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Sample records for jet impingement cooling

  1. Rewetting of hot vertical rod during jet impingement surface cooling

    NASA Astrophysics Data System (ADS)

    Agrawal, Chitranjan; Kumar, Ravi; Gupta, Akhilesh; Chatterjee, Barun

    2016-06-01

    A stainless steel (SS-316) vertical rod of 12 mm diameter at 800 ± 10 °C initial temperature was cooled by normal impinging round water jet. The surface rewetting phenomenon was investigated for a range of jet diameter 2.5-4.8 mm and jet Reynolds number 5000-24,000 using a straight tube type nozzle. The investigation were made from the stagnation point to maximum 40 mm downstream locations, simultaneously for both upside and downside directions. The cooling performance of the vertical rod was evaluated on the basis of rewetting parameters i.e. rewetting temperature, wetting delay, rewetting velocity and the maximum surface heat flux. Two separate Correlations have been proposed for the dimensionless rewetting velocity in terms of rewetting number and the maximum surface heat flux that predicts the experimental data within an error band of ±20 and ±15 % respectively.

  2. Modeling Single-Phase and Boiling Liquid Jet Impingement Cooling in Power Electronics

    SciTech Connect

    Narumanchi, S. V. J.; Hassani, V.; Bharathan, D.

    2005-12-01

    Jet impingement has been an attractive cooling option in a number of industries over the past few decades. Over the past 15 years, jet impingement has been explored as a cooling option in microelectronics. Recently, interest has been expressed by the automotive industry in exploring jet impingement for cooling power electronics components. This technical report explores, from a modeling perspective, both single-phase and boiling jet impingement cooling in power electronics, primarily from a heat transfer viewpoint. The discussion is from the viewpoint of the cooling of IGBTs (insulated-gate bipolar transistors), which are found in hybrid automobile inverters.

  3. Modular jet impingement assemblies with passive and active flow control for electronics cooling

    DOEpatents

    Zhou, Feng; Dede, Ercan Mehmet; Joshi, Shailesh

    2016-09-13

    Power electronics modules having modular jet impingement assembly utilized to cool heat generating devices are disclosed. The modular jet impingement assemblies include a modular manifold having a distribution recess, one or more angled inlet connection tubes positioned at an inlet end of the modular manifold that fluidly couple the inlet tube to the distribution recess and one or more outlet connection tubes positioned at an outlet end of the modular manifold that fluidly coupling the outlet tube to the distribution recess. The modular jet impingement assemblies include a manifold insert removably positioned within the distribution recess and include one or more inlet branch channels each including an impinging slot and one or more outlet branch channels each including a collecting slot. Further a heat transfer plate coupled to the modular manifold, the heat transfer plate comprising an impingement surface including an array of fins that extend toward the manifold insert.

  4. Traction Drive Inverter Cooling with Submerged Liquid Jet Impingement on Microfinned Enhanced Surfaces (Presentation)

    SciTech Connect

    Waye, S.; Narumanchi, S.; Moreno, G.

    2014-09-01

    Jet impingement is one means to improve thermal management for power electronics in electric-drive traction vehicles. Jet impingement on microfin-enhanced surfaces further augments heat transfer and thermal performance. A channel flow heat exchanger from a commercial inverter was characterized as a baseline system for comparison with two new prototype designs using liquid jet impingement on plain and microfinned enhanced surfaces. The submerged jets can target areas with the highest heat flux to provide local cooling, such as areas under insulated-gate bipolar transistors and diode devices. Low power experiments, where four diodes were powered, dissipated 105 W of heat and were used to validate computational fluid dynamics modeling of the baseline and prototype designs. Experiments and modeling used typical automotive flow rates using water-ethylene glycol as a coolant (50%-50% by volume). The computational fluid dynamics model was used to predict full inverter power heat dissipation. The channel flow and jet impingement configurations were tested at full inverter power of 40 to 100 kW (output power) on a dynamometer, translating to an approximate heat dissipation of 1 to 2 kW. With jet impingement, the cold plate material is not critical for the thermal pathway. A high-temperature plastic was used that could eventually be injection molded or formed, with the jets formed from a basic aluminum plate with orifices acting as nozzles. Long-term reliability of the jet nozzles and impingement on enhanced surfaces was examined. For jet impingement on microfinned surfaces, thermal performance increased 17%. Along with a weight reduction of approximately 3 kg, the specific power (kW/kg) increased by 36%, with an increase in power density (kW/L) of 12% compared with the baseline channel flow configuration.

  5. Advanced Liquid Cooling for a Traction Drive Inverter Using Jet Impingement and Microfinned Enhanced Surfaces: Preprint

    SciTech Connect

    Waye, S. K.; Narumanchi, S.; Mihalic, M.; Moreno, G.; Bennion, K.; Jeffers, J.

    2014-08-01

    Jet impingement on plain and micro-finned enhanced surfaces was compared to a traditional channel flow configuration. The jets provide localized cooling to areas heated by the insulated-gate bipolar transistor and diode devices. Enhanced microfinned surfaces increase surface area and thermal performance. Using lighter materials and designing the fluid path to manage pressure losses increases overall performance while reducing weight, volume, and cost. Powering four diodes in the center power module of the inverter and computational fluid dynamics (CFD) modeling was used to characterize the baseline as well as jet-impingement-based heat exchangers. CFD modeling showed the thermal performance improvements should hold for a fully powered inverter. Increased thermal performance was observed for the jet-impingement configurations when tested at full inverter power (40 to 100 kW output power) on a dynamometer. The reliability of the jets and enhanced surfaces over time was also investigated. Experimentally, the junction-to- coolant thermal resistance was reduced by up to 12.5% for jet impingement on enhanced surfaces s compared to the baseline channel flow configuration. Base plate-to-coolant (convective) resistance was reduced by up to 37.0% for the jet-based configuration compared to the baseline, suggesting that while improvements to the cooling side reduce overall resistance, reducing the passive stack resistance may contribute to lowering overall junction-to-coolant resistance. Full inverter power testing showed reduced thermal resistance from the middle of the module baseplate to coolant of up to 16.5%. Between the improvement in thermal performance and pumping power, the coefficient of performance improved by up to 13% for the jet-based configuration.

  6. Evaluation of cooling performance of impinging jet array over various dimpled surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Sun-Min; Kim, Kwang-Yong

    2016-04-01

    Various configurations of an impinging jet-dimple array cooling system were evaluated in terms of their heat transfer and pressure drop performances. The steady incompressible laminar flow and heat transfer in the cooling system were analyzed using three-dimensional Navier-Stokes equations. The obtained numerical results were validated by a comparison with experimental data for the local Nusselt number distribution. The area-averaged Nusselt number on the projected area and the pressure drop through the system were selected as the performance parameters. Among the four tested configurations—inline concave, staggered concave, inline convex, and staggered convex—the staggered convex impinging jet-dimple array showed the best heat transfer performance whereas the staggered-concave configuration showed the lowest pressure drop. A parametric study with two geometric variables, i.e., the height of dimple and the diameter of dimple, was also conducted for the staggered-convex impinging jet-dimple array. As a result, the best heat transfer and pressure drop performances were achieved when the ratio of the height of dimple to the diameter of jet was 0.8. And, the increase in the ratio of the diameter of dimple to the diameter of jet yielded monotonous increase in the heat transfer performance.

  7. Prediction of jet impingement cooling scheme characteristics (airfoil leading edge application)

    NASA Astrophysics Data System (ADS)

    Riahi, A.; Saabas, H. J.; Messeh, W. Abdel

    1993-02-01

    A control volume, finite difference method based on the work of Rhie in conjunction with a high Reynolds k-epsilon model and a two layer turbulence model was used to predict the heat transfer coefficients underneath an impinging circular jet in the absence of cross flow. The numerical results are compared to experimental measurements for two different impingement height to jet diameter ratios: H/D = 2, and H/D = 10. The comparisons indicate that, although both the k-epsilon and the two layer turbulence models are adequate in the prediction of the flow field, the two layer model resulted in heat transfer predictions that were closer to experimental observations. It was also observed that the predicted heat transfer coefficients for the case of H/D = 2 were sensitive to the assumed jet exit turbulence levels, whereas they were not for H/D = 10. This information is useful to the designer of cooled turbine components.

  8. Effect of surface thickness on the wetting front velocity during jet impingement surface cooling

    NASA Astrophysics Data System (ADS)

    Agrawal, Chitranjan; Gotherwal, Deepesh; Singh, Chandradeep; Singh, Charan

    2016-06-01

    A hot stainless steel (SS-304) surface of 450 ± 10 °C initial temperature is cooled with a normally impinging round water jet. The experiments have been performed for the surface of different thickness e.g. 1, 2, 3 mm and jet Reynolds number in the range of Re = 26,500-48,000. The cooling performance of the hot test surface is evaluated on the basis of wetting front velocity. The wetting front velocity is determined for 10-40 mm downstream spatial locations away from the stagnation point. It has been observed that the wetting front velocity increase with the rise in jet flow rate, however, diminishes towards the downstream spatial location and with the rise in surface thickness. The proposed correlation for the dimensionless wetting front velocity predicts the experimental data well within the error band of ±30 %, whereas, 75 % of experimental data lies within the range of ±20 %.

  9. Three-Dimensional Numerical Study of Impinging Water Jets in Runout Table Cooling Processes

    NASA Astrophysics Data System (ADS)

    Cho, Myung Jong; Thomas, Brian G.; Lee, Pil Jong

    2008-07-01

    Cooling from impinging water jets in runout table (ROT) processing depends on the fluid flow and depth of water accumulated in the water pool that forms on the surface of the moving steel strip. This effect is investigated with a three-dimensional (3-D) computational model of fluid flow, pressure, and free surface motion for realistic banks of nozzles within the flow rate region of the ROT process (2400 to 9200 L/min m2). The volume of fluid (VOF) method with the high-resolution interface capturing (HRIC) scheme was implemented to handle the free surface flow of the water jet, and the k-ɛ model was used for turbulence. The governing equations are discretized by a second-order accurate scheme and solved with the computational fluid dynamics (CFD) code Fluent. The model was validated with experimental measurements of free-surface shape and hydraulic jump position for a single water jet impinging onto a moving surface that included turbulent flow and multiphase regions of mixed bubbles and water. For banks of water jets impinging onto the surface of the moving strip in a realistic ROT, the free surface shape, velocity, and pressure distributions have been calculated for various flow rates and surface widths. A deeper water pool is expected on the moving surface with increasing water flow rate and with increasing width. In addition, as the water pool height increases, the pressure variations on the moving surface below the water jets decrease. A simple relation to predict the water pool height from the water flow rate per unit area and strip width has been derived. The predictions agree well with both the 3-D calculations and measurements from water model experiments.

  10. Large Eddy Simulation of a cooling impinging jet to a turbulent crossflow

    NASA Astrophysics Data System (ADS)

    Georgiou, Michail; Papalexandris, Miltiadis

    2015-11-01

    In this talk we report on Large Eddy Simulations of a cooling impinging jet to a turbulent channel flow. The impinging jet enters the turbulent stream in an oblique direction. This type of flow is relevant to the so-called ``Pressurized Thermal Shock'' phenomenon that can occur in pressurized water reactors. First we elaborate on issues related to the set-up of the simulations of the flow of interest such as, imposition of turbulent inflows, choice of subgrid-scale model and others. Also, the issue of the commutator error due to the anisotropy of the spatial cut-off filter induced by non-uniform grids is being discussed. In the second part of the talk we present results of our simulations. In particular, we focus on the high-shear and recirculation zones that are developed and on the characteristics of the temperature field. The budget for the mean kinetic energy of the resolved-scale turbulent velocity fluctuations is also discussed and analyzed. Financial support has been provided by Bel V, a subsidiary of the Federal Agency for Nuclear Control of Belgium.

  11. SiO2 nanofluid planar jet impingement cooling on a convex heated plate

    NASA Astrophysics Data System (ADS)

    Asghari Lafmajani, Neda; Ebrahimi Bidhendi, Mahsa; Ashjaee, Mehdi

    2016-02-01

    The main objective of this paper is to investigate the heat transfer coefficient of a planar jet of SiO2 nanofluid that impinges vertically on the middle of a convex heated plate for cooling purposes. The planar jet issues from a rectangular slot nozzle. The convex aluminum plate has a thickness, width and length of 0.2, 40 and 130 mm, respectively, and is bent with a radius of 200 mm. A constant heat-flux condition is employed. 7 nm SiO2 particles are added to water to prepare the nanofluid with 0.1, 1 and 2 % (ml SiO2/ml H2O) concentrations. The tests are also performed at different Reynolds numbers from 1803 to 2782. Results indicate that adding the SiO2 nanoparticles can effectively increase both local and average heat transfer coefficients up to 39.37 and 32.78 %, respectively. These positive effects often are more pronounced with increasing Reynolds numbers. This enhancement increases with ascending the concentration of nanofluid, especially from 0.1 to 1 %.

  12. Mixed convection cooling of a cylinder using slot jet impingement at different circumferential angles

    NASA Astrophysics Data System (ADS)

    Naderipour, S.; Yousefi, T.; Ashjaee, M.; Naylor, D.

    2015-08-01

    An experimental study using Mach-Zehnder interferometer has been carried out to investigate the heat transfer from an isothermal horizontal circular cylinder, which is exposed to an air slot jet at different angles of jet impingement. A square edged nozzle is mounted parallel with the cylinder axis and jet flow impinges on the side of the cylinder at angles Θ = 0°, 30°, 60° and 90°. The Reynolds number varied from 240 to 1900 while the Grashof number and slot- to cylinder-spacing is kept constant at Gr = 22,300 and H/w = 7 respectively. The Richardson number varied from 0.006 to 0.4. The flow field is greatly influenced by the slot exit velocity and the buoyancy force due to density change. The local Nusselt number around the cylinder has been calculated using the infinite fringe interferograms at 10° intervals. Average Nusselt number shows that heat transfer is decreased when the angle of jet impingement is increased .

  13. Mixed convection cooling of a cylinder using slot jet impingement at different circumferential angles

    NASA Astrophysics Data System (ADS)

    Naderipour, S.; Yousefi, T.; Ashjaee, M.; Naylor, D.

    2016-08-01

    An experimental study using Mach-Zehnder interferometer has been carried out to investigate the heat transfer from an isothermal horizontal circular cylinder, which is exposed to an air slot jet at different angles of jet impingement. A square edged nozzle is mounted parallel with the cylinder axis and jet flow impinges on the side of the cylinder at angles Θ = 0°, 30°, 60° and 90°. The Reynolds number varied from 240 to 1900 while the Grashof number and slot- to cylinder-spacing is kept constant at Gr = 22,300 and H/w = 7 respectively. The Richardson number varied from 0.006 to 0.4. The flow field is greatly influenced by the slot exit velocity and the buoyancy force due to density change. The local Nusselt number around the cylinder has been calculated using the infinite fringe interferograms at 10° intervals. Average Nusselt number shows that heat transfer is decreased when the angle of jet impingement is increased .

  14. Experimental and numerical investigations on slot air jet impingement cooling of a heated cylindrical concave surface

    NASA Astrophysics Data System (ADS)

    Nouri-Bidgoli, H.; Ashjaee, M.; Yousefi, T.

    2014-04-01

    Experimental and numerical studies have been carried out for slot air jet impingement on a heated concave surface of a partially opened-top horizontal cylinder of length L = 20 cm. The slot jet is situated at the symmetry line of the partially opened-top cylinder along the gravity vector and impinges to the bottom of the cylinder which is designated as θ = 0°. The width of the opening at the top of the horizontal cylinder is W = 3 cm which corresponds to a circumferential angle Δθ = 50.8°. The experiments are performed by a Mach-Zehnder interferometer which enables to measure the local convection heat transfer coefficient. Also, a finite volume method based on the SIMPLE algorithm and non-orthogonal grid discretization scheme is used to solve the continuity, momentum, and energy equations. The Poisson equations are solved for (x, y) to find the grid points which are distributed in a non-uniform manner with higher concentration close to the solid regions. The effects of jet Reynolds number ( Re j) in the range from 190 to 1,600 and the ratio of spacing between nozzle and cylinder surface to the jet width from H = 1.5 to H = 10.7 on the local and average Nusselt numbers are examined. It is observed that maximum Nusselt number occurs at the stagnation point at (θ = 0°) and the local heat transfer coefficient decreases on the circumferential surface of the cylinder with increase of θ as a result of thermal boundary layer thickness growth. Also results show that the local and average heat transfer coefficients are raised by increasing the jet Reynolds number and by decreasing the nozzle-to-surface spacing.

  15. Additions to compact heat exchanger technology: Jet impingement cooling & flow & heat transfer in metal foam-fins

    NASA Astrophysics Data System (ADS)

    Onstad, Andrew J.

    Compact heat exchangers have been designed following the same basic methodology for over fifty years. However, with the present emphasis on energy efficiency and light weight of prime movers there is increasing demand for completely new heat exchangers. Moreover, new materials and mesoscale fabrication technologies offer the possibility of significantly improving heat exchanger performance over conventional designs. This work involves fundamental flow and heat transfer experimentation to explore two new heat exchange systems: in Part I, large arrays of impinging jets with local extraction and in Part II, metal foams used as fins. Jet impingement cooling is widely used in applications ranging from paper manufacturing to the cooling of gas turbine blades because of the very high local heat transfer coefficients that are possible. While the use of single jet impingement results in non-uniform cooling, increased and more uniform mean heat transfer coefficients may be attained by dividing the total cooling flow among an array of smaller jets. Unfortunately, when the spent fluid from the array's central jets interact with the outer jets, the overall mean heat transfer coefficient is reduced. This problem can be alleviated by locally extracting the spent fluid before it is able to interact with the surrounding jets. An experimental investigation was carried out on a compact impingement array (Xn/Djet = 2.34) utilizing local extraction of the spent fluid (Aspent/Ajet = 2.23) from the jet exit plane. Spatially resolved measurements of the mean velocity field within the array were carried out at jet Reynolds numbers of 2300 and 5300 by magnetic resonance velocimetry, MRV. The geometry provided for a smooth transition from the jet to the target surface and out through the extraction holes without obvious flow recirculation. Mean Nusselt number measurements were also carried out for a Reynolds number range of 2000 to 10,000. The Nusselt number was found to increase with the

  16. Design Of A Hybrid Jet Impingement / Microchannel Cooling Device For Densely Packed PV Cells Under High Concentration

    NASA Astrophysics Data System (ADS)

    Barrau, Jérôme; Rosell, Joan; Ibañez, Manel

    2010-10-01

    A hybrid jet impingement / microchannel cooling scheme was designed and applied to densely packed PV cells under high concentration. An experimental study allows validating the principles of the design and confirming its applicability to the cited system. In order to study the characteristics of the device in a wide range of conditions, a numerical model was developed and experimentally validated. The results allow evaluating the contributions of the cooling device to the performances of densely packed PV cells under high concentration. The main advantages of the system are related to its compactness, its good capacity of heat extraction associated to relatively low pressure losses and its capability to improve the temperature uniformity of the PV receiver with respect to other cooling schemes. These features improve the net electric output of the whole system and its reliability.

  17. Visualization of flow and heat transfer augmentation by oblique impingement jets.

    PubMed

    Kimoto, Hideo; Nuntadusit, Chayut; Hamabe, Kenji

    2002-10-01

    Various nozzle geometries for impingement cooling jets have recently been devised and favorable designs for cooling effectiveness have been reported. However, impinging flow and the characteristics of impingement cooling are not sufficiently clear. This paper reports on an investigation of impingement jet cooling techniques. The impingement cooling characteristics by oblique jets through a rectangular nozzle have been clarified. Preliminary numerical simulations have not necessarily presented the details of heat transfer characteristics of the oblique jets. PMID:12496016

  18. Rotational effects on impingement cooling

    NASA Astrophysics Data System (ADS)

    Epstein, A. H.; Kerrebrock, J. L.; Koo, J. J.; Preiser, U. Z.

    The present consideration of rotation effects on heat transfer in a radially exhausted, impingement-cooled turbine blade model gives attention to experimental results for Reynolds and Rossby numbers and blade/coolant temperature ratio values that are representative of small gas turbine engines. On the basis of a model that encompasses the effects of Coriolis force and buoyancy on heat transfer, bouyancy is identified as the cause of an average Nusselt number that is 20-30 percent lower than expected from previous nonrotating data. A heuristic model is proposed which predicts that the impingement jets nearest the blade roots should deflect inward, due to a centripetal force generated by their tangential velocity counter to the blade motion. Potentially serious thermal stresses must be anticipated from rotation effects in the course of blade design.

  19. Regeneratively cooled transition duct with transversely buffered impingement nozzles

    SciTech Connect

    Morrison, Jay A; Lee, Ching-Pang; Crawford, Michael E

    2015-04-21

    A cooling arrangement (56) having: a duct (30) configured to receive hot gases (16) from a combustor; and a flow sleeve (50) surrounding the duct and defining a cooling plenum (52) there between, wherein the flow sleeve is configured to form impingement cooling jets (70) emanating from dimples (82) in the flow sleeve effective to predominately cool the duct in an impingement cooling zone (60), and wherein the flow sleeve defines a convection cooling zone (64) effective to cool the duct solely via a cross-flow (76), the cross-flow comprising cooling fluid (72) exhausting from the impingement cooling zone. In the impingement cooling zone an undimpled portion (84) of the flow sleeve tapers away from the duct as the undimpled portion nears the convection cooling zone. The flow sleeve is configured to effect a greater velocity of the cross-flow in the convection cooling zone than in the impingement cooling zone.

  20. Heat transfer characteristics for jet array impingement with initial crossflow

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.; Su, C. C.

    1983-01-01

    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. In addition to the crossflow which originates from the jets following impingement, an initial crossflow is present which approaches the array through an upstream extension of the channel. The temperature of the initial crossflow air may differ from the jet air temperature. The configurations considered are intended to model the impingement cooled midchord region of gas turbine airfoils in cases where an initial crossflow is also present. Nusselt numbers and dimensionless adiabatic wall temperatures resolved to one streamwise jet hole spacing were experimentally determined for ratios of the initial crossflow rate to the total jet flow rate ranging from zero to unity. These are presented and discussed relative to the flow and geometric parameters.

  1. Profile shape optimization in multi-jet impingement cooling of dimpled topologies for local heat transfer enhancement

    NASA Astrophysics Data System (ADS)

    Negi, Deepchand Singh; Pattamatta, Arvind

    2015-04-01

    The present study deals with shape optimization of dimples on the target surface in multi-jet impingement heat transfer. Bezier polynomial formulation is incorporated to generate profile shapes for the dimple profile generation and a multi-objective optimization is performed. The optimized dimple shape exhibits higher local Nusselt number values compared to the reference hemispherical dimpled plate optimized shape which can be used to alleviate local temperature hot spots on target surface.

  2. 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.

  3. Nanofluid impingement jet heat transfer.

    PubMed

    Zeitoun, Obida; Ali, Mohamed

    2012-01-01

    Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters. PMID:22340669

  4. Nanofluid impingement jet heat transfer

    PubMed Central

    2012-01-01

    Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters. PMID:22340669

  5. Single and multiple jet impingement heat transfer on rotating disks

    NASA Astrophysics Data System (ADS)

    Metzger, D. E.; Partipilo, V. A.

    1989-01-01

    In some gas turbine engine designs cooling air jets are directed at the rotating disk in an atempt to enhance the convection coefficients and reduce the amount of gas flow required for cooling. The jet-impingement scheme is particularly attractive for achieving intense cooling at a specific radial location, such as the blade attachment region. In earlier single-jet studies, the interaction between an impinging jet and rotating disk has been found to involve a flow regime transition. The present study extends the previously acquired data base with new results from both heat-transfer and flow-visualization testing, including effects of hub size, jet travel distance, and the number of jets. Results include a superposition scheme for predicting heat transfer for multiple jets and a criterion for the minimum amount of flow required through each jet nozzle to assure enhancement of the disk convection.

  6. Experimental simulation of impingement cooling in midchord region of turbine blade

    NASA Astrophysics Data System (ADS)

    Li, Liguo; Jiang, Jun; Chang, Haiping; Zhang, Donglia

    1989-10-01

    Simulation experiments have been completed to research the characteristics of impingement cooling in the midchord region of a turbine blade for a given geometric parameter of jet array, initial crossflow, and pressure ratios of the film-cooling exhaust. Comparative experiments have been made on curvilinear and flat plate impinged surfaces, and impinged surfaces with and without a chordwise fin. Moreover, the thermal patterns from a liquid crystal show that the jet hole arrangement and distance between cooled surface and jet plate affect the heat transfer distributions for jet array impingement. Finally, the effects of the cooling air axially injected into guide tube on radial jet flow have also been determined.

  7. Bistability and hysteresis of annular impinging jets

    NASA Astrophysics Data System (ADS)

    Tisovsky, Tomas

    2016-06-01

    In present study, the bistability and hysteresis of annular impinging jets is investigated. Annular impinging jets are simulated using open source CFD code - OpenFOAM. Both flow field patterns of interest are obtained and hysteresis is found by means of dynamic mesh simulation. Effect of nozzle exit velocity on resulting hysteresis loop is also illustrated.

  8. Fundamental studies of impingement cooling thermal boundary conditions

    NASA Astrophysics Data System (ADS)

    Lucas, M. G.; Ireland, P. T.; Wang, Z.; Jones, T. V.; Pearce, W. J.

    1993-02-01

    Measurements were made of the local heat transfer at the surface of a flat plate underneath a confined impinging jet. Thermochromic liquid crystals were used to measure the surface temperature of a uniformly heated plate cooled by an impinging jet. The temperature of the wall through which the jet passes was controlled, and experiments were performed to measure the two heat transfer coefficients which arise from this three temperature problem. The effect of Reynolds number and plate to jet spacing on heat transfer was investigated. The heat transfer results are discussed in terms of the interpreted flow field.

  9. Fluorescence Imaging Study of Impinging Underexpanded Jets

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Nowak, Robert J.; Alderfer, David W.

    2008-01-01

    An experiment was designed to create a simplified simulation of the flow through a hole in the surface of a hypersonic aerospace vehicle and the subsequent impingement of the flow on internal structures. In addition to planar laser-induced fluorescence (PLIF) flow visualization, pressure measurements were recorded on the surface of an impingement target. The PLIF images themselves provide quantitative spatial information about structure of the impinging jets. The images also help in the interpretation of impingement surface pressure profiles by highlighting the flow structures corresponding to distinctive features of these pressure profiles. The shape of the pressure distribution along the impingement surface was found to be double-peaked in cases with a sufficiently high jet-exit-to-ambient pressure ratio so as to have a Mach disk, as well as in cases where a flow feature called a recirculation bubble formed at the impingement surface. The formation of a recirculation bubble was in turn found to depend very sensitively upon the jet-exit-to-ambient pressure ratio. The pressure measured at the surface was typically less than half the nozzle plenum pressure at low jet pressure ratios and decreased with increasing jet pressure ratios. Angled impingement cases showed that impingement at a 60deg angle resulted in up to a factor of three increase in maximum pressure at the plate compared to normal incidence.

  10. Acoustics measurements in normal jet impingement

    NASA Technical Reports Server (NTRS)

    Kleis, S. J.

    1977-01-01

    The dependence of far field acoustic measurements for a uniform jet on nozzle to plate spacing for small dimensionless spacings (h/d - 0.75 to 3.0) was investigated. Spectra from a real time analyzer were read and processed by an HP 2116 minicomputer in on-line mode. Similar data was generated for a fully developed pipe flow exit condition jet to compare with other investigations. The data base for normal jet impingement was extended to smaller values of nozzle to plate spacing. The effects of slight noise heating (30 deg rise) of the jet on the far field noise produced by the impinging jet are demonstrated.

  11. Microtextured Surfaces for Turbine Blade Impingement Cooling

    NASA Technical Reports Server (NTRS)

    Fryer, Jack

    2014-01-01

    Gas turbine engine technology is constantly challenged to operate at higher combustor outlet temperatures. In a modern gas turbine engine, these temperatures can exceed the blade and disk material limits by 600 F or more, necessitating both internal and film cooling schemes in addition to the use of thermal barrier coatings. Internal convective cooling is inadequate in many blade locations, and both internal and film cooling approaches can lead to significant performance penalties in the engine. Micro Cooling Concepts, Inc., has developed a turbine blade cooling concept that provides enhanced internal impingement cooling effectiveness via the use of microstructured impingement surfaces. These surfaces significantly increase the cooling capability of the impinging flow, as compared to a conventional untextured surface. This approach can be combined with microchannel cooling and external film cooling to tailor the cooling capability per the external heating profile. The cooling system then can be optimized to minimize impact on engine performance.

  12. Spray formation processes of impinging jet injectors

    NASA Technical Reports Server (NTRS)

    Anderson, W. E.; Ryan, H. M.; Pal, S.; Santoro, R. J.

    1993-01-01

    A study examining impinging liquid jets has been underway to determine physical mechanisms responsible for combustion instabilities in liquid bi-propellant rocket engines. Primary atomization has been identified as an important process. Measurements of atomization length, wave structure, and drop size and velocity distribution were made under various ambient conditions. Test parameters included geometric effects and flow effects. It was observed that pre-impingement jet conditions, specifically whether they were laminar or turbulent, had the major effect on primary atomization. Comparison of the measurements with results from a two dimensional linear aerodynamic stability model of a thinning, viscous sheet were made. Measured turbulent impinging jet characteristics were contrary to model predictions; the structure of waves generated near the point of jet impingement were dependent primarily on jet diameter and independent of jet velocity. It has been postulated that these impact waves are related to pressure and momentum fluctuations near the impingement region and control the eventual disintegration of the liquid sheet into ligaments. Examination of the temporal characteristics of primary atomization (ligament shedding frequency) strongly suggests that the periodic nature of primary atomization is a key process in combustion instability.

  13. Improved Stirling engine performance using jet impingement

    NASA Technical Reports Server (NTRS)

    Johnson, D. C.; Britt, E. J.; Thieme, L. G.

    1982-01-01

    Of the many factors influencing the performance of a Stirling engine, that of transferring the combustion gas heat into the working fluid is crucial. By utilizing the high heat transfer rates obtainable with a jet impingement heat transfer system, it is possible to reduce the flame temperature required for engine operation. Also, the required amount of heater tube surface area may be reduced, resulting in a decrease in the engine nonswept volume and a related increase in engine efficiency. A jet impingement heat transfer system was designed by Rasor Associates, Inc., and tested in the GPU-3 Stirling engine at the NASA Lewis Research Center. For a small penalty in pumping power (less than 0.5% of engine output) the jet impingement heat transfer system provided a higher combustion-gas-side heat transfer coefficient and a smoothing of heater temperature profiles resulting in lower combustion system temperatures and a 5 to 8% increase in engine power output and efficiency.

  14. Numerical investigation of heat transfer under confined impinging turbulent slot jets

    SciTech Connect

    Tzeng, P.Y.; Soong, C.Y.; Hsieh, C.D. )

    1999-06-01

    Impinging jet systems are extensively used to provide rapid heating, cooling, or drying in diverse industrial applications. Among these applications are the annealing of metals and plastic sheets; tempering and shaping of glass; drying of textiles, veneer, paper, and film materials; and cooling of combustion walls, turbine blades, and electronic components. This work numerically investigates confined impinging turbulent slot jets. Eight turbulence models, including one standard and seven low-Reynolds-number [kappa]-[epsilon] models, are employed and tested to predict the heat transfer performance of multiple impinging jets. Validation results indicate that the prediction by each turbulence model depends on grid distribution and numerical scheme used in spatial discretization. In addition, spent fluid exits are set between impinging jets to reduce the cross-flow effect in degradation of the heat transfer of downstream impinging jets. The overall heat transfer performance can be enhanced by proper spent fluid removal.

  15. Circular and Elliptic Submerged Impinging Water Jets

    NASA Astrophysics Data System (ADS)

    Claudey, Eric; Benedicto, Olivier; Ravier, Emmanuel; Gutmark, Ephraim

    1999-11-01

    Experiments and CFD have been performed to study circular and elliptic jets in a submerged water jet facility. The tests included discharge coefficient measurement to evaluate pressure losses encountered in noncircular nozzles compared to circular ones. Three-dimensional pressure mappings on the impingement surface and PIV measurement of the jet mean and turbulent velocity have been performed at different compound impingement angles relative to the impingement surface and at different stand-off distances. The objective was to investigate the effect of the non-circular geometry on the flow field and on the impact region. The tests were performed in a close loop system in which the water was pumped through the nozzles into a clear Plexiglas tank. The Reynolds numbers were typically in the range of 250000. Discharge coefficients of the elliptic nozzle was somewhat lower than that of the circular jet but spreading rate and turbulence level were higher. Pressure mapping showed that the nozzle exit geometry had an effect on the pressure distribution in the impact region and that high-pressure zones were generated at specific impact points. PIV measurements showed that for a same total exit area, the elliptic jets affected a surface area that is 8the equivalent circular. The turbulence level in the elliptic jet tripled due to the nozzle design. Results of the CFD model were in good agreement with the experimental data.

  16. Industrial stator vane with sequential impingement cooling inserts

    DOEpatents

    Jones, Russell B; Fedock, John A; Goebel, Gloria E; Krueger, Judson J; Rawlings, Christopher K; Memmen, Robert L

    2013-08-06

    A turbine stator vane for an industrial engine, the vane having two impingement cooling inserts that produce a series of impingement cooling from the pressure side to the suction side of the vane walls. Each insert includes a spar with a row of alternating impingement cooling channels and return air channels extending in a radial direction. Impingement cooling plates cover the two sides of the insert and having rows of impingement cooling holes aligned with the impingement cooling channels and return air openings aligned with the return air channel.

  17. An approximation technique for jet impingement flow

    SciTech Connect

    Najafi, Mahmoud; Fincher, Donald; Rahni, Taeibi; Javadi, KH.; Massah, H.

    2015-03-10

    The analytical approximate solution of a non-linear jet impingement flow model will be demonstrated. We will show that this is an improvement over the series approximation obtained via the Adomian decomposition method, which is itself, a powerful method for analysing non-linear differential equations. The results of these approximations will be compared to the Runge-Kutta approximation in order to demonstrate their validity.

  18. Gas turbine bucket with impingement cooled platform

    DOEpatents

    Jones, Raphael Durand

    2002-01-01

    In a turbine bucket having an airfoil portion and a root portion, with a substantially planar platform at an interface between the airfoil portion and root portion, a platform cooling arrangement including at least one bore in the root portion and at least one impingement cooling tube seated in the bore, the tube extending beyond the bore with an outlet in close proximity to a targeted area on an underside of the platform.

  19. Investigations of scaling laws for jet impingement

    NASA Technical Reports Server (NTRS)

    Morton, J. B.; Haviland, J. K.; Catalano, G. D.; Herling, W. W.

    1976-01-01

    The statistical properties of tangential flows over surfaces were investigated by two techniques. In one, a laser-Doppler velocimeter was used in a smoke-laden jet to measure one-point statistical properties, including mean velocities, turbulent intensities, intermittencies, autocorrelations, and power spectral densities. In the other technique, free stream and surface pressure probes connected to 1/8 inch microphones were used to obtain single point rms and 1/3 octave pressures, as well as two point cross correlations, the latter being converted to auto spectra, amplitude ratios, phase lags, and coherences. The results of these studies support the vortex model of jets, give some insights into the effects of surface impingement, and confirm that jet diameter and velocity are the scaling parameters for circular jets, while Reynolds number is relatively unimportant.

  20. Sessile drop deformations under an impinging jet

    NASA Astrophysics Data System (ADS)

    Feng, James Q.

    2015-08-01

    The problem of steady axisymmetric deformations of a liquid sessile drop on a flat solid surface under an impinging gas jet is of interest for understanding the fundamental behavior of free surface flows as well as for establishing the theoretical basis in process design for the Aerosol direct-write technology. It is studied here numerically using a Galerkin finite-element method, by computing solutions of Navier-Stokes equations. For effective material deposition in Aerosol printing, the desired value of Reynolds number for the laminar gas jet is found to be greater than ~500. The sessile drop can be severely deformed by an impinging gas jet when the capillary number is approaching a critical value beyond which no steady axisymmetric free surface deformation can exist. Solution branches in a parameter space show turning points at the critical values of capillary number, which typically indicate the onset of free surface shape instability. By tracking solution branches around turning points with an arc-length continuation algorithm, critical values of capillary number can be accurately determined. Near turning points, all the free surface profiles in various parameter settings take a common shape with a dimple at the center and bulge near the contact line. An empirical formula for the critical capillary number for sessile drops with contact angle is derived for typical ranges of jet Reynolds number and relative drop sizes especially pertinent to Aerosol printing.

  1. Effects of rotation on impingement cooling of turbine blades

    NASA Technical Reports Server (NTRS)

    Kreatsoulas, J. C.; Kerrebrock, J. L.; Epstein, A. H.; Rogo, C.

    1985-01-01

    The effects of rotation on impingement cooling of turbine blades were studied experimentally as a specialized facility at M.I.T. A foil heated resistively was cooled by a jet flow on one side and temperature monitored on the other. Rotating the blade limits the heat transfer path to conduction through the support structure and radiation. IR radiometry furnishes the temperature distributions on the chamber wall, permitting the internal heat transfer coefficient to be measured. The heat transfer efficiency has been found to fall as much as 30 percent as rotational speed increases. The conditions observed confirm the significance of rotational effects, particularly with regard to potential early blade failure.

  2. Impingement cooling with film coolant extraction in the airfoil leading edge regions

    NASA Astrophysics Data System (ADS)

    Li, Liguo; Li, Zhaohui

    An extensive experimental study is conducted to determine the heat transfer characteristics of arrays of air jets impinging on perforated target surfaces in turbine blade leading edge regions by six large-scale models. The relations of pressure loss and Nusselt number to jet Reynolds number are obtained in a wide range of parameter combinations of interest in cooled airfoil practice for various models, respectively. These parameter combinations are covered in a test matrix, including combinations of variations in jet Reynolds number, airfoil leading edge curvature radius-to-diameter ratio, jet pitch-to-diameter ratio, and jet impingement gap-to-diameter ratio.

  3. Turbulence modeling for impinging jet flows

    NASA Technical Reports Server (NTRS)

    Childs, Robert E.; Rodman, Laura C.; Bradshaw, Peter; Bott, Donald M.; Shoemaker, William C.

    1992-01-01

    The objective of the present work is to improve the accuracy of the k-epsilon turbulence model for flows involving one or more jets impinging on a plate in a crossflow which generate a horseshoe vortex. The k-epsilon model is modified by adding source terms to the epsilon equation, which enables it to more accurately predict the shear stress in flows subject to streamline curvature and vortex stretching (or lateral divergence). Calculations with the modified model predict the ground vortex core to be about 15 percent upstream of its experimental location. This is a significant improvement over the standard model which yields higher errors for calculation of the vortex-core location.

  4. Local heat transfer in internally cooled turbine airfoil leading edge regions. I - Impingement cooling without film coolant extraction. II - Impingement cooling with film coolant extraction

    NASA Astrophysics Data System (ADS)

    Bunker, R. S.; Metzger, D. E.

    The highly localized internal heat transfer characteristics of large-scale models of impingement-cooled turbine blade leading edge regions presently studied derives its cooling from a single line of equally-spaced multiple jets aimed at the leading-edge apex, and exiting the leading-edge region in the opposite or chordwise direction. Detailed two-dimensional local surface Nusselt number distributions have been obtained with temperature-indicating coatings. Results indicate generally increasing heat transfer with the 0.6 power of jet Reynolds number. In the second part of this study, in which the same cooling process is used in conjunction with the extraction of the coolant fluid, the results obtained indicate that heat transfer is primarily dependent on jet Reynolds number, with smaller influences from the flow-extraction rate.

  5. Round impinging jets with relatively large stand-off distance

    NASA Astrophysics Data System (ADS)

    Shademan, Mehrdad; Balachandar, Ram; Roussinova, Vesselina; Barron, Ron

    2016-07-01

    Large eddy simulation and particle image velocimetry measurements have been performed to evaluate the characteristics of a turbulent impinging jet with large nozzle height-to-diameter ratio (H/D = 20). The Reynolds number considered is approximately 28 000 based on the jet exit velocity and nozzle diameter. Mean normalized centerline velocity in both the free jet and impingement regions and pressure distribution over the plate obtained from simulations and experiments show good agreement. The ring-like vortices generated due to the Kelvin-Helmholtz instabilities at the exit of the nozzle merge, break down and transform into large scale structures while traveling towards the impingement plate. A Strouhal number of 0.63 was found for the vortices generated at the exit of the nozzle. However, this parameter is reduced along the centerline towards the impingement zone. A characteristic frequency was also determined for the large scale structures impinging on the plate. The expansion, growth, tilt, and three-dimensionality of the impinging structures cause dislocation of the impinging flow from the centerline, which is significantly larger when compared with flows having small H/D ratios. Contrary to the behavior of impinging jets with small stand-off distance, due to the loss of coherence, the large scale structures do not result in significant secondary vortices in the wall jet region and consequently less fluctuations were observed for wall shear stress.

  6. Surface pressure fluctuations due to an impinging underexpanded supersonic jet

    NASA Astrophysics Data System (ADS)

    Pundir, Binu

    The impingement of supersonic jets on surfaces is of interest because of its important application to jet blast deflectors (JBD), and short takeoff and vertical landing aircraft (STOVL) during hover. Typically, on an aircraft carrier deck, the impingement of the jet blast on the deflector generates impingement tones, and structural vibrations, not only on the JBD but also on the ship deck. Therefore, apart from direct transmission of jet noise to the gallery level, there is a component of noise transmitted due to the impingement of the jet on the JBD. The objectives of this work are to study the pressure spectra (i) on a flat plate, and separately on a cone due to axisymmetric impingement of a supersonic underexpanded cold jet issuing from a convergent-divergent nozzle and (ii) on a plane jet impinging on a finite plate and an adjoining ground plane due to the impingement of a planar jet on the plate. The characteristics of the surface pressure fluctuations are numerically investigated using WIND-US 2.0. The time-dependent, compressible Euler equations for perfect gas are employed for the present computations. The impingement distance between the jet nozzle and the deflector plate, and the plate inclination with respect to the incident jet are varied. The impingement zone stagnation bubble and a high-speed radial jet with several embedded structures (shocklets) were identified on the perpendicular plate. Flows involving cones reveal the presence of detached cone shocks, enclosing a recirculation zone. The location and magnitude of the peak pressure on the cone surface are a strong function of the cone apex angle. For the two-dimensional jet impingement on angled plate the peak value of pressure occurs at normal jet impingement. The pressure at the intersection point of the plate and the ground plane is sometimes higher than the peak pressure on the plate. Beyond this point there is a sharp decrease in pressure. As the flow accelerates, an oblique shock is sometimes

  7. Experimental study of turbulence in isothermal jet impingement at intermediate plate spacings

    NASA Astrophysics Data System (ADS)

    Landfried, D. Tyler; Valentino, Alex; Mazumdar, Sagnik; Jana, Anirban; Kimber, Mark

    2013-11-01

    One fundamental problem in fluid dynamics is that of the axisymmetric round flow impinging on a plate placed some distance downstream of the jet. Impinging jets have a rich history of applications including small plate spacings, H/D ~ 1, such as encountered in electronics cooling, or large plate spacings, H/D ~ 102, such as vertical takeoff aircrafts and rocket engines. However, intermediate plate spacings, such as the lower plenum of the next generation nuclear reactors, are not typically studied. In this paper, an experimental study is conducted investigating the effect of the impingement plate on the flow behavior compared to the near free jet behavior when the plate is removed. Using air as the working fluid, a single jet is considered at jet Reynolds numbers of 10000, 20000, and 30000. A three-wire anemometer probe is used to quantify the mean components of velocities as well as the Reynolds stress and the third-order moments in the flow field at various distances between the jet outlet and the impingement plate. When present, the impingement plate is placed a distance of 8, 11, 14, and 17 diameters downstream of the jet. Additionally trends in the kinetic energy and dissipation are investigated for validation with numerical models.

  8. Numerical study of a confined slot impinging jet with nanofluids

    PubMed Central

    2011-01-01

    Background Heat transfer enhancement technology concerns with the aim of developing more efficient systems to satisfy the increasing demands of many applications in the fields of automotive, aerospace, electronic and process industry. A solution for obtaining efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the possibility of increasing the thermal performances of the working fluids can be taken into account, and the introduction of nanoparticles in a base fluid can be considered. Results In this article, a numerical investigation on confined impinging slot jet working with a mixture of water and Al2O3 nanoparticles is described. The flow is turbulent and a constant temperature is applied on the impinging. A single-phase model approach has been adopted. Different geometric ratios, particle volume concentrations and Reynolds number have been considered to study the behavior of the system in terms of average and local Nusselt number, convective heat transfer coefficient and required pumping power profiles, temperature fields and stream function contours. Conclusions The dimensionless stream function contours show that the intensity and size of the vortex structures depend on the confining effects, given by H/W ratio, Reynolds number and particle concentrations. Furthermore, for increasing concentrations, nanofluids realize increasing fluid bulk temperature, as a result of the elevated thermal conductivity of mixtures. The local Nusselt number profiles show the highest values at the stagnation point, and the lowest at the end of the heated plate. The average Nusselt number increases for increasing particle concentrations and Reynolds numbers; moreover, the highest values are observed for H/W = 10, and a maximum increase of 18% is detected at a concentration equal to 6%. The required pumping power as well as Reynolds number increases and particle concentrations grow, which is almost 4.8 times greater than the

  9. Impinging jet separators for liquid metal magnetohydrodynamic power cycles

    NASA Technical Reports Server (NTRS)

    Bogdanoff, D. W.

    1973-01-01

    In many liquid metal MHD power, cycles, it is necessary to separate the phases of a high-speed liquid-gas flow. The usual method is to impinge the jet at a glancing angle against a solid surface. These surface separators achieve good separation of the two phases at a cost of a large velocity loss due to friction at the separator surface. This report deals with attempts to greatly reduce the friction loss by impinging two jets against each other. In the crude impinging jet separators tested to date, friction losses were greatly reduced, but the separation of the two phases was found to be much poorer than that achievable with surface separators. Analyses are presented which show many lines of attack (mainly changes in separator geometry) which should yield much better separation for impinging jet separators).

  10. Supersonic moist air jet impingements on flat surface

    NASA Astrophysics Data System (ADS)

    Alam, Miah Md. Ashraful; Matsuo, Shigeru; Setoguchi, Toshiaki

    2010-02-01

    Pronounced aeroacoustic resonances are exhibited in the flowfield where a jet emerges from an orifice or a nozzle and impinges on a solid surface. One instance where such resonances are produced is in a high speed jet impingement, such as in the space launch vehicle systems, jet-engine exhaust impingement, and in the short take-off and vertical landing (STOVL) aircraft, etc. A highly unsteady flowfield leading to a drastic increase of noise level with very high dynamic pressure and thermal loads are noticed on nearby surfaces results dramatic lift loss, severe ground erosion and hot gas ingestion to the inlet in the jet engines. This highly unsteady behavior of the impinging jets is due to a feedback loop between the fluid and acoustic fields. In actual jet flow, the working gas may contain condensable gas such as steam or moist air. In these cases, the non-equilibrium condensation may occur at the region between nozzle exit and an object. The jet flow with non-equilibrium condensation may be quite different from that without condensation. Therefore, in this study, the effect of the non-equilibrium condensation of moist air on the axisymmetric under-expanded supersonic impinging jet on a vertical flat plate was investigated numerically.

  11. Two stage serial impingement cooling for isogrid structures

    DOEpatents

    Lee, Ching-Pang; Morrison, Jay A.

    2014-09-09

    A system for cooling a wall (24) of a component having an outer surface with raised ribs (12) defining a structural pocket (10), including: an inner wall (26) within the structural pocket and separating the wall outer surface within the pocket into a first region (28) outside of the inner wall and a second region (40) enclosed by the inner wall; a plate (14) disposed atop the raised ribs and enclosing the structural pocket, the plate having a plate impingement hole (16) to direct cooling air onto an impingement cooled area (38) of the first region; a cap having a skirt (50) in contact with the inner wall, the cap having a cap impingement hole (20) configured to direct the cooling air onto an impingement cooled area (44) of the second region, and; a film cooling hole (22) formed through the wall in the second region.

  12. Shear layer characteristics of supersonic free and impinging jets

    NASA Astrophysics Data System (ADS)

    Davis, T. B.; Kumar, R.

    2015-09-01

    The initial shear layer characteristics of a jet play an important role in the initiation and development of instabilities and hence radiated noise. Particle image velocimetry has been utilized to study the initial shear layer development of supersonic free and impinging jets. Microjet control employed to reduce flow unsteadiness and jet noise appears to affect the development of the shear layer, particularly near the nozzle exit. Velocity field measurements near the nozzle exit show that the initially thin, uncontrolled shear layer develops at a constant rate while microjet control is characterized by a rapid nonlinear thickening that asymptotes downstream. The shear layer linear growth rate with microjet control, in both the free and the impinging jet, is diminished. In addition, the thickened shear layer with control leads to a reduction in azimuthal vorticity for both free and impinging jets. Linear stability theory is used to compute unstable growth rates and convection velocities of the resultant velocity profiles. The results show that while the convection velocity is largely unaffected, the unstable growth rates are significantly reduced over all frequencies with microjet injection. For the case of the impinging jet, microjet control leads to near elimination of the impingement tones and an appreciable reduction in broadband levels. Similarly, for the free jet, significant reduction in overall sound pressure levels in the peak radiation direction is observed.

  13. Performance studies of energy consumption for single and multiple nozzle systems under impinging air jets

    NASA Astrophysics Data System (ADS)

    Etemoglu, Akin Burak; Can, Muhiddin

    2013-08-01

    Impinging air jets of various shapes, sizes and configurations are commonly used in heating, cooling and drying industrial processes. An analytical study has been carried out to optimise the thermal performance of single and multiple nozzle systems using impinging air jets. The optimisation of the nozzle array was given for practical purposes. The results show that within practical limits, a narrower nozzle size results in a greater heat and mass transfer coefficient. An economical analysis of the drying processes is also given for slot nozzles.

  14. Impingement of supersonic jets on an axisymmetric deflector

    NASA Astrophysics Data System (ADS)

    Prasad, J. K.; Mehta, R. C.; Sreekanth, A. K.

    1994-07-01

    Experimental and numerical studies are carried out to investigate impingement flowfield produced on a typical axisymmetric jet deflector. The experiments consisted of schlieren flow visualization and measurements of pressure. The present study will be useful for the design of a typical axisymmetric jet deflector during the liftoff phase of a rocket.

  15. Impingement of supersonic jets on an axisymmetric deflector

    NASA Astrophysics Data System (ADS)

    Prasad, J. K.; Mehta, R. C.; Sreekanth, A. K.

    1994-07-01

    The phenomenon of supersonic jets and their interaction with solid surfaces is found in many engineering applications such as impingement of exhaust from launch vehicles during the liftoff phase, during stage separation of multistage rockets, and VTOL/STOL operation of aircraft, etc. In this paper, experimental and numerical studies are carried out to investigate impingement flowfield produced on a typical axisymmetric jet deflector. The experiments consisted of schlieren flow visualization and measurements of pressure. The present study will be useful for the design of a typical axisymmetric jet deflector during the liftoff phase of a rocket.

  16. Experimental and Computational Study of Underexpanded Jet Impingement Heat Transfer

    NASA Technical Reports Server (NTRS)

    Rufer, Shann J.; Nowak, Robert J.; Daryabeigi, Kamran; Picetti, Donald

    2009-01-01

    An experiment was performed to assess CFD modeling of a hypersonic-vehicle breach, boundary-layer flow ingestion and internal surface impingement. Tests were conducted in the NASA Langley Research Center 31-Inch Mach 10 Tunnel. Four simulated breaches were tested and impingement heat flux data was obtained for each case using both phosphor thermography and thin film gages on targets placed inside the model. A separate target was used to measure the surface pressure distribution. The measured jet impingement width and peak location are in good agreement with CFD analysis.

  17. Heat transfer and flow visualization of swirling impinging jets

    SciTech Connect

    Huang, L.; El-Genk, M.S.

    1996-12-31

    The heat transfer performance of swirling impinging jets was experimentally investigated, and the flow fields were visualized for a jet diameter, d{sub j} = 12.7 mm and swirl angles, {theta} = 15{degree}, 30{degree}, and 45{degree}. Other experimental parameters included Reynolds number, Re = 3,620--17,600, vertical jet spacing, h = 12.7--76.2 mm, and radial distance from the stagnation point, r = 0--65 mm. The results showed significant enhancement in the heat transfer coefficient, both with respect to radial uniformity and local values, compared to a circular straight impinging jet of the same dimensions at the same test conditions. The flow field visualizations confirmed the measured enhancement in the heat transfer coefficient for the swirling jets as well as the radial distribution of local Nusselt number.

  18. Water cooled steam jet

    DOEpatents

    Wagner, Jr., Edward P.

    1999-01-01

    A water cooled steam jet for transferring fluid and preventing vapor lock, or vaporization of the fluid being transferred, has a venturi nozzle and a cooling jacket. The venturi nozzle produces a high velocity flow which creates a vacuum to draw fluid from a source of fluid. The venturi nozzle has a converging section connected to a source of steam, a diffuser section attached to an outlet and a throat portion disposed therebetween. The cooling jacket surrounds the venturi nozzle and a suction tube through which the fluid is being drawn into the venturi nozzle. Coolant flows through the cooling jacket. The cooling jacket dissipates heat generated by the venturi nozzle to prevent vapor lock.

  19. Water cooled steam jet

    DOEpatents

    Wagner, E.P. Jr.

    1999-01-12

    A water cooled steam jet for transferring fluid and preventing vapor lock, or vaporization of the fluid being transferred, has a venturi nozzle and a cooling jacket. The venturi nozzle produces a high velocity flow which creates a vacuum to draw fluid from a source of fluid. The venturi nozzle has a converging section connected to a source of steam, a diffuser section attached to an outlet and a throat portion disposed there between. The cooling jacket surrounds the venturi nozzle and a suction tube through which the fluid is being drawn into the venturi nozzle. Coolant flows through the cooling jacket. The cooling jacket dissipates heat generated by the venturi nozzle to prevent vapor lock. 2 figs.

  20. Experimental Analysis of Impinging Single and Twin Circular Synthetic Jets

    NASA Astrophysics Data System (ADS)

    Cardone, Gennaro; Greco, Carlo Salvatore; Castrillo, Giusy; Astarita, Tommaso; Experimental Thermo-Fluid-Dynamics Research Team

    2015-11-01

    The behavior of impinging single synthetic jet and twin circular synthetic jets in phase opposition is experimentally investigated by using Particle Image Velocimetry (PIV) at Reynolds and Strouhal numbers equal to 5100 and 0.024, respectively. Different inter-axes distances for the twin configuration and several nozzle-to-plate distances have been investigated. The time-averaged behavior of the all velocity components are reported and discussed. Their distributions, near the impinging plate, are described for both the synthetic jet configurations and for all the nozzle-to-plate distances. At low nozzle-to-plate distance (H/D <4) the axial velocity profile near the impinging plate shows a double peak with a minimum on the jet axis. Instead, at high nozzle-to-plate distance (H/D >6), the axial velocity profile is bell-shaped. This is ascribed to the adverse pressure gradient strength and the potential core-like region extension. Indeed, the turbulence distribution shows a region characterized by low values, resembling the potential core region of continuous jets. Comparing the two synthetic jet configurations, a higher centerline velocity and a smaller jet width have been found for the twin case.

  1. Splattering during turbulent liquid jet impingement on solid targets

    SciTech Connect

    Bhunia, S.K.; Lienhard, J.H. V . Dept. of Mechanical Engineering)

    1994-06-01

    In turbulent liquid jet impingement, a spray of droplets often breaks off of the liquid layer formed on the target. This splattering of liquid alters the efficiencies of jet impingement heat transfer processes and chemical containment safety devices, and leads to problems of aerosol formation in jet impingement cleaning processes. In this paper, the authors present a more complete study of splattering and improved correlations that extend and supersede the previous reports on this topic. The authors report experimental results on the amount of splattering for jets of water, isopropanol-water solutions, and soap-water mixtures. Jets were produced by straight tube nozzles of diameter 0.8--5.8 mm, with fully developed turbulent pipe-flow upstream of the nozzle exist. These experiments cover Weber numbers between 130--31,000, Reynolds numbers between 2,700--98,000, and nozzle-to-target separations of 0.2 [<=]l/d[<=]125. Splattering of up to 75 percent of the incoming jet liquid is observed. The results show that only the Weber number and l/d affect the fraction of jet liquid splattered. The presence of surfactants does not alter the splattering. A new correlation for the onset condition for splattering is given. In addition, the authors establish the range of applicability of the model of Lienhard et al. and the authors provide a more accurate set of coefficients for their correlation.

  2. Effects of Forcing Frequency in Controlling a Supersonic Impinging Jet

    NASA Astrophysics Data System (ADS)

    Kastner, Jeff; Samimy, Mo

    2002-11-01

    A series of experiments were performed to explore the effects of forcing frequency in controlling an ideally expanded Mach 1.3 axisymmetric impinging jet operating in a strong resonance regime. The Hartmann Tube Fluidic Actuator (HTFA), which is an actuator with high bandwidth and high amplitude characteristics, was used for the forcing. Three HTFAs with zero frequency (steady injection), low frequency of 5.4 kHz (near the impinging jet resonance frequency of 5.3 kHz), and high frequency of 12 kHz were used. Measurements were performed to characterize the near- and far-field acoustic of the unforced and forced jets. Detailed flow visualization is currently being used to correlate changes in the acoustic field with changes in the large-scale coherent structures. The results show that using steady injection and high frequency forcing behave similarly in suppressing the impingement tone, but both raise the broadband acoustic level around the impingement tone. The low frequency forcing also suppresses the impingement tone but with less rise in the broadband noise. Both the high frequency and low frequency forcing leave their imprint at the forcing frequency.

  3. The Effect of Impingement on Transitional Behavior in Underexpanded Jets

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Nowak, Robert J.; Alderfer, David W.

    2009-01-01

    An investigation into the development of flow unsteadiness in impinging axisymmetric underexpanded jets has been conducted at NASA Langley Research Center. The study has examined the effect of an impingement target placed at various distances and angles on transitional behavior of such jets. Two nozzles, with exit Mach numbers of 1.0 and 2.6, were used in this investigation. Planar laser-induced fluorescence of nitric oxide (NO PLIF) has been used to identify flow unsteadiness and to image transitional and turbulent flow features. Measurements of the location of the onset of various degrees of unsteady flow behavior have been made using these PLIF images. Both qualitative and quantitative comparisons are presented to demonstrate the observed effects of impingement and flow parameters on the process of the transition to turbulence. The presence of the impingement target was found to significantly shorten the distance to transition to turbulence by up to a factor of approximately three, with closer targets resulting in slightly shorter distance to transition and turbulence. The location at which the flow first exhibits unsteadiness was found to have a strong dependence on the presence and location of key flow structures. This paper presents quantitative results on transition criteria for free and impinging jets.

  4. Local jet impingement boiling heat transfer with R113

    NASA Astrophysics Data System (ADS)

    Zhou, D. W.; Ma, C. F.

    An experimental study was performed to characterize the boiling heat transfer of impinging circular submerged jets on simulated microelectronic chips with a nominal area of 5 mm × 5 mm. The heat transfer modes included natural convection, partially developed nucleate boiling, fully developed nucleate boiling and critical heat flux. The study included the effects of jet parameters and fluid subcooling on the nucleate boiling. The results showed that the nucleate boiling data varied only with fluid subcooling regardless of jet parameters and that both the pool and impingement nucleate boiling curves at the same subcooling condition were well correlated. The high heat flux portions of the boiling curves with jet exit velocities greater than 10 m/s were corrected for the elevated saturation temperature. A new expression was developed with an interpolation method to construct the partially developed nucleate boiling curve.

  5. Thermal Management Using Pulsating Jet Cooling Technology

    NASA Astrophysics Data System (ADS)

    Alimohammadi, S.; Dinneen, P.; Persoons, T.; Murray, D. B.

    2014-07-01

    The existing methods of heat removal from compact electronic devises are known to be deficient as the evolving technology demands more power density and accordingly better cooling techniques. Impinging jets can be used as a satisfactory method for thermal management of electronic devices with limited space and volume. Pulsating flows can produce an additional enhancement in heat transfer rate compared to steady flows. This article is part of a comprehensive experimental and numerical study performed on pulsating jet cooling technology. The experimental approach explores heat transfer performance of a pulsating air jet impinging onto a flat surface for nozzle-to-surface distances 1 <= H/D <= 6, Reynolds numbers 1,300 <= Re <= 2,800 pulsation frequency 2Hz <= f <= 65Hz, and Strouhal number 0.0012 <= Sr = fD/Um <= 0.084. The time-resolved velocity at the nozzle exit is measured to quantify the turbulence intensity profile. The numerical methodology is firstly validated using the experimental local Nusselt number distribution for the steady jet with the same geometry and boundary conditions. For a time-averaged Reynolds number of 6,000, the heat transfer enhancement using the pulsating jet for 9Hz <= f <= 55Hz and 0.017 <= Sr <= 0.102 and 1 <= H/D <= 6 are calculated. For the same range of Sr number, the numerical and experimental methods show consistent results.

  6. Directional transport of impinging capillary jet on wettability engineered surfaces

    NASA Astrophysics Data System (ADS)

    Ghosh, Aritra; Chatterjee, Souvick; Sinha Mahapatra, Pallab; Ganguly, Ranjan; Megaridis, Constantine

    2015-11-01

    Impingement of capillary jet on a surface is important for applications like heat transfer, or for liquid manipulation in bio-microfluidic devices. Using wettability engineered surfaces, we demonstrate pump-less and directional transport of capillary jet on a flat surface. Spatial contrast of surface energy and a wedge-shape geometry of the wettability confined track on the substrate facilitate formation of instantaneous spherical bulges upon jet impingement; these bulges are further transported along the superhydrophilic tracks due to Laplace pressure gradient. Critical condition warranted for formation of liquid bulge along the varying width of the superhydrophilic track is calculated analytically and verified experimentally. The work throws light on novel fluid phenomena of unidirectional jet impingement on wettability confined surfaces and provides a platform for innovative liquid manipulation technique for further application. By varying the geometry and wettability contrast on the surface, one can achieve volume flow rates of ~ O(100 μL/sec) and directionally guided transport of the jet liquid, pumplessly at speeds of ~ O(10cm/sec).

  7. Jet array impingement with crossflow-correlation of streamwise resolved flow and heat transfer distributions

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.; Truman, C. R.

    1981-01-01

    Correlations for heat transfer coefficients for jets of circular offices and impinging on a surface parallel to the jet orifice plate are presented. The air, following impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer (impingement) surface. The downstream jets are subjected to a crossflow originating from the upstream jets. Impingement surface heat transfer coefficients resolved to one streamwise jet orifice spacing, averaged across the channel span, are correlated with the associated individual spanwise orifice row jet and crossflow velocities, and with the geometric parameters.

  8. Thermal chip fabrication with arrays of sensors and heaters for micro-scale impingement cooling heat transfer analysis and measurements.

    PubMed

    Shen, C H; Gau, C

    2004-07-30

    The design and fabrication for a thermal chip with an array of temperature sensors and heaters for study of micro-jet impingement cooling heat transfer process are presented. This thermal chip can minimize the heat loss from the system to the ambient and provide a uniform heat flux along the wall, thus local heat transfer processes along the wall can be measured and obtained. The fabrication procedure presented can reach a chip yield of 100%, and every one of the sensors and heaters on the chip is in good condition. In addition, micro-jet impingement cooling experiments are performed to obtain the micro-scale local heat transfer Nusselt number along the wall. Flow visualization for the micro-impinging jet is also made. The experimental results indicate that both the micro-scale impinging jet flow structure and the heat transfer process along the wall is significantly different from the case of large-scale jet impingement cooling process. PMID:15142582

  9. Mach number effect on jet impingement heat transfer.

    PubMed

    Brevet, P; Dorignac, E; Vullierme, J J

    2001-05-01

    An experimental investigation of heat transfer from a single round free jet, impinging normally on a flat plate is described. Flow at the exit plane of the jet is fully developed and the total temperature of the jet is equal to the ambient temperature. Infrared measurements lead to the characterization of the local and averaged heat transfer coefficients and Nusselt numbers over the impingement plate. The adiabatic wall temperature is introduced as the reference temperature for heat transfer coefficient calculation. Various nozzle diameters from 3 mm to 15 mm are used to make the injection Mach number M vary whereas the Reynolds number Re is kept constant. Thus the Mach number influence on jet impingement heat transfer can be directly evaluated. Experiments have been carried out for 4 nozzle diameters, for 3 different nozzle-to-target distances, with Reynolds number ranging from 7200 to 71,500 and Mach number from 0.02 to 0.69. A correlation is obtained from the data for the average Nusselt number. PMID:11460655

  10. Experimental study of highly viscous impinging jets

    SciTech Connect

    Gomon, M.

    1998-12-01

    The objective of this research is to study the behavior of highly viscous gravity-driven jets filling a container. Matters of interest are the formation of voids in the fluid pool during the filling process and the unstable behavior of the fluid in the landing region which manifests itself as an oscillating motion. The working fluids used in this research are intended to simulate the flow behavior of molten glass. Qualitative and quantitative results are obtained in a parametric study. The fraction of voids present in the fluid pool after the filling of the container is measured for different parameter values of viscosity and mass flow rate. Likewise, frequencies of the oscillating jet are measured. Results are inconclusive with regard to a correlation between parameter settings and void fractions. As for frequencies, power law correlations are established.

  11. Heat transfer measurements and CFD simulations of an impinging jet

    NASA Astrophysics Data System (ADS)

    Petera, Karel; Dostál, Martin

    2016-03-01

    Heat transport in impinging jets makes a part of many experimental and numerical studies because some similarities can be identified between a pure impingement jet and industrial processes like, for example, the heat transfer at the bottom of an agitated vessel. In this paper, experimental results based on measuring the response to heat flux oscillations applied to the heat transfer surface are compared with CFD simulations. The computational cost of a LES-based approach is usually too high therefore a comparison with less computationally expensive RANS-based turbulence models is made in this paper and a possible improvement of implementing an anisotropic explicit algebraic model for the turbulent heat flux model is evaluated.

  12. Computational analysis for dry-ice sublimation assisted CO2 jet impingement flow

    NASA Astrophysics Data System (ADS)

    Kwak, Songmi; Lee, Jaeseon

    2015-11-01

    The flow and heat transfer characteristics of the novel gas-solid two-phase jet impingement are investigated computationally. When the high pressure carbon dioxide (CO2) flow passes through a nozzle or orifice, it experiences the sudden expansion and the rapid temperature drop occurred by Joule-Thomson effect. This temperature drop causes the lower bulk jet fluid temperature than the CO2 sublimation line, so dry-ice becomes formed. By using CO2 gas-solid mixture as a working fluid of jet impingement, it is expected the heat transfer enhancement can be achieved due to the low bulk temperature and the additional phase change latent heat. In this study, 2D CFD model is created to predict the cooling effect of gas-solid CO2 jet. The gas-solid CO2 flow is considered by Euler-Lagrangian approach of mixed phase and the additional heat transfer module is embedded to account for the sublimation phenomena of the solid state CO2. The jet flow and heat transfer performance of gas-solid CO2 jet is investigated by the variance of flow parameter like Reynolds number, solid phase concentration and jet geometries.

  13. Vortical structures and heat transfer in a round impinging jet

    NASA Astrophysics Data System (ADS)

    Had?Iabdi?, M.; Hanjali?, K.

    In order to gain a better insight into flow, vortical and turbulence structure and their correlation with the local heat transfer in impinging flows, we performed large-eddy simulations (LES) of a round normally impinging jet issuing from a long pipe at Reynolds number Re = 20000 at the orifice-to-plate distance H = 2D, where D is the jet-nozzle diameter. This configuration was chosen to match previous experiments in which several phenomena have been detected, but the underlying physics remained obscure because of limitations in the measuring techniques applied. The instantaneous velocity and temperature fields, generated by the LES, revealed interesting time and spatial dynamics of the vorticity and eddy structures and their imprints on the target wall, characterized by tilting and breaking of the edge ring vortices before impingement, flapping, precessing, splitting and pairing of the stagnation point/line, local unsteady separation and flow reversal at the onset of radial jet spreading, streaks pairing and branching in the near-wall region of the radial jets, and others. The LES data provided also a basis for plausible explanations of some of the experimentally detected statistically-averaged flow features such as double peaks in the Nusselt number and the negative production of turbulence energy in the stagnation region. The simulations, performed with an in-house unstructured finite-volume code T-FlowS, using second-order-accuracy discretization schemes for space and time and the dynamic subgrid-scale stress/flux model for unresolved motion, showed large sensitivity of the results to the grid resolution especially in the wall vicinity, suggesting care must be taken in interpreting LES results in impinging flows.

  14. Numerical evaluation of single central jet for turbine disk cooling

    NASA Astrophysics Data System (ADS)

    Subbaraman, M. R.; Hadid, A. H.; McConnaughey, P. K.

    The cooling arrangement of the Space Shuttle Main Engine High Pressure Oxidizer Turbopump (HPOTP) incorporates two jet rings, each of which produces 19 high-velocity coolant jets. At some operating conditions, the frequency of excitation associated with the 19 jets coincides with the natural frequency of the turbine blades, contributing to fatigue cracking of blade shanks. In this paper, an alternate turbine disk cooling arrangement, applicable to disk faces of zero hub radius, is evaluated, which consists of a single coolant jet impinging at the center of the turbine disk. Results of the CFD analysis show that replacing the jet ring with a single central coolant jet in the HPOTP leads to an acceptable thermal environment at the disk rim. Based on the predictions of flow and temperature fields for operating conditions, the single central jet cooling system was recommended for implementation into the development program of the Technology Test Bed Engine at NASA Marshall Space Flight Center.

  15. A computational study of highly viscous impinging jets

    SciTech Connect

    Silva, M.W.

    1998-11-01

    Two commercially-available computational fluid dynamics codes, FIDAP (Fluent, Inc., Lebanon, NH) and FLOW-3D (Flow Science, Inc., Los Alamos, NM), were used to simulate the landing region of jets of highly viscous fluids impinging on flat surfaces. The volume-of-fluid method was combined with finite difference and finite element approaches to predict the jet behavior. Several computational models with varying degrees of physical realism were developed, and the results were compared with experimental observations. In experiments, the jet exhibited several complex behaviors. As soon as it exited the nozzle, the jet began to neck down and become narrower. When it impacted the solid surface, the jet developed an instability near the impact point and buckled to the side. This buckling became a spiraling motion, and the jet spiraled about the impact point. As the jet spiraled around, a cone-shaped pile was build up which eventually became unstable and slumped to the side. While all of these behaviors were occurring, air bubbles, or voids, were being entrapped in the fluid pool. The results obtained from the FLOW-3D models more closely matched the behavior of real jets than the results obtained from /the FIDAP models. Most of the FLOW-3D models predicted all of the significant jet behaviors observed in experiments: necking, buckling, spiraling, slumping, and void entrapment. All of the FIDAP models predicted that the jet would buckle relatively far from the point of impact, whereas the experimentally observed jet behavior indicates that the jets buckle much nearer the impact point. Furthermore, it was shown that FIDAP is incapable of incorporating heat transfer effects into the model, making it unsuitable for this work.

  16. Experimental Optimisation of the Thermal Performance of Impinging Synthetic Jet Heat Sinks

    NASA Astrophysics Data System (ADS)

    Marron, Craig; Persoons, Tim

    2014-07-01

    Zero-net-mass flow synthetic jet devices offer a potential solution for energy- efficient cooling of medium power density electronic components. There remains an incomplete understanding of the interaction of these flows with extended surfaces, which prevents the wider implementation of these devices in the field. This study examines the effect of the main operating parameters on the heat transfer rate and electrical power consumption for a synthetic jet cooled heat sink. Three different heat sink geometries are tested. The results find that a modified sink with a 14 × 14 pin array with the central 6 × 6 pins removed provides superior cooling to either a fully pinned sink or flat plate. Furthermore each heat sink is found to have its own optimum jet orifice-to-sink spacing for heat transfer independent of flow conditions. The optimum heat transfer for the modified sink is H = 34 jet diameters. The effect of frequency on heat transfer is also studied. It is shown that heat transfer increases superlinearly with frequency at higher stroke lengths. The orientation of the impingement surface with respect to gravity has no effect on the heat transfer capabilities of the tested device. These tests are the starting point for further investigation into enhanced synthetic jet impingement surfaces. The equivalent axial fan cooled pinned heat sink (Malico Inc. MFP40- 18) has a thermal resistance of 1.93K/W at a fan power consumption of 0.12W. With the modified pinned heat sink, a synthetic jet at Re = 911, L0/D = 10, H/D = 30 provides a thermal resistance of 2.5K/W at the same power consumption.

  17. Sound source mechanisms in under-expanded impinging jets

    NASA Astrophysics Data System (ADS)

    Sinibaldi, Giorgia; Marino, Luca; Romano, Giovanni Paolo

    2015-05-01

    Experiments on the aeroacoustics of an under-expanded supersonic jet impinging on a flat plate are presented and thoroughly discussed. A wide range of nozzle pressure ratios and of nozzle-to-plate distances has been analyzed with particular attention to the behavior of the discrete component of the noise. The investigation has been carried out by means of acoustic, particle image velocimetry and wall pressure measurements. The analysis of the relationship between the acoustic data and the fluid dynamic fields allows to examine the different source mechanisms of the discrete component of the noise and to evaluate the link between the jet flow structure and the acoustic tone features. Specifically, two ranges of nozzle pressure ratio have been observed showing different acoustic behaviors, characterized by distinct mechanisms of discrete noise generation. These regions are separated by a range of nozzle pressure ratios where impinging tones are not observed. The present experimental data extend previously published results, improving the analysis of the connection between fluid dynamic and acoustic fields and leading to a better comprehension of the impinging tone source mechanisms.

  18. Full surface local heat transfer coefficient measurements in a model of an integrally cast impingement cooling geometry

    SciTech Connect

    Gillespie, D.R.H.; Wang, Z.; Ireland, P.T.; Kohler, S.T.

    1998-01-01

    Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate, are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer have been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.

  19. Large-eddy simulation of heat transfer from impinging slot jets

    SciTech Connect

    Cziesla, T.; Tandogan, E.; Mitra, N.K.

    1997-07-01

    Impinging jet flows have become a well-established object of investigation in recent years because of their increasing significance in both fundamental and applied fluid mechanics. Examples of a wide range of applications, are the drying of textiles, film, and paper; annealing of glass; processing of some metals and glass; cooling of gas turbine components and the outer wall of combustors and electronic equipment; and freezing of tissue. Here Nusselt number distributions are presented for impinging jet flow of an array of slot nozzles (rectangular jets). The tools to calculate the present turbulent flow are large-eddy simulation (LES) using a dynamic subgrid stress model and the direct numerical simulation (DNS). The numerical code has been validated by comparing computed Nusselt number distributions on the impingement plate for two-dimensional flow with experimental results. A comparison between LES using a logarithmic law of the wall and the DNS shows good agreement of Nusselt number in the Reynolds number range of 600--3,000. The velocity profile at the feed tube exit strongly influences the maximum heat transfer at the stagnation point.

  20. Large eddy simulations of a forced semiconfined circular impinging jet

    NASA Astrophysics Data System (ADS)

    Olsson, M.; Fuchs, L.

    1998-02-01

    Large eddy simulations (LES) of a forced semiconfined circular impinging jet were carried out. The Reynolds number was 104 and the inflow was forced at a Strouhal number of 0.27. The separation between the jet inlet and the opposing wall was four jet inlet diameters. Four different simulations were made. Two simulations were performed without any explicit sub-grid-scale (SGS) model using 1283 and 963 grid points, respectively. Two simulations were performed with two different SGS-models using 963 grid points; one with a dynamic Smagorinsky based model and one with a stress-similarity model. The simulations were performed to study the mean velocity, the turbulence statistics, the SGS-model effects, the dynamic behavior of the jet with a focus on the near wall region. The existence of separation vortices in the wall jet region was confirmed. These secondary vortices were found to be related to the radially deflected primary vortices generated by the circular shear layer of the jet. It was also shown that the primary vortex structures that reach the wall were helical and not axisymmetric. A quantitative gain was found in the simulations with SGS-models. The stress-similarity model simulation correlated slightly better with the higher resolution simulation than the other coarse grid simulations. The variations in the results predicted by the different simulations were larger for the turbulence statistics than for the mean velocity. However, the variation among the different simulations in terms of the turbulence intensity was less than 10%.

  1. Impinging jet spray formation using non-Newtonian liquids

    NASA Astrophysics Data System (ADS)

    Rodrigues, Neil S.

    Over the past two decades there has been a heightened interest in implementing gelled propellants for rocket propulsion, especially for hypergolic bi-propellants such as monomethylhydrazine (MMH) and nitrogen tetroxide oxidizer (NTO). Due to the very high level of toxicity of hypergolic liquid rocket propellants, increasing safety is an important area of need for continued space exploration and defense operations. Gelled propellants provide an attractive solution to meeting the requirements for safety, while also potentially improving performance. A gelling agent can be added to liquid propellants exhibiting Newtonian behavior to transform the liquid into a non-Newtonian fluid with some solid-like behavior, i.e. a gel. Non-Newtonian jet impingement is very different from its Newtonian counterpart in terms of fluid flow, atomization, and combustion. This is due to the added agents changing physical properties such as the bulk rheology (viscosity) and interfacial rheology (surface tension). Spray characterization of jet impingement with Newtonian liquids has been studied extensively in existing literature. However, there is a scarcity in literature of studies that consider the spray characterization of jet impingement with gelled propellants. This is a rather critical void since a major tradeoff of utilizing gelled propellants is the difficulty with atomization due to the increased effective viscosity. However, this difficulty can be overcome by using gels that exhibit shear-thinning behavior---viscosity decreases with increasing strain rate. Shear-thinning fluids are ideal because they have the distinct advantage of only flowing easily upon pressure. Thereby, greatly reducing the amount of propellant that could be accidentally leaked during both critical functions such as liftoff or engagement in the battlefield and regular tasks like refilling propellant tanks. This experimental work seeks to help resolve the scarcity in existing literature by providing drop size

  2. The impingement of sonic and sub-sonic jets onto a flat plate at inclined angles

    NASA Astrophysics Data System (ADS)

    Crafton, Jimmy Wayne

    The flow field associated with a jet impinging onto a surface at an inclined angle is investigated using the image-based technologies of Temperature- and Pressure-Sensitive Paints and Particle Image Velocimetry. These diagnostics are used to produce two-dimensional measurements of temperature, Nusselt number, and pressure on the impingement surface and two-components of velocity above the surface. In the process of measuring Nusselt number a novel technique for determining the adiabatic wall temperature has been developed. This image-based technique was used to measure the adiabatic wall temperature on the impingement surface beneath both compressible and incompressible jets. The results of this investigation indicate that as a free jet impinges on a flat surface at an inclined angle the jet is turned by and spread laterally onto the impingement surface. The impingement angle of the jet is the dominant parameter in determining the rate of turning/spreading for the jet. Qualitatively, the structure of the half maximum pressure contour on the impingement surface is similar to an ellipse created by projecting the nozzle through the impingement surface. The center of the ellipse is located near the location of maximum pressure and the eccentricity is a function of the impingement angle. The width of the minor axis is just over one jet diameter. The point of maximum pressure, Nusselt number, and the stagnation point are each located upstream of the geometric impingement point, and this location is a strong function of impingement angle. The relative locations of the stagnation point, the point of maximum Nusselt number, the point of maximum pressure, and the geometric impingement point are identified and a simple correlation for the location of each of these points relative to the geometric impingement point is presented. Finally, the maximum value of both pressure and Nusselt number are found to be a function of impingement distance and impingement angle.

  3. Discharge coefficients of impingement and film cooling holes

    NASA Astrophysics Data System (ADS)

    Chu, T.; Brown, A.; Garret, S.

    1985-03-01

    In this article measurements of fluid flow through impingement and film cooling holes for typical turbine blade cooling systems are presented. The purpose of the measurements was to determine hole discharge coefficients over a range of Reynolds numbers from 5,000 to 30,000 and to observe in this range the dependence of discharge coefficient on Reynolds number. The effect of hole geometry, that is, sharp edged inlet or corner radius inlet, on discharge coefficients is also measured. Correlations relating discharge coefficients to Reynolds number, corner radius to hole diameter ratio, and blowing parameter are suggested.

  4. Impinging laminar jets at moderate Reynolds numbers and separation distances.

    PubMed

    Bergthorson, Jeffrey M; Sone, Kazuo; Mattner, Trent W; Dimotakis, Paul E; Goodwin, David G; Meiron, Dan I

    2005-12-01

    An experimental and numerical study of impinging, incompressible, axisymmetric, laminar jets is described, where the jet axis of symmetry is aligned normal to the wall. Particle streak velocimetry (PSV) is used to measure axial velocities along the centerline of the flow field. The jet-nozzle pressure drop is measured simultaneously and determines the Bernoulli velocity. The flow field is simulated numerically by an axisymmetric Navier-Stokes spectral-element code, an axisymmetric potential-flow model, and an axisymmetric one-dimensional stream-function approximation. The axisymmetric viscous and potential-flow simulations include the nozzle in the solution domain, allowing nozzle-wall proximity effects to be investigated. Scaling the centerline axial velocity by the Bernoulli velocity collapses the experimental velocity profiles onto a single curve that is independent of the nozzle-to-plate separation distance. Axisymmetric direct numerical simulations yield good agreement with experiment and confirm the velocity profile scaling. Potential-flow simulations reproduce the collapse of the data; however, viscous effects result in disagreement with experiment. Axisymmetric one-dimensional stream-function simulations can predict the flow in the stagnation region if the boundary conditions are correctly specified. The scaled axial velocity profiles are well characterized by an error function with one Reynolds-number-dependent parameter. Rescaling the wall-normal distance by the boundary-layer displacement-thickness-corrected diameter yields a collapse of the data onto a single curve that is independent of the Reynolds number. These scalings allow the specification of an analytical expression for the velocity profile of an impinging laminar jet over the Reynolds number range investigated of . PMID:16486059

  5. Multiple jet impingement heat transfer characteristic: Experimental investigation of in-line and staggered arrays with crossflow

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Metzger, D. E.; Takeuchi, D. I.; Berry, R. A.

    1980-01-01

    Heat transfer characteristics were obtained for configurations designed to model the impingement cooled midchord region of air cooled gas turbine airfoils. The configurations tested were inline and staggered two-dimensional arrays of circular jets with ten spanwise rows of holes. The cooling air was constrained to exit in the chordwise direction along the channel formed by the jet orifice plate and the heat transfer surface. Tests were run for chordwise jet hole spacings of five, ten, and fifteen hole diameters; spanwise spacings of four, six, and eight diameters; and channel heights of one, two, three, and six diameters. Mean jet Reynolds numbers ranged from 5000 to 50,000. The thermal boundary condition at the heat transfer test surface was isothermal. Tests were run for sets of geometrically similar configurations of different sizes. Mean and chordwise resolved Nusselt numbers were determined utilizing a specially constructed test surface which was segmented in the chordwise direction.

  6. Normal Impingement of a Circular Liquid Jet onto a Screen in a Weightless Environment

    NASA Technical Reports Server (NTRS)

    Symons, E. P.

    1976-01-01

    The normal impingement of a circular liquid jet onto a fine-mesh screen in a weightless environment was investigated. Equations were developed to predict the velocity of the emerging jet on the downstream side of the screen as a function of screen and liquid parameters and of the velocity of the impinging jet. Additionally, the stability of the emerging jet was found to be Weber number dependent. In general, excepting at high velocities, the screen behaved much as a baffle, deflecting the major portion of the impinging flow.

  7. Global mode decomposition of supersonic impinging jet noise

    NASA Astrophysics Data System (ADS)

    Hildebrand, Nathaniel; Nichols, Joseph W.

    2015-11-01

    We apply global stability analysis to an ideally expanded, Mach 1.5, turbulent jet that impinges on a flat surface. The analysis extracts axisymmetric and helical instability modes, involving coherent vortices, shocks, and acoustic feedback, which we use to help explain and predict the effectiveness of microjet control. High-fidelity large eddy simulations (LES) were performed at nozzle-to-wall distances of 4 and 4.5 throat diameters with and without sixteen microjets positioned uniformly around the nozzle lip. These flow configurations conform exactly to experiments performed at Florida State University. Stability analysis about LES mean fields predicted the least stable global mode with a frequency that matched the impingement tone observed in experiments at a nozzle-to-wall distance of 4 throat diameters. The Reynolds-averaged Navier-Stokes (RANS) equations were solved at five nozzle-to-wall distances to create base flows that were used to investigate the influence of this parameter. A comparison of the eigenvalue spectra computed from the stability analysis about LES and RANS base flows resulted in good agreement. We also investigate the effect of the boundary layer state as it emerges from the nozzle using a multi-block global mode solver. Computational resources were provided by the Argonne Leadership Computing Facility.

  8. Heat transfer characteristic of an impingement cooling system with different nozzle geometry

    NASA Astrophysics Data System (ADS)

    Marzec, K.; Kucaba-Pietal, A.

    2014-08-01

    The influence of different geometries of the nozzles of an impingement cooling array of six jets directed to the flat surface on the flow mechanism and the heat transfer were investigated numerically. Basically the setup consisted of a cylindrical plenum with an inline array of impingement jets. Simulation were performed using Computational Fluid Dynamics (CFD) code Ansys CFX. The k - ω shear stress transport (SST) turbulence model was used in calculations. The physical model was simplified by using the steady state three-dimensional analysis and incompressible and viscous flow of the fluid. The study focused on an usage of different nozzles shapes in the cooling system for constant inlet flow parameters and boundary conditions. The numerical analysis of the different mesh density resulted in good convergence of the GCI index, what excluded mesh size dependency. The obtained results indicate, that the usage of various types of nozzles results in different values of the heat transfer coefficient and the Nusselt number in the affected area.

  9. Erosion and transport of particulates by forced jet impinging jet on a mobile sediment bed

    NASA Astrophysics Data System (ADS)

    Corfman, Kyle; Mulinti, Rahul; Kiger, Kenneth

    2013-11-01

    The work reports on the erosion and suspended flux characteristics of a forced impinging jet, as a prototypical surrogate to better understand the problem of rotorcraft brownout. Coherent vortex rings are generated through oscillatory forcing of a vertical impinging jet onto a sediment bed. Early in the flow development, annular ripple dunes are formed and steadily grow, the wavelength and growth rate depending largely on the particle size and flow conditions. In order to provide a reliable prediction of erosion for more realistic flows, such as those found in rotorcrafts, a parametric study was performed for several particle sizes and mixtures. PTV is used to correlate vertical and horizontal fluxes with resulting changes in the ground profiles. A single-phase PIV study detailing the changes in the vortex ring characteristics after the bed has reached a stable erosion pattern is also reported. This work is supported by the AFSOR under grant FA95500810406.

  10. Impingement.

    ERIC Educational Resources Information Center

    Uziel, Mary S.

    1978-01-01

    Presents a literature review of the impact of impingement in fishery resources at different power plants in the United States, covering publications of 1976-77. Consideration is given to engineering studies and biological effects for reducing impingement. A list of 96 references is also presented. (HM)

  11. 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.

  12. Large-eddy simulations of axisymmetric excitation effects on a row of impinging jets

    NASA Astrophysics Data System (ADS)

    Rizk, Magdi H.; Menon, Suresh

    1988-07-01

    Numerical simulations of a row of impinging jets are performed. Both the impinging jets and the fountains caused by the collision of the wall jets are modeled in the simulation. The problem considered contains the essential features of twin jets impinging on the ground, simulating the hovering configuration of a vertical takeoff and landing (VTOL) aircraft. The flow is assumed to be governed by the time-dependent, incompressible Navier-Stokes equations. The large-eddy simulation approach is followed. The present study focuses on the motion and dynamics of large-scale structures that have been experimentally observed in jet flows. The behavior of the jets and the fountain caused by the introduction of axisymmetric disturbances at the jet exits are investigated.

  13. Mixing and Noise Benefit Versus Thrust Penalty in Supersonic Jets Using Impingement Tones

    NASA Technical Reports Server (NTRS)

    Raman, Ganesh; Rice, Edward J.

    1994-01-01

    This paper reports the results of an experimental investigation on the effect of impingement tones generated by obstacles of various geometries on the spreading of a supersonic jet flow. A rectangular supersonic jet was produced using a convergent-divergent nozzle that was operated near its design point (with shocks minimized). The immersion of obstacles in the flow produced an intense impingement tone which then propagated upstream (as feedback) to the jet lip and excited the antisymmetric hydrodynamic mode in the jet, thus setting up a resonant self-sustaining loop. The violent flapping motion of the jet due to excitation of the antisymmetric mode, combined with the unsteady wakes of the obstacles, produced large changes in jet mixing. It was possible to control the frequency and amplitude of the impingement tone excitation by varying the nozzle-to-obstacle distance and the obstacle immersion. By proper shaping of the obstacles it was possible to reduce the thrust penalty significantly.

  14. Turbulence in a microscale planar confined impinging-jets reactor.

    PubMed

    Liu, Ying; Olsen, Michael G; Fox, Rodney O

    2009-04-21

    Confined impinging-jets reactors (CIJR) offer many advantages for rapid chemical processing at the microscale in applications such as precipitation and the production of organic nanoparticles. It has been demonstrated that computational fluid dynamics (CFD) is a promising tool for "experiment-free" design and scale-up of such reactors. However, validation of the CFD model used for the microscale turbulence applications requires detailed experimental data on the unsteady flow, the availability of which has until now been very limited. In this work, microscopic particle-image velocimetry (microPIV) techniques were employed to measure the instantaneous velocity field for various Reynolds numbers in a planar CIJR. In order to illustrate the validation procedure, the performance of a particular CFD model, the two-layer k-epsilon model, was evaluated by comparing the predicted flow field with the experimental data. To our knowledge, this study represents the first attempt to directly measure and quantify velocity and turbulence in a microreactor and to use the results to validate a CFD model for microscale turbulent flows. PMID:19350093

  15. The oblique impingement of an axisymmetric jet. [flow characteristics of jet flow over flat plates

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

    The mechanics of the oblique impingement of an axisymmetric jet on a plane surface are examined in detail. The stagnation point is discussed. A schematic drawing of the problem and coordinate system used to describe the flow field are given. The kinematic features of the flow above the plate are examined in the context of the conservation of mass, the vorticity of the jet, and the vorticity introduced by the jetplate interaction. The dynamic features of the flow are examined in terms of the surface pressure distribution and the cause-effect relationships which exist between the pressure and velocity/vorticity distributions. Flow calculations performed are given. The investigation is relevant to the flow resulting from the interaction of the propulsion jet with the main airfoil (STOL aircraft), and is appropriate to an over- or under- wing configuration.

  16. Experimental Investigation of Jet Impingement Heat Transfer Using Thermochromic Liquid Crystals

    NASA Technical Reports Server (NTRS)

    Dempsey, Brian Paul

    1997-01-01

    Jet impingement cooling of a hypersonic airfoil leading edge is experimentally investigated using thermochromic liquid crystals (TLCS) to measure surface temperature. The experiment uses computer data acquisition with digital imaging of the TLCs to determine heat transfer coefficients during a transient experiment. The data reduction relies on analysis of a coupled transient conduction - convection heat transfer problem that characterizes the experiment. The recovery temperature of the jet is accounted for by running two experiments with different heating rates, thereby generating a second equation that is used to solve for the recovery temperature. The resulting solution requires a complicated numerical iteration that is handled by a computer. Because the computational data reduction method is complex, special attention is paid to error assessment. The error analysis considers random and systematic errors generated by the instrumentation along with errors generated by the approximate nature of the numerical methods. Results of the error analysis show that the experimentally determined heat transfer coefficients are accurate to within 15%. The error analysis also shows that the recovery temperature data may be in error by more than 50%. The results show that the recovery temperature data is only reliable when the recovery temperature of the jet is greater than 5 C, i.e. the jet velocity is in excess of 100 m/s. Parameters that were investigated include nozzle width, distance from the nozzle exit to the airfoil surface, and jet velocity. Heat transfer data is presented in graphical and tabular forms. An engineering analysis of hypersonic airfoil leading edge cooling is performed using the results from these experiments. Several suggestions for the improvement of the experimental technique are discussed.

  17. Computational study of triangular waveform oscillation mode to the temperature distribution of a heated wall impinged by a synthetic jet

    NASA Astrophysics Data System (ADS)

    Harinaldi, Rhakasywi, Damora; Defriadi, Rikko

    2012-06-01

    This research is a continuation of synthetic jet characteristics investigation over convective cooling of impinging jet model. The synthetic jet cooling uses an air flowing in a vertical direction into the heated wall. This model uses an oscilating membrane to push and pull the air from and to the cavity. The purpose of this model of synthetic jet is to create vortices pair to come out from nozzle which will accelerate the heat transfer process occurring at the wall. This heat transfer enhancement principle has became the basis to simulate an alternative cooling system in order to substitute the conventional fan cooling in electronic devices due to its advantage for having a small form factor and low noise. The investigation is conducted in the computational work. In this research, the synthetic jet prototype model was simulated to examine the distribution of heat flow on the walls using a mathematical turbulent model k-ω SST. Meshing order was elements Tet/Hybrid and type Tgrid and the number of grid was more than 233.886 in order to ensure detail discretization and more accurate calculation results. This simulation used a triangular waveform as it excitation source. The frequencies of excitation were 80 Hz, 120 Hz, 160 Hz and the amplitude was 1 m/s. Using this variation, the main goal is to increase the heat transfer coefficient generated by the synthetic jet blow.

  18. Fluorescence imaging study of free and impinging supersonic jets: Jet structure and turbulent transition

    NASA Astrophysics Data System (ADS)

    Inman, Jennifer Ann

    A series of experiments into the behavior of underexpanded jet flows has been conducted at NASA Langley Research Center. This work was conducted in support of the Return to Flight effort following the loss of the Columbia. The tests involved simulating flow through a hypothetical breach in the leading edge of the Space Shuttle Orbiter along its reentry trajectory, with the goal of generating a data set with which other researchers can test and validate computational modeling tools. Two nozzles supplied with high-pressure gas were used to generate axisymmetric underexpanded jets exhausting into a low-pressure chamber. These nozzles had exit Mach numbers of 1 and 2.6. Reynolds numbers based on nozzle exit conditions ranged from about 200 to 35,000, and nozzle exit-to-ambient jet pressure ratios ranged from about 1 to 37. Both free and impinging jets were studied, with impingement distances ranging from 10 to 40 nozzle diameters, and impingement angles of 45°, 60°, and 90°. For the majority of cases, the jet fluid was a mixture of 99.5% nitrogen seeded with 0.5% nitric oxide (NO). Planar laser-induced fluorescence (PLIF) of NO was used to non-intrusively visualize the flow with a temporal resolution on the order of lets. PLIF images were used to identify and measure the location and size of flow structures. PLIF images were further used to identify unsteady jet behavior in order to quantify the conditions governing the transition to turbulent flow. This dissertation will explain the motivation behind the work, provide details of the laser system and test hardware components, discuss the theoretical aspects of laser-induced fluorescence, give an overview of the spectroscopy of nitric oxide, and summarize the governing fluid mechanical concepts. It will present measurements of the size and location of flow structures, describe the basic mechanisms and origins of unsteady behavior in these flows, and discuss the dependence of such behavior on particular flow

  19. Numerical modeling of normal turbulent plane jet impingement on solid wall

    NASA Astrophysics Data System (ADS)

    Guo, C.-Y.; Maxwell, W. H. C.

    1984-10-01

    Attention is given to a numerical turbulence model for the impingement of a well developed normal plane jet on a solid wall, by means of which it is possible to express different jet impingement geometries in terms of different boundary conditions. Examples of these jets include those issuing from VTOL aircraft, chemical combustors, etc. The two-equation, turbulent kinetic energy-turbulent dissipation rate model is combined with the continuity equation and the transport equation of vorticity, using an iterative finite difference technique in the computations. Peak levels of turbulent kinetic energy occur not only in the impingement zone, but also in the intermingling zone between the edges of the free jet and the wall jet.

  20. Numerical modeling of normal turbulent plane jet impingement on solid wall

    SciTech Connect

    Guo, C.Y.; Maxwell, W.H.C.

    1984-10-01

    Attention is given to a numerical turbulence model for the impingement of a well developed normal plane jet on a solid wall, by means of which it is possible to express different jet impingement geometries in terms of different boundary conditions. Examples of these jets include those issuing from VTOL aircraft, chemical combustors, etc. The two-equation, turbulent kinetic energy-turbulent dissipation rate model is combined with the continuity equation and the transport equation of vorticity, using an iterative finite difference technique in the computations. Peak levels of turbulent kinetic energy occur not only in the impingement zone, but also in the intermingling zone between the edges of the free jet and the wall jet. 20 references.

  1. Jet array impingement flow distributions and heat transfer characteristics. Effects of initial crossflow and nonuniform array geometry

    NASA Astrophysics Data System (ADS)

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

    1982-11-01

    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.

  2. Trailing edge cooling using angled impingement on surface enhanced with cast chevron arrangements

    SciTech Connect

    Lee, Ching-Pang; Heneveld, Benjamin E.; Brown, Glenn E.; Klinger, Jill

    2015-05-26

    A gas turbine engine component, including: a pressure side (12) having an interior surface (34); a suction side (14) having an interior surface (36); a trailing edge portion (30); and a plurality of suction side and pressure side impingement orifices (24) disposed in the trailing edge portion (30). Each suction side impingement orifice is configured to direct an impingement jet (48) at an acute angle (52) onto a target area (60) that encompasses a tip (140) of a chevron (122) within a chevron arrangement (120) formed in the suction side interior surface. Each pressure side impingement orifice is configured to direct an impingement jet at an acute angle onto an elongated target area that encompasses a tip of a chevron within a chevron arrangement formed in the pressure side interior surface.

  3. On the effect of fractal generated turbulence on the heat transfer of circular impinging jets

    NASA Astrophysics Data System (ADS)

    Astarita, Tommaso; Cafiero, Gioacchino; Discetti, Stefano

    2013-11-01

    The intense local heat transfer achieved by circular impinging jets is exploited in countless industrial applications (cooling of turbine blades, paper drying, tempering of glass and metals, etc). The heat transfer rate depends mainly on the Reynolds number, the nozzle-to-plate distance and the upstream turbulence. It is possible to enhance the heat transfer by exciting/altering the large scale structures embedded within the jet. In this work turbulent energy is injected by using a fractal grid at the nozzle exit. Fractal grids can generate more intense turbulence with respect to regular grids with the same blockage ratio by enhancing the jet turbulence over different scales. Consequently, they are expected to improve the convective heat transfer. The results outline that a significant improvement is achieved (for small nozzle-to-plate distances up to 100% at the stagnation point and more than 10% on the integral heat transfer over a circular area of 3 nozzle diameters) under the same power input.

  4. Jet Velocity Profile Effects on Spray Characteristics of Impinging Jets at High Reynolds and Weber Numbers

    NASA Astrophysics Data System (ADS)

    Rodrigues, Neil S.; Kulkarni, Varun; Sojka, Paul E.

    2014-11-01

    While like-on-like doublet impinging jet atomization has been extensively studied in the literature, there is poor agreement between experimentally observed spray characteristics and theoretical predictions (Ryan et al. 1995, Anderson et al. 2006). Recent works (Bremond and Villermaux 2006, Choo and Kang 2007) have introduced a non-uniform jet velocity profile, which lead to a deviation from the standard assumptions for the sheet velocity and the sheet thickness parameter. These works have assumed a parabolic profile to serve as another limit to the traditional uniform jet velocity profile assumption. Incorporating a non-uniform jet velocity profile results in the sheet velocity and the sheet thickness parameter depending on the sheet azimuthal angle. In this work, the 1/7th power-law turbulent velocity profile is assumed to provide a closer match to the flow behavior of jets at high Reynolds and Weber numbers, which correspond to the impact wave regime. Predictions for the maximum wavelength, sheet breakup length, ligament diameter, and drop diameter are compared with experimental observations. The results demonstrate better agreement between experimentally measured values and predictions, compared to previous models. U.S. Army Research Office under the Multi-University Research Initiative Grant Number W911NF-08-1-0171.

  5. Visualization of impingement field of real-rocket-exhausted jets by using moire deflectometry

    NASA Astrophysics Data System (ADS)

    He, An-Zhi; Yan, Da-Peng; Miao, Peng C.; Wang, Hai-Ling

    1991-12-01

    The experimental methods and results of an impingement field of a real rocket exhausted jet are presented. By using large aperture and long path moire deflector, the moire deflectograms of rocket free jet and rocket jet impingement field are obtained. From these moire deflectograms, the location of the Mach disk, the oblique shock wave, and the value of boundary are calculated quantitatively and compared with the results of numerical simulating and wind tunnel simulating. At the same time, we have found five new shock wave structures from the experiments.

  6. Heat transfer and flow characteristics of jets impinging on a concave hemispherical plate

    NASA Technical Reports Server (NTRS)

    Hrycak, P.

    1982-01-01

    The present study is concerned with an experimental investigation of the flow characteristics and heat transfer from turbulent air jets impinging normally on a concave hemispherical plate (CHP). It is found that the incompressible, turbulent jets impinging on a CHP are in many respects similar to the jets impinging on a flat plate. The observed differences are due to effects of curvature and to a slightly higher turbulence level inside of the CHP. Attention is given to the experimental apparatus, aspects of inner boundary layer development, the maximum velocity decay in a wall jet, the derivation of a maximum velocity decay formula, the influence of curvature on stagnation point heat transfer, and heat transfer calculations for a concave hemispherical plate.

  7. Conjugate heat transfer study of a turbulent slot jet impinging on a moving plate

    NASA Astrophysics Data System (ADS)

    Achari, A. Madhusudana; Das, Manab Kumar

    2016-07-01

    Numerical simulation of the flow field and conjugate heat transfer in an impinging jet with moving impingement plate is one of the important problems as it mimics closely with practical applications in industries. The Yang-Shih version of low Reynolds number k-ɛ model has been used to resolve the flow field and the temperature field in a two-dimensional, steady, incompressible, confined, turbulent slot jet impinging normally on a moving flat plate of finite thickness. The turbulence intensity and the Reynolds number considered at the inlet are 2 % and 15,000, respectively. The bottom face of the impingement plate has been maintained at a constant temperature higher than the nozzle exit temperature. The confinement plate has been considered to be adiabatic. The nozzle-to-surface spacing for the above study has been taken to be 6 and the surface-to-jet velocity ratios have been taken over a range of 0.25-1. The effects of impingement plate motion on the flow field and temperature field have been discussed elaborately with reference to stationary impingement plate. The dependence of flow field and fluid temperature field on impingement plate motion has been analyzed by plotting streamlines, isotherms for different plate speeds. A thorough study of flow characteristics for different surface-to-jet velocity ratios has been carried out by plotting profiles of mean vertical and horizontal components of velocity, pressure distribution, local shear stress distribution. The isotherms in the impingement plate of finite thickness, the distributions of solid-fluid interface temperature, the local Nusselt number, and the local heat flux for different surface-to-jet velocity ratios added to the understanding of conjugate heat transfer phenomenon.

  8. Heat transfer from a liquid bath due to an impinging gas jet: A numerical study

    SciTech Connect

    Qian, F.; Farouk, B.; Mutharasan, R.

    1995-12-31

    An impinging gasjet on a liquid surface is found in many industrial processes such as electric arc furnace steel-making and welding. Fundamental understanding of the interaction of a gas or plasmajet impinging on a liquid pool can provide important insights into process behavior resulting in improved efficiency. A numerical model is developed for solving both the impinging gas jet and the liquid pool temperature and flow fields along with the deformed interface shape for the above processing operation. Using curvilinear coordinates, the Navier-Stokes equations of each phase are solved separately and then coupled via continuity of static pressure, shear stress, temperature and heat flux at the interface.

  9. Experimental study of convective heat transfer under arrays of impinging air jets from slots and circular holes

    NASA Astrophysics Data System (ADS)

    Can, M.; Etemog✓lu, A. B.; Avci, A.

    Impinging air jets are widely used in industry, for heating, cooling, drying, etc, because of the high heat transfer rates which is developed in the impingement region. To provide data for designers of industrial equipment, a large multi-nozzle rig was used to measure average heat transfer coefficients under arrays of both slot nozzles and circular holes. The aim of the present paper is to develop the relationship between heat transfer coefficient, air mass flow and fan power which is required for the optimum design of nozzle systems. The optimum free area was obtained directly from experimental results. The theory of optimum free area was analysed and good agreement was found between theoretical and experimental results. It was also possible to optimise the variables, to achieve minimum capital and running costs.

  10. Flow characteristics in free impinging jet reactor by particle image velocimetry (PIV) investigation

    NASA Astrophysics Data System (ADS)

    Zhang, Jun; Liu, Youzhi; Qi, Guisheng; Jiao, Weizhou; Yuan, Zhiguo

    2016-08-01

    The flow characteristics in free impinging jet reactors (FIJRs) were investigated using particle image velocimetry (PIV). The effects of the Reynolds number (Re) and the ratio of jet distance to jet diameter (w/d) on flow behavior were discussed for equal volumetric flow rates of the two jets. The impingement plane, instantaneous velocity, mean velocity, and turbulent kinetic energy (TKE) distribution of FIJRs are measured from captured images using the PIV technique. As Re increases, the average diameter of the impingement plane linearly increases. The instability of the liquid is closely related to the jet velocity or the Re. However, the stagnation point is insensitive to the variation of the Re. The droplets break up from the turbulent liquid in the ‘wall-free’ environment of FIJRs, so that the liquid back-flow found in confined impinging jet reactors (CIJRs) is not observed. Increasing the Re from 1800–4100 or decreasing the w/d from 20–6 plays a similar role in increasing the TKE values and intensifying turbulence, which promotes the momentum transfer and mixing efficiency in FIJRs.

  11. Shock structures and instabilities formed in an underexpanded jet impinging on to cylindrical sections

    NASA Astrophysics Data System (ADS)

    Mason-Smith, N.; Edgington-Mitchell, D.; Buchmann, N. A.; Honnery, D. R.; Soria, J.

    2015-11-01

    Schlieren visualisations are used to investigate the influence of cylindrical surface curvature on both the time-invariant and oscillatory behaviour of the shock structures within underexpanded jets impinging on to a surface. At moderate standoff distances ( h/d < 5) , the impingement surface curvature affects the temporal behaviour of the flow significantly, but with only slight variations in the time-invariant structure. A convex surface curvature constrains flapping oscillations to a single plane, the normal of which is parallel to the cylinder axis; the oscillation frequency is largely unaffected. For the standoff distances and nozzle pressure ratios studied, concave surface curvature suppresses the formation of impingement tones. A mechanism is proposed whereby entrainment of the recirculated wall jet flow alters the shear layer receptivity to acoustic disturbances, breaking the acoustic feedback loop that drives the jet oscillations.

  12. Instability of a confined jet impinging on a water/air free surface

    NASA Astrophysics Data System (ADS)

    Bouchet, G.; Climent, E.; Maurel, A.

    2002-09-01

    Self-sustained oscillations in sinuous mode occur when a water jet impinges from below on a water/air free surface. Confined jet instability is experimentally investigated by image processing and velocity measurements. Despite small deformations of the surface, dynamic response of the jet provides unusual behaviour with comparable configurations (hole-tone, jet edge ...). The central feature is a bounded evolution of the oscillation frequency. Modal transitions are observed when physical parameters are varied. Each frequency jump is related to wavelength modification of the spatial pattern. Atypical evolution of the predominant length scale has to be connected to strong coupling with the weak deformations induced by the impinging jet on the free surface.

  13. Apparatus and methods for impingement cooling of a side wall of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian

    2002-01-01

    A gas turbine nozzle segment has outer and inner bands and a vane therebetween. Each band includes a nozzle wall, a side wall, a cover and an impingement plate between the cover and the nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. The impingement plate has a turned flange welded to the inturned flange. A backing plate overlies the turned flange and aligned apertures are formed through the backing plate and turned flange to direct and focus cooling flow onto the side wall of the nozzle segment.

  14. Aeroacoustics and aerodynamics of impinging supersonic jets: Analysis of the screech tones

    NASA Astrophysics Data System (ADS)

    Sinibaldi, G.; Lacagnina, G.; Marino, L.; Romano, G. P.

    2013-08-01

    The interaction between acoustics and aerodynamics of a supersonic jet is an actual fundamental topic which has been a matter of discussion in the last decades. The present paper is devoted to the experimental analysis of free and impinging jets with particular attention on the effect of an impinging surface on screech tones. The acoustics is studied using free-field microphones, while Particle Image Velocimetry is used to investigate the velocity field. The analysis of acquired data allowed to verify and explain the coupling between acoustic discrete tones and mean and fluctuating flow velocities.

  15. Computation of Tone Noise From Supersonic Jet Impinging on Flat Plates

    NASA Technical Reports Server (NTRS)

    Loh, Ching Y.; Blech, Richard A. (Technical Monitor)

    2005-01-01

    A supersonic jet impinging normally on a flat plate has both practical importance and theoretical interests. The physical phenomenon is not fully understood yet. Research concentrates either on the hydrodynamics (e.g., lift loss for STOVL) or on the aeroacoustic loading. In this paper, a finite volume scheme - the space-time conservation element and solution element (CE/SE) method - is employed to numerically study the near-field noise of an underexpanded supersonic jet from a converging nozzle impinging normally on a flat plate. The numerical approach is of the MILES type (monotonically integrated large eddy simulation). The computed results compare favorably with the experimental findings.

  16. Large-eddy numerical simulation of an array of three-dimensional impinging jets

    NASA Astrophysics Data System (ADS)

    Rizk, M. H.; Menon, S.

    1987-04-01

    Numerical simulations of a row of impinging jets are performed. Both the impinging jets and the fountains caused by the collision of the wall jets are modeled in the simulations. The problem considered contains the essential features of twin jets impinging on the ground, simulating the hovering configuration of a VTOL aircraft. The flow is assumed to be governed by the time-dependent, incompressible Navier-Stokes equations. The large-eddy simulation approach is followed in which all scales resolvable by the grid resolution are computed explicitly, while the small-scale turbulence structures, which are nearly universal in character, are modeled by an eddy viscosity formulation that simulates the energy cascade into the small scales. The Navier-Stokes equations are solved using a staggered computational mesh. Central finite differencing is used to discretize all terms except the convective terms, which are discretized using the QUICK scheme. The Adams-Bashforth scheme is used to advance the solution in time. The pressure Poisson equation is used in place of the continuity equation. Efficient direct solutions are obtained for the pressure field, which allows the continuity equation to be satisfied at each time step. This study focuses on the motion and dynamics of large-scale structures that have been experimentally observed in jet flows. The behavior of the jets and the fountain due to introducing axisymmetric, azimuthal and random disturbances at the jet exits is investigated.

  17. Spatial Characteristics of Water Spray Formed by Two Impinging Jets at Several Jet Velocities in Quiescent Air

    NASA Technical Reports Server (NTRS)

    Foster, Hampton H.; Heidmann, Marcus F.

    1960-01-01

    The spatial characteristics of a spray formed by two impinging water jets in quiescent air were studied over a range of nominal jet velocities of 30 to 74 feet per second. The total included angle between the 0.089-inch jets was 90 deg. The jet velocity, spray velocity, disappearance of the ligaments just before drop formation, mass distribution, and size and position of the largest drops were measured in a circumferential survey around the point of jet impingement. Photographic techniques were used in the evaluations. The distance from the point of jet impingement to ligament breakup into drops was about 4 inches on the spray axis and about 1.3 inches in the radial position +/-90 deg from the axis. The distance tended to increase slightly with increase in jet velocity. The spray velocity varied from about 99 to about 72 percent of the jet velocity for a change in circumferential position from the spray axis to the +/-80 deg positions. The percentages tended to increase slightly with an increase in jet velocity. Fifty percent of the mass was distributed about the spray axis in an included angle of slightly less than 40 deg. The effect of jet velocity was small. The largest observed drops (2260-micron or 0.090-in. diam.) were found on and about the spray axis. The size of the largest drops decreased for an increase in radial angular position, being about 1860 microns (0.074 in.) at the +/-90 deg positions. The largest drop sizes tended to decrease for an increase in jet velocity, although the velocity effect was small. A drop-size distribution analysis indicated a mass mean drop size equal to 54 percent of an extrapolated maximum drop size.

  18. Secondary Peak in Nusselt Number for Jet Impinging Flows: LES Study

    NASA Astrophysics Data System (ADS)

    Dutta, Rabijit; Dewan, Anupam; Srinivasan, Balaji

    2013-11-01

    Jet impingement heat transfer is widely studied because of its industrial and as well as fundamental relevance. A secondary peak in Nusselt number at some distance away from the stagnation point is observed for both round and slot jet impingement flows at a small nozzle-to-plate spacing. Although various researchers have studied the reason behind this secondary peak, it is still an open question in the literature. We present large eddy simulation (LES) of turbulent slot jet impingement heat transfer to gain further insight into the phenomenon of secondary peak in Nusselt number. Profiles of mean velocities, turbulent fluctuating velocities and Nusselt numbers have been analyzed along the impingement plate. A sudden increase in the wall normal turbulence fluctuations have been observed in the region where the secondary peak in Nusselt number occurs. Further, an analysis of vortex structures of the flow showed that the increase in the wall normal turbulence could be associated with the secondary vortex observed near the impingement wall. PhD candidate.

  19. Investigation of impinging jet resonant modes using unsteady pressure-sensitive paint measurements

    NASA Astrophysics Data System (ADS)

    Davis, Timothy; Edstrand, Adam; Alvi, Farrukh; Cattafesta, Louis; Yorita, Daisuke; Asai, Keisuke

    2015-05-01

    At given nozzle to plate spacings, the flow field of high-speed impinging jets is known to be characterized by a resonance phenomenon. Large coherent structures that convect downstream and impinge on the surface create strong acoustic waves that interact with the inherently unstable shear layer at the nozzle exit. This feedback mechanism, driven by the coherent structures in the jet shear layer, can either be axisymmetric or helical in nature. Fast-response pressure-sensitive paint (PSP) is applied to the impingement surface to map the unsteady pressure distribution associated with these resonant modes. Phase-averaged results acquired at several kHz are obtained using a flush mounted unsteady pressure transducer on the impingement plate as a reference signal. Tests are conducted on a Mach 1.5 jet at nozzle to plate spacings of . The resulting phase-averaged distribution reveals dramatically different flow fields at the corresponding impingement heights. The existence of a purely axisymmetric mode with a frequency of 6.3 kHz is identified at and is characterized by concentric rings of higher/lower pressure that propagate radially with increasing phase. Two simultaneous modes are observed at with one being a dominant symmetric mode at 7.1 kHz and the second a sub-dominant helical mode at 4.3 kHz. Complimentary phase-conditioned Schlieren images are also obtained visualizing the flow structures associated with each mode and are consistent with the PSP results.

  20. Characterization of an impinging jet into porous media

    NASA Astrophysics Data System (ADS)

    Wang, Cong; Alhani, Salwan; Gharib, Morteza

    2015-11-01

    In this work, characteristic behavior of a liquid jet into porous hydrophobic / hydrophilic particle media is investigated. In porous media, the capillary effect becomes significant, especially when the jet Reynolds Number is low. To analyze the cavity creation phenomena, the effect of jet's diameter, speed and acceleration as well as particles' size are carefully studied. Such knowledge of fluid behavior will provide guidance for medicine injection process. This work is supported by Caltech GALCIT STEM program.

  1. Unsteady flow and heat transfer analysis of an impinging synthetic jet

    NASA Astrophysics Data System (ADS)

    Bazdidi-Tehrani, Farzad; Karami, Mahdi; Jahromi, Mehdi

    2011-11-01

    The present paper focuses on the analysis of unsteady flow and heat transfer regarding an axisymmetric impinging synthetic jet on a constant heat flux disc. Synthetic jet is a zero net mass flux jet that provides an unsteady flow without any external source of fluid. Present results are validated against the available experimental data showing that the SST/ k - ω turbulence model is more accurate and reliable than the standard and low- Re k - ɛ models for predicting heat transfer from an impinging synthetic jet. It is found that the time-averaged Nusselt number enhances as the nozzle-to-plate distance is increased. As the oscillation frequency in the range of 16-400 Hz is increased, the heat transfer is enhanced. It is shown that the instantaneous Nu distribution along the wall is influenced mainly by the interaction of produced vortex ring and wall boundary layer. Also, the fluctuation level of Nu decreases as the frequency is raised.

  2. Laser-Induced Fluorescence Velocity Measurements in Supersonic Underexpanded Impinging Jets

    NASA Technical Reports Server (NTRS)

    Inman, Jennifer A.; Danehy, Paul M.; Barthel, Brett; Alderfer, David W.; Novak, Robert J.

    2010-01-01

    We report on an application of nitric oxide (NO) flow-tagging velocimetry to impinging underexpanded jet flows issuing from a Mach 2.6 nozzle. The technique reported herein utilizes a single laser, single camera system to obtain planar maps of the streamwise component of velocity. Whereas typical applications of this technique involve comparing two images acquired at different time delays, this application uses a single image and time delay. The technique extracts velocity by assuming that particular regions outside the jet flowfield have negligible velocity and may therefore serve as a stationary reference against which to measure motion of the jet flowfield. By taking the average of measurements made in 100 single-shot images for each flow condition, streamwise velocities of between -200 and +1,000 m/s with accuracies of between 15 and 50 m/s are reported within the jets. Velocity measurements are shown to explain otherwise seemingly anomalous impingement surface pressure measurements.

  3. Apparatus for impingement cooling a side wall adjacent an undercut region of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian

    2002-01-01

    A gas turbine nozzle segment has outer and inner bands and vanes therebetween. Each band includes a side wall, a cover and an impingement plate between the cover and nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. Slots are formed through the inturned flange along the nozzle side wall. A plate having through-apertures extending between opposite edges thereof is disposed in each slot, the slots and plates being angled such that the cooling medium exiting the apertures in the second cavity lie close to the side wall for focusing and targeting cooling medium onto the side wall.

  4. Investigation of flow structure and heat transfer characteristics in an array of impinging slot jets

    NASA Astrophysics Data System (ADS)

    Ozmen, Yucel; Ipek, Gokhan

    2016-04-01

    In this study, an experimental and numerical study is carried out to investigate flow field and heat transfer characteristics of unconfined and confined arrays of four turbulent slot air jets issuing from the lower surface and impinging normally on the upper surface. Pressure and temperature distributions on the surfaces were obtained for the nozzle-to-plate spacing (H/W) of 1-10 and for the Reynolds numbers in the range of 5000-15,000 at the jet-to-jet centerline spacing (S/W) of 9. The effects of jet confinement, Reynolds number and nozzle-to-plate spacing on the flow structure and heat transfer were investigated. Pressure distributions are obtained experimentally and numerically, while heat transfer distributions are computed numerically. It is observed that the surface pressure distributions on both impingement and confinement plates are independent from the Reynolds number, while they have been largely affected from the nozzle-to-plate spacing. Jet confinement causes a considerable difference at the flow field especially for small nozzle-to-plate spacings. Subatmospheric regions are not observed for unconfined jet. However three different types of subatmospheric pressure regions occur on both impingement and confinement plates for confined jet. Nusselt distributions on the impingement plate for both unconfined and confined jet configurations depend on the Reynolds number and nozzle-to-plate spacing. It is concluded that there is a strong correlation between subatmospheric regions and secondary peaks in Nusselt distributions. The numerical results obtained using the Realizable k-ɛ turbulence model is in good accordance with the experimental results for moderate values of nozzle-to-plate spacings.

  5. Liquid jet impingement normal to a disk in zero gravity. Ph.D. Thesis - Toledo Univ.

    NASA Technical Reports Server (NTRS)

    Labus, T. L.

    1976-01-01

    An experimental and analytical investigation was conducted to determine the free surface shapes of circular liquid jets impinging normal to sharp-edged disks under both normal and zero gravity conditions. An order of magnitude analysis was conducted indicating regions where viscous forces were not significant when computing free surface shapes. The demarcation between the viscous and inviscid region was found to depend upon the flow Reynolds number and the ratio between the jet and disk radius.

  6. OVERFLOW Validation for Predicting Plume Impingement of Underexpanded Axisymmetric Jets onto Angled Flat Plates

    NASA Technical Reports Server (NTRS)

    Lee, Henry C.; Klopfer, Goetz

    2011-01-01

    This report documents how OVERFLOW, a computational fluid dynamics code, predicts plume impingement of underexpanded axisymmetric jets onto both perpendicular and inclined flat plates. The effects of the plume impinging on a range of plate inclinations varying from 90deg to 30deg are investigated and compared to the experimental results in Reference 1 and 2. The flow fields are extremely complex due to the interaction between the shock waves from the free jet and those deflected by the plate. Additionally, complex mixing effects create very intricate structures in the flow. The experimental data is very limited, so these validation studies will focus only on cold plume impingement on flat and inclined plates. This validation study will help quantify the error in the OVERFLOW simulation when applied to stage separation scenarios.

  7. Self-excited oscillations of a high-speed impinging planar jet

    NASA Astrophysics Data System (ADS)

    Arthurs, David; Ziada, Samir

    2012-10-01

    This paper examines aeroacoustic tone generation of a high-speed planar gas jet impinging normally on a flat, rigid surface. Experiments are performed over the complete range of subsonic jet velocities for which tones are generated, and over the complete range of impingement distance for which tones occur for a single nozzle thickness of h = 3 mm. The behavior of the planar impinging jet case is compared to that of the axisymmetric case and found to be significantly different, with tones being excited at much larger impingement ratios and lower flow velocities. The acoustic tones have been found to be generated by both symmetric and anti-symmetric jet instabilities, coupled with resonant acoustic modes occurring between the nozzle and plate surface. The nature of the flow instabilities has been investigated using phase-averaged particle image velocimetry measurements. The frequency behavior of the resulting tones is predicted using a simple feedback model, which allows the identification of the various shear layer modes of the instabilities driving tone generation. Finally, a thorough dimensionless analysis is performed in order to quantify the system behavior in terms of the appropriate length and velocity scales.

  8. Jet impingement heat transfer enhancement for the GPU-3 Stirling engine

    NASA Technical Reports Server (NTRS)

    Johnson, D. C.; Congdon, C. W.; Begg, L. L.; Britt, E. J.; Thieme, L. G.

    1981-01-01

    A computer model of the combustion-gas-side heat transfer was developed to predict the effects of a jet impingement system and the possible range of improvements available. Using low temperature (315 C (600 F)) pretest data in an updated model, a high temperature silicon carbide jet impingement heat transfer system was designed and fabricated. The system model predicted that at the theoretical maximum limit, jet impingement enhanced heat transfer can: (1) reduce the flame temperature by 275 C (500 F); (2) reduce the exhaust temperature by 110 C (200 F); and (3) increase the overall heat into the working fluid by 10%, all for an increase in required pumping power of less than 0.5% of the engine power output. Initial tests on the GPU-3 Stirling engine at NASA-Lewis demonstrated that the jet impingement system increased the engine output power and efficiency by 5% - 8% with no measurable increase in pumping power. The overall heat transfer coefficient was increased by 65% for the maximum power point of the tests.

  9. Excavation of Regolith by Impinging Jets of Gas

    NASA Technical Reports Server (NTRS)

    Metzger, Philip T.; Immer, Christopher D.; Vu, Bruce T.; Donahue, Carly M.

    2006-01-01

    There are many situations in nature and technology where particulate matter is excavated by a fluid jet. Such a process is often used to excavate soil or to dig wells. Air jets are often used to transport particulate matter such as powders in various industrial processes. Similar situations occur in nature, as when waterfalls scour holes in sand. In other cases, the excavation is unwanted such as when a rocket lands on the sandy or dusty surface of a planet or moon. Recent research into regolith excavation by gas jets has obtained new insights into the physical processes of that excavation, and these may lead to new advances in technology for more efficient fluid-jet excavation processes and for better control of the unwanted excavation effects of landing rockets. This talk will explain the new insights and point to future work supporting lunar exploration.

  10. Turbulent Heat Transfer From a Slot Jet Impinging on a Flat Plate.

    PubMed

    Benmouhoub, Dahbia; Mataoui, Amina

    2013-10-01

    The flow field and heat transfer of a plane impinging jet on a hot moving wall were investigated using one point closure turbulence model. Computations were carried out by means of a finite volume method. The evolutions of mean velocity components, vorticity, skin friction coefficient, Nusselt number and pressure coefficient are examined in this paper. Two parameters of this type of interaction are considered for a given impinging distance of 8 times the nozzle thickness (H/e = 8): the jet-surface velocity ratio and the jet exit Reynolds number. The flow field structure at a given surface-to-jet velocity ratio is practically independent to the jet exit Reynolds number. A slight modification of the flow field is observed for weak surface-to-jet velocity ratios while the jet is strongly driven for higher velocity ratio. The present results satisfactorily compare to the experimental data available in the literature for Rsj ≤ 1.The purpose of this paper is to investigate this phenomenon for higher Rsj values (0 ≤ Rsj ≤ 4). It follows that the variation of the mean skin friction and the Nusselt number can be correlated according to the surface-to-jet velocity ratios and the Reynolds numbers. PMID:24895466

  11. Heat transfer characteristics within an array of impinging jets. Effects of crossflow temperature relative to jet temperature

    NASA Technical Reports Server (NTRS)

    Florschuetz, L. W.; Su, C. C.

    1985-01-01

    Spanwise average heat fluxes, resolved in the streamwise direction to one stream-wise hole spacing were measured for two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate. The jet flow, after impingement, was constrained to exit in a single direction along the channel formed by the jet orifice plate and heat transfer surface. The crossflow originated from the jets following impingement and an initial crossflow was present that approached the array through an upstream extension of the channel. The regional average heat fluxes are considered as a function of parameters associated with corresponding individual spanwise rows within the array. A linear superposition model was employed to formulate appropriate governing parameters for the individual row domain. The effects of flow history upstream of an individual row domain are also considered. The results are formulated in terms of individual spanwise row parameters. A corresponding set of streamwise resolved heat transfer characteristics formulated in terms of flow and geometric parameters characterizing the overall arrays is described.

  12. ANSYS Fluent Modelling of an Underexpanded Supersonic Sootblower Jet Impinging into Recovery Boiler Tube Geometries

    NASA Astrophysics Data System (ADS)

    Doroudi, Shahed

    Sootblowers generate high pressure supersonic steam jets to control fireside deposition on heat transfer tubes of a kraft recovery boiler. Sootblowing is energy expensive, using 3-12% of the mill's total steam production. This motivates research on the dynamics of sootblower jet interaction with tubes and deposits, to optimize their use. A CFD investigation was performed using ANSYS Fluent 15.0 to model three-dimensional steady-state impingement of a Mach 2.5 mildly underexpanded (PR 1.2) air jet onto arrays of cylindrical tubes with and without fins, at various nozzle-to-tube centerline offsets. A free jet and four impingement cases for each of the economizer and generating bank geometries are compared to experimental visualizations. Pressure distributions on impinging surfaces suggest that the fins in the economizer produce a reduced but uniform sootblowing force. Pressure contours along the tubes (in the vertical direction) show a sharp decline one tube diameter away from the jet mid-plane.

  13. 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.

  14. Development of an Impinging-jet Fuel-injection Valve Nozzle

    NASA Technical Reports Server (NTRS)

    Spanogle, J A; Hemmeter, G H

    1931-01-01

    During an investigation to determine the possibilities and limitations of a two-stroke-cycle engine and ignition, it was necessary to develop a fuel injection valve nozzle to produce a disk-shaped, well dispersed spray. Preliminary tests showed that two smooth jets impinging upon each other at an angle of 74 degrees gave a spray with the desired characteristics. Nozzles were built on this basis and, when used in fuel-injection valves, produced a spray that fulfilled the original requirements. The spray is so well dispersed that it can be carried along with an air stream of comparatively low velocity or entrained with the fuel jet from a round-hole orifice. The characteristics of the spray from an impinging-jet nozzle limits its application to situations where wide dispersion is required by the conditions in the engine cylinder and the combustion chamber.

  15. Method for analyzing the gas jet impinging on a liquid surface

    NASA Astrophysics Data System (ADS)

    Mordasov, M. M.; Savenkov, A. P.; Chechetov, K. E.

    2016-05-01

    The impingement of a gas jet on a liquid surface in the stable-state regime is analyzed theoretically. We consider the case of the perpendicular jet action. It is found that for describing analytically the processes occurring in this case, it is necessary to employ the balance equation for forces at the interface and not the balance equation for pressures at the lowest point of cavity, which was used in most available publications. Recommendations for experimental studies of a gas jet impinging on a liquid surface are formulated. We report on the results of experiments confirming the correctness of our theoretical analysis and making it possible to determine the empirical value of the shape factor. The experiments were carried out with air and epoxy resin. The cavity formed on the liquid surface had radius R 0 = 1-8 mm and depth h = 0.2-12.5 mm.

  16. Analysis of heat transfer for a normally impinging liquid-metal slot jet

    NASA Technical Reports Server (NTRS)

    Siegel, R.

    1973-01-01

    A two-dimensional liquid-metal slot jet that is impinging normally against a uniformly heated flat plate is analyzed. The distributions of wall temperature and heat-transfer coefficient are obtained as functions of position along the plate. The liquid-metal assumptions are made that the jet is inviscid and that molecular condition is dominating heat diffusion. The solution is obtained by mapping the jet flow region into a potential plane where it occupies a strip of uniform width. The energy equation is transformed into potential coordinates, and an exact solution obtained in the strip region. Conformal mapping is then used to transform the solution into the physical plane.

  17. Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator

    NASA Technical Reports Server (NTRS)

    Brehm, Christoph; Housman, Jeffrey A.; Kiris, Cetin C.; Hutcheson, Florence V.

    2015-01-01

    The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition of the flow field is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortex tubes in the center of the impingement region. The causality method based on Lighthill's acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term in the Lighthill's stress tensor plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a reduced-order linear acoustic model of the four-jet impingement device. Finally, three linear acoustic FJID models are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data.

  18. Experimental investigation of the wall shear stress and the vortex dynamics in a circular impinging jet

    NASA Astrophysics Data System (ADS)

    El Hassan, Mouhammad; Assoum, Hassan Hassan; Sobolik, Vaclav; Vétel, Jérôme; Abed-Meraim, Kamel; Garon, André; Sakout, Anas

    2012-06-01

    The wall shear stress and the vortex dynamics in a circular impinging jet are investigated experimentally for Re = 1,260 and 2,450. The wall shear stress is obtained at different radial locations from the stagnation point using the polarographic method. The velocity field is given from the time resolved particle image velocimetry (TR-PIV) technique in both the free jet region and near the wall in the impinging region. The distribution of the momentum thickness is also inspected from the jet exit toward the impinged wall. It is found that the wall shear stress is correlated with the large-scale vortex passing. Both the primary vortices and the secondary structures strongly affect the variation of the wall shear stress. The maximum mean wall shear stress is obtained just upstream from the secondary vortex generation where the primary structures impinge the wall. Spectral analysis and cross-correlations between the wall shear stress fluctuations show that the vortex passing influences the wall shear stress at different locations simultaneously. Analysis of cross-correlations between temporal fluctuations of the wall shear stress and the transverse vorticity brings out the role of different vortical structures on the wall shear stress distribution for the two Reynolds numbers.

  19. Investigation of the interaction of a turbulent impinging jet and a heated, rotating disk

    NASA Astrophysics Data System (ADS)

    Manceau, R.; Perrin, R.; Hadžiabdić, M.; Benhamadouche, S.

    2014-03-01

    The case of a turbulent round jet impinging perpendicularly onto a rotating, heated disc is investigated, in order to understand the mechanisms at the origin of the influence of rotation on the radial wall jet and associated heat transfer. The present study is based on the complementary use of an analysis of the orders of magnitude of the terms of the mean momentum and Reynolds stress transport equations, available experiments, and dedicated Reynolds-averaged Navier-Stokes computations with refined turbulence models. The Reynolds number Rej = 14 500, the orifice-to-plate distance H = 5D, where D is the jet-orifice diameter, and the four rotation rates were chosen to match the experiments of Minagawa and Obi ["Development of turbulent impinging jet on a rotating disk," Int. J. Heat Fluid Flow 25, 759-766 (2004)] and comparisons are made with the Nusselt number distribution measured by Popiel and Boguslawski ["Local heat transfer from a rotating disk in an impinging round jet," J. Heat Transfer 108, 357-364 (1986)], at a higher Reynolds number. The overestimation of turbulent mixing in the free-jet before the impact on the disk is detrimental to the prediction of the impingement region, in particular of the Nusselt number close to the symmetry axis, but the self-similar wall jet developing along the disk is correctly reproduced by the models. The analysis, experiments, and computations show that the rotational effect do not directly affect the outer layer, but only the inner layer of the wall jet. A noteworthy consequence is that entrainment at the outer edge of the wall jet is insensitive to rotation, which explains the dependence of the wall-jet thickness on the inverse of the non-dimensional rotation rate, observed in the experiments and the Reynolds stress model computations, but not reproduced by the eddy-viscosity models, due to the algebraic dependence to the mean flow. The analysis makes moreover possible the identification of a scenario for the appearance of

  20. Visualization and structure of confined, milliscale, unsteady impinging slot jets and associated vortices

    NASA Astrophysics Data System (ADS)

    Lee, Dae Hee; Park, Hyun Jin; Ligrani, Phil

    2013-01-01

    Flow characteristics of confined, laminar milliscale slot jets are investigated from visualizations, as they impinge upon a flat target plate, with a fully developed velocity profile at the nozzle exit. The effects of Reynolds number Re and normalized nozzle-to-plate distance H/B are considered for a nozzle width B of 1.0 mm. Transition from a stable symmetric jet to an unsteady oscillating jet is observed as the Reynolds number increases (with H/B constant), where the Reynolds number associated with this transition decreases as the normalized nozzle-to-plate distance H/B increases. Instantaneous visualizations show unsteady lateral distortions of jet columns at experimental conditions corresponding to the presence of continuous sinusoidal oscillations, intermittent oscillating motion of the jet column, and jet flow fluctuation/flapping motion. Also apparent in flow visualization sequences are smoke signatures associated with instantaneous vortex structures, which form as secondary flows develop in fluid which, initially, is just adjacent to and within the jet column. Associated jet and vortex structural changes are described as different modes of unsteadiness are present, including characterization of jet column unsteadiness using jet column oscillation frequency, and lateral and streamwise extents of jet distortion.

  1. Visualization and structure of confined, milliscale, unsteady impinging slot jets and associated vortices

    NASA Astrophysics Data System (ADS)

    Lee, Dae Hee; Park, Hyun Jin; Ligrani, Phil

    2012-12-01

    Flow characteristics of confined, laminar milliscale slot jets are investigated from visualizations, as they impinge upon a flat target plate, with a fully developed velocity profile at the nozzle exit. The effects of Reynolds number Re and normalized nozzle-to-plate distance H/B are considered for a nozzle width B of 1.0 mm. Transition from a stable symmetric jet to an unsteady oscillating jet is observed as the Reynolds number increases (with H/B constant), where the Reynolds number associated with this transition decreases as the normalized nozzle-to-plate distance H/B increases. Instantaneous visualizations show unsteady lateral distortions of jet columns at experimental conditions corresponding to the presence of continuous sinusoidal oscillations, intermittent oscillating motion of the jet column, and jet flow fluctuation/flapping motion. Also apparent in flow visualization sequences are smoke signatures associated with instantaneous vortex structures, which form as secondary flows develop in fluid which, initially, is just adjacent to and within the jet column. Associated jet and vortex structural changes are described as different modes of unsteadiness are present, including characterization of jet column unsteadiness using jet column oscillation frequency, and lateral and streamwise extents of jet distortion.

  2. An investigation of axisymmetric excitation effects on a row of impinging jets using large-eddy simulations

    NASA Astrophysics Data System (ADS)

    Rizk, Magdi H.; Menon, Suresh

    Numerical simulations of a row of impinging jets are performed. Both the impinging jets and the fountains caused by the collision of the wall jets are modeled in the simulations. The problem considered contains the essential features of twin jets impinging on the ground, simulating the hovering configuration of a vertical takeoff and landing (VTOL) aircraft. The flow is assumed to be governed by the time-dependent, incompressible Navier-Stokes equations. The large-eddy simulation approach is followed. The present study focuses on the motion and dynamics of large-scale structures that have been experimentally observed in jet flows. The behavior of the jets and the fountain due to the introduction of axisymmetric disturbances at the jet exits is investigated.

  3. Local quenching phenomena of a lean premixed flat flame impinging with a pulsating air jet

    NASA Astrophysics Data System (ADS)

    Yahagi, Y.; Makino, I.

    2014-08-01

    Local quenching phenomena of a lean methane air premixed flat flame formed horizontally in a wall stagnating flow impinging with a pulsating air jet has been investigated experimentally. The burner system consists of 40mm inverted nozzle burner and a solid wall with 8mm diameter air jet placed in line vertically. The pulsating frequencies set up to 100Hz while the jet intensities generate up to 6 m/s by a loud speaker. Approximately '00mm disk shape flame front is curved by the pulsating air jet and the air jet impacting point is locally quenched. The fuel concentration of quenching start condition increases with increasing the intensity of air jet, because the increased jet intensity linked with the flame strain rate gain. For weak jet intensity range, the quenching hole becomes directly to develop the whole flame extinction. On the other hand, for moderate or strong jet condition, the flame can recover from the local quenching phenomena. In this condition, once the quenching hole creates, but the hole may close by the flame propagation or reigniting process. Then, the whole flame extinction limits are lower than no jet impacting condition depending on the circumstances.

  4. Air jet erosion test on plasma sprayed surface by varying erodent impingement pressure and impingement angle

    NASA Astrophysics Data System (ADS)

    Behera, Ajit; Behera, Asit; Mishra, S. C.; Pani, S.; Parida, P.

    2015-02-01

    Fly-ash premixed with quartz and illmenite powder in different weight proportions are thermal sprayed on mild steel and copper substrates at various input power levels of the plasma torch ranging from 11 kW to 21 kW DC. The erosion test has done using Air Jet erosion test Reg (As per ASTM G76) with silica erodent typically 150-250 pm in size. Multiple tests were performed at increasing the time duration from 60 sec to 180 sec with increasing pressure (from 1 bar to 2.5 bar) and angle (60° & 90°). This study reveals that the impact velocity and impact angle are two most significant parameters among various factors influencing the wear rate of these coatings. The mechanisms and microstructural changes that arise during erosion wear are studied by using SEM. It is found that, when erodent are impacting the fresh un-eroded surface, material removal occurs by the continuous evolution of craters on the surface. Upper layer splats are removed out after 60 sec and second layer splat erosion starts. Based on these observations Physical models are developed. Some graphs plotted between mass loss-rate versus time period/impact Pressure/impact Angle gives good correlation with surface features observed.

  5. Heat transfer from an open-wedge cavity to a symmetrically impinging slot air jet

    NASA Astrophysics Data System (ADS)

    Rahimi, Mostafa; Mazraeh, Adel Etefagh

    2014-08-01

    Heat transfer from an open-wedge cavity to a symmetrically impinging slot air jet is investigated at the present study. The effect of the cavity angle was mainly examined on the Nusselt number distribution. Based on the results, heat transfer was generally poor at the vicinity of the apex, rising to form a maximum at the impingement and then followed by a moderate decline at further distances. The region of maximum heat transfer on the surfaces shifted outward the cavity as the cavity angle was decreased. Also, average Nusselt number over an effective length of the surface remained almost constant and independent of the cavity angle for a specified jet Reynolds number and nozzle-to-apex spacing.

  6. Analysis of potential for jet-impingement erosion from leaking steam generator tubes during severe accidents.

    SciTech Connect

    Majumdar, S.; Diercks, D. R.; Shack, W. J.; Energy Technology

    2002-05-01

    This report summarizes analytical evaluation of crack-opening areas and leak rates of superheated steam through flaws in steam generator tubes and erosion of neighboring tubes due to jet impingement of superheated steam with entrained particles from core debris created during severe accidents. An analytical model for calculating crack-opening area as a function of time and temperature was validated with tests on tubes with machined flaws. A three-dimensional computational fluid dynamics code was used to calculate the jet velocity impinging on neighboring tubes as a function of tube spacing and crack-opening area. Erosion tests were conducted in a high-temperature, high-velocity erosion rig at the University of Cincinnati, using micrometer-sized nickel particles mixed in with high-temperature gas from a burner. The erosion results, together with analytical models, were used to estimate the erosive effects of superheated steam with entrained aerosols from the core during severe accidents.

  7. Growth of MgB2 Films by an Impinging Jet HPCVD Reactor Design

    NASA Astrophysics Data System (ADS)

    Lamborn, Daniel; Wilke, R. H. T.; Li, Qi; Xi, Xiaoxing; Snyder, D. W.; Wang, Shufang; Redwing, Joan

    2008-03-01

    An impinging jet hybrid physical-chemical vapor deposition (HPCVD) reactor design was used for the growth of both thin and thick MgB2 films. This technique was able to independently control the substrate and Mg supply temperatures, and still maintained sufficient Mg overpressure to ensure phase stability. Thin films were predominantly axis oriented with the (0001) sapphire substrate while the thick films were either polycrystalline or showed preferred orientation. Thick films (˜10 μm) were deposited at a growth rate of ˜ 110 μm/hr and showed a maximum Tc of 39.8 K and residual resistivity ratio of 6.6. The thick films also showed a high Jc of 2x10^6 A/cm^2 at low applied magnetic fields even at 20 K. The results indicate that the impinging jet HPCVD configuration shows promise for coated conductor processes.

  8. Characteristic and mechanism of pressure fluctuation caused by self-induced oscillation of supersonic impinging jet

    NASA Astrophysics Data System (ADS)

    Yasunobu, Tsuyoshi; Otobe, Yumiko; Kashimura, Hideo

    2013-04-01

    When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related with the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, have to be clarified to control various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of an oscillation have to be more cleared to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position and the mechanism of self-induced flow oscillation by numerical analysis and experiment, when the underexpanded supersonic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of the self-induced flow oscillation depends on the pressure balance in the flowfield.

  9. An Evaluation of Jet Impingement Heat Transfer Correlations for Piccolo Tube Application

    NASA Technical Reports Server (NTRS)

    Bond, Thomas (Technical Monitor); Wright, William B.

    2004-01-01

    Impinging jets have been used for a wide variety of applications where high rates of heat transfer are desired. This report will present a review of heat transfer correlations that have been published. The correlations were then added to the LEWICE software to evaluate the applicability of these correlations to a piccolo tube anti-icing system. The results of this analysis were then compared quantitatively to test results on a representative piccolo tube system.

  10. Role of the confinement of a root canal on jet impingement during endodontic irrigation

    NASA Astrophysics Data System (ADS)

    Verhaagen, B.; Boutsioukis, C.; Heijnen, G. L.; van der Sluis, L. W. M.; Versluis, M.

    2012-12-01

    During a root canal treatment the root canal is irrigated with an antimicrobial fluid, commonly performed with a needle and a syringe. Irrigation of a root canal with two different types of needles can be modeled as an impinging axisymmetric or non-axisymmetric jet. These jets are investigated experimentally with high-speed Particle Imaging Velocimetry, inside and outside the confinement (concave surface) of a root canal, and compared to theoretical predictions for these jets. The efficacy of irrigation fluid refreshment with respect to the typical reaction time of the antimicrobial fluid with a biofilm is characterized with a non-dimensional Damköhler number. The pressure that these jets induce on a wall or at the apex of the root canal is also measured. The axisymmetric jet is found to be stable and its velocity agrees with the theoretical prediction for this type of jet, however, a confinement causes instabilities to the jet. The confinement of the root canal has a pronounced influence on the flow, for both the axisymmetric and non-axisymmetric jet, by reducing the velocities by one order of magnitude and increasing the pressure at the apex. The non-axisymmetric jet inside the confinement shows a cascade of eddies with decreasing velocities, which at the apex does not provide adequate irrigation fluid refreshment.

  11. Surface Pressure Fluctuations Produced by an Axisymmetric Impinging Jet: Generation Mechanisms

    NASA Astrophysics Data System (ADS)

    Al-Aweni, Malek; Naguib, Ahmed

    2013-11-01

    This study is motivated by understanding the mechanisms leading to unsteady surface pressure generation in impinging jet flows. Employing an extensive database of concurrent time-resolved flow visualization and time series from a surface-embedded microphone array, two dominant mechanisms are found to affect the space-time evolution of the pressure within the wall-jet zone: vortex-wall and vortex-vortex interaction. To gain deeper insight into these mechanisms, two closely-related model problems are studied computationally using Fluent. The problems involve the impingement of a single or two axisymmetric vortex rings on a flat wall. The resulting spatio-temporally resolved computations are used in conjunction with Possion's equation for pressure to investigate the nature of the pressure-generating sources, their relative importance, and their relation to the observed surface pressure signature. The findings provide significant information towards realization of efficient, structure-based models for computing the unsteady wall pressure in impinging jets. Partly funded by NSF grant OISE-0611984 and Libyan-North American Scholarship program.

  12. Optimization of an inclined elliptic impinging jet with cross flow for enhancing heat transfer

    NASA Astrophysics Data System (ADS)

    Heo, Man-Woong; Lee, Ki-Don; Kim, Kwang-Yong

    2011-06-01

    This work presents a parametric study and optimization of a single impinging jet with cross flow to enhance heat transfer with two design variables. The fluid flow and heat transfer have been analyzed using three-dimensional compressible Reynolds-averaged Navier-Stokes equations with a uniform heat flux condition being applied to the impingement plate. The aspect ratio of the elliptic jet hole and the angle of inclination of the jet nozzle are chosen as the two design variables, and the area-averaged Nusselt number on a limited target plate is set as the objective function. The effects of the design variables on the heat transfer performance have been evaluated, and the objective function has been found to be more sensitive to the angle of inclination of the jet nozzle than to the aspect ratio of the elliptic jet hole. The optimization has been performed by using the radial basis neural network model. Through the optimization, the area-averaged Nusselt number increased by 7.89% compared to that under the reference geometry.

  13. Self-induced sloshing caused by an upward round jet impinging on the free surface

    SciTech Connect

    Madarame, Haruki; Okamoto, Koji; Iida, Masao

    1995-11-01

    The demand for compact design of FBR made it necessary to study the interaction between high speed coolant flow and the free surface. Self-induced sloshing was found to occur with an upward round jet making a surface swell at the impinging point. The conditions under which the sloshing occurred were investigated experimentally together with the sloshing modes and frequencies. Without exception the induced mode had only one diametrical node, which was accompanied by the lateral motion of the swell. The mode was replaced by lower one with increasing the inlet-surface distance and the velocity, the reason of which was explained by the following assumption; the oscillation of water columns on both sides of the jet connected by a virtual cross flow through the jet, i.e., jet-flutter, was coupled with the sloshing and supplied energy to it.

  14. Apparatus and methods for impingement cooling of an undercut region adjacent a side wall of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian; Itzel, Gary Michael

    2001-01-01

    A gas turbine nozzle segment has outer and inner bands. Each band includes a side wall, a cover and an impingement plate between the cover and nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. The inturned flange has a plurality of apertures for directing cooling steam to cool the side wall between adjacent nozzle segments.

  15. The Effects of Crossflow on the Pressures and Lift Induced by the Fountain Generated Between Two Impinging Jets

    NASA Technical Reports Server (NTRS)

    Kuhn, Richard E.

    1998-01-01

    When a jet STOVL aircraft is hovering, or in a crossflow, while close to the ground wall jets flowing radially outward from the impingement points of the jets are generated. An upflow, or fountain, is generated where the wall jets from adjacent jets meet on the ground surface. The induced lift and suckdown generated by the impingement of the fountain on the lower surface of the configuration has been the subject of previous studies. This study analyzes the limited available pressure and force data on the effect of crossflow on the fountain induced lift and suckdown. The analysis includes the effects of jet spacing, height and operating conditions. However, it is limited to twin jet configurations of circular, vertical jets operating at subcritical nozzle pressure ratios over a fixed ground surface.

  16. Passive control of wall shear stress and mass transfer generated by submerged lobed impinging jet

    NASA Astrophysics Data System (ADS)

    Sodjavi, Kodjovi; Montagné, Brice; Meslem, Amina; Byrne, Paul; Serres, Laurent; Sobolik, Vaclav

    2016-05-01

    Particle image velocimetry was used to investigate the flow field in an impinging lobed daisy hemispherical nozzle jet in comparison to its counterpart round jet, at a Reynolds number of 5620 based on the exit velocity and the equivalent diameter D e of the nozzle. The limitations of the PIV technique in the vicinity of the target wall due to the laser scattering were addressed by using the electrodiffusion (ED) technique to determine the wall shear rate distribution. The distribution of the mass transfer coefficient is also obtained using the ED technique. The target wall is placed at a distance H = 2 D e from the plane tangent to the nozzle, at the center of the orifice. The entrainment of ambient fluid in the free jet region, which is larger in the lobed jet compared to the round jet, feeds in turn the wall jet region. The maximum wall shear rate was found significantly higher in the daisy jet, with an excess of 93 % compared to the reference round jet. The maximum mass transfer is 35 % higher in the former compared to the latter. Therefore, the hemispherical daisy nozzle is an excellent candidate in passive strategies to enhance local skin-friction and the subsequent local mass transfer at a constant exit Reynolds number.

  17. Channel flow modeling of impingement cooling of a rotating turbine blade

    NASA Technical Reports Server (NTRS)

    Koo, J. J.

    1984-01-01

    Local heat transfer distributions in impingement cooling have been measured by Kreatsoulas and Prieser for a range of conditions which model those in actual turbine blades, including the effects of rotation. These data were reported as local Nusselt numbers, but referred to coolant supply conditions. By means of a channel flow modeling of the flow in the supply and impingement passages, the same data are here presented in terms of local Nusselt number distributions such as are used in design. The results in this form are compared to the nonrotating impingement results of Chupp and to the rotating but nonimpingement results of Morris. Rotation reduces the mean Nusselt numbers from these found by Chupp by about 30 percent, and introduces important radial variations which are sensitive to rotation and to leading edge stagger angle.

  18. On the effect of fractal geometric parameters on the heat transfer features of circular impinging jets

    NASA Astrophysics Data System (ADS)

    Astarita, Tommaso; Castrillo, Giusy; Cafiero, Gioacchino

    2015-11-01

    Several solutions have been proposed over the last decades to increase the heat transfer rate of impinging jets. In all cases the heat transfer enhancement is obtained by exciting/altering the structure and organization of large scale turbulence, which is widely recognized to be the main agent in heat and mass transfer mechanism of impinging jets. Tampering with the large coherent turbulent structures is the key to achieve a significant heat transfer enhancement. In a recent work we demonstrated the effectiveness of fractal turbulence in this sense. Its effect is such that the heat transfer rate increases up to 63% in the stagnation region with respect to the well-known circular jet under the same power input. However, a systematic analysis of the effect of the singular geometric parameters of the fractal grid (such thickness ratio and length ratio) onto the spatial distribution of the Nusselt number has not been proposed yet. In this work we propose the analysis of the heat transfer enhancement produced by a class of turbulence promoters located in correspondence of the nozzle exit section of a circular jet. The upward shift of the turbulence intensity profile due to the blockage effect induced by the growing shear layer is discussed in terms of heat transfer enhancement.

  19. Rolling up of Large-scale Laminar Vortex Ring from Synthetic Jet Impinging onto a Wall

    NASA Astrophysics Data System (ADS)

    Xu, Yang; Pan, Chong; Wang, Jinjun; Flow Control Lab Team

    2015-11-01

    Vortex ring impinging onto a wall exhibits a wide range of interesting behaviors. The present work devotes to an experimental investigation of a series of small-scale vortex rings impinging onto a wall. These laminar vortex rings were generated by a piston-cylinder driven synthetic jet in a water tank. Laser Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV) were used for flow visualization/quantification. A special scenario of vortical dynamic was found for the first time: a large-scale laminar vortex ring is formed above the wall, on the outboard side of the jet. This large-scale structure is stable in topology pattern, and continuously grows in strength and size along time, thus dominating dynamics of near wall flow. To quantify its spatial/temporal characteristics, Finite-Time Lyapunov Exponent (FTLE) fields were calculated from PIV velocity fields. It is shown that the flow pattern revealed by FTLE fields is similar to the visualization. The size of this large-scale vortex ring can be up to one-order larger than the jet vortices, and its rolling-up speed and entrainment strength was correlated to constant vorticity flux issued from the jet. This work was supported by the National Natural Science Foundation of China (Grants No.11202015 and 11327202).

  20. Heat transfer and vortical structures of a plane impinging jet excited by spanwise periodic disturbances

    NASA Astrophysics Data System (ADS)

    Miyoshi, Yoshifumi; Kaneko, Jun-Ichi; Sakakibara, Jun

    2001-11-01

    Wall temperature and vorticity distribution of a stagnation region of a plane impinging jet with spanwise and temporal periodic disturbances has been measured by using thermochromic liquid crystal (TLC) and PIV. The plane jet of water was excited in time and space by adding suction/blowing type disturbances produced by servomotor-driven injectors. Stainless foil heaters with TLC coating glued on a Plexiglass plate was used as a heated impingement wall. The TLC surface was observed by 3 monochrome CCD cameras through RGB filters to acquire color distribution, and the velocity and vorticity field in a center-plane of the jet have been measured by PIV. Strouhal and Reynolds number were set respectively at St=0.45 and Re=2300. Surface temperature distribution showed unsteady streaks in parallel with a wall jet direction. It was evident from the PIV results that these streaks were caused by counter-rotating vortices induced on the wall. The vorticity magnitude and heat transfer rate could be modified by the temporal phase angle between disturbances added in adjacent spanwise locations.

  1. Determination of Cavity Dimensions Induced by Impingement of Gas Jets onto a Liquid Bath

    NASA Astrophysics Data System (ADS)

    Li, Mingming; Li, Qiang; Kuang, Shibo; Zou, Zongshu

    2016-02-01

    This paper presents an experimental and theoretical study on the cavity profile induced by the impingement of top-blown multiple gas jets onto a water or oil/water bath. The depth and diameter of the cavity were measured with respect to the lance height, gas flow rate, jets inclination angle, and oil volume. The experimental results show that the cavity depth increases with the increase of gas flow rate or oil thickness but the decrease of lance height or jets inclination angle. The cavity diameter is much less affected by gas flow rate compared to other variables. Then, the importance of the surface tension in the modeling of the cavity was theoretically identified. It was found that in the cratering process, the effect of the liquid surface tension on the cavity depth could be remarkably significant for a basic oxygen furnace (BOF) cold model but negligible for a real BOF steelmaking system. An improved theoretical model was hence proposed and validated using the experimental data obtained from both the single- or two-layer liquid baths. The new model includes not only the explicit consideration of the liquid surface tension but also that of the energy utilization efficiency of the jets impinging kinetic energy contributed to the cratering process.

  2. The influence of the stagnation zone on the fluid dynamics at the nozzle exit of a confined and submerged impinging jet

    NASA Astrophysics Data System (ADS)

    Jeffers, Nicholas; Stafford, Jason; Conway, Ciaran; Punch, Jeff; Walsh, Edmond

    2016-02-01

    Low profile impinging jets provide a means to achieve high heat transfer coefficients while occupying a small quantity of space. Consequently, they are found in many engineering applications such as electronics cooling, annealing of metals, food processing, and others. This paper investigates the influence of the stagnation zone fluid dynamics on the nozzle exit flow condition of a low profile, submerged, and confined impinging water jet. The jet was geometrically constrained to a round, 16-mm diameter, square-edged nozzle at a jet exit to target surface spacing ( H/ D) that varied between 0.25 < {{ H}{/}{ D}} < 8.75. The influence of turbulent flow regimes is the main focus of this paper; however, laminar flow data are also presented between 1350 < Re < 17{,}300. A custom measurement facility was designed and commissioned to utilise particle image velocimetry in order to quantitatively measure the fluid dynamics both before and after the jet exits its nozzle. The velocity profiles are normalised with the mean velocity across the nozzle exit, and turbulence statistics are also presented. The primary objective of this paper is to present accurate flow profiles across the nozzle exit of an impinging jet confined to a low H/ D, with a view to guide the boundary conditions chosen for numerical simulations confined to similar constraints. The results revealed in this paper suggest that the fluid dynamics in the stagnation zone strongly influences the nozzle exit velocity profile at confinement heights between 0 < {{ H}{/}{ D}} < 1. This is of particular relevance with regard to the choice of inlet boundary conditions in numerical models, and it was found that it is necessary to model a jet tube length {{ L}{/}{ D}} > 0.5—where D is the inner diameter of the jet—in order to minimise modelling uncertainty.

  3. Experimental data correlations for the effects of rotation on impingement cooling of turbine blades

    NASA Technical Reports Server (NTRS)

    Kreatsoulas, J. C.

    1987-01-01

    The effects of rotation on impingement cooling have been experimentally studied under simulated gas turbine operating conditions. A large scale model of a blade is spun in vacuum. External heating is simulated by resistve dissipation in the thin wall of the model, which is impingement cooled. The local internal Nu is measured by an IR radiometric technique with high spatial resolution. At low rotational speeds the data agree well with published measurements taken under stationary conditions. At higher speeds, a decrease in the average Nu by up to 20-30 percent is observed. Severe gradients are generated near the hub region. Empirical correlations, which fit the data well and render it more useful for design purposes, are presented. Measurements and correlations suggest that rotational effects are very important and can cause premature blade failure.

  4. Mean velocity, turbulence intensity, and scale in a subsonic turbulent jet impinging normal to a large flat plate

    NASA Technical Reports Server (NTRS)

    Boldman, D. R.; Brinich, P. F.

    1977-01-01

    To explain the increase in noise when a jet impinges on a large flat plate, mean velocity, turbulence intensity, and scale were measured at nominal nozzle-exit velocities of 61, 138, and 192 meters per second with the plate located 7.1 nozzle-exit diameters from the nozzle. The maximum turbulence intensities in free and impinging jets were about the same; however, the integral length scale near the plate surface was only about one-half the free jet scale. The measured intensities and length scales, in conjunction with a contemporary theory of aerodynamic noise, provided a good explanation for the observed increase in noise associated with the impinging jet. An increase in the volume of highly turbulent flow could be the principal reason for the increase in noise.

  5. Mucosal deformation from an impinging transonic gas jet and the ballistic impact of microparticles

    NASA Astrophysics Data System (ADS)

    Hardy, M. P.; Kendall, M. A. F.

    2005-10-01

    By means of a transonic gas jet, gene guns ballistically deliver microparticle formulations of drugs and vaccines to the outer layers of the skin or mucosal tissue to induce unique physiological responses for the treatment of a range of conditions. Reported high-speed imaging experiments show that the mucosa deforms significantly while subjected to an impinging gas jet from a biolistic device. In this paper, the effect of this tissue surface deformation on microparticle impact conditions is simulated with computational fluid dynamics (CFD) calculations. The microparticles are idealized as spheres of diameters 26.1, 39 and 99 µm and a density of 1050 kg m-3. Deforming surface calculations of particle impact conditions are compared directly with an immobile surface case. The relative velocity and obliquity of the deforming surface decrease the normal component of particle impact velocity by up to 30% at the outer edge of the impinging gas jet. This is qualitatively consistent with reported particle penetration profiles in the tissue. It is recommended that these effects be considered in biolistic studies requiring quantified particle impact conditions.

  6. Confined swirling jet impingement on a flat plate at moderate Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Herrada, M. A.; Del Pino, C.; Ortega-Casanova, J.

    2009-01-01

    The behavior of a swirling jet issuing from a pipe and impinging on a flat smooth wall is analyzed numerically by means of axisymmetric simulations. The axial velocity profile at the pipe outlet is assumed flat while the azimuthal velocity profile is a Burger's vortex characterized by two non-dimensional parameters; a swirl number S and a vortex core length δ. We concentrate on the effects of these two parameters on the mechanical characteristics of the flow at moderate Reynolds numbers. Our results for S =0 are in agreement with Phares et al. [J. Fluid Mech. 418, 351 (2000)], who provide a theoretical determination of the wall shear stress under nonswirling impinging jets at high Reynolds numbers. In addition, we show that the swirl number has an important effect on the jet impact process. For a fixed nozzle-to-plate separation, we found that depending on the value of δ and the Reynolds number Re, there is a critical swirl number, S =S∗(δ ,Re), above which recirculating vortex breakdown bubbles are observed in the near axis region. For S >S∗, the presence of these bubbles enhances the transition from a steady to a periodic regime. For S

  7. An experimental study of the aeroacoustics of a subsonic jet impinging normal to a large rigid surface

    NASA Technical Reports Server (NTRS)

    Preisser, J. S.; Block, P. J. W.

    1976-01-01

    This paper presents results from an experimental study of unsteady surface pressures and far-field noise produced by a subsonic jet impinging normal to a large, rigid, flat surface. The tests were performed in an anechoic room for jet Mach numbers from 0.54 to 0.85, and for jet-to-surface heights of from 5 to 10 jet diameters. Results showed that the root-mean-square surface pressure levels were proportional to jet dynamic pressure and were independent of jet height for radial distances from the stagnation point greater than 3 jet diameters. Far-field measurements indicated a significant increase in noise over that of a free jet for all cases of impingement. Cross spectral calculations between the surface and the far field suggested that at a Mach number of 0.70 and a height of 5 jet diameters the additional noise originated mainly in the outer edge of the impingement region between 1 and 3 jet diameters from the stagnation point.

  8. Heat transfer from impinging jets to a flat plate with conical and ring protuberances

    NASA Astrophysics Data System (ADS)

    Hrycak, P.

    1984-11-01

    An experimental investigation of heat transfer from round jets, impinging normally on a flat plate with exchangeable, heat transfer enhancing protuberances, has been carried out, and the pertinent literature surveyed, for Reynolds numbers ranging from 14,000 to 67,000, and nozzle diameters from 3.18 to 9.52 mm. The experimental data at the stagnation point indicated laminar flow, and a significant enhancement of heat transfer there, due to the introduction of the spike protuberance; the ring protuberance reduced the local heat flux somewhat. Data have also been correlated by means of dimensional analysis and compared with the conical flow theory.

  9. Thermal performance analysis of optimized hexagonal finned heat sinks in impinging air jet

    NASA Astrophysics Data System (ADS)

    Yakut, Kenan; Yeşildal, Faruk; Karabey, Altuǧ; Yakut, Rıdvan

    2016-04-01

    In this study, thermal performance analysis of hexagonal finned heat sinks which optimized according to the experimental design and optimization method of Taguchi were investigated. Experiments of air jet impingement on heated hexagonal finned heat sinks were carried out adhering to the L18(21*36) orthogonal array test plan. Optimum geometries were determined and named OH-1, OH-2. Enhancement efficiency with the first law of thermodynamics was analyzed for optimized heat sinks with 100, 150, 200 mm heights of hexagonal fin. Nusselt correlations were found out and variations of enhancement efficiency with Reynolds number presented in η-Re graphics.

  10. Proper Orthogonal Decomposition Analysis of Turbulent Jet Impingement on Rib-roughened Surface

    NASA Astrophysics Data System (ADS)

    Lam, Prasanth Anand Kumar; Karaiyan, Arul Prakash; Thermo-Fluid Dynamics Laboratory Team

    2015-11-01

    A Proper Orthogonal Decomposition (POD) analysis on turbulent flow dynamics of confined slot jet impinging on rib-roughened surface is numerically investigated. The data for POD analysis has been obtained by solving mass, momentum and energy equations in Cartesian framework using Streamline Upwind/Petrov-Galerkin Finite element method. Further, turbulent kinetic energy (k) and its dissipation rate (ɛ) are modeled using standard k- ɛ turbulence model with standard wall functions. POD is applied to computational data for a wide range of Reynolds number (Re) = 5000 - 30000 and non-dimensional channel height (H/L) = 0.5 - 4.0 to reveal large scale vortical structures in the flow field. The simulated results demonstrate a better understanding on effect of turbulence and its influence on individual vortical structures for enhancement of heat transfer. The enhancement of heat transfer in stagnation region due to combined effect of oscillation in impingement position caused by large vortical structures and strong acceleration of fluid during impingement is quantified. Furthermore, non-dimensional correlations have been derived for pressure drop and Surface averaged Nusselt number.

  11. Visualization of flow patterns induced by an impinging jet issuing from a circular planform

    NASA Astrophysics Data System (ADS)

    Saripalli, K. R.

    1983-12-01

    A four-jet impingement flow with application to high-performance VTOL aircraft is investigated. Flow visualization studies were conducted with water as the working medium. Photographs of different cross sections of the flow are presented to describe the properties of the fountain upwash and the stagnation-line patterns. The visualization technique involves the introduction of fluorescein-sodium, a fluorescent dye, into the jet flow and illumination by a sheet of light obtained by spreading a laser beam. Streak-line photographs were also taken using air bubbles as tracer particles. The strength and orientation of the fountain(s) were observed for different heights of the nozzle configuration above the ground and inclination angles of the forward nozzles.

  12. Application of the Bernoulli enthalpy concept to the study of vortex noise and jet impingement noise

    NASA Technical Reports Server (NTRS)

    Yates, J. E.

    1978-01-01

    A complete theory of aeroacoustics of homentropic fluid media is developed and compared with previous theories. The theory is applied to study the interaction of sound with vortex flows, for the DC-9 in a standard take-off configuration. The maximum engine-wake interference noise is estimated to be 3 or 4 db in the ground plane. It is shown that the noise produced by a corotating vortex pair departs significantly from the compact M scaling law for eddy Mach numbers (M) greater than 0.1. An estimate of jet impingement noise is given that is in qualitative agreement with experimental results. The increased noise results primarily from the nonuniform acceleration of turbulent eddies through the stagnation point flow. It is shown that the corotating vortex pair can be excited or de-excited by an externally applied sound field. The model is used to qualitatively explain experimental results on excited jets.

  13. Rupture of thin liquid films induced by impinging air-jets.

    PubMed

    Berendsen, Christian W J; Zeegers, Jos C H; Kruis, Geerit C F L; Riepen, Michel; Darhuber, Anton A

    2012-07-01

    Thin liquid films on partially wetting substrates are subjected to laminar axisymmetric air-jets impinging at normal incidence. We measured the time at which film rupture occurs and dewetting commences as a function of diameter and Reynolds number of the air-jet. We developed numerical models for the air flow as well as the height evolution of the thin liquid film. The experimental results were compared with numerical simulations based on the lubrication approximation and a phenomenological expression for the disjoining pressure. We achieved quantitative agreement for the rupture times. We found that the film thickness profiles were highly sensitive to the presence of minute quantities of surface-active contaminants. PMID:22671425

  14. Preliminary results for a large angle oblique jet impingement and flow and for the effect of initial conditions on the near field of an axisymmetric jet

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    The structure of an axisymmetric jet in the near field is discussed for jet noise and for jet impingment schemes for STOL aircraft. It is inferred from previous studies, and the inference is supported by analysis, that the scale and intensity of the turbulence structure at the jet exit plane are the important boundary conditions which effect the development of the flow in the near field. The techniques to study these effects while maintaining a uniform mean flow and the results which document the range of the initial conditions are presented. The large angle, oblique jet impingment condition is of interest in terms of the jet/flap interaction. Detailed turbulence data can be obtained with the specially constructed facility. The development of the flow and instrumentation system and initial data from the new facility are presented.

  15. Free impinging jet microreactors: controlling reactive flows via surface tension and fluid viscoelasticity.

    PubMed

    Erni, Philipp; Elabbadi, Amal

    2013-06-25

    We investigate the use of impinging free liquid jets as wall-free continuous microreactors. The collision of two reactant jets forming a free-standing thin liquid sheet allows us to perform rapid precipitation reactions to form colloidal particles, enhance micromixing, and master challenging reactions with very fast kinetics. To control the shape, size, and hydrodynamics of the impingement zone between the two liquid streams, it is crucial to understand the interplay among surface tension, fluid viscoelasticity, and reaction kinetics. Here, we study these aspects using model fluids, each illustrating a different physical effect of surface and bulk fluid properties. First, solutions of sodium dodecyl sulfate below, near, and above the critical micelle concentration are used to assess the role of static and dynamic surface tension. Second, we demonstrate how dilute solutions of high-molecular-weight polymers can be used to control the morphology of the free surface flow. If properly controlled, these effects can enhance the micromixing time scales to the extent that very rapid reactions can be performed with outstanding selectivity. We quantitatively assess the interplay between the free surface flow and reaction kinetics using parallel-competitive reactions and demonstrate how these results can be used to control the particle size in precipitation processes. PMID:23755870

  16. Verification and validation of impinging round jet simulations using an adaptive FEM

    NASA Astrophysics Data System (ADS)

    Pelletier, Dominique; Turgeon, Éric; Tremblay, Dominique

    2004-03-01

    This paper illustrates the use of an adaptive finite element method as a means of achieving verification of codes and simulations of impinging round jets, that is obtaining numerical predictions with controlled accuracy. Validation of these grid-independent solution is then performed by comparing predictions to measurements. We adopt the standard and accepted definitions of verification and validation (Technical Report AIAA-G-077-1998, American Institute of Aeronautics and Astronautics, 1998; Verification and Validation in Computational Science and Engineering. Hermosa Publishers: Albuquerque, NM, 1998). Mesh adaptation is used to perform the systematic and rigorous grid refinement studies required for both verification and validation in CFD. This ensures that discrepancies observed between predictions and measurements are due to deficiencies in the mathematical model of the flow. Issues in verification and validation are discussed. The paper presents an example of code verification by the method of manufactured solution. Examples of successful and unsuccessful validation for laminar and turbulent impinging jets show that agreement with experiments is achieved only with a good mathematical model of the flow physics combined with accurate numerical solution of the differential equations. The paper emphasizes good CFD practice to systematically achieve verification so that validation studies are always performed on solid grounds.

  17. CFD study of Jet Impingement Test erosion using Ansys Fluent® and OpenFOAM®

    NASA Astrophysics Data System (ADS)

    López, Alejandro; Nicholls, William; Stickland, Matthew T.; Dempster, William M.

    2015-12-01

    The initial aim of this study was to compare OpenFoam and Ansys Fluent in order to verify OpenFoam's Lagrangian Library and erosion capabilities. However, it was found that previous versions of Fluent have been providing wrong results for the discrete phase and the differences with the latest version (Ansys Fluent 15) are shown. A Submerged Jet Impingement Test is an effective method for studying erosion created by solid particles entrained in a liquid. When considering low particle concentrations a Lagrangian modeling of the particulate phase is a reasonable approach. Proper linkage between OpenFOAM's Lagrangian library and the solver pimpleFoam for incompressible transient flows allows two-phase simulations to be undertaken for comparison with Ansys Fluent with the aim of verifying OpenFoam's accuracy. Steady state convergence for the fluid flow is first accomplished and the results are compared, confirming a good agreement between the two packages. A transient simulation was then set up and spherical particles incorporated into the fluid flow. An assessment of the two codes' discrete phase models was carried out, focusing on the differences between impact angles and velocities yielded at the impingement plate's surface employing a similar strategy to that outlined first by Hattori et al. (2008) and later by Gnanavelu et al. (2009, 2011). In the comparison of OpenFoam with the latest version of Fluent, the main differences between the injection models are highlighted and the coupling possibilities between phases are taken into consideration. Agreement between trends for both impact angles and velocities is satisfactory when the last version of the commercial package is considered and the average discrepancy between numerical values is very low, verifying OpenFoam's Lagrangian library. Two different Jet Impingement Test configurations are also compared and the differences highlighted.

  18. Computation of Turbulent Recirculating Flow in Channels, and for Impingement Cooling

    NASA Technical Reports Server (NTRS)

    Chang, Byong Hoon

    1992-01-01

    Fully elliptic forms of the transport equations have been solved numerically for two flow configurations. The first is turbulent flow in a channel with transverse rectangular ribs, and the second is impingement cooling of a plane surface. Both flows are relevant to proposed designs for active cooling of hypersonic vehicles using supercritical hydrogen as the coolant. Flow downstream of an abrupt pipe expansion and of a backward-facing step were also solved with various near-wall turbulence models as benchmark problems. A simple form of periodicity boundary condition was used for the channel flow with transverse rectangular ribs. The effects of various parameters on heat transfer in channel flow with transverse ribs and in impingement cooling were investigated using the Yap modified Jones and Launder low Reynolds number k-epsilon turbulence model. For the channel flow, predictions were in adequate agreement with experiment for constant property flow, with the results for friction superior to those for heat transfer. For impingement cooling, the agreement with experiment was generally good, but the results suggest that improved modelling of the dissipation rate of turbulence kinetic energy is required in order to obtain improved heat transfer prediction, especially near the stagnation point. The k-epsilon turbulence model was used to predict the mean flow and heat transfer for constant and variable property flows. The effect of variable properties for channel flow was investigated using the same turbulence model, but comparison with experiment yielded no clear conclusions. Also, the wall function method was modified for use in the variable properties flow with a non-adiabatic surface, and an empirical model is suggested to correctly account for the behavior of the viscous sublayer with heating.

  19. Liquid and gelled sprays for mixing hypergolic propellants using an impinging jet injection system

    NASA Astrophysics Data System (ADS)

    James, Mark D.

    The characteristics of sprays produced by liquid rocket injectors are important in understanding rocket engine ignition and performance. The includes, but is not limited to, drop size distribution, spray density, drop velocity, oscillations in the spray, uniformity of mixing between propellants, and the spatial distribution of drops. Hypergolic ignition and the associated ignition delay times are also important features in rocket engines, providing high reliability and simplicity of the ignition event. The ignition delay time is closely related to the level and speed of mixing between a hypergolic fuel and oxidizer, which makes the injection method and conditions crucial in determining the ignition performance. Although mixing and ignition of liquid hypergolic propellants has been studied for many years, the processes for injection, mixing, and ignition of gelled hypergolic propellants are less understood. Gelled propellants are currently under investigation for use in rocket injectors to combine the advantages of solid and liquid propellants, although not without their own difficulties. A review of hypergolic ignition has been conducted for selected propellants, and methods for achieving ignition have been established. This research is focused on ignition using the liquid drop-on-drop method, as well as the doublet impinging jet injector. The events leading up to ignition, known as pre-ignition stage are discussed. An understanding of desirable ignition and combustion performance requires a study of the effects of injection, temperature, and ambient pressure conditions. A review of unlike-doublet impinging jet injection mixing has also been conducted. This includes mixing factors in reactive and non-reactive sprays. Important mixing factors include jet momentum, jet diameter and length, impingement angle, mass distribution, and injector configuration. An impinging jet injection system is presented using an electro-mechanically driven piston for injecting liquid

  20. Experimental and numerical investigation of flow field and heat transfer from electronic components in a rectangular channel with an impinging jet

    NASA Astrophysics Data System (ADS)

    Calisir, Tamer; Fevzi Koseoglu, M.; Kilic, Mustafa; Baskaya, Senol

    2015-05-01

    Thermal control of electronic components is a continuously emerging problem as power loads keep increasing. The present study is mainly focused on experimental and numerical investigation of impinging jet cooling of 18 (3 × 6 array) flash mounted electronic components under a constant heat flux condition inside a rectangular channel in which air, following impingement, is forced to exit in a single direction along the channel formed by the jet orifice plate and impingement plate. Copper blocks represent heat dissipating electronic components. Inlet flow velocities to the channel were measured by using a Laser Doppler Anemometer (LDA) system. Flow field observations were performed using a Particle Image Velocimetry (PIV) and thermocouples were used for temperature measurements. Experiments and simulations were conducted for Re = 4000 - 8000 at fixed value of H = 10 × Dh. Flow field results were presented and heat transfer results were interpreted using the flow measurement observations. Numerical results were validated with experimental data and it was observed that the results are in agreement with the experiments.

  1. Numerical simulation of liquid-layer breakup on a moving wall due to an impinging jet

    NASA Astrophysics Data System (ADS)

    Yu, Taejong; Moon, Hojoon; You, Donghyun; Kim, Dokyun; Ovsyannikov, Andrey

    2014-11-01

    Jet wiping, which is a hydrodynamic method for controlling the liquid film thickness in coating processes, is constrained by a rather violent film instability called splashing. The instability is characterized by the ejection of droplets from the runback flow and results in an explosion of the film. The splashing phenomenon degrades the final coating quality. In the present research, a volume-of-fluid (VOF)-based method, which is developed at Cascade Technologies, is employed to simulate the air-liquid multiphase flow dynamics. The present numerical method is based on an unstructured-grid unsplit geometric VOF scheme and guarantees strict conservation of mass of two-phase flow, The simulation results are compared with experimental measurements such as the liquid-film thickness before and after the jet wiping, wall pressure and shear stress distributions. The trajectories of liquid droplets due to the fluid motion entrained by the gas-jet operation, are also qualitatively compared with experimental visualization. Physical phenomena observed during the liquid-layer breakup due to an impinging jet is characterized in order to develop ideas for controlling the liquid-layer instability and resulting splash generation and propagation. Supported by the Grant NRF-2012R1A1A2003699, the Brain Korea 21+ program, POSCO, and 2014 CTR Summer Program.

  2. Role of fluid elasticity on the dynamics of rinsing flow by an impinging jet

    NASA Astrophysics Data System (ADS)

    Hsu, Tienyi T.; Walker, Travis W.; Frank, Curtis W.; Fuller, Gerald G.

    2011-03-01

    Rinsing flows are common processes where a jet of one liquid impinges upon a layer of a second liquid for the purpose of removing the second liquid. An imaging setup has been developed to obtain both qualitative and quantitative data on the rinsing flow of a jet of water impinging on either layers of Newtonian or elastic fluids. Three classes of test fluids have been investigated: a Newtonian glycerol-water solution, a semidilute aqueous solution of high molecular weight polyacrylamide solution displaying both elasticity and shear thinning, and an elastic but non-shear thinning Boger fluid. The fluids were designed to have approximately equal zero-shear viscosities. For all cases, a circular hydraulic jump occurs and Saffman-Taylor instabilities were observed at the interface between the low viscosity jet and the higher viscosity coating liquids. Results show that the elasticity (extensional viscosity) of the samples influences the pattern of the instabilities and contributes to dampening surface disturbances in the vicinity of the hydraulic jump. Quantitative measurements of liquid layer thicknesses were obtained using a laser triangulation technique. We observed that shear thinning contributes to increasing the velocity of the hydraulic jump circle growth, and the growth profile appears to be linear instead of logarithmic-like as in the Newtonian fluids. Shear thinning characteristics of the samples also contribute to a larger vertical height of the hydraulic jump and an undercutting phenomenon. The elasticity of the fluids contributes to a "recoil" of the hydraulic jump circle, causing the circle, after initial expansion, to shrink in size before expanding again.

  3. Investigation of impingement region and wall jets formed by the interaction of high aspect ratio lift jets and a ground plane

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    Flow characteristics of impinging jets emanating from rectangular exit area converging nozzles of exit area aspect ratio four, six, and eight were investigated. Azimuthal distributions of wall jet radial momentum flux in the ground plane were strongly directional and sensitive to rectangular nozzle exit area aspect ratio, jet impingement angle, and height above ground, H/D. Effects of jet exit velocity profile nonuniformities were also investigated. Data from the single nozzle rectangular jet impringement investigations were incorporated into an existing VTOL aircraft ground flow field computer program. It is suggested that this program together with the Douglas Neumann program modified for V/STOL applications may be used for the analysis and prediction of flow fields and resulting forces and moments on multijet V/STOL aircraft hovering in ground effect.

  4. Fluid dynamics and convective heat transfer in impinging jets through implementation of a high resolution liquid crystal technique

    NASA Technical Reports Server (NTRS)

    Kim, K.; Wiedner, B.; Camci, C.

    1993-01-01

    A combined convective heat transfer and fluid dynamics investigation in a turbulent round jet impinging on a flat surface is presented. The experimental study uses a high resolution liquid crystal technique for the determination of the convective heat transfer coefficients on the impingement plate. The heat transfer experiments are performed using a transient heat transfer method. The mean flow and the character of turbulent flow in the free jet is presented through five hole probe and hot wire measurements, respectively. The flow field character of the region near the impingement plate plays an important role in the amount of convective heat transfer. Detailed surveys obtained from five hole probe and hot wire measurements are provided. An extensive validation of the liquid crystal based heat transfer method against a conventional technique is also presented. After a complete documentation of the mean and turbulent flow field, the convective heat transfer coefficient distributions on the impingement plate are presented. The near wall of the impingement plate and the free jet region is treated separately. The current heat transfer distributions are compared to other studies available from the literature. The present paper contains complete sets of information on the three dimensional mean flow, turbulent velocity fluctuations, and convective heat transfer to the plate. The experiments also prove that the present nonintrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with a heat transfer coefficient uncertainty of 5.7 percent.

  5. Characterization of an inline row impingement channel for turbine blade cooling applications

    NASA Astrophysics Data System (ADS)

    Ricklick, Mark A.

    Gas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, 'micro' turbines capable of producing efficient portable power. Part of the turbine's success is the fact that their efficiency levels have continuously risen since their introduction in the early 1800's. Along with improvements in our understanding and designs of the aerodynamic components of the turbine, as well as improvements in the areas of material design and combustion control, advances in component cooling techniques have predominantly contributed to this success. This is the result of a simple thermodynamic concept; as the turbine inlet temperature is increased, the overall efficiency of the machine increases as well. Designers have exploited this fact to the extent that modern gas turbines produce rotor inlet temperatures beyond the melting point of the sophisticated materials used within them. This has only been possible through the use of sophisticated cooling techniques, particularly in the 1st stage vanes and blades. Some of the cooling techniques employed today have been internal cooling channels enhanced with various features, film and showerhead cooling, as well as internal impingement cooling scenarios. Impingement cooling has proven to be one of the most capable heat removal processes, and the combination of this cooling feature with that of channel flow, as is done in impingement channel cooling, creates a scenario that has understandably received a great deal of attention in recent years. This study has investigated several of the unpublished characteristics of these impingement channels, including the channel

  6. Simulation and stability analysis of supersonic impinging jet noise with microjet control

    NASA Astrophysics Data System (ADS)

    Hildebrand, Nathaniel; Nichols, Joseph W.

    2014-11-01

    A model for an ideally expanded 1.5 Mach turbulent jet impinging on a flat plate using unstructured high-fidelity large eddy simulations (LES) and hydrodynamic stability analysis is presented. Note the LES configuration conforms exactly to experiments performed at the STOVL supersonic jet facility of the Florida Center for Advanced Aero-Propulsion allowing validation against experimental measurements. The LES are repeated for different nozzle-wall separation distances as well as with and without the addition of sixteen microjets positioned uniformly around the nozzle lip. For some nozzle-wall distances, but not all, the microjets result in substantial noise reduction. Observations of substantial noise reduction are associated with a relative absence of large-scale coherent vortices in the jet shear layer. To better understand and predict the effectiveness of microjet noise control, the application of global stability analysis about LES mean fields is used to extract axisymmetric and helical instability modes connected to the complex interplay between the coherent vortices, shocks, and acoustic feedback. We gratefully acknowledge computational resources provided by the Argonne Leadership Computing Facility.

  7. Experimental investigation of the wall shear stress in a circular impinging jet

    NASA Astrophysics Data System (ADS)

    El Hassan, M.; Assoum, H. H.; Martinuzzi, R.; Sobolik, V.; Abed-Meraim, K.; Sakout, A.

    2013-07-01

    The influence of the large-scale vortical structures on the wall shear stress in a circular impinging jet is investigated experimentally for a Reynolds number of 1260. Time-resolved particle image velocimetry and polarographic measurements are performed simultaneously. It is found that the instantaneous wall shear stress is strongly dependent on the vortex dynamics, particularly for different parts of the transverse vortex. The influence of the vortex ring, the secondary and tertiary vortices on the ejection/sweep process near the wall is the main mechanism involved in the wall shear stress variation. In the region of the boundary layer separation, the wall shear stress amplitude increases just upstream of the separation and dramatically decreases in the recirculation zone downstream from the separation. The interaction between primary and secondary structures and their pairing process with the tertiary structure affects the sweep/ejection process near the wall and subsequently the wall shear stress variation. A comparison between the Finite Time Lyapunov Exponent (FTLE) method and the phase average technique is performed. It is shown that both methods describe the flow dynamics in the impinging region of the vortex ring. However, the FTLE method is more suitable for describing the unsteady separation of the boundary layer.

  8. A Water Model Study of Impinging Gas Jets on Liquid Surfaces

    NASA Astrophysics Data System (ADS)

    Hwang, Ho Yong; Irons, Gordon A.

    2012-04-01

    Water modeling experiments were designed to observe the deformation of a liquid surface by impinging the gas jet. Video images were taken and processed in a systematic way. The important surface cavity parameters, such as depth, width, and their frequency of oscillation, were obtained. The relation between surface depression depth and the supplied gas momentum were consistent with previous findings and were extended to higher flow rates. The surface instability and the onset of splashing were observed and interpreted with the Blowing number. The wave behaviors were described qualitatively with a combination of photographic evidence and power spectral density analysis to extract the characteristic wave numbers for each gas flow rate. The analysis of the time series of the surface variables showed a connection to the attenuation of turbulence gas pressure fluctuation and the surface deformation by the gas impingement. Bath velocities were measured with a particle image velocimetry (PIV) technique. To quantify the transfer of kinetic energy from the gas to the liquid, an energy transfer index was defined and calculated with the PIV data. The index was insensitive to gas flow rate but increased with cavity width. The momentum transfer across the interface was also analyzed, and a similar cavity width dependence was found. A correlation between the cavity shape and momentum transfer was proposed.

  9. Deposition of micron liquid droplets on wall in impinging turbulent air jet

    NASA Astrophysics Data System (ADS)

    Liu, Tianshu; Nink, Jacob; Merati, Parviz; Tian, Tian; Li, Yong; Shieh, Tom

    2010-06-01

    The fluid mechanics of the deposition of micron liquid (olive oil) droplets on a glass wall in an impinging turbulent air jet is studied experimentally. The spatial patterns of droplets deposited on a wall are measured by using luminescent oil visualization technique, and the statistical data of deposited droplets are obtained through microscopic imagery. Two distinct rings of droplets deposited on a wall are found, and the mechanisms of the formation of the inner and outer rings are investigated based on global diagnostics of velocity and skin friction fields. In particular, the intriguing effects of turbulence, including large-scale coherent vortices and small-scale random turbulence, on micron droplet deposition on a wall and coalescence in the air are explored.

  10. Incident Shock-Transverse Jet Interactions at Mach 1.9: Effect of Shock Impingement Location

    NASA Astrophysics Data System (ADS)

    Zare-Behtash, H.; Lo, K. H.; Erdem, E.; Kontis, K.; Lin, J.; Ukai, T.; Obayashi, S.

    The scramjet engine is an efficient design for high-speed propulsion, requiring injection of fuel into a supersonic flow in a short amount of time. Due to the nature of the flow numerous shock waves exist within the combustor of a scramjet, significantly altering the flow characteristics and performance of the engine as the flow Mach number or attitude is changed. According to Mai et al. [1] the location of impingement of the incident shock, relative to the fuel injection location, has significant impact on the mixing and flame-holding properties. This emphasises the importance of understanding and hence the need for controlling the dynamic interactions that are created. Of course another fertile area where transverse jet injections are studied for their application is the creation of forces and moments for pitch and attitude control [2, 3].

  11. Liquid jet impingement normal to a disk in zero gravity. Ph.D. Thesis Toledo Univ.

    NASA Technical Reports Server (NTRS)

    Labus, T. L.

    1977-01-01

    The free surface shapes of circular liquid jets impinging normal to sharp-edged disks in zero gravity are determined. Zero gravity drop tower experiments yielded three distinct flow patterns that were classified in terms of the relative effects of surface tension and inertial forces. An order of magnitude analysis was conducted that indicated regions where viscous forces were not significant in the computation of free surface shapes. The free surface analysis was simplified by transforming the governing potential flow equations and boundary conditions into the inverse plane, where the stream function and velocity potential became the coordinates. The resulting nonlinear equations were solved by standard finite difference methods, and comparisons were made with the experimental data for the inertia dominated regime.

  12. Two-phase liquid-liquid flows generated by impinging liquid jets

    NASA Astrophysics Data System (ADS)

    Tsaoulidis, Dimitrios; Li, Qi; Angeli, Panagiota

    2015-11-01

    Two-phase flows in intensified small-scale systems find increasing applications in (bio)chemical analysis and synthesis, fuel cells, polymerisation, and separation processes (solvent extraction). Current nuclear spent fuel reprocessing separation technologies have been developed many decades ago and have not taken account recent advances on process intensification which can drive down plant size and economics. In this work, intensified impinging jets will be developed to create dispersions by bringing the two liquid phases into contact through opposing small channels. A systematic set of experiments has been undertaken, to investigate the hydrodynamic characteristics, to develop predictive models, and enable comparisons with other contactors. Drop size distribution and mixing intensity will be investigated for liquid-liquid mixtures as a function of various parameters using high speed imaging and conductivity probes.

  13. Numerical Solution of a Plane Jet Impingement on an Infinite Flat Surface

    NASA Astrophysics Data System (ADS)

    Arora, S.; Irfan, Nagma

    2015-03-01

    In this paper numerical solution of the unsteady plane incompressible viscous jet impinging on to an infinite flat surface are presented for Re=450. In the present study, all calculations have been done by using Dufort Frankel scheme and over relaxation scheme. Result and graphs have been obtained by using MATLAB programming. The obtained results explain the flow of water after exhaling from nozzle and the streamlines and vorticity of flow ofwater after striking with flat infinite surface. The solutions obtained by proposed method indicate that this approach is easy to implement and computationally very attractive and the results of our investigation are in qualitative agreement with those available in the literature [1, 9]. This method is capable of greatly reducing the size of calculations while still maintaining high accuracy of the numerical solution.

  14. Computer program for generating input for analysis of impingement-cooled, axial-flow turbine blade

    NASA Astrophysics Data System (ADS)

    Rosenbaum, D.

    1980-01-01

    A computer program, TACTGRID, was developed to generate the geometrical input for the TACTI program, a program that calculates transient and steady state temperatures, pressures, and cooling flows in an impingement cooled turbine blade. Using spline curves, the TACTGRID program constructs the blade internal geometry from the previously designed external blade surface and newly selected wall and channel thicknesses. The TACTGRID program generates the TACTI calculational grid, calculates arc length between grid points required by TACTI as input, and prepares the namelist input data set used by TACTI for the blade geometry. In addition, TACTGRID produces a scaled computer plot of each blade slice, detailing the grid and calculational stations, and thus eliminates the need for intermediate drafting.

  15. Rapid PCR amplification using a microfluidic device with integrated microwave heating and air impingement cooling.

    PubMed

    Shaw, Kirsty J; Docker, Peter T; Yelland, John V; Dyer, Charlotte E; Greenman, John; Greenway, Gillian M; Haswell, Stephen J

    2010-07-01

    A microwave heating system is described for performing polymerase chain reaction (PCR) in a microfluidic device. The heating system, in combination with air impingement cooling, provided rapid thermal cycling with heating and cooling rates of up to 65 degrees C s(-1) and minimal over- or under-shoot (+/-0.1 degrees C) when reaching target temperatures. In addition, once the required temperature was reached it could be maintained with an accuracy of +/-0.1 degrees C. To demonstrate the functionality of the system, PCR was successfully performed for the amplification of the Amelogenin locus using heating rates and quantities an order of magnitude faster and smaller than current commercial instruments. PMID:20414500

  16. Correlation of steel corrosion in pipe flow with jet impingement and rotating cylinder tests

    SciTech Connect

    Efird, K.D.; Wright, E.J.; Boros, J.A.; Hailey, T.G.

    1993-12-01

    The relationship of laboratory fluid flow corrosion test techniques to flow-accelerated corrosion in field applications and the parameters required to apply laboratory data effectively in the field were studied. Single-phase, aqueous, sweet corrosion of steel in turbulent pipe flow was correlated to corrosion in jet impingement and rotating cylinder tests. All tests were conducted simultaneously, using the same test fluid to minimize environmental variables and to allow a direct, realistic comparison of test methods. Rotating cylinder electrode corrosion rates did not correlate with pipe flow based on wall shear stress or mass transfer for flow-accelerated corrosion of carbon (C) steel in the environment studied. Jet impingement corrosion rates for the test ring at r/r{sub 0} = 3 correlated with pipe flow based on wall shear stress. The general equation for flow-accelerated corrosion of C steel under turbulent flow conditions in this environment was expressed as: R = a{tau}{sub w}{sup b} where R was the C steel corrosion rate in mm/y and {tau}{sub w} was the wall shear stress in N/m{sup 2}. Effects of solution chemistry were contained in the equation coefficient and exponent and require further experimental definition. The physical fluid and hydrodynamic parameters were included in {tau}{sub w}. Use of wall shear stress as the correlating factor did not imply a shear mechanism for corrosion acceleration. Wall shear stress was found to be a hydrodynamic factor that can be used effectively to relate fluid flow in different geometries, allowing valid comparison of laboratory tests and field operations.

  17. An Analysis of the Pressures, Forces and Moments Induced by the Ground Vortex Generated by a Single Impinging Jet

    NASA Technical Reports Server (NTRS)

    Kuhn, Richard E.

    1997-01-01

    When a jet STOVL aircraft is in STOL operation the jets impinge on the ground and generate wall jets flowing radially outward from the points at which the jets impinge. When the forward flowing part of a wall jet meets the free stream flow it is rolled back on itself forming a parabolic shaped ground vortex. Positive pressures are induced on the lower surface of the configuration ahead of the ground vortex and suction pressures are induced over the ground vortex itself. In addition, the suction pressures induced aft of the jet out of ground effect are reduced and lifting pressures are induced on the upper surface. This study analyzes available pressure and force data and develops a method for estimating the forces and moments induced in ground effect. The method includes the effects of configuration variables, height and operating conditions, as well as the effects of the location, deflection and shape of the jet. However, it is limited to single jets at subcritical nozzle pressure ratios. An analysis of the effects of moving over the ground vs. tests over a fixed ground plane is included.

  18. The flow and mixing mechanisms caused by the impingement of an immiscible interface with a vertical jet

    NASA Astrophysics Data System (ADS)

    Friedman, P. D.; Katz, J.

    1999-09-01

    This paper summarizes a series of experiments to determine the effects of impinging a water and diesel fuel interface with a water jet. Four distinct flow regimes and associated mixing mechanisms were identified as primarily a function of an interface Richardson number, Rii and to a lesser extent the Reynolds number, Re. In flow regime 1, which occurred at Rii>15, the jet impinged the interface and formed a slight deformation. Flow behaved similarly to a jet impinging a solid boundary and no mixing was observed. Regime 2 occurred at 15>Rii>1.1. With decreasing Rii, the interfacial deformation became taller and steeper and a flow separation developed at its edge. Mixing resulted from the formation of a fuel lip at the flow separation point. In regime 3, which occurred at Rii<1.1, the water jet penetrated deeply into the fuel layer causing an unstable deformation that successively collapsed and reformed. Mixing resulted from the impact of the collapsing deformation. Finally, in regime 4, the jet's momentum was sufficient to impact the solid boundary at the top of the fuel layer, creating a cloud of water droplets.

  19. Effect of coating material on heat transfer and skin friction due to impinging jet onto a laser producedhole

    NASA Astrophysics Data System (ADS)

    Shuja, S. Z.; Yilbas, B. S.

    2013-07-01

    Jet impingement onto a two-layer structured hole in relation to laser drilling is investigated. The hole consists of a coating layer and a base material. The variations in the Nusselt number and the skin friction are predicted for various coating materials. The Reynolds stress turbulent model is incorporated to account for the turbulence effect of the jet flow and nitrogen is used as the working fluid. The study is extended to include two jet velocities emanating from the conical nozzle. It is found that coating material has significant effect on the Nusselt number variation along the hole wall. In addition, the skin friction varies considerably along the coating thickness in thehole.

  20. Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

    NASA Astrophysics Data System (ADS)

    Long, J.; New, T. H.

    2016-07-01

    Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

  1. Experimental analysis of the aero-acoustic coupling in a plane impinging jet on a slotted plate

    NASA Astrophysics Data System (ADS)

    Assoum, Hassan H.; El Hassan, Mouhammad; Abed-Meraïm, Kamel; Martinuzzi, Robert; Sakout, Anas

    2013-08-01

    Impinging jets are encountered in many industrial applications and suppression of the noise generated by these jets is of great fundamental and practical interest. The vortex dynamics and the interaction between the vortical structures and the impinging wall should be understood in order to control the aero-acoustic coupling between shear layer oscillation and the acoustic modes (self-sustained tones). In this study, a plane jet issuing from a rectangular nozzle and impinging on a plate is considered for Re = 3900. The sound pressure, the vibration of the impinged plate and the spatial velocity field are obtained simultaneously using a microphone, an accelerometer and the time-resolved particle image velocimetry technique, respectively. Spectra and cross-correlations are used to educe the role of different vortical structures leading to the aero-acoustic coupling. The results show the evolution of the correlation between acoustic and transverse velocity fields in the longitudinal direction. A pre-whitening technique is used to investigate the coupling between the acoustic and the velocity signals. This method shows that the correlation between the two signals has a centred peak that is not directly related to the passage of the dominant Kelvin-Helmholtz vortices.

  2. Large-eddy simulations of impinging jets at high Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Wu, Wen; Piomelli, Ugo

    2013-11-01

    We have performed large-eddy simulations of an impinging jet with embedded azimuthal vortices. We used a hybrid approach in which the near-wall layer is modelled using the RANS equations with the Spalart-Allmaras model, while away from the wall Lagrangian-averaged dynamic eddy-viscosity modelled LES is used. This method allowed us to reach Reynolds numbers that would be prohibitively expensive for wall-resolving LES. First, we compared the results of the hybrid calculation with a wall-resolved one at moderate Reynolds number, Re = 66 , 000 (based on jet diameter and velocity). The mean velocity and Reynolds stresses were in good agreement between the simulations, and, in particular, the generation of secondary vorticity at the wall and its liftup were captured well. The simulation cost was reduced by 86%. We then carried out simulations at Re = 266 , 000 and 1.3 million. The effect of Reynolds number on vortex development will be discussed. Canada Research Chair in Computational Turbulence, HPCVL-Sun Microsystems Chair in Computational Science and Engineering.

  3. 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

  4. Drop Characteristics of non-Newtonian Impinging Jets at High Generalized Bird-Carreau Jet Reynolds Numbers

    NASA Astrophysics Data System (ADS)

    Sojka, Paul E.; Rodrigues, Neil S.

    2015-11-01

    The current study investigates the drop characteristics of three Carboxymethylcellulose (CMC) sprays produced by the impingement of two liquid jets. The three water-based solutions used in this work (0.5 wt.-% CMC-7MF, 0.8 wt.-% CMC-7MF, and 1.4 wt.-% CMC-7MF) exhibited strong shear-thinning, non-Newtonian behavior - characterized by the Bird-Carreau rheological model. A generalized Bird-Carreau jet Reynolds number was used as the primary parameter to characterize the drop size and the drop velocity, which were measured using Phase Doppler Anemometry (PDA). PDA optical configuration enabled a drop size measurement range of approximately 2.3 to 116.2 μm. 50,000 drops were measured at each test condition to ensure statistical significance. The arithmetic mean diameter (D10) , Sauter mean diameter (D32) , and mass median diameter (MMD) were used as representative diameters to characterize drop size. The mean axial drop velocity Uz -mean along with its root-mean square Uz -rms were used to characterize drop velocity. Incredibly, measurements for all three CMC liquids and reference DI water sprays seemed to follow a single curve for D32 and MMD drop diameters in the high generalized Bird-Carreau jet Reynolds number range considered in this work (9.21E +03

  5. The Fluid Dynamics of Secondary Cooling Air-Mist Jets

    NASA Astrophysics Data System (ADS)

    Hernández C., I.; Acosta G., F. A.; Castillejos E., A. H.; Minchaca M., J. I.

    2008-10-01

    For the conditions of thin-slab continuous casting, air-mist secondary cooling occurs in the transition-boiling regime, possibly as a result of an enhanced intermittent contact of high- momentum water drops with the hot metallic surface. The dynamics of the intermittent contact or wetting/dewetting process should be primarily dependent on the drop size, drop impact-velocity and -angle and water-impact flux, which results from the nozzle design and the interaction of the drops with the conveying and entrained air stream. The aim of this article was to develop a model for predicting the last three parameters based on the design and operating characteristics of air-mist nozzles and on experimentally determined drop-size distributions. To do this, the Eulerian fluid-flow field of the air in three dimensions and steady state and the Lagrangian velocities and trajectories of water drops were computed by solving the turbulent Navier Stokes equation for the air coupled to the motion equation for the water drops. In setting this model, it was particularly important to specify appropriately the air-velocity profile at the nozzle orifice, as well as, the water-flux distribution, and the velocities (magnitude and angle) and exit positions of drops with the different sizes generated, hence special attention was given to these aspects. The computed drop velocities, water-impact flux distributions, and air-mist impact-pressure fields compared well with detailed laboratory measurements carried out at ambient temperature. The results indicate that under practical nozzle-operating conditions, the impinging-droplet Weber numbers are high, over most of the water footprint, suggesting that the droplets should establish an intimate contact with the solid surface. However, the associated high mean-droplet fluxes hint that this contact may be obstructed by drop interference at the surface, which would undermine the heat-extraction effectiveness of the impinging mist. The model also points

  6. Spatially-resolved, three-dimensional spray characterization of impinging jets by digital in-line holography

    NASA Astrophysics Data System (ADS)

    Gao, Jian; Rodrigues, Neil; Sojka, Paul; Chen, Jun

    2014-11-01

    The impinging jet injector is a preferred method for the atomization of liquid rocket propellants. The majority of experimental studies in literature are not spatially-resolved due to the limitations of widely available point-wise and two-dimensional (2D) diagnostic techniques such as phase Doppler anemometry (PDA), which requires significant experimental repetitions to give spatially-resolved measurements. In the present study, digital in-line holography (DIH) is used to provide spatially-resolved, three-dimensional (3D) characteristics of impinging jet sprays. A double-exposure DIH setup is configured to measure droplet 3D, three-component velocity as well as the size distribution. The particle information is extracted by the hybrid method, which is recently proposed as a particle detection method. To enlarge the detection volume, two parallel, collimated laser beams are used to simultaneously probe the spray at two locations, and two identical cameras are used to record the corresponding holograms. Such a setup has a detection volume of approximately 20 cm by 3.6 cm by 4.8 cm. Sprays of both Newtonian and non-Newtonian liquids corresponding to regimes at relatively lower jet Reynolds and Weber numbers are investigated. Measurements from DIH are further verified by comparison with experimental data obtained from shadowgraph and PDA. It is revealed that DIH is particularly suitable to provide spatially-resolved, 3D measurements of impinging jet sprays that are not particularly dense.

  7. The Stability of Radiatively Cooling Jets I. Linear Analysis

    NASA Technical Reports Server (NTRS)

    Hardee, Philip E.; Stone, James M.

    1997-01-01

    The results of a spatial stability analysis of a two-dimensional slab jet, in which optically thin radiative cooling is dynamically important, are presented. We study both magnetized and unmagnetized jets at external Mach numbers of 5 and 20. We model the cooling rate by using two different cooling curves: one appropriate to interstellar gas, and the other to photoionized gas of reduced metallicity. Thus, our results will be applicable to both protostellar (Herbig-Haro) jets and optical jets from active galactic nuclei. We present analytical solutions to the dispersion relations in useful limits and solve the dispersion relations numerically over a broad range of perturbation frequencies. We find that the growth rates and wavelengths of the unstable Kelvin-Helmholtz (K-H) modes are significantly different from the adiabatic limit, and that the form of the cooling function strongly affects the results. In particular, if the cooling curve is a steep function of temperature in the neighborhood of the equilibrium state, then the growth of K-H modes is reduced relative to the adiabatic jet. On the other hand, if the cooling curve is a shallow function of temperature, then the growth of K-H modes can be enhanced relative to the adiabatic jet by the increase in cooling relative to heating in overdense regions. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between an adiabatic jet and a cooling jet, provided the jet is highly supermagnetosonic and not magnetic pressure-dominated. In the latter case, the unstable modes behave more like the transmagnetosonic magnetic pressure-dominated adiabatic limit. We also plot fluid displacement surfaces associated with the various waves in a cooling jet in order to predict the structures that might arise in the nonlinear regime. This analysis predicts that low-frequency surface waves and the lowest order body modes will be the most effective at producing observable features in

  8. Analysis of a Cylindrical Specimen Heated by an Impinging Hot Hydrogen Jet

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Luong, Van; Foote, John; Litchford, Ron; Chen, Yen-Sen

    2006-01-01

    A computational conjugate heat transfer methodology was developed, as a first step towards an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber and components. A solid conduction heat transfer procedure was implemented onto a pressure-based, multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, and unstructured grid computational fluid dynamics formulation. The conjugate heat transfer of a cylindrical material specimen heated by an impinging hot hydrogen jet inside an enclosed test fixture was simulated and analyzed. The solid conduction heat transfer procedure was anchored with a standard solid heat transfer code. Transient analyses were then performed with ,variable thermal conductivities representing three composites of a material utilized as flow element in a legacy engine test. It was found that material thermal conductivity strongly influences the transient heat conduction characteristics. In addition, it was observed that high thermal gradient occur inside the cylindrical specimen during an impulsive or a 10 s ramp start sequence, but not during steady-state operations.

  9. Performance Enhancement of a High Speed Jet Impingement System for Nonvolatile Residue Removal

    NASA Technical Reports Server (NTRS)

    Klausner, James F.; Mei, Renwei; Near, Steve; Stith, Rex

    1996-01-01

    A high speed jet impingement cleaning facility has been developed to study the effectiveness of the nonvolatile residue removal. The facility includes a high pressure air compressor which charges the k-bottles to supply high pressure air, an air heating section to vary the temperature of the high pressure air, an air-water mixing chamber to meter the water flow and generate small size droplets, and a converging- diverging nozzle to deliver the supersonic air-droplet mixture flow to the cleaning surface. To reliably quantify the cleanliness of the surface, a simple procedure for measurement and calibration is developed to relate the amount of the residue on the surface to the relative change in the reflectivity between a clean surface and the greased surface. This calibration procedure is economical, simple, reliable, and robust. a theoretical framework is developed to provide qualitative guidance for the design of the test and interpretation of the experimental results. The result documented in this report support the theoretical considerations.

  10. Experimental and numerical investigations of the impingement of an oblique liquid jet onto a superhydrophobic surface: energy transformation

    NASA Astrophysics Data System (ADS)

    Kibar, Ali

    2016-02-01

    This study presents the theory of impinging an oblique liquid jet onto a vertical superhydrophobic surface based on both experimental and numerical results. A Brassica oleracea leaf with a 160° apparent contact angle was used for the superhydrophobic surface. Distilled water was sent onto the vertical superhydrophobic surface in the range of 1750-3050 Reynolds number, with an inclination angle of 20°-40°, using a circular glass tube with a 1.75 mm inner diameter. The impinging liquid jet spread onto the surface governed by the inertia of the liquid and then reflected off the superhydrophobic surface due to the surface energy of the spreading liquid. Two different energy approaches, which have time-scale and per-unit length, were performed to determine transformation of the energy. The kinetic energy of the impinging liquid jet was transformed into the surface energy with an increasing interfacial surface area between the liquid and air during spreading. Afterwards, this surface energy of the spreading liquid was transformed into the reflection kinetic energy.

  11. Ultra-high-speed 3D astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets

    NASA Astrophysics Data System (ADS)

    Buchmann, N. A.; Cierpka, C.; Kähler, C. J.; Soria, J.

    2014-11-01

    The paper demonstrates ultra-high-speed three-component, three-dimensional (3C3D) velocity measurements of micron-sized particles suspended in a supersonic impinging jet flow. Understanding the dynamics of individual particles in such flows is important for the design of particle impactors for drug delivery or cold gas dynamic spray processing. The underexpanded jet flow is produced via a converging nozzle, and micron-sized particles ( d p = 110 μm) are introduced into the gas flow. The supersonic jet impinges onto a flat surface, and the particle impact velocity and particle impact angle are studied for a range of flow conditions and impingement distances. The imaging system consists of an ultra-high-speed digital camera (Shimadzu HPV-1) capable of recording rates of up to 1 Mfps. Astigmatism particle tracking velocimetry (APTV) is used to measure the 3D particle position (Cierpka et al., Meas Sci Technol 21(045401):13, 2010) by coding the particle depth location in the 2D images by adding a cylindrical lens to the high-speed imaging system. Based on the reconstructed 3D particle positions, the particle trajectories are obtained via a higher-order tracking scheme that takes advantage of the high temporal resolution to increase robustness and accuracy of the measurement. It is shown that the particle velocity and impingement angle are affected by the gas flow in a manner depending on the nozzle pressure ratio and stand-off distance where higher pressure ratios and stand-off distances lead to higher impact velocities and larger impact angles.

  12. The Stability of Radiatively Cooling Jets. 2: Nonlinear Evolution

    NASA Technical Reports Server (NTRS)

    Stone, James M.; Xu, Jianjun; Hardee, Philip

    1997-01-01

    We use two-dimensional time-dependent hydrodynamical simulations to follow the growth of the Kelvin-Helmholtz (K-H) instability in cooling jets into the nonlinear regime. We focus primarily on asymmetric modes that give rise to transverse displacements of the jet beam. A variety of Mach numbers and two different cooling curves are studied. The growth rates of waves in the linear regime measured from the numerical simulations are in excellent agreement with the predictions of the linear stability analysis presented in the first paper in this series. In the nonlinear regime, the simulations show that asymmetric modes of the K-H instability can affect the structure and evolution of cooling jets in a number of ways. We find that jets in which the growth rate of the sinusoidal surface wave has a maximum at a so-called resonant frequency can be dominated by large-amplitude sinusoidal oscillations near this frequency. Eventually, growth of this wave can disrupt the jet. On the other hand, nonlinear body waves tend to produce low-amplitude wiggles in the shape of the jet but can result in strong shocks in the jet beam. In cooling jets, these shocks can produce dense knots and filaments of cooling gas within the jet. Ripples in the surface of the jet beam caused by both surface and body waves generate oblique shock "spurs" driven into the ambient gas. Our simulations show these shock "spurs" can accelerate ambient gas at large distances from the jet beam to low velocities, which represents a new mechanism by which low-velocity bipolar outflows may be driven by high-velocity jets. Rapid entrainment and acceleration of ambient gas may also occur if the jet is disrupted. For parameters typical of protostellar jets, the frequency at which K-H growth is a maximum (or highest frequency to which the entire jet can respond dynamically) will be associated with perturbations with a period of - 200 yr. Higher frequency (shorter period) perturbations excite waves associated with body

  13. Evaluation of sensing and actuation capabilities of piezoelectric composites in the impingement surface of a supersonic jet

    NASA Astrophysics Data System (ADS)

    Freeborn-Scott, Christopher

    A short takeoff and vertical landing aircraft in hover creates a highly unsteady flowfield dominated by resonance. The supersonic impinging jet created by this aircraft causes damage to the aircraft and nearby structures, lift loss, hot exhaust/debris ingestion by the engine inlet and it is harmful to people in the vicinity. This unsteadiness is caused by a feedback loop, which begins with a disturbance as the nozzle exit that excites the shear layer causing an instability to travel down through the shear layer. As that instability travels downward, it grows and impinges on the ground creating a strong acoustic wave that travels up through the ambient air to the nozzle lip, thus closing the loop. The harmful effects of this flowfield are the motivation for this study. Many flow control techniques have been attempted to reduce the detrimental impact of this flowfield, most notably microjet injection around the periphery of the nozzle exit. This method has been shown to work well; however, this study focuses on implementing ground-based control. Piezoelectric composites have been successful both as frequency sensors and as actuators for vibration suppression. By implementing two piezoelectric composites, the macro-fiber composite and Quick Pack, into the impingement surface of a supersonic jet, an evaluation of the sensing and control capabilities of the devices can be evaluated. Both elements are glued to the underside of a thin, flexible plate, which is placed in the ground, and subjected to a supersonic impinging jet. The jet is ideally expanded at Mach 1.5 with a stagnation temperature equal to the ambient temperature. Narrowband acoustic and unsteady pressure spectra show that at h/d = 4, the presence of a compliant plate causes a shift in the dominant mode, which amounts to a shift in the main impingement tone frequency from 5.7 Hz to 7.1 Hz. Comparison of the power spectral density to the noise and pressure spectra showed that the piezofiber composites are

  14. Analysis of noise produced by jet impingement near the trailing edge of a flat and a curved plate

    NASA Technical Reports Server (NTRS)

    Mckinzie, D. J., Jr.; Burns, R. J.

    1975-01-01

    The sound fields produced by the interaction of a subsonic cold gas jet with the trailing edge of a large flat plate and a curved plate were analyzed. The analyses were performed to obtain a better understanding of the dominant noise source and the mechanism governing the peak sound-pressure-level frequencies of the broadband spectra. An analytical expression incorporating an available theory and experimental data predicts sound field data over an arc of approximately 105 deg measured from the upstream jet axis for the two independent sets of data. The dominant noise as detected on the impingement side of either plate results from the jet impact (eighth power of the velocity dependence) rather than a trailing-edge disturbance (fifth or sixth power of the velocity dependence). Also, the frequency of the peak SPL may be governed by a phenomenon which produces periodic formation and shedding of ring vortices from the nozzle lip.

  15. Numerical Investigation of the Flow Dynamics and Evaporative Cooling of Water Droplets Impinging onto Heated Surfaces: An Effective Approach To Identify Spray Cooling Mechanisms.

    PubMed

    Chen, Jian-Nan; Zhang, Zhen; Xu, Rui-Na; Ouyang, Xiao-Long; Jiang, Pei-Xue

    2016-09-13

    Numerical investigations of the dynamics and evaporative cooling of water droplets impinging onto heated surfaces can be used to identify spray cooling mechanisms. Droplet impingement dynamics and evaporation are simulated using the presented numerical model. Volume-of-fluid method is used in the model to track the free surface. The contact line dynamics was predicted from a dynamic contact angle model with the evaporation rate predicted by a kinetic theory model. A species transport equation was solved in the gas phase to describe the vapor convection and diffusion. The numerical model was validated by experimental data. The physical effects including the contact angle hysteresis and the thermocapillary effect are analyzed to offer guidance for future numerical models of droplet impingement cooling. The effects of various parameters including surface wettability, surface temperature, droplet velocity, droplet size, and droplet temperature were numerically studied from the standpoint of spray cooling. The numerical simulations offer profound analysis and deep insight into the spray cooling heat transfer mechanisms. PMID:27531256

  16. Physical and Mathematical Modeling of Thin Steel Slab Continuous Casting Secondary Cooling Zone Air-Mist Impingement

    NASA Astrophysics Data System (ADS)

    de León B., Melecio; Castillejos E., A. Humberto

    2015-10-01

    This study is an attempt to unveil the fluid dynamic phenomena occurring during interaction of air-mists with the surface of the steel strand during its pass through the continuous casting secondary cooling system. Air-mists generated under conditions of practical interest are studied while impacting on a vertical wall at room temperature. Experimentally a spatial multiple-counting technique based on capturing instantaneous double-exposure shadowgraphs is used to visualize the internal structure of mists at distances between 0 and 4 mm from the wall. Analysis of single exposure images allows determination of size distributions of primary (impinging) and secondary (ejecting) drops and of fluctuating thickness of water films formed on the wall surface. Besides, examination of image pairs enables measurement of velocity and trajectory angles of both kinds of drops. These results aided in the formulation and validation of a transient, turbulent, 3D, multiphase fluid dynamic model for simulating impinging air-mists. The model is based on KIVA-3V and for simulating the airborne mist region it solves the continuity equations—mass, momentum, turbulence quantities—for the air coupled with the equation of motion for drops sampled randomly from distributions assumed to govern their size and volume flux at the nozzle orifice. While for the impingement region submodels are established to estimate the results of drop/wall interaction, i.e., the dynamics of secondary drops and water films formed by the impingement of primary drops. The model forecasts reasonably well the random distributions of diameters, velocities, trajectory angles, and Weber numbers of both kind of drops moving near the wall. Additionally, it predicts well the average thickness of the water film and the important effect that air nozzle pressure has on the normal impinging velocity of drops; high pressures result in large drop velocities favoring intimate contact with the surface.

  17. Effect of plate position and size for self-induced flow oscillation of underexpanded supersonic jet impinging on perpendicular plate

    NASA Astrophysics Data System (ADS)

    Yasunobu, Tsuyoshi; Otobe, Yumiko; Kashimura, Hideo

    2011-09-01

    When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.

  18. 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. PMID:11460645

  19. 2D numerical simulation of impinging jet onto the concave surface by k - w - overline{{v2 }} - f turbulence model

    NASA Astrophysics Data System (ADS)

    Seifi, Zeinab; Nazari, Mohammad Reza; Khalaji, Erfan

    2016-03-01

    In the present article, the characteristics of turbulent jet impinging onto a concave surface is studied using k - w - overline{{v2 }} - f turbulence model. Dependent parameters such as inlet Reynolds number (2960 < Re < 12,000), nozzle-plate distance (4 < H/B < 10), concavity (D/B = 30, 60) of confined and unconfined impinging jet are scrutinized to find out whether this approach would bring any privileges compared to other investigations or not. The obtained results indicate better performance in low nozzle-plate distance in comparison with those mentioned in other literatures. Furthermore, the average Nusselt number of confined impinging jet overtakes unconfined one (similar circumstances) while this trend will decline as relative concavity increases. Moreover, local heat transfer of stagnation area and wall jet goes up and down through nozzle-plate distance enhancement respectively. Finally, the effects of sinusoidal pulsed inlet profile on heat transfer of unconfined impinging jet indicate direct affiliation of amplitude and neutral impact of frequency on Nusselt number distribution.

  20. Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a slot air jet

    NASA Astrophysics Data System (ADS)

    Adimurthy, M.; Katti, Vadiraj V.

    2016-06-01

    Local distribution of wall static pressure and heat transfer on a smooth flat plate impinged by a normal slot air jet is experimental investigated. Present study focuses on the influence of jet-to-plate spacing (Z/D h ) (0.5-10) and Reynolds number (2500-20,000) on the fluid flow and heat transfer distribution. A single slot jet with an aspect ratio (l/b) of about 22 is chosen for the current study. Infrared Thermal Imaging technique is used to capture the temperature data on the target surface. Local heat transfer coefficients are estimated from the thermal images using `SMART VIEW' software. Wall static pressure measurement is carried out for the specified range of Re and Z/D h . Wall static pressure coefficients are seen to be independent of Re in the range between 5000 and 15,000 for a given Z/D h . Nu values are higher at the stagnation point for all Z/D h and Re investigated. For lower Z/D h and higher Re, secondary peaks are observed in the heat transfer distributions. This may be attributed to fluid translating from laminar to turbulent flow on the target plate. Heat transfer characteristics are explained based on the simplified flow assumptions and the pressure data obtained using Differential pressure transducer and static pressure probe. Semi-empirical correlation for the Nusselt number in the stagnation region is proposed.

  1. Stagnation point properties for non-continuum gaseous jet impinging at a flat plate surface from a planar exit

    NASA Astrophysics Data System (ADS)

    Cai, Chunpei

    2013-10-01

    In this paper, we investigate highly rarefied gaseous jet flows out of a planar exit and impinging at a normally set flat plate. Especially, we concentrate on the plate center stagnation point pressure and heat flux coefficients. For a specular reflective plate, the stagnation point pressure coefficient can be represented using two non-dimensional factors: the characteristic gas exit speed ratio S0 and the geometry ratio of H/L, where H is the planar exit semi-height and L is the center-to-center distance from the exit to the plate. For a diffuse reflective plate, the stagnation point pressure and heat flux coefficients involve an extra factor of T0/Tw, i.e., the ratio of exit gas temperature to the plate wall temperature. These results allow us to develop four diagrams, from which we can conveniently obtain the pressure and heat flux coefficients for the stagnation impingement point, at the collisionless flow limit. After normalization with these maximum coefficients, the pressure and heat flux coefficient distributions along the surface essentially degenerate to almost identical curves. As a result, with known plate surface pressure coefficient distributions and these diagrams, we can conveniently construct the heat flux coefficient distributions along the plate surface, and vice versa.

  2. Effect of Inner-tube Position on Heat Transfer of Laminar Annular Impinging Jet with Confined Wall

    NASA Astrophysics Data System (ADS)

    Ichimiya, Koichi; Fukumoto, Hiromichi; Miyazawa, Toshiyoshi

    Present paper describes on the heat transfer and flow characteristics of a laminar annular impinging jet for various positions of inner-tube. In the first case, inner-tube is protruded to the flow passage. In the second case, inner-tube is retracted and relatively, outer-tube with confined insulated wall is protruded. Numerical values were obtained for the dimensionless distance between nozzle and impingement surface, H =0.5,1.0, the diameter ratio, d/D=0.2~0.6, the protrusion or retraction dimensionless length, L/H=0.0~0.8 at the Reynolds number, Re=1,000,the Prandtl number, Pr =0.72 and Grashof number, Gr = 1,000, In the first case, the flow is divided into the stagnant regionand the recirculated region in the minor flow and the major flow region. The local heat transfer for minor flow is depressed with increase of L/H. In the second case, the heat transfer increases locally with increase of L/H. Consequently, local heat transfer is controlled by combining protrusion and retraction.

  3. Numerical analysis of an impinging jet reactor for the CVD and gas-phase nucleation of titania

    NASA Astrophysics Data System (ADS)

    Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

    1994-06-01

    We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

  4. Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

    1994-01-01

    We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

  5. Evaluation of the sensitivity and response of IR thermography from a transparent heater under liquid jet impingement

    NASA Astrophysics Data System (ADS)

    Haustein, H. D.; Rohlfs, W.; Al-Sibai, F.; Kneer, R.

    2012-11-01

    The feasibility of a visible/IR transparent heater and its suitability for IR thermography is experimentally examined. The most common transparent conductive coating, Indium Tin Oxide (ITO), is quite reflective and its optical properties depend on thickness and manufacturing process. Therefore, the optical properties of several thicknesses and types of ITO, coated on an IR window (BaF2), are examined. A highly transparent Cadmium Oxide (CdO) coating on a ZnS window, also examined, is found to be unusable. Transmissivity is found to increase with a decrease in coating thickness, and total emittance is relatively low. A thick ITO coating was examined for IR thermography in the challenging test case of submerged water jet impingement, where temperature differences were characteristically small and distributed. The measurements under steady state conditions were found to agree well with the literature, and the method was validated. Comparison of two IR cameras did not show the LWIR low-temperature advantage, up to the maximal acquisition rate examined, 1.3KHz. Rather the MWIR camera had a stronger signal to noise ratio, due to the higher emissivity of the heater in this range. The transient response of the transparent heater showed no time-delay, though the substrