat

2012-11-01

The effect of subgrid-scale (SGS) models in the jet spreading rate and centreline passive scalar decay rates are assessed and compared. The modelling of the subgrid-scale fluxes is particularly challenging in the turbulent/nonturbulent (T/NT) region that divides the two regions in the jet flow: the outer region where the flow is irrotational and the inner region where the flow is turbulent: it has been shown that important Reynolds stresses exist near the T/NT interface and that these stresses determine in part the mixing and combustion rates in jets. In this work direct and large-eddy simulations (DNS/LES) of turbulent planar jets are used to study the role of subgrid-scale models in the integral characteristics of the passive scalar mixing in a jet. LES show that different SGS modes lead to different spreading rates for the velocity and scalar fields, and the scalar quantities are more affected than the velocity e.g. SGS models affect strongly the centreline mean scalar decay than the centreline mean velocity decay. The results suggest the need for a minimum resolution close to the Taylor micro-scale in order to recover the correct results for the integral quantities and this can be explained by recent results on the dynamics of the T/NT interface.

Identifying Coherent Structures in a 3-Stream Supersonic Jet Flow using Time-Resolved Schlieren Imaging

NASA Astrophysics Data System (ADS)

Tenney, Andrew; Coleman, Thomas; Berry, Matthew; Magstadt, Andy; Gogineni, Sivaram; Kiel, Barry

2015-11-01

Shock cells and large scale structures present in a three-stream non-axisymmetric jet are studied both qualitatively and quantitatively. Large Eddy Simulation is utilized first to gain an understanding of the underlying physics of the flow and direct the focus of the physical experiment. The flow in the experiment is visualized using long exposure Schlieren photography, with time resolved Schlieren photography also a possibility. Velocity derivative diagnostics are calculated from the grey-scale Schlieren images are analyzed using continuous wavelet transforms. Pressure signals are also captured in the near-field of the jet to correlate with the velocity derivative diagnostics and assist in unraveling this complex flow. We acknowledge the support of AFRL through an SBIR grant.

Multiple jet study data correlations. [data correlation for jet mixing flow of air jets

NASA Technical Reports Server (NTRS)

Walker, R. E.; Eberhardt, R. G.

1975-01-01

Correlations are presented which allow determination of penetration and mixing of multiple cold air jets injected normal to a ducted subsonic heated primary air stream. Correlations were obtained over jet-to-primary stream momentum flux ratios of 6 to 60 for locations from 1 to 30 jet diameters downstream of the injection plane. The range of geometric and operating variables makes the correlations relevant to gas turbine combustors. Correlations were obtained for the mixing efficiency between jets and primary stream using an energy exchange parameter. Also jet centerplane velocity and temperature trajectories were correlated and centerplane dimensionless temperature distributions defined. An assumption of a Gaussian vertical temperature distribution at all stations is shown to result in a reasonable temperature field model. Data are presented which allow comparison of predicted and measured values over the range of conditions specified above.

The Dynamics of Shock Dispersion and Interactions in Supersonic Freestreams with Counterflowing Jets

NASA Technical Reports Server (NTRS)

Daso, Endwell O.; Pritchett, Victor E.; Wang, Ten-See; Ota, Dale K.; Blankson, Isaiah M.; Auslender, Aaron H.

2007-01-01

An active flow control concept using counterflowing jets to significantly modify the external flowfields and strongly weaken or disperse the shock-waves of supersonic and hypersonic vehicles to reduce the aerothermal loads and wave drag was investigated. Experiments were conducted in a trisonic blow-down wind-tunnel, complemented by pre-test computational fluid dynamics (CFD) analysis of a 2.6% scale model of Apollo capsule, with and without counterflowing jets, in Mach 3.48 and 4.0 freestreams, to assess the potential aerothermal and aerodynamic benefits of this concept. The model was instrumented with heat flux gauges, thermocouples and pressure taps, and employed five counterflowing jet nozzles (three sonic and other two supersonic with design Mach numbers of 2.44 and 2.94) and nozzle exit diameters ranging from 0.25 to 0.5 inch. Schlieren data show that at low jet flow rates of 0.05 and 0.1lb(sub m)/sec, the interactions result in a long penetration mode (LPM) jet, while the short penetration mode (SPM) jet is observed at flow rates greater than 0.1 lb(sub m)/sec., consistent with the pre-test CFD predictions. For the LPM, the jet appears to be nearly fully-expanded, resulting in a very unsteady and oscillatory flow structure in which the bow shock becomes highly dispersed such that it is no longer discernable. Higher speed camera Schlieren data reveal the shock to be dispersed into striations of compression waves, which suddenly coalesce to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. The pronounced shock dispersion could significantly impact the aerodynamic performance (L/D) and heat flux reduction of spacecraft in atmospheric entry and re-entry, and could also attenuate the entropy layer in hypersonic blunt body flows. For heat transfer, the results show significant reduction in heat flux, even giving negative heat flux for some of the SPM interactions, indicating that the flow wetting the model is cooling

On the efficiency of jet production in FR II radio galaxies and quasars

NASA Astrophysics Data System (ADS)

Rusinek, Katarzyna; Sikora, Marek; Kozieł-Wierzbowska, Dorota; Godfrey, Leith

2017-04-01

Jet powers in many radio galaxies with extended radio structures appear to exceed their associated accretion luminosities. In systems with very low accretion rates, this is likely due to the very low accretion luminosities resulting from radiatively inefficient accretion flows. In systems with high accretion rates, the accretion flows are expected to be radiatively efficient, and the production of such powerful jets may require an accretion scenario, which involves magnetically arrested discs (MADs). However, numerical simulations of the MAD scenario indicate that jet production efficiency is large only for geometrically thick accretion flows and scales roughly with (H/R)2, where H is the disc height and R is the distance from the black hole. Using samples of FR II radio galaxies and quasars accreting at moderate accretion rates, we show that their jets are much more powerful than predicted by the MAD scenario. We discuss possible origins of this discrepancy, suggesting that it can be related to approximations adopted in magnetohydrodynamic simulations to treat optically thick accretion flow within the MAD zone, or may indicate that accretion discs are geometrically thicker than the standard theory predicts.

Flow characteristics around a deformable stenosis under pulsatile flow condition

NASA Astrophysics Data System (ADS)

Choi, Woorak; Park, Jun Hong; Byeon, Hyeokjun; Lee, Sang Joon

2018-01-01

A specific portion of a vulnerable stenosis is deformed periodically under a pulsatile blood flow condition. Detailed analysis of such deformable stenosis is important because stenotic deformation can increase the likelihood of rupture, which may lead to sudden cardiac death or stroke. Various diagnostic indices have been developed for a nondeformable stenosis by using flow characteristics and resultant pressure drop across the stenosis. However, the effects of the stenotic deformation on the flow characteristics remain poorly understood. In this study, the flows around a deformable stenosis model and two different rigid stenosis models were investigated under a pulsatile flow condition. Particle image velocimetry was employed to measure flow structures around the three stenosis models. The deformable stenosis model was deformed to achieve high geometrical slope and height when the flow rate was increased. The deformation of the stenotic shape enhanced jet deflection toward the opposite vessel wall of the stenosis. The jet deflection in the deformable model increased the rate of jet velocity and turbulent kinetic energy (TKE) production as compared with those in the rigid models. The effect of stenotic deformation on the pulsating waveform related with the pressure drop was analyzed using the TKE production rate. The deformable stenosis model exhibited a phase delay of the peak point in the waveform. These results revealed the potential use of pressure drop waveform as a diagnostic index for deformable stenosis.

Numerical Experiments of Counterflowiing Jet Effects on Supersonic Slender-Body Configurations

NASA Technical Reports Server (NTRS)

Venkatachari, Balaji Shankar; Mullane, Michael; Cheng, Gary C.; Chang, Chau-Lyan

2015-01-01

Previous studies have demonstrated that the use of counterflowing jets can greatly reduce the drag and heat loads on blunt-body geometries, especially when the long penetration mode jet condition can be established. Previously, the authors had done some preliminary numerical studies to determine the ability to establish long penetration mode jets on a typical Mach 1.6 slender configuration, and study its impact on the boom signature. The results indicated that a jet with a longer penetration length was required to achieve any impact on the boom signature of a typical Mach 1.6 slender configuration. This paper focuses on an in-depth parametric study, done using the space-time conservation element solution element Navier-Stokes flow solver, for investigating the effect of various counterflowing jet conditions/configurations on two supersonic slender-body models (cone-cylinder and quartic body of revolution). The study is aimed at gaining a better understanding of the relationship between the shock penetration length and reduction of drag and boom signature for these two supersonic slender-body configurations. Different jet flow rates, Mach numbers, nozzle jet exit diameters and jet-to-base diameter ratios were examined. The results show the characteristics of a short-to-long-to-short penetration-mode pattern with the increase of jet mass flow rates, observed across various counterflowing jet nozzle configurations. Though the optimal shock penetration length for potential boom-signature mitigation is tied to the long penetration mode, it often results in a very unsteady flow and leads to large oscillations of surface pressure and drag. Furthermore, depending on the geometry of the slender body, longer jet penetration did not always result in maximum drag reduction. For the quartic geometry, the maximum drag reduction corresponds well to the longest shock penetration length, while this was not the case for the cone-cylinder-as the geometry was already optimized for

Evidence of Standing Waves in Arc Jet Nozzle Flow

NASA Technical Reports Server (NTRS)

Driver, David M.; Hartman, Joe; Philippidis, Daniel; Noyes, Eric; Hui, Frank; Terrazas-Salinas, Imelda

2017-01-01

Waves spawned by the nozzle in the NASA Ames 60 MW Interaction Heating Facility arc jet were experimentally observed in pressure surveys at the exit of the nozzle. The waves have been seen in past CFD simulations, but were away from the region where models were tested (for the existing nozzles). However, a recent test series with a new nozzle extension (229 mm exit diameter) revealed that these waves intersect the centerline of the jet in a region where it is desirable to put test articles, and that the waves may be contributing to non-uniform recession behavior seen in Teflon (trademark) sublimation test articles tested in this new nozzle. It is reasonable to assume the ablation recession of thermal protection models will also be nonuniform due to exposure to these waves. This work shows that ablation response is sensitive to the location of test samples in the free jet relative to the location of the wave interaction, and that the issues with these waves can be avoided by choosing an optimum position for a test article in the free jet. This work describes the experimental observations along with the CFD simulations that have identified the waves emanating from the nozzle, as well as the instrumentation used to detect them. The work describes a recommended solution, derived by CFD analysis, which if implemented, should significantly reduce these flow disturbance and pressure anomalies in future nozzles.

Sound Sources Identified in High-Speed Jets by Correlating Flow Density Fluctuations With Far-Field Noise

NASA Technical Reports Server (NTRS)

Panda, Jayanta; Seasholtz, Richard G.

2003-01-01

Noise sources in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn Research Center in support of NASA s initiative to reduce the noise emitted by commercial airplanes. Previous efforts to use this correlation method have failed because the tools for measuring jet turbulence were intrusive. In the present experiment, a molecular Rayleigh-scattering technique was used that depended on laser light scattering by gas molecules in air. The technique allowed accurate measurement of air density fluctuations from different points in the plume. The study was conducted in shock-free, unheated jets of Mach numbers 0.95, 1.4, and 1.8. The turbulent motion, as evident from density fluctuation spectra was remarkably similar in all three jets, whereas the noise sources were significantly different. The correlation study was conducted by keeping a microphone at a fixed location (at the peak noise emission angle of 30 to the jet axis and 50 nozzle diameters away) while moving the laser probe volume from point to point in the flow. The following figure shows maps of the nondimensional coherence value measured at different Strouhal frequencies ([frequency diameter]/jet speed) in the supersonic Mach 1.8 and subsonic Mach 0.95 jets. The higher the coherence, the stronger the source was.

Aeroacoustics of supersonic jet flows from contoured and solid/porous conical plug-nozzles

NASA Technical Reports Server (NTRS)

Dosanjh, Darshan S.; Das, Indu S.

1987-01-01

The results of an experimental study of the acoustic far-field, the shock associated noise, and the nature of the repetitive shock structure of supersonic jet flows issuing from plug-nozzles having externally-expanded plugs with pointed termination operated at a range of supercritical pressure ratios Xi approaching 2 to 4.5 are reported. The plug of one of these plug-nozzles was contoured. The other plug-nozzles had short conical plugs with either a solid surface or a combination of solid/porous surface of different porosities. The contoured and the uncontoured plug-nozzles had the same throat area and the same annulus-radius ratio K = R sub p/R sub N = 0.43. As the result of modifications of the shock structure, the acoustic performance of improperly expanded jet flows of an externally-expanded short uncontoured plug of an appropriate geometry with suitably perforated plug and a pointed termination, is shown to approach the acoustic performance of a shock-free supersonic jet issuing from an equivalent externally-expanded contoured plug-nozzle.

Temporally resolved ozone distribution of a time modulated RF atmospheric pressure argon plasma jet: flow, chemical reaction, and transient vortex

NASA Astrophysics Data System (ADS)

Zhang, S.; Sobota, A.; van Veldhuizen, E. M.; Bruggeman, P. J.

2015-08-01

The ozone density distribution in the effluent of a time modulated RF atmospheric pressure plasma jet (APPJ) is investigated by time and spatially resolved by UV absorption spectroscopy. The plasma jet is operated with an averaged dissipated power of 6.5 W and gas flow rate 2 slm argon  +2% O2. The modulation frequency of the RF power is 50 Hz with a duty cycle of 50%. To investigate the production and destruction mechanism of ozone in the plasma effluent, the atomic oxygen and gas temperature is also obtained by TALIF and Rayleigh scattering, respectively. A temporal increase in ozone density is observed close to the quartz tube exit when the plasma is switched off due to the decrease in O density and gas temperature. Ozone absorption at different axial positions indicates that the ozone distribution is dominated by the convection induced by the gas flow and allows estimating the on-axis local gas velocity in the jet effluent. Transient vortex structures occurring during the switch on and off of the RF power also significantly affect the ozone density in the far effluent.

Nonlinear Dynamics in Viscoelastic Jets

NASA Astrophysics Data System (ADS)

Majmudar, Trushant; Varagnat, Matthieu; McKinley, Gareth

2008-11-01

Instabilities in free surface continuous jets of non-Newtonian fluids, although relevant for many industrial processes, remain poorly understood in terms of fundamental fluid dynamics. Inviscid, and viscous Newtonian jets have been studied in considerable detail, both theoretically and experimentally. Instability in viscous jets leads to regular periodic coiling of the jet, which exhibits a non-trivial frequency dependence with the height of the fall. Here we present a systematic study of the effect of viscoelasticity on the dynamics of continuous jets of worm-like micellar surfactant solutions of varying viscosities and elasticities. We observe complex nonlinear spatio-temporal dynamics of the jet, and uncover a transition from periodic to quasi-periodic to a multi-frequency, broad-spectrum dynamics. Beyond this regime, the jet dynamics smoothly crosses over to exhibit the ``leaping shampoo'' or the Kaye effect. We examine different dynamical regimes in terms of scaling variables, which depend on the geometry (dimensionless height), kinematics (dimensionless flow rate), and the fluid properties (elasto-gravity number) and present a regime map of the dynamics of the jet in terms of these dimensionless variables.

Nonlinear Dynamics in Viscoelastic Jets

NASA Astrophysics Data System (ADS)

Majmudar, Trushant; Varagnat, Matthieu; McKinley, Gareth

2009-03-01

Instabilities in free surface continuous jets of non-Newtonian fluids, although relevant for many industrial processes, remain poorly understood in terms of fundamental fluid dynamics. Inviscid, and viscous Newtonian jets have been studied in considerable detail, both theoretically and experimentally. Instability in viscous jets leads to regular periodic coiling of the jet, which exhibits a non-trivial frequency dependence with the height of the fall. Here we present a systematic study of the effect of viscoelasticity on the dynamics of continuous jets of worm-like micellar surfactant solutions of varying viscosities and elasticities. We observe complex nonlinear spatio-temporal dynamics of the jet, and uncover a transition from periodic to quasi-periodic to a multi-frequency, broad-spectrum dynamics. Beyond this regime, the jet dynamics smoothly crosses over to exhibit the ``leaping shampoo'' or the Kaye effect. We examine different dynamical regimes in terms of scaling variables, which depend on the geometry (dimensionless height), kinematics (dimensionless flow rate), and the fluid properties (elasto-gravity number) and present a regime map of the dynamics of the jet in terms of these dimensionless variables.

Investigation of Flow Conditioners for Compact Jet Engine Simulator Rig Noise Reduction

NASA Technical Reports Server (NTRS)

Doty, Michael J.; Haskin, Henry H.

2011-01-01

The design requirements for two new Compact Jet Engine Simulator (CJES) units for upcoming wind tunnel testing lead to the distinct possibility of rig noise contamination. The acoustic and aerodynamic properties of several flow conditioner devices are investigated over a range of operating conditions relevant to the CJES units to mitigate the risk of rig noise. An impinging jet broadband noise source is placed in the upstream plenum of the test facility permitting measurements of not only flow conditioner self-noise, but also noise attenuation characteristics. Several perforated plate and honeycomb samples of high porosity show minimal self-noise but also minimal attenuation capability. Conversely, low porosity perforated plate and sintered wire mesh conditioners exhibit noticeable attenuation but also unacceptable self-noise. One fine wire mesh sample (DP450661) shows minimal selfnoise and reasonable attenuation, particularly when combined in series with a 15.6 percent open area (POA) perforated plate upstream. This configuration is the preferred flow conditioner system for the CJES, providing up to 20 dB of broadband attenuation capability with minimal self-noise.

Jets or vortices - what flows are generated by an inverse turbulent cascade?

NASA Astrophysics Data System (ADS)

Frishman, Anna; Laurie, Jason; Falkovich, Gregory

An inverse cascade-energy transfer to progressively larger scales - is a salient feature of two-dimensional turbulence. If the cascade reaches the system scale, it creates a coherent flow expected to have the largest available scale and conform with the symmetries of the domain. In a doubly periodic rectangle, the mean flow with zero total momentum was therefore believed to be unidirectional, with two jets along the short side; while for an aspect ratio close to unity, a vortex dipole was expected. Using direct numerical simulations, we show that in fact neither the box symmetry is respected nor the largest scale is realized: the flow is never purely unidirectional since the inverse cascade produces coherent vortices, whose number and relative motion are determined by the aspect ratio. This spontaneous symmetry breaking is closely related to the hierarchy of averaging times. Long-time averaging restores translational invariance due to vortex wandering along one direction, and gives jets whose profile, however, can be deduced neither from the largest-available-scale argument, nor from the often employed maximum-entropy principle or quasi-linear approximation.

Jets or vortices—What flows are generated by an inverse turbulent cascade?

NASA Astrophysics Data System (ADS)

Frishman, Anna; Laurie, Jason; Falkovich, Gregory

2017-03-01

An inverse cascade, energy transfer to progressively larger scales, is a salient feature of two-dimensional turbulence. If the cascade reaches the system scale, it creates a coherent flow expected to have the largest available scale and conform with the symmetries of the domain. In a doubly periodic rectangle, the mean flow with zero total momentum was therefore believed to be unidirectional, with two jets along the short side; while for an aspect ratio close to unity, a vortex dipole is expected. Using direct numerical simulations, we show that in fact neither is the box symmetry respected nor the largest scale realized: the flow is never purely unidirectional since the inverse cascade produces coherent vortices, whose number and relative motion are determined by the aspect ratio. This spontaneous symmetry breaking is closely related to the hierarchy of averaging times. Long-time averaging restores translational invariance due to vortex wandering along one direction, and gives jets whose profile, however, can neither be deduced from the largest-available-scale argument, nor from the often employed maximum-entropy principle or quasilinear approximation.

Jet reconstruction and performance using particle flow with the ATLAS Detector

DOE PAGES

Aaboud, M.; Aad, G.; Abbott, B.; ...

2017-07-13

This paper describes the implementation and performance of a particle flow algorithm applied to 20.2 fb –1 of ATLAS data from 8 TeV proton–proton collisions in Run 1 of the LHC. The algorithm removes calorimeter energy deposits due to charged hadrons from consideration during jet reconstruction, instead using measurements of their momenta from the inner tracker. This improves the accuracy of the charged-hadron measurement, while retaining the calorimeter measurements of neutral-particle energies. The paper places emphasis on how this is achieved, while minimising double-counting of charged-hadron signals between the inner tracker and calorimeter. In conclusion, the performance of particle flowmore » jets, formed from the ensemble of signals from the calorimeter and the inner tracker, is compared to that of jets reconstructed from calorimeter energy deposits alone, demonstrating improvements in resolution and pile-up stability.« less

Preferential Flow Paths and Recirculation-Disrupting Jets in the Leeside of Self-Forming Coarse-Grained Laboratory Bedforms

NASA Astrophysics Data System (ADS)

Lichtner, D.; Christensen, K. T.; Best, J.; Blois, G.

2014-12-01

Exchange of fluid in the near-subsurface of a streambed is influenced by turbulence in the free flow, as well as by bed topography and permeability. Macro-roughness elements such as bedforms are known to produce pressure gradients that drive fluid into the streambed on their stoss sides and out of the bed on their lee sides. To study the modification of the near-bed flow field by self-forming permeable bedforms, laboratory experiments were conducted in a 5 mm wide flume filled with 1.3 mm glass beads. The narrow width of the flume permitted detailed examination of the fluid exiting the bed immediately downstream of a bedform. Dense 2-D velocity field measurements were gathered using particle image velocimetry (PIV). In up to 8% of instantaneous PIV realizations, the flow at the near-bed presented a component perpendicular to the streambed, indicating flow across the interface. At the downstream side of the bedform, such flow disrupted the mean recirculation pattern that is typically observed in finer sediment beds. It is hypothesized that the coarse grain size and the resulting high bed permeability promote such near-surface jet events. A qualitative analysis of raw image frames indicated that an in-place jostling of sediment is associated with these jets thus suggesting that subsurface flow may be characterized by impulsive events. These observations are relevant to hyporheic exchange rates in coarse sediments and can have strong morphodynamic implications as they can explain the lack of ripples and characteristics of dunes in high permeability gravels. Overall, further study of the flow structure over highly permeable streambeds is needed to understand subsurface exchange and bedform initiation.

Theoretical analysis and design of hydro-hammer with a jet actuator: An engineering application to improve the penetration rate of directional well drilling in hard rock formations.

PubMed

He, Jiang-Fu; Liang, Yun-Pei; Li, Li-Jia; Luo, Yong-Jiang

2018-01-01

Rapid horizontal directional well drilling in hard or fractured formations requires efficient drilling technology. The penetration rate of conventional hard rock drilling technology in horizontal directional well excavations is relatively low, resulting in multiple overgrinding of drill cuttings in bottom boreholes. Conventional drilling techniques with reamer or diamond drill bit face difficulties due to the long construction periods, low penetration rates, and high engineering costs in the directional well drilling of hard rock. To improve the impact energy and penetration rate of directional well drilling in hard formations, a new drilling system with a percussive and rotary drilling technology has been proposed, and a hydro-hammer with a jet actuator has also been theoretically designed on the basis of the impulse hydro-turbine pressure model. In addition, the performance parameters of the hydro-hammer with a jet actuator have been numerically and experimentally analyzed, and the influence of impact stroke and pumped flow rate on the motion velocity and impact energy of the hydro-hammer has been obtained. Moreover, the designed hydro-hammer with a jet actuator has been applied to hard rock drilling in a trenchless drilling program. The motion velocity of the hydro-hammer ranges from 1.2 m/s to 3.19 m/s with diverse flow rates and impact strokes, and the motion frequency ranges from 10 Hz to 22 Hz. Moreover, the maximum impact energy of the hydro-hammer is 407 J, and the pumped flow rate is 2.3 m3/min. Thus, the average penetration rate of the optimized hydro-hammer improves by over 30% compared to conventional directional drilling in hard rock formations.

Theoretical analysis and design of hydro-hammer with a jet actuator: An engineering application to improve the penetration rate of directional well drilling in hard rock formations

PubMed Central

He, Jiang-fu; Li, Li-jia; Luo, Yong-jiang

2018-01-01

Rapid horizontal directional well drilling in hard or fractured formations requires efficient drilling technology. The penetration rate of conventional hard rock drilling technology in horizontal directional well excavations is relatively low, resulting in multiple overgrinding of drill cuttings in bottom boreholes. Conventional drilling techniques with reamer or diamond drill bit face difficulties due to the long construction periods, low penetration rates, and high engineering costs in the directional well drilling of hard rock. To improve the impact energy and penetration rate of directional well drilling in hard formations, a new drilling system with a percussive and rotary drilling technology has been proposed, and a hydro-hammer with a jet actuator has also been theoretically designed on the basis of the impulse hydro-turbine pressure model. In addition, the performance parameters of the hydro-hammer with a jet actuator have been numerically and experimentally analyzed, and the influence of impact stroke and pumped flow rate on the motion velocity and impact energy of the hydro-hammer has been obtained. Moreover, the designed hydro-hammer with a jet actuator has been applied to hard rock drilling in a trenchless drilling program. The motion velocity of the hydro-hammer ranges from 1.2 m/s to 3.19 m/s with diverse flow rates and impact strokes, and the motion frequency ranges from 10 Hz to 22 Hz. Moreover, the maximum impact energy of the hydro-hammer is 407 J, and the pumped flow rate is 2.3 m3/min. Thus, the average penetration rate of the optimized hydro-hammer improves by over 30% compared to conventional directional drilling in hard rock formations. PMID:29768421

Sweeping Jet Optimization Studies

NASA Technical Reports Server (NTRS)

Melton, LaTunia Pack; Koklu, Mehti; Andino, Marlyn; Lin, John C.; Edelman, Louis

2016-01-01

Progress on experimental efforts to optimize sweeping jet actuators for active flow control (AFC) applications with large adverse pressure gradients is reported. Three sweeping jet actuator configurations, with the same orifice size but di?erent internal geometries, were installed on the flap shoulder of an unswept, NACA 0015 semi-span wing to investigate how the output produced by a sweeping jet interacts with the separated flow and the mechanisms by which the flow separation is controlled. For this experiment, the flow separation was generated by deflecting the wing's 30% chord trailing edge flap to produce an adverse pressure gradient. Steady and unsteady pressure data, Particle Image Velocimetry data, and force and moment data were acquired to assess the performance of the three actuator configurations. The actuator with the largest jet deflection angle, at the pressure ratios investigated, was the most efficient at controlling flow separation on the flap of the model. Oil flow visualization studies revealed that the flow field controlled by the sweeping jets was more three-dimensional than expected. The results presented also show that the actuator spacing was appropriate for the pressure ratios examined.

Film cooling: case of double rows of staggered jets.

PubMed

Dorignac, E; Vullierme, J J; Noirault, P; Foucault, E; Bousgarbiès, J L

2001-05-01

An experimental investigation of film cooling of a wall in a case of double rows of staggered hot jets (65 degrees C) in an ambient air flow. The wall is heated at a temperature value between the one of the jets and the one of the main flow. Experiments have been carried out for different injection rates, the main flow velocity is maintained at 32 m/s. Association of the measures of temperature profiles by cold wire and the measures of wall temperature by infrared thermography allows us to describe the behaviour of the flows and to propose the best injection which assures a good cooling of the plate.

Effect of the gas flow rate on the spatiotemporal distribution of Ar(1s5) absolute densities in a ns pulsed plasma jet impinging on a glass surface

NASA Astrophysics Data System (ADS)

Gazeli, K.; Bauville, G.; Fleury, M.; Jeanney, P.; Neveu, O.; Pasquiers, S.; Santos Sousa, J.

2018-06-01

This work presents spatial (axial-z and transversal-y) and temporal distributions of Ar(1s5) metastable absolute densities in an atmospheric pressure argon micro-plasma jet impinging on an ungrounded glass surface. Guided streamers are generated with a DBD device driven by pulsed positive high voltages of 6 kV in amplitude, 224 +/- 3 ns in FWHM and 20 kHz in frequency. The argon flow rate is varied between 200 and 600 sccm. The glass plate is placed at 5 mm away from the reactor’s nozzle and perpendicular to the streamers propagation. At these conditions, a diffuse stable discharge is established after the passage of the streamers allowing the quantification of the Ar(1s5) absolute density by means of a conventional TDLAS technique coupled with emission spectroscopy and ICCD imaging. The good reproducibility of the absorption signals is demonstrated. The experiments show the strong dependence of the maximum density ({0.5-4}× {10}13 {{{cm}}}-3) on the gas flow rate and the axial and transversal position. At 200 sccm, high maximum densities (> 2.4× {10}13 {{{cm}}}-3) are obtained in a small area close to the plasma source, while with increasing flow rate this area expands towards the glass plate. In the transversal direction, density maxima are obtained in a small zone around the propagation axis of the streamers. Finally, a noticeable increase is measured on the Ar(1s5) effective lifetime close to the glass surface by varying the flow rate from 200 to 600 sccm. In overall, the effective lifetime varies between ∼25 and ∼550 ns, depending on the gas flow rate and the values of z and y coordinates. The results obtained suggest that the present system can be implemented in various applications and particularly in what concerns the detection of weakly volatile organic compounds present in trace amounts on different surfaces.

Jet Interactions in a Feedback-Free Fluidic Oscillator in the Transition Region

NASA Astrophysics Data System (ADS)

Tomac, Mehmet; Gregory, James

2013-11-01

The details of the jet interactions and oscillation mechanism of a feedback-free type fluidic oscillator are studied in this work. Flow rate-frequency measurements indicate the existence of three distinct operating regimes: low flow rate, transition, and high flow rate regions. This study presents results from the transition regime, extracted by using refractive index-matched particle image velocimetry (PIV). A newly-developed sensor configuration for frequency measurements in the refractive index-matched fluid and a phase-averaging method that minimizes jitter will be discussed. Experimental results indicate that the interactions of the two jets create three main vortices in the mixing chamber. One vortex vanishes and forms depending on the oscillation phase and plays a key role in the oscillation mechanism. The other two vortices sustain their existence throughout the oscillation cycle; however, both continuously change their size and strength. The resulting complex flow field with self-sustained oscillations is a result of the combination of many interesting phenomena such as jet interactions and bifurcations, viscous effects, vortex-shear layer interactions, vortex-wall interactions, instabilities, and saddle point creations.

Experimental study of secondary flow in the presence of two jet arrays on the wall of a turbine blade

NASA Astrophysics Data System (ADS)

Seddini, Abdelali

A experimental study of the interaction of the secondary turbine flow with the cooling jets injected at the base of the blades is presented. Subsonic wind tunnel tests were carried on using a gas turbine wheel. The hot wire sensor and the five orifices pressure transducer used in the tests are described. The results allow a satisfactory description of the evolution of the jets in the space between blades and give some indications of the interactions of jets with secondary flows, passing vortices and between themselves.

Computational simulation of laboratory-scale volcanic jets

NASA Astrophysics Data System (ADS)

Solovitz, S.; Van Eaton, A. R.; Mastin, L. G.; Herzog, M.

2017-12-01

Volcanic eruptions produce ash clouds that may travel great distances, significantly impacting aviation and communities downwind. Atmospheric hazard forecasting relies partly on numerical models of the flow physics, which incorporate data from eruption observations and analogue laboratory tests. As numerical tools continue to increase in complexity, they must be validated to fine-tune their effectiveness. Since eruptions are relatively infrequent and challenging to observe in great detail, analogue experiments can provide important insights into expected behavior over a wide range of input conditions. Unfortunately, laboratory-scale jets cannot easily attain the high Reynolds numbers ( 109) of natural volcanic eruption columns. Comparisons between the computational models and analogue experiments can help bridge this gap. In this study, we investigate a 3-D volcanic plume model, the Active Tracer High-resolution Atmospheric Model (ATHAM), which has been used to simulate a variety of eruptions. However, it has not been previously validated using laboratory-scale data. We conducted numerical simulations of three flows that we have studied in the laboratory: a vertical jet in a quiescent environment, a vertical jet in horizontal cross flow, and a particle-laden jet. We considered Reynolds numbers from 10,000 to 50,000, jet-to-cross flow velocity ratios of 2 to 10, and particle mass loadings of up to 25% of the exit mass flow rate. Vertical jet simulations produce Gaussian velocity profiles in the near exit region by 3 diameters downstream, matching the mean experimental profiles. Simulations of air entrainment are of the correct order of magnitude, but they show decreasing entrainment with vertical distance from the vent. Cross flow simulations reproduce experimental trajectories for the jet centerline initially, although confinement appears to impact the response later. Particle-laden simulations display minimal variation in concentration profiles between cases with

Interfacial condensation induced by sub-cooled liquid jet

NASA Astrophysics Data System (ADS)

Rame, Enrique; Balasubramaniam, R.

2016-11-01

When a sub-cooled liquid jet impinges on the free surface between a liquid and its vapor, vapor will condense at a rate dependent on the sub-cooling, the jet strength and fluid properties. In 1966 and during the examination of a different type of condensation flow, Shekriladeze found an approximate result, valid at large condensation rates, that decouples the flow in the liquid phase from that of the vapor, without putting it in the context of a formal asymptotic approximation. In this talk we will develop an asymptotic approximation that contains Shekriladze's result, and extend the calculations to the case when a non-condensable gas is present in the vapor phase.

The Effect of Break Edge Configuration on the Aerodynamics of Anti-Ice Jet Flow

NASA Astrophysics Data System (ADS)

Tatar, V.; Yildizay, H.; Aras, H.

2015-05-01

One of the components of a turboprop gas turbine engine is the Front Bearing Structure (FBS) which leads air into the compressor. FBS directly encounters with ambient air, as a consequence ice accretion may occur on its static vanes. There are several aerodynamic parameters which should be considered in the design of anti-icing system of FBS, such as diameter, position, exit angle of discharge holes, etc. This research focuses on the effects of break edge configuration over anti-ice jet flow. Break edge operation is a process which is applied to the hole in order to avoid sharp edges which cause high stress concentration. Numerical analyses and flow visualization test have been conducted. Four different break edge configurations were used for this investigation; without break edge, 0.35xD, 74xD, 0.87xD. Three mainstream flow conditions at the inlet of the channel are defined; 10m/s, 20 m/s and 40 m/s. Shear stresses are extracted from numerical analyses near the trailing edge of pressure surface where ice may occur under icing conditions. A specific flow visualization method was used for the experimental study. Vane surface near the trailing edge was dyed and thinner was injected into anti-ice jet flow in order to remove dye from the vane surface. Hence, film effect on the surface could be computed for each testing condition. Thickness of the dye removal area of each case was examined. The results show noticeable effects of break edge operation on jet flow, and the air film effectiveness decreases when mainstream inlet velocity decreases.

Structure of supersonic jet flow and its radiated sound

NASA Technical Reports Server (NTRS)

Mankbadi, Reda R.; Hayer, M. Ehtesham; Povinelli, Louis A.

1994-01-01

The present paper explores the use of large-eddy simulations as a tool for predicting noise from first principles. A high-order numerical scheme is used to perform large-eddy simulations of a supersonic jet flow with emphasis on capturing the time-dependent flow structure representating the sound source. The wavelike nature of this structure under random inflow disturbances is demonstrated. This wavelike structure is then enhanced by taking the inflow disturbances to be purely harmonic. Application of Lighthill's theory to calculate the far-field noise, with the sound source obtained from the calculated time-dependent near field, is demonstrated. Alternative approaches to coupling the near-field sound source to the far-field sound are discussed.

Mathematical model of an indirect action fuel flow controller for aircraft jet engines

NASA Astrophysics Data System (ADS)

Tudosie, Alexandru-Nicolae

2017-06-01

The paper deals with a fuel mass flow rate controller with indirect action for aircraft jet engines. The author has identified fuel controller's main parts and its operation mode, then, based on these observations, one has determined motion equations of each main part, which have built system's non-linear mathematical model. In order to realize a better study this model was linearised (using the finite differences method) and then adimensionalized. Based on this new form of the mathematical model, after applying Laplace transformation, the embedded system (controller+engine) was described by the block diagram with transfer functions. Some Simulink-Matlab simulations were performed, concerning system's time behavior for step input, which lead to some useful conclusions and extension possibilities.

STOL landing thrust: Reverser jet flowfields

NASA Technical Reports Server (NTRS)

Kotansky, D. R.; Glaze, L. W.

1987-01-01

Analysis tools and modeling concepts for jet flow fields encountered upon use of thrust reversers for high performance military aircraft are described. A semi-empirical model of the reverser ground wall jet interaction with the uniform cross flow due to aircraft forward velocity is described. This ground interaction model is used to demonstrate exhaust gas ingestion conditions. The effects of control of exhaust jet vector angle, lateral splay, and moving versus fixed ground simulation are discussed. The Adler/Baron jet-in-cross flow model is used in conjunction with three dimensional panel methods to investigate the upper surface jet induced flow field.

Effect of LES models on the entrainment of a passive scalar in a turbulent planar jet

NASA Astrophysics Data System (ADS)

Chambel Lopes, Diogo; da Silva, Carlos; Reis, Ricardo; Raman, Venkat

2011-11-01

Direct and large-eddy simulations (DNS/LES) of turbulent planar jets are used to study the role of subgrid-scale models in the integral characteristics of the passive scalar mixing in a jet. Specifically the effect of subgrid-scale models in the jet spreading rate and centreline passive scalar decay rates are assessed and compared. The modelling of the subgrid-scale fluxes is particularly challenging in the turbulent/nonturbulent (T/NT) region that divides the two regions in the jet flow: the outer region where the flow is irrotational and the inner region where the flow is turbulent. It has been shown that important Reynolds stresses exist near the T/NT interface and that these stresses determine in part the mixing and combustion rates in jets. The subgrid scales of motion near the T/NT interface are far from equilibrium and contain an important fraction of the total kinetic energy. Model constants used in several subgrid-scale models such as the Smagorinsky and the gradient models need to be corrected near the jet edge. The procedure used to obtain the dynamic Smagorinsky constant is not able to cope with the intermittent nature of this region.

Advanced Modified High Performance Synthetic Jet Actuator with Curved Chamber

NASA Technical Reports Server (NTRS)

Xu, Tian-Bing (Inventor); Su, Ji (Inventor); Jiang, Xiaoning (Inventor)

2014-01-01

The advanced modified high performance synthetic jet actuator with optimized curvature shape chamber (ASJA-M) is a synthetic jet actuator (SJA) with a lower volume reservoir or chamber. A curved chamber is used, instead of the conventional cylinder chamber, to reduce the dead volume of the jet chamber and increase the efficiency of the synthetic jet actuator. The shape of the curvature corresponds to the maximum displacement (deformation) profile of the electroactive diaphragm. The jet velocity and mass flow rate for the ASJA-M will be several times higher than conventional piezoelectric actuators.

Flow visualization and acoustic consequences of the air moving through a static model of the human larynx.

PubMed

Kucinschi, Bogdan R; Scherer, Ronald C; DeWitt, Kenneth J; Ng, Terry T M

2006-06-01

Flow visualization with smoke particles illuminated by a laser sheet was used to obtain a qualitative description of the air flow structures through a dynamically similar 7.5x symmetric static scale model of the human larynx (divergence angle of 10 deg, minimal diameter of 0.04 cm real life). The acoustic level downstream of the vocal folds was measured by using a condenser microphone. False vocal folds (FVFs) were included. In general, the glottal flow was laminar and bistable. The glottal jet curvature increased with flow rate and decreased with the presence of the FVFs. The glottal exit flow for the lowest flow rate showed a curved jet which remained laminar for all geometries. For the higher flow rates, the jet flow patterns exiting the glottis showed a laminar jet core, transitioning to vortical structures, and leading spatially to turbulent dissipation. This structure was shortened and tightened with an increase in flow rate. The narrow FVF gap lengthened the flow structure and reduced jet curvature via acceleration of the flow. These results suggest that laryngeal flow resistance and the complex jet flow structure exiting the glottis are highly affected by flow rate and the presence of the false vocal folds. Acoustic consequences are discussed in terms of the quadrupole- and dipole-type sound sources due to ordered flow structures.

The acoustic and instability waves of jets confined inside an acoustically lined rectangular duct

NASA Technical Reports Server (NTRS)

Hu, Fang Q.

1993-01-01

An analysis of linear wave modes associated with supersonic jets confined inside an acoustically lined rectangular duct is presented. Mathematical formulations are given for the vortex-sheet model and continuous mean flow model of the jet flow profiles. Detailed dispersion relations of these waves in a two-dimensional confined jet as well as an unconfined free jet are computed. Effects of the confining duct and the liners on the jet instability and acoustic waves are studied numerically. It is found that the effect of the liners is to attenuate waves that have supersonic phase velocities relative to the ambient flow. Numerical results also show that the growth rates of the instability waves could be reduced significantly by the use of liners. In addition, it is found that the upstream propagating neutral waves of an unconfined jet could become attenuated when the jet is confined.

Three-dimensional computer simulation of non-reacting jet-gas flow mixing in an MHD second stage combustor

NASA Astrophysics Data System (ADS)

Chang, S. L.; Lottes, S. A.; Berry, G. F.

Argonne National Laboratory is investigating the non-reacting jet-gas mixing patterns in a magnetohydrodynamics (MHD) second stage combustor by using a three-dimensional single-phase hydrodynamics computer program. The computer simulation is intended to enhance the understanding of flow and mixing patterns in the combustor, which in turn may improve downstream MHD channel performance. The code is used to examine the three-dimensional effects of the side walls and the distributed jet flows on the non-reacting jet-gas mixing patterns. The code solves the conservation equations of mass, momentum, and energy, and a transport equation of a turbulence parameter and allows permeable surfaces to be specified for any computational cell.

Investigation of compound jet electrospray: Particle encapsulation

NASA Astrophysics Data System (ADS)

Mei, Fan; Chen, Da-Ren

2007-10-01

Experiments were performed to investigate the effect of surface tension on the particle encapsulation formation in the compound jet electrospray process. The outer liquid used in this study were olive oil and mineral oil; and inner liquids were ethanol, tri-butyl phosphate, ethylene glycol, and triethylene glycol. It was found that the core-shell structured droplets are formed only when the ratio of charge relaxation lengths of the inner and outer jets [i.e., rO*/rI*, where r *=(Qɛɛ0/K)1/3, in which ɛ is the dielectric constant of liquid] is less than 500, and the ratio of inertial breakup lengths of the inner and outer jets [i.e., RO*/RI*, where R *=(ρQ2/γ)1/3, in which ρ and γ are the density and surface tension of liquid, respectively] is less than 0.015. In this work we further studied the effect of inner and outer liquid flow rates on the size of compound droplets using an Aerosizer (TSI model 3220). The parameters affecting the droplet size distribution were obtained. We also observed that the spray current emitted through the compound jet was merely a linear function of the inner jet flow rate. This observation implies that olive oil and mineral oil, as the outer liquids, serve as an electrically insulated layer during the spray process.

Measurement of αs from jet rates in deep inelastic scattering at HERA

NASA Astrophysics Data System (ADS)

Derrick, M.; Krakauer, D.; Magill, S.; Mikunas, D.; Musgrave, B.; Repond, J.; Stanek, R.; Talaga, R. L.; Zhang, H.; Ayad, R.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Bruni, P.; Cara Romeo, G.; Castellini, G.; Chiarini, M.; Cifarelli, L.; Cindolo, F.; Contin, A.; Corradi, M.; Gialas, I.; Giusti, P.; Iacobucci, G.; Laurenti, G.; Levi, G.; Margotti, A.; Massam, T.; Nania, R.; Nemoz, C.; Palmonari, F.; Polini, A.; Sartorelli, G.; Timellini, R.; Zamora Garcia, Y.; Zichichi, A.; Bargende, A.; Bornheim, A.; Crittenden, J.; Desch, K.; Diekmann, B.; Doeker, T.; Eckert, M.; Feld, L.; Frey, A.; Geerts, M.; Grothe, M.; Hartmann, H.; Heinloth, K.; Hilger, E.; Jakob, H.-P.; Katz, U. F.; Mengel, S.; Mollen, J.; Paul, E.; Pfeiffer, M.; Rembser, Ch.; Schramm, D.; Stamm, J.; Wedemeyer, R.; Campbell-Robson, S.; Cassidy, A.; Cottingham, W. N.; Dyce, N.; Foster, B.; George, S.; Hayes, M. E.; Heath, G. P.; Heath, H. F.; Morgado, C. J. S.; O'Mara, J. A.; Piccioni, D.; Roff, D. G.; Tapper, R. J.; Yoshida, R.; Rau, R. R.; Arneodo, M.; Capua, M.; Garfagnini, A.; Iannotti, L.; Schioppa, M.; Susinno, G.; Bernstein, A.; Caldwell, A.; Cartiglia, N.; Parsons, J. A.; Ritz, S.; Sciulli, F.; Straub, P. B.; Wai, L.; Yang, S.; Zhu, Q.; Borzemski, P.; Chwastowski, J.; Eskreys, A.; Piotrzkowski, K.; Zachara, M.; Zawiejski, L.; Adamczyk, L.; Bednarek, B.; Jeleń, K.; Kisielewska, D.; Kowalski, T.; Rulikowska-Zarȩbska, E.; Suszycki, L.; Zajaç, J.; Kotański, A.; Przybycień, M.; Bauerdick, L. A. T.; Behrens, U.; Beier, H.; Bienlein, J. K.; Coldewey, C.; Deppe, O.; Desler, K.; Drews, G.; Flasiński, M.; Gilkinson, D. J.; Glasman, C.; Göttlicher, P.; Große-Knetter, J.; Gutjahr, B.; Haas, T.; Hain, W.; Hasell, D.; Heßling, H.; Iga, Y.; Johnson, K. F.; Joos, P.; Kasemann, M.; Klanner, R.; Koch, W.; Köpke, L.; Kötz, U.; Kowalski, H.; Labs, J.; Ladage, A.; Löhr, B.; Löwe, M.; Lüke, D.; Mainusch, J.; Mańczak, O.; Monteiro, T.; Ng, J. S. T.; Nickel, S.; Notz, D.; Ohrenberg, K.; Roco, M.; Rohde, M.; Roldán, J.; Schneekloth, U.; Schulz, W.; Selonke, F.; Stiliaris, E.; Surrow, B.; Voß, T.; Westphal, D.; Wolf, G.; Youngman, C.; Zeuner, W.; Zhou, J. F.; Grabosch, H. J.; Kharchilava, A.; Leich, A.; Mattingly, M. C. K.; Mari, S. M.; Meyer, A.; Schlenstedt, S.; Wulff, N.; Barbagli, G.; Pelfer, P.; Anzivino, G.; Maccarrone, G.; De Pasquale, S.; Votano, L.; Bamberger, A.; Eisenhardt, S.; Freidhof, A.; Söldner-Rembold, S.; Schroeder, J.; Trefzger, T.; Brook, N. H.; Bussey, P. J.; Doyle, A. T.; Saxon, D. H.; Utley, M. L.; Wilson, A. S.; Dannemann, A.; Holm, U.; Horstmann, D.; Neumann, T.; Sinkus, R.; Wick, K.; Badura, E.; Burow, B. D.; Hagge, L.; Lohrmann, E.; Milewski, J.; Nakahata, M.; Pavel, N.; Poelz, G.; Schott, W.; Zetsche, F.; Bacon, T. C.; Bruemmer, N.; Butterworth, I.; Gallo, E.; Harris, V. L.; Hung, B. Y. H.; Long, K. R.; Miller, D. B.; Morawitz, P. P. O.; Prinias, A.; Sedgbeer, J. K.; Whitfield, A. F.; Mallik, U.; McCliment, E.; Wang, M. Z.; Wang, S. M.; Wu, J. T.; Cloth, P.; Filges, D.; An, S. H.; Hong, S. M.; Nam, S. W.; Park, S. K.; Suh, M. H.; Yon, S. H.; Imlay, R.; Kartik, S.; Kim, H.-J.; McNeil, R. R.; Metcalf, W.; Nadendla, V. K.; Barreiro, F.; Cases, G.; Fernandez, J. P.; Graciani, R.; Hernández, J. M.; Hervás, L.; Labarga, L.; Martinez, M.; del Peso, J.; Puga, J.; Terron, J.; de Trocóniz, J. F.; Smith, G. R.; Corriveau, F.; Hanna, D. S.; Hartmann, J.; Hung, L. W.; Lim, J. N.; Matthews, C. G.; Patel, P. M.; Sinclair, L. E.; Stairs, D. G.; St. Laurent, M.; Ullmann, R.; Zacek, G.; Bashkirov, V.; Dolgoshein, B. A.; Stifutkin, A.; Bashindzhagyan, G. L.; Ermolov, P. F.; Gladilin, L. K.; Golubkov, Yu. A.; Kobrin, V. D.; Korzhavina, I. A.; Kuzmin, V. A.; Lukina, O. Yu.; Proskuryakov, A. S.; Savin, A. A.; Shcheglova, L. M.; Solomin, A. N.; Zotov, N. P.; Botje, M.; Chlebana, F.; Dake, A.; Engelen, J.; de Kamps, M.; Kooijman, P.; Kruse, A.; Tiecke, H.; Verkerke, W.; Vreeswijk, M.; Wiggers, L.; de Wolf, E.; van Woudenberg, R.; Acosta, D.; Bylsma, B.; Durkin, L. S.; Gilmore, J.; Honscheid, K.; Li, C.; Ling, T. Y.; McLean, K. W.; Murray, W. N.; Nylander, P.; Park, I. H.; Romanowski, T. A.; Seidlein, R.; Bailey, D. S.; Byrne, A.; Cashmore, R. J.; Cooper-Sarkar, A. M.; Devenish, R. C. E.; Harnew, N.; Lancaster, M.; Lindemann, L.; McFall, J. D.; Nath, C.; Noyes, V. A.; Quadt, A.; Tickner, J. R.; Uijterwaal, H.; Walczak, R.; Waters, D. S.; Wilson, F. F.; Yip, T.; Abbiendi, G.; Bertolin, A.; Brugnera, R.; Carlin, R.; Dal Corso, F.; De Giorgi, M.; Dosselli, U.; Limentani, S.; Morandin, M.; Posocco, M.; Stanco, L.; Stroili, R.; Voci, C.; Bulmahn, J.; Butterworth, J. M.; Feild, R. G.; Oh, B. Y.; Okrasinski, J. R.; Whitmore, J. J.; D'Agostini, G.; Marini, G.; Nigro, A.; Tassi, E.; Hart, J. C.; McCubbin, N. A.; Prytz, K.; Shah, T. P.; Short, T. L.; Barberis, E.; Dubbs, T.; Heusch, C.; Van Hook, M.; Lockman, W.; Rahn, J. T.; Sadrozinski, H. F.-W.; Seiden, A.; Williams, D. C.; Biltzinger, J.; Seifert, R. J.; Schwarzer, O.; Walenta, A. H.; Zech, G.; Abramowicz, H.; Briskin, G.; Dagan, S.; Händel-Pikielny, C.; Levy, A.; Fleck, J. I.; Hasegawa, T.; Hazumi, M.; Ishii, T.; Kuze, M.; Mine, S.; Nagasawa, Y.; Nakao, M.; Suzuki, I.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Chiba, M.; Hamatsu, R.; Hirose, T.; Homma, K.; Kitamura, S.; Nakamitsu, Y.; Yamauchi, K.; Cirio, R.; Costa, M.; Ferrero, M. I.; Lamberti, L.; Maselli, S.; Peroni, C.; Sacchi, R.; Solano, A.; Staiano, A.; Dardo, M.; Bailey, D. C.; Bandyopadhyay, D.; Benard, F.; Brkic, M.; Gingrich, D. M.; Hartner, G. F.; Joo, K. K.; Levman, G. M.; Martin, J. F.; Orr, R. S.; Polenz, S.; Sampson, C. R.; Teuscher, R. J.; Catterall, C. D.; Jones, T. W.; Kaziewicz, P. B.; Lane, J. B.; Saunders, R. L.; Shulman, J.; Blankenship, K.; Lu, B.; Mo, L. W.; Bogusz, W.; Charchuła, K.; Ciborowski, J.; Gajewski, J.; Grzelak, G.; Kasprzak, M.; Krzyżanowski, M.; Muchorowski, K.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Wróblewski, A. K.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Eisenberg, Y.; Karshon, U.; Revel, D.; Zer-Zion, D.; Ali, I.; Badgett, W. F.; Behrens, B.; Dasu, S.; Fordham, C.; Foudas, C.; Goussiou, A.; Loveless, R. J.; Reeder, D. D.; Silverstein, S.; Smith, W. H.; Vaiciulis, A.; Wodarczyk, M.; Tsurugai, T.; Bhadra, S.; Cardy, M. L.; Fagerstroem, C.-P.; Frisken, W. R.; Furutani, K. M.; Khakzad, M.; Schmidke, W. B.; ZEUS Collaboration

1995-02-01

Jet production in deep inelastic scattering for 120 < Q2 < 3600 GeV 2 has been studied using data from an integrated luminosity of 3.2 pb -1 collected with the ZEUS detector at HERA. Jets are identified with the JADE algorithm. A cut on the angular distribution of parton emission in the γ ∗- parton centre-of-mass system minimises the experimental and theoretical uncertainties in the determination of the jet rates. The jet rates, when compared to O( αs2) perturbative QCD calculations, allow a precise determination of αs( Q) in three Q2-intervals. The values are consistent with a running of ifαs( Q), as expected from QCD. Extrapolating to Q = M Z 0αs( MZ0) = 0.117 ± 0.005 (stat) -0.005+0.004 (syst exp) ± 0.007 (syst theory).

Shear flow control of cold and heated rectangular jets by mechanical tabs. Volume 2: Tabulated data

NASA Technical Reports Server (NTRS)

Brown, W. H.; Ahuja, K. K.

1989-01-01

The effects of mechanical protrusions on the jet mixing characteristics of rectangular nozzles for heated and unheated subsonic and supersonic jet plumes were studied. The characteristics of a rectangular nozzle of aspect ratio 4 without the mechanical protrusions were first investigated. Intrusive probes were used to make the flow measurements. Possible errors introduced by intrusive probes in making shear flow measurements were also examined. Several scaled sizes of mechanical tabs were then tested, configured around the perimeter of the rectangular jet. Both the number and the location of the tabs were varied. From this, the best configuration was selected. This volume contains tabulated data for each of the data runs cited in Volume 1. Baseline characteristics, mixing modifications (subsonic and supersonic, heated and unheated) and miscellaneous charts are included.

Experimental Study of an Inclined Jet-In-Cross-Flow Interacting with a Vortex Generator

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Rigby, D. L.; Heidmann, J. D.

2010-01-01

An experiment is conducted on the effectiveness of a vortex generator (VG) in preventing lift-off of a jet-in-cross-flow (JICF), with film-cooling application in mind. The jet issues into the boundary layer at an angle of 20 to the free-stream. The effect of a triangular ramp-shaped VG is studied while varying its geometry and location. Detailed flow-field properties are documented for a specific case in which the height of the VG and the diameter of the orifice are comparable to the approach boundary layer thickness. This combination of VG and JICF produce a streamwise vortex pair with vorticity magnitude three times larger (and of opposite sense) than that found in the JICF alone. Such a VG appears to be most effective in keeping the jet attached to the wall. While most of the data are taken at a jet-to-freestream momentum flux ratio (J) of 2, limited surveys are done for varying J. The VG is found to have a significant effect even at the highest J (=11) covered in the experiment. Effect of parametric variation is studied mostly from surveys ten diameters downstream from the orifice. When the VG height is halved there is a lift-off of the jet. On the other hand, when the height is doubled, the jet core is dissipated due to larger turbulence intensities. Varying the location of the VG, over a distance of three diameters from the orifice, is found to have little impact. Rounding off the edges of the VG with increasing radius of curvature progressively diminishes the effect. However, a small radius of curvature may be quite tolerable in practice.

Multiple jet study

NASA Technical Reports Server (NTRS)

Walker, R. E.; Kors, D. L.

1973-01-01

Test data is presented which allows determination of jet penetration and mixing of multiple cold air jets into a ducted subsonic heated mainstream flow. Jet-to-mainstream momentum flux ratios ranged from 6 to 60. Temperature profile data is presented at various duct locations up to 24 orifice diameters downstream of the plane of jet injection. Except for two configurations, all geometries investigated had a single row of constant diameter orifices located transverse to the main flow direction. Orifice size and spacing between orifices were varied. Both of these were found to have a significant effect on jet penetration and mixing. The best mixing of the hot and cold streams was achieved with duct height.

Experimental and numerical investigation of liquid jet impingement on superhydrophobic and hydrophobic convex surfaces

NASA Astrophysics Data System (ADS)

Kibar, Ali

2017-02-01

Experiments and numerical simulations were carried out to examine the vertical impingement a round liquid jet on the edges of horizontal convex surfaces that were either superhydrophobic or hydrophobic. The experiments examine the effects on the flow behaviour of curvature, wettability, inertia of the jet, and the impingement rate. Three copper pipes with outer diameters of 15, 22, and 35 mm were investigated. The pipes were wrapped with a piece of a Brassica oleracea leaf or a smooth Teflon sheet, which have apparent contact angles of 160° and 113°. The Reynolds number ranged from 1000 to 4500, and the impingement rates of the liquid jets were varied. Numerical results show good agreement with the experimental results for explaining flow and provide detailed information about the impingement on the surfaces. The liquid jet reflected off the superhydrophobic surfaces for all conditions. However, the jet reflected or deflected off the hydrophobic surface, depending on the inertia of the jet, the curvature of the surface, and the impingement rate. The results suggest that pressure is not the main reason for the bending of the jet around the curved hydrophobic surface.

Turbulent two-dimensional jet flow and its effect on laser beam degradation

NASA Technical Reports Server (NTRS)

Catalano, G. D.; Cudahy, G. F.; Vankuren, J. T.; Wright, H. E.

1980-01-01

An experiment in which visible wavelength lasers traversed a well-documented two dimensional jet was conducted. Temperature perturbations varied from 0.25 to 1.80 K and velocity fluctuations ranged from 9.2 to 30.8 m/sec. Measured central spot intensities were as low as 18% of the undisturbed beam, depending on jet Mach number, beam position theory and experiment was two percent in terms of far field intensity. To supplement the flow field information, a laser Doppler velocimeter was developed to measure both mean and fluctuating velocities and a photo correlator was used as a signal processor.

Jet-mixing of initially-stratified liquid-liquid pipe flows: experiments and numerical simulations

NASA Astrophysics Data System (ADS)

Wright, Stuart; Ibarra-Hernandes, Roberto; Xie, Zhihua; Markides, Christos; Matar, Omar

2016-11-01

Low pipeline velocities lead to stratification and so-called 'phase slip' in horizontal liquid-liquid flows due to differences in liquid densities and viscosities. Stratified flows have no suitable single point for sampling, from which average phase properties (e.g. fractions) can be established. Inline mixing, achieved by static mixers or jets in cross-flow (JICF), is often used to overcome liquid-liquid stratification by establishing unstable two-phase dispersions for sampling. Achieving dispersions in liquid-liquid pipeline flows using JICF is the subject of this experimental and modelling work. The experimental facility involves a matched refractive index liquid-liquid-solid system, featuring an ETFE test section, and experimental liquids which are silicone oil and a 51-wt% glycerol solution. The matching then allows the dispersed fluid phase fractions and velocity fields to be established through advanced optical techniques, namely PLIF (for phase) and PTV or PIV (for velocity fields). CFD codes using the volume of a fluid (VOF) method are then used to demonstrate JICF breakup and dispersion in stratified pipeline flows. A number of simple jet configurations are described and their dispersion effectiveness is compared with the experimental results. Funding from Cameron for Ph.D. studentship (SW) gratefully acknowledged.

Effect of reaction control system jet-flow field interactions on a 0.015 scale model space shuttle orbiter aerodynamic characteristics

NASA Technical Reports Server (NTRS)

Monta, W. J.; Rausch, J. R.

1973-01-01

The effects of the reaction control system (RCS) jet-flow field interactions on the space shuttle orbiter system during entry are discussed. The primary objective of the test program was to obtain data for the shuttle orbiter configuration to determine control amplification factors resulting from jet interaction between the RCS plumes and the external flow over the vehicle. A secondary objective was to provide data for comparison and improvement of analytic jet interaction prediction techniques. The test program was divided into two phases; (1) force and moment measurements were made with and without RCS blowing, investigating environment parameters (R sub e, Alpha, Beta), RCS plume parameters (Jet pressure ratio, momentum ratio and thrust level), and geometry parameters (RCS pod locations) on the orbiter model, (2) oil flow visualization tests were conducted on a dummy balance at the end of the test.

Launching of Active Galactic Nuclei Jets

NASA Astrophysics Data System (ADS)

Tchekhovskoy, Alexander

As black holes accrete gas, they often produce relativistic, collimated outflows, or jets. Jets are expected to form in the vicinity of a black hole, making them powerful probes of strong-field gravity. However, how jet properties (e.g., jet power) connect to those of the accretion flow (e.g., mass accretion rate) and the black hole (e.g., black hole spin) remains an area of active research. This is because what determines a crucial parameter that controls jet properties—the strength of large-scale magnetic flux threading the black hole—remains largely unknown. First-principles computer simulations show that due to this, even if black hole spin and mass accretion rate are held constant, the simulated jet powers span a wide range, with no clear winner. This limits our ability to use jets as a quantitative diagnostic tool of accreting black holes. Recent advances in computer simulations demonstrated that accretion disks can accumulate large-scale magnetic flux on the black hole, until the magnetic flux becomes so strong that it obstructs gas infall and leads to a magnetically-arrested disk (MAD). Recent evidence suggests that central black holes in jetted active galactic nuclei and tidal disruptions are surrounded by MADs. Since in MADs both the black hole magnetic flux and the jet power are at their maximum, well-defined values, this opens up a new vista in the measurements of black hole masses and spins and quantitative tests of accretion and jet theory.

Enthalpy Distributions of Arc Jet Flow Based on Measured Laser Induced Fluorescence, Heat Flux and Stagnation Pressure Distributions

NASA Technical Reports Server (NTRS)

Suess, Leonard E.; Milhoan, James D.; Oelke, Lance; Godfrey, Dennis; Larin, Maksim Y.; Scott, Carl D.; Grinstead, Jay H.; DelPapa, Steven

2011-01-01

The centerline total enthalpy of arc jet flow is determined using laser induced fluorescence of oxygen and nitrogen atoms. Each component of the energy, kinetic, thermal, and chemical can be determined from LIF measurements. Additionally, enthalpy distributions are inferred from heat flux and pressure probe distribution measurements using an engineering formula. Average enthalpies are determined by integration over the radius of the jet flow, assuming constant mass flux and a mass flux distribution estimated from computational fluid dynamics calculations at similar arc jet conditions. The trends show favorable agreement, but there is an uncertainty that relates to the multiple individual measurements and assumptions inherent in LIF measurements.

The effects of profiles on supersonic jet noise

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Bhat, T. R. S.

1994-01-01

The effect of velocity profiles on supersonic jet noise are studied by using stability calculations made for a shock-free coannular jet, with both the inner and outer flows supersonic. The Mach wave emission process is modeled as the noise generated by the large scale turbulent structures or the instability waves in the mixing region. Both the vortex-sheet and the realistic finite thickness shear layer models are considered. The stability calculations were performed for both inverted and normal velocity profiles. Comparisons are made with the results for an equivalent single jet, based on equal thrust, mass flow rate and exit area to that of the coannular jet. The advantages and disadvantages of these velocity profiles as far as noise radiation is concerned are discussed. It is shown that the Rayleigh's model prediction of the merits and demerits of different velocity profiles are in good agreement with the experimental data.

Acoustic measurement of the Deepwater Horizon Macondo well flow rate

PubMed Central

Camilli, Richard; Di Iorio, Daniela; Bowen, Andrew; Reddy, Christopher M.; Techet, Alexandra H.; Yoerger, Dana R.; Whitcomb, Louis L.; Seewald, Jeffrey S.; Sylva, Sean P.; Fenwick, Judith

2012-01-01

On May 31, 2010, a direct acoustic measurement method was used to quantify fluid leakage rate from the Deepwater Horizon Macondo well prior to removal of its broken riser. This method utilized an acoustic imaging sonar and acoustic Doppler sonar operating onboard a remotely operated vehicle for noncontact measurement of flow cross-section and velocity from the well’s two leak sites. Over 2,500 sonar cross-sections and over 85,000 Doppler velocity measurements were recorded during the acquisition process. These data were then applied to turbulent jet and plume flow models to account for entrained water and calculate a combined hydrocarbon flow rate from the two leak sites at seafloor conditions. Based on the chemical composition of end-member samples collected from within the well, this bulk volumetric rate was then normalized to account for contributions from gases and condensates at initial leak source conditions. Results from this investigation indicate that on May 31, 2010, the well’s oil flow rate was approximately 0.10 ± 0.017 m3 s-1 at seafloor conditions, or approximately 85 ± 15 kg s-1 (7.4 ± 1.3 Gg d-1), equivalent to approximately 57,000 ± 9,800 barrels of oil per day at surface conditions. End-member chemical composition indicates that this oil release rate was accompanied by approximately an additional 24 ± 4.2 kg s-1 (2.1 ± 0.37 Gg d-1) of natural gas (methane through pentanes), yielding a total hydrocarbon release rate of 110 ± 19 kg s-1 (9.5 ± 1.6 Gg d-1). PMID:21903931

Investigation of turbulent swirling jet-flames by PIV / OH PLIF / HCHO PLIF

NASA Astrophysics Data System (ADS)

Lobasov, A. S.; Chikishev, L. M.

2018-03-01

The present paper reports on the investigation of fuel-lean and fuel-rich turbulent combustion in a high-swirl jet. Swirl rate of the flow exceeded a critical value for breakdown of the swirling jet’s vortex core and formation of the recirculation zone at the jet axis. The measurements were performed by the stereo PIV, OH PLIF and HCHO PLIF techniques, simultaneously. The Reynolds number based on the flow rate and viscosity of the air was fixed as 5 000 (the bulk velocity was U 0 = 5 m/s). Three cases of the equivalence ratio ϕ of the mixture issuing from the nozzle-burner were considered, viz., 0.7, 1.4 and 2.5. The latter case corresponded to a lifted flame of fuel-rich swirling jet flow, partially premixed with the surrounding air. In all cases the flame front was subjected to deformations due to large-scale vortices, which rolled-up in the inner (around the central recirculation zone) and outer (between the annular jet core and surrounding air) mixing layers.

Flow Separation Control on A Full-Scale Vertical Tail Model Using Sweeping Jet Actuators

NASA Technical Reports Server (NTRS)

Andino, Marlyn Y.; Lin, John C.; Washburn, Anthony E.; Whalen, Edward A.; Graff, Emilio C.; Wygnanski, Israel J.

2015-01-01

This paper describes test results of a joint NASA/Boeing research effort to advance Active Flow Control (AFC) technology to enhance aerodynamic efficiency. A full-scale Boeing 757 vertical tail model equipped with sweeping jets AFC was tested at the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel at NASA Ames Research Center. The flow separation control optimization was performed at 100 knots, a maximum rudder deflection of 30deg, and sideslip angles of 0deg and -7.5deg. Greater than 20% increments in side force were achieved at the two sideslip angles with a 31-actuator AFC configuration. Flow physics and flow separation control associated with the AFC are presented in detail. AFC caused significant increases in suction pressure on the actuator side and associated side force enhancement. The momentum coefficient (C sub mu) is shown to be a useful parameter to use for scaling-up sweeping jet AFC from sub-scale tests to full-scale applications. Reducing the number of actuators at a constant total C(sub mu) of approximately 0.5% and tripling the actuator spacing did not significantly affect the flow separation control effectiveness.

Analysis of screeching in a cold flow jet experiment

NASA Technical Reports Server (NTRS)

Wang, M. E.; Slone, R. M., Jr.; Robertson, J. E.; Keefe, L.

1975-01-01

The screech phenomenon observed in a one-sixtieth scale model space shuttle test of the solid rocket booster exhaust flow noise has been investigated. A critical review is given of the cold flow test data representative of Space Shuttle launch configurations to define those parameters which contribute to screech generation. An acoustic feedback mechanism is found to be responsible for the generation of screech. A simple equation which permits prediction of screech frequency in terms of basic testing parameters such as the jet exhaust Mach number and the separating distance from nozzle exit to the surface of model launch pad is presented and is found in good agreement with the test data. Finally, techniques are recommended to eliminate or reduce the screech.

CFD Simulations of the IHF Arc-Jet Flow: Compression-Pad/Separation Bolt Wedge Tests

NASA Technical Reports Server (NTRS)

Gokcen, Tahir; Skokova, Kristina A.

2017-01-01

This paper reports computational analyses in support of two wedge tests in a high enthalpy arc-jet facility at NASA Ames Research Center. These tests were conducted using two different wedge models, each placed in a free jet downstream of a corresponding different conical nozzle in the Ames 60-MW Interaction Heating Facility. Panel test articles included a metallic separation bolt imbedded in the compression-pad and heat shield materials, resulting in a circular protuberance over a flat plate. As part of the test calibration runs, surface pressure and heat flux measurements on water-cooled calibration plates integrated with the wedge models were also obtained. Surface heating distributions on the test articles as well as arc-jet test environment parameters for each test configuration are obtained through computational fluid dynamics simulations, consistent with the facility and calibration measurements. The present analysis comprises simulations of the non-equilibrium flow field in the facility nozzle, test box, and flow field over test articles, and comparisons with the measured calibration data.

Episodic Jet Power Extracted from a Spinning Black Hole Surrounded by a Neutrino-dominated Accretion Flow in Gamma-Ray Bursts

NASA Astrophysics Data System (ADS)

Cao, Xinwu; Liang, En-Wei; Yuan, Ye-Fei

2014-07-01

It was suggested that the relativistic jets in gamma-ray bursts (GRBs) are powered via the Blandford-Znajek (BZ) mechanism or the annihilation of neutrinos and anti-neutrinos from a neutrino cooling-dominated accretion flow (NDAF). The advection and diffusion of the large-scale magnetic field of an NDAF is calculated, and the external magnetic field is found to be dragged inward efficiently by the accretion flow for a typical magnetic Prandtl number \\mathscr{P}_m=η /ν ˜ 1. The maximal BZ jet power can be ~1053-1054 erg s-1 for an extreme Kerr black hole, if an external magnetic field with 1014 Gauss is advected by the NDAF. This is roughly consistent with the field strength of the disk formed after a tidal disrupted magnetar. The accretion flow near the black hole horizon is arrested by the magnetic field if the accretion rate is below than a critical value for a given external field. The arrested accretion flow fails to drag the field inward and the field strength decays, and then the accretion re-starts, which leads to oscillating accretion. The typical timescale of such episodic accretion is of an order of one second. This can qualitatively explain the observed oscillation in the soft extended emission of short-type GRBs.

Analytical and experimental investigation of flow fields of annular jets with and without swirling flow

NASA Technical Reports Server (NTRS)

Simonson, M. R.; Smith, E. G.; Uhl, W. R.

1974-01-01

Analytical and experimental studies were performed to define the flowfield of annular jets, with and, without swirling flow. The analytical model treated configurations with variations of flow angularities, radius ratio, and swirl distributions. Swirl distributions characteristic of stator vanes and rotor blade rows, where the total pressure and swirl distributions are related were incorporated in the mathematical model. The experimental studies included tests of eleven nozzle models, both with and, without swirling exhaust flow. Flowfield surveys were obtained and used for comparison with the analytical model. This comparison of experimental and analytical studies served as the basis for evaluation of several empirical constants as required for application of the analysis to the general flow configuration. The analytical model developed during these studies is applicable to the evaluation of the flowfield and overall performance of the exhaust of statorless lift fan systems that contain various levels of exhaust swirl.

Long Penetration Mode Counterflowing Jets for Supersonic Slender Configurations - A Numerical Study

NASA Technical Reports Server (NTRS)

Venkatachari, Balaji Shankar; Cheng, Gary; Chang, Chau-Layn; Zichettello, Benjamin; Bilyeu, David L.

2013-01-01

A novel approach of using counterflowing jets positioned strategically on the aircraft and exploiting its long penetration mode (LPM) of interaction towards sonic-boom mitigation forms the motivation for this study. Given that most previous studies on the counterflowing LPM jet have all been on blunt bodies and at high supersonic or hypersonic flow conditions, exploring the feasibility to obtain a LPM jet issuing from a slender body against low supersonic freestream conditions is the main focus of this study. Computational fluid dynamics computations of axisymmetric models (cone-cylinder and quartic geometry), of relevance to NASA's High Speed project, are carried out using the space-time conservation element solution element viscous flow solver with unstructured meshes. A systematic parametric study is conducted to determine the optimum combination of counterflowing jet size, mass flow rate, and nozzle geometry for obtaining LPM jets. Details from these computations will be used to assess the potential of the LPM counterflowing supersonic jet as a means of active flow control for enabling supersonic flight over land and to establish the knowledge base for possible future implementation of such technologies.

Reversing cooling flows with AGN jets: shock waves, rarefaction waves and trailing outflows

NASA Astrophysics Data System (ADS)

Guo, Fulai; Duan, Xiaodong; Yuan, Ye-Fei

2018-01-01

The cooling flow problem is one of the central problems in galaxy clusters, and active galactic nucleus (AGN) feedback is considered to play a key role in offsetting cooling. However, how AGN jets heat and suppress cooling flows remains highly debated. Using an idealized simulation of a cool-core cluster, we study the development of central cooling catastrophe and how a subsequent powerful AGN jet event averts cooling flows, with a focus on complex gasdynamical processes involved. We find that the jet drives a bow shock, which reverses cooling inflows and overheats inner cool-core regions. The shocked gas moves outward in a rarefaction wave, which rarefies the dense core and adiabatically transports a significant fraction of heated energy to outer regions. As the rarefaction wave propagates away, inflows resume in the cluster core, but a trailing outflow is uplifted by the AGN bubble, preventing gas accumulation and catastrophic cooling in central regions. Inflows and trailing outflows constitute meridional circulations in the cluster core. At later times, trailing outflows fall back to the cluster centre, triggering central cooling catastrophe and potentially a new generation of AGN feedback. We thus envisage a picture of cool cluster cores going through cycles of cooling-induced contraction and AGN-induced expansion. This picture naturally predicts an anti-correlation between the gas fraction (or X-ray luminosity) of cool cores and the central gas entropy, which may be tested by X-ray observations.

Simultaneous velocity measurements of particle and gas phase in particle-laden co-flowing pipe jets

NASA Astrophysics Data System (ADS)

Saridakis, Isaac; Lau, Timothy; Djenidi, Lyazid; Nathan, Graham

2016-11-01

Simultaneous planar velocity measurements of both the carrier gas and particles are reported of well-characterized particle-laden co-flowing pipe jets. It is proposed to present measurements that were obtained through application of a median-filter discrimination technique to separate the Particle Image Velocimetry (PIV) signals of the 0.5 μm diameter fluid tracers from those of the larger particles of diameter 20 μm and 40 μm. Instantaneous particle and fluid planar velocity distributions were measured for three Reynold's numbers ranging from 10,000 to 40,000 and five Stokes numbers from 1 to 22, at a jet bulk fluid velocity to co-flow velocity ratio of 12. Selected results will be presented which show that the slip velocity is dependent on the local Stokes number. These are the first simultaneous carrier gas and particle velocity measurements in particle-laden jets and provide new understanding of fluid-particle interactions. Financial support from Australian Research Council and Australian Renewable Energy Agency.

Experimental investigation of supersonic low pressure air plasma flows obtained with different arc-jet operating conditions

NASA Astrophysics Data System (ADS)

Lago, Viviana; Ndiaye, Abdoul-Aziz

2012-11-01

A stationary arc-jet plasma flow at low pressure is used to simulate some properties of the gas flow surrounding a vehicle during its entry into celestial body's atmospheres. This paper presents an experimental study concerning plasmas simulating a re-entry into our planet. Optical measurements have been carried out for several operating plasma conditions in the free stream, and in the shock layer formed in front of a flat cylindrical plate, placed in the plasma jet. The analysis of the spectral radiation enabled the identification of the emitting species, the determination of the rotational and vibrational temperatures in the free-stream and in the shock layer and the determination of the distance of the shock to the flat plate face. Some plasma fluid parameters like, stagnation pressure, specific enthalpy and heat flux have been determined experimentally along the plasma-jet axis.

An experimental investigation of delta wing vortex flow with and without external jet blowing

NASA Technical Reports Server (NTRS)

Iwanski, Kenneth P.; Ng, T. Terry; Nelson, Robert C.

1989-01-01

A visual and quantitative study of the vortex flow field over a 70-deg delta wing with an external jet blowing parallel to and at the leading edge was conducted. In the experiment, the vortex core was visually marked with TiCl4, and LDA was used to measure the velocity parallel and normal to the wing surface. It is found that jet blowing moved vortex breakdown farther downstream from its natural position and influenced the breakdown characteristics.

Advanced high performance horizontal piezoelectric hybrid synthetic jet actuator

NASA Technical Reports Server (NTRS)

Xu, Tian-Bing (Inventor); Jiang, Xiaoning (Inventor); Su, Ji (Inventor)

2012-01-01

The present invention comprises a high performance, horizontal, zero-net mass-flux, synthetic jet actuator for active control of viscous, separated flow on subsonic and supersonic vehicles. The present invention is a horizontal piezoelectric hybrid zero-net mass-flux actuator, in which all the walls of the chamber are electrically controlled synergistically to reduce or enlarge the volume of the synthetic jet actuator chamber in three dimensions simultaneously and to reduce or enlarge the diameter of orifice of the synthetic jet actuator simultaneously with the reduction or enlargement of the volume of the chamber. The present invention is capable of installation in the wing surface as well as embedding in the wetted surfaces of a supersonic inlet. The jet velocity and mass flow rate for the SJA-H will be several times higher than conventional piezoelectric actuators.

Distance effect on the behavior of an impinging swirling jet by PIV and flow visualizations

NASA Astrophysics Data System (ADS)

Felli, Mario; Falchi, Massimo; Pereira, Francisco Josè Alves

2010-02-01

The present paper deals with the problem of an impinging swirling jet against a wall. The study concerned a detailed experimental investigation on the jet-wall interaction using PIV and flow visualizations over a range of operating conditions in which the distance of the ducted propeller from the wall was changed. The influence of the impingement distance and the swirl number (i.e., ratio between the axial fluxes of the swirl and the axial momentum) as well as the interaction between the jet deformation and the perturbation induced on the wall is discussed in this paper.

Large amplitude forcing of a high speed 2-dimensional jet

NASA Technical Reports Server (NTRS)

Bernal, L.; Sarohia, V.

1984-01-01

The effect of large amplitude forcing on the growth of a high speed two dimensional jet was investigated experimentally. Two forcing techniques were utilized: mass flow oscillations and a mechanical system. The mass flow oscillation tests were conducted at Strouhal numbers from 0.00052 to 0.045, and peak to peak amplitudes up to 50 percent of the mean exit velocity. The exit Mach number was varied in the range 0.15 to 0.8. The corresponding Reynolds numbers were 8,400 and 45,000. The results indicate no significant change of the jet growth rate or centerline velocity decay compared to the undisturbed free jet. The mechanical forcing system consists of two counter rotating hexagonal cylinders located parallel to the span of the nozzle. Forcing frequencies up to 1,500 Hz were tested. Both symmetric and antisymmetric forcing can be implemented. The results for antisymmetric forcing showed a significant (75 percent) increase of the jet growth rate at an exit Mach number of 0.25 and a Strouhal number of 0.019. At higher rotational speeds, the jet deflected laterally. A deflection angle of 39 deg with respect to the centerline was measured at the maximum rotational speed.

Implications of Upwells as Hydrodynamic Jets in a Pulse Jet Mixed System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pease, Leonard F.; Bamberger, Judith A.; Minette, Michael J.

This report evaluates the physics of the upwell flow in pulse jet mixed systems in the Hanford Tank Waste Treatment and Immobilization Plant (WTP). Although the initial downward flow and radial flow from jets characteristic of pulse jet mixers (PJMs) has been analyzed, the upwells have received considerably less attention despite having significant implications for vessel mixing. Do the upwells behave like jets? How do the upwells scale? When will the central upwell break through? What proportion of the vessel is blended by the upwells themselves? Indeed, how the physics of the central upwell is affected by multiple PJMs (e.g.,more » six in the proposed mixing vessels), non-Newtonian rheology, and significant multicomponent solids loadings remain unexplored.« less

Entrainment of Air into Vertical Jets in a Crosswind

NASA Astrophysics Data System (ADS)

Roberts, K. K.; Solovitz, S.; Freedland, G.; Camp, E.; Cal, R. B.; Mastin, L. G.

2015-12-01

During volcanic eruptions, ash concentration must be determined for aviation safety, but the limiting threshold is difficult to distinguish visually. Computational models are typically used to predict ash concentrations, using inputs such as plume height, eruptive duration, and wind speeds. The models also depend on empirical parameters, such as the entrainment of atmospheric air as a ratio of the air inflow speed and the jet speed. Entrainment of atmospheric air plays a critical role in the behavior of volcanic plumes in the atmosphere, impacting the mass flow rate, buoyancy, and particle concentration of the plume. This process is more complex in a crosswind, leading to greater uncertainty in the model results. To address these issues, a laboratory-scale study has been conducted to improve the entrainment models. Observations of a vertical, unconfined jet are performed using Particle Image Velocimetry, while varying jet density using different compressed gases and Reynolds number. To test the effects of a crosswind on plume entrainment rates, these are then compared with similar jet experiments in a wind tunnel. A series of jet geometries, jet speeds and tunnel speeds are considered. The measured velocities are used to determine the entrainment response, which can be used to determine ash concentration over time as atmospheric air is entrained into the plume. We also quantify the mean and the fluctuations in flow velocity.

Mixing Enhancement by Tabs in Round Supersonic Jets

NASA Technical Reports Server (NTRS)

Seiner, John M.; Grosch, C. E.

1998-01-01

The objective of this study was to analyze jet plume mass flow entrainment rates associated with the introduction of counter-rotating streamwise vorticity by prism shaped devices (tabs) located at the lip of the nozzle. We have examined the resulting mixing process through coordinated experimental tests and numerical simulations of the supersonic flow from a model axisymmetric nozzle. In the numerical simulations, the total induced vorticity was held constant while varying the distribution of counter-rotating vorticity around the nozzle lip training edge. In the experiment, the number of tabs applied was varied while holding the total projected area constant. Evaluations were also conducted on initial vortex strength. The results of this work show that the initial growth rate of the jet shear layer is increasingly enhanced as more tabs are added, but that the lowest tab count results in the largest entrained mass flow. The numerical simulations confirm these results.

Combustion rate limits of hydrogen plus hydrocarbon fuel: Air diffusion flames from an opposed jet burner technique

NASA Technical Reports Server (NTRS)

Pellett, Gerald L.; Guerra, Rosemary; Wilson, Lloyd G.; Reeves, Ronald N.; Northam, G. Burton

1987-01-01

Combustion of H2/hydrocarbon (HC) fuel mixtures may be considered in certain volume-limited supersonic airbreathing propulsion applications. Effects of HC addition to H2 were evaluated, using a recent argon-bathed, coaxial, tubular opposed jet burner (OJB) technique to measure the extinction limits of counterflow diffusion flames. The OJB flames were formed by a laminar jet of (N2 and/or HC)-diluted H2 mixture opposed by a similar jet of air at ambient conditions. The OJB data, derived from respective binary mixtures of H2 and methane, ethylene, or propane HCs, were used to characterize BLOWOFF and RESTORE. BLOWOFF is a sudden breaking of the dish-shaped OJB flame to a stable torus or ring shape, and RESTORE marks sudden restoration of the central flame by radial inward flame propagation. BLOWOFF is a measure of kinetically-limited flame reactivity/speed under highly stretched, but relatively ideal impingement flow conditions. RESTORE measures inward radial flame propagation rate, which is sensitive to ignition processes in the cool central core. It is concluded that relatively small molar amounts of added HC greatly reduce the reactivity characteristics of counterflow hydrogen-air diffusion flames, for ambient initial conditions.

Nonlinear dynamics of coiling, and mounding in viscoelastic jets

NASA Astrophysics Data System (ADS)

Majmudar, Trushant; Ober, Thomas; McKinley, Gareth

2009-11-01

Free surface continuous jets of non-Newtonian fluids, although relevant for many industrial processes like bottle filling, remain poorly understood in terms of fundamental fluid dynamics. Here we present a systematic study of the effect of viscoelasticity on the dynamics of continuous jets of worm-like micellar surfactant solutions of varying viscosities and elasticities, and model yield-stress fluids. We systematically vary the height of the drop and the flow rate in order to study the effects of varying geometric and kinematic parameters. We observe that for fluids with higher elastic relaxation times, folding is the preferred mode. In contrast, for low elasticity fluids we observe complex nonlinear dynamics consisting of coiling, folding, and irregular meandering as the height of the fall increases. Beyond this regime, the jet dynamics smoothly crosses over to exhibit the ``leaping shampoo" or the Kaye effect. Upon increasing the flow rate to very high values, the ``leaping shampoo" state disappears and is replaced by a pronounced mounding or ``heaping". A subsequent increase in the flow rate results in finger-like protrusions to emerge out of the mound and climb up towards the nozzle. This novel transition is currently under investigation and remains a theoretical challenge.

Unsteady Flow Simulation of a Sweeping Jet Actuator Using a Lattice-Boltzmann Method

NASA Technical Reports Server (NTRS)

Duda, B.; Wessels, M.; Fares, E.; Vatsa, V.

2016-01-01

Active flow control technology is increasingly used in aerospace applications to control flow separation and to improve aerodynamic performance. In this paper, PowerFLOW is used to simulate the flow through a sweeping jet actuator at two different pressure ratios. The lower pressure ratio leads to a high subsonic flow, whereas the high pressure ratio produces a choked flow condition. Comparison of numerical results with experimental data is shown, which includes qualitatively good agreement of pressure histories and spectra. PIV measurements are also available but the simulation overestimates mean and fluctuation quantities outside the actuator. If supply pressure is matched at one point inside the mixing chamber a good qualitative agreement is achieved at all other monitor points.

Effects of core turbulence on jet excitability

NASA Technical Reports Server (NTRS)

Mankbadi, Reda R.; Raman, Ganesh; Rice, Edward J.

1989-01-01

The effects of varying freestream core turbulence on the evolution of a circular jet with and without tonal excitation are examined. Measurements are made on an 8.8 cm diameter jet at a Mach number of 0.3. The jet is excitated by plane waves at Strouhal number 0.5. For the excited and unexcited cases the turbulence level is varied by screens and grids placed upstream of the nozzle exit. The experiment results are compared with a theoretical model which incorporates a variable core turbulence and considers the energy interactions between the mean flow, the turbulence and the forced component. Both data and theory indicate that increasing the freestream turbulence diminishes the excitability of the jet and reduces the effect of excitation on the spreading rate of the jet.

Prospects for Nonlinear Laser Diagnostics in the Jet Noise Laboratory

NASA Technical Reports Server (NTRS)

Herring, Gregory C.; Hart, Roger C.; Fletcher, mark T.; Balla, R. Jeffrey; Henderson, Brenda S.

2007-01-01

Two experiments were conducted to test whether optical methods, which rely on laser beam coherence, would be viable for off-body flow measurement in high-density, compressible-flow wind tunnels. These tests measured the effects of large, unsteady density gradients on laser diagnostics like laser-induced thermal acoustics (LITA). The first test was performed in the Low Speed Aeroacoustics Wind Tunnel (LSAWT) of NASA Langley Research Center's Jet Noise Laboratory (JNL). This flow facility consists of a dual-stream jet engine simulator (with electric heat and propane burners) exhausting into a simulated flight stream, reaching Mach numbers up to 0.32. A laser beam transited the LSAWT flow field and was imaged with a high-speed gated camera to measure beam steering and transverse mode distortion. A second, independent test was performed on a smaller laboratory jet (Mach number < 1.2 and mass flow rate < 0.1 kg/sec). In this test, time-averaged LITA velocimetry and thermometry were performed at the jet exit plane, where the effect of unsteady density gradients is observed on the LITA signal. Both experiments show that LITA (and other diagnostics relying on beam overlap or coherence) faces significant hurdles in the high-density, compressible, and turbulent flow environments similar to those of the JNL.

Rapid Confined Mixing with Transverse Jets Part 1: Single Jet

NASA Astrophysics Data System (ADS)

Salazar, David; Forliti, David

2012-11-01

Transverse jets have been studied extensively due to their relevance and efficiency in fluid mixing applications. Gas turbine burners, film cooling, and chemical reactors are some examples of rapid transverse jet mixing. Motivated by a lack of universal scaling laws for confined and unconfined transverse jets, a newly developed momentum transfer parameter was found to improve correlation of literature data. Jet column drag and entrainment arguments for momentum transfer are made to derive the parameter. A liquid-phase mixing study was conducted to investigate confined mixing for a low number of jets. Planar laser induced fluorescence was implemented to measure mixture fraction for a single confined transverse jet. Time-averaged cross-sectional images were taken with a light sheet located three diameters downstream of transverse injection. A mixture of water and sodium fluorescein was used to distinguish jet fluid from main flow fluid for the test section images. Image data suggest regimes for under- and overpenetration of jet fluid into the main flow. The scaling parameter is found to correlate optimum unmixedness for multiple diameter ratios at a parameter value of 0.75. Distribution A: Public Release, Public Affairs Clearance Number: 12655.

Effects of confinement, geometry, inlet velocity profile, and Reynolds number on the asymmetry of opposed-jet flows

NASA Astrophysics Data System (ADS)

Ansari, Abtin; Chen, Kevin K.; Burrell, Robert R.; Egolfopoulos, Fokion N.

2018-04-01

The opposed-jet counterflow configuration is widely used to measure fundamental flame properties that are essential targets for validating chemical kinetic models. The main and key assumption of the counterflow configuration in laminar flame experiments is that the flow field is steady and quasi-one-dimensional. In this study, experiments and numerical simulations were carried out to investigate the behavior and controlling parameters of counterflowing isothermal air jets for various nozzle designs, Reynolds numbers, and surrounding geometries. The flow field in the jets' impingement region was analyzed in search of instabilities, asymmetries, and two-dimensional effects that can introduce errors when the data are compared with results of quasi-one-dimensional simulations. The modeling involved transient axisymmetric numerical simulations along with bifurcation analysis, which revealed that when the flow field is confined between walls, local bifurcation occurs, which in turn results in asymmetry, deviation from the one-dimensional assumption, and sensitivity of the flow field structure to boundary conditions and surrounding geometry. Particle image velocimetry was utilized and results revealed that for jets of equal momenta at low Reynolds numbers of the order of 300, the flow field is asymmetric with respect to the middle plane between the nozzles even in the absence of confining walls. The asymmetry was traced to the asymmetric nozzle exit velocity profiles caused by unavoidable imperfections in the nozzle assembly. The asymmetry was not detectable at high Reynolds numbers of the order of 1000 due to the reduced sensitivity of the flow field to boundary conditions. The cases investigated computationally covered a wide range of Reynolds numbers to identify designs that are minimally affected by errors in the experimental procedures or manufacturing imperfections, and the simulations results were used to identify conditions that best conform to the assumptions of

Increasing jet entrainment, mixing and spreading

DOEpatents

Farrington, Robert B.

1994-01-01

A free jet of air is disturbed at a frequency that substantially matches natural turbulences in the free jet to increase the entrainment, mixing, and spreading of air by the free jet, for example in a room or other enclosure. The disturbances are created by pulsing the flow of air that creates the free jet at the desired frequency. Such pulsing of the flow of air can be accomplished by sequentially occluding and opening a duct that confines and directs the flow of air, such as by rotating a disk on an axis transverse to the flow of air in the duct.

Transient gas jets into liquids

NASA Astrophysics Data System (ADS)

Lin, Jane Ming-Chin

An experimental investigation of the development of high velocity, impulsively initiated gas jets into liquid was conducted in an effort to understand some of the physical processes that occur for a jet of very light fluid into a dense ambient atmosphere. Four gases, refrigerants 12 and 22, nitrogen, and helium were injected into water at nozzle exit Mach numbers from 1.0 to 2.2.The study showed that a gas jet into water develops in at least three stages: startup, transition, and global steady state. The startup is characterized by bubble growth; the growth rate is well predicted by classical bubble-growth theory. Jet transition is marked by axially directed flow, which penetrates through the startup bubble and which forms a cylindrical protrusion along the axis of symmetry. A combination of strong recirculating flow and liquid entrainment causes the startup bubble to deflate and to lift off and move downstream. In the steady state, instantaneous photographs show small-scale fluctuations of the jet boundary, but time-averaged photographs show the expected conical spreading of the steady jet; the measured spreading angles range from 18-25 degrees.However, the most significant finding of this study is that under some conditions, the gas jet into liquid never reaches the global steady state. Instead, the jet boundary exhibits chugging: large nonlinear oscillations which lead to irregular collapses of the gas column followed by explosive outward bursts of gas. The unsteadiness observed is much more violent than the familiar fluctuations typical of constant-density jets. The length scale of the motion is generally on the order of several jet diameters; the time scale is on the order of the period for bubble collapse.It was found that the amplitude and frequency of chugging are strongly dependent on the ratio of the liquid density to the gas density, the jet Mach number, and the operating pressure ratio. The conditions under which unsteadiness occurs were determined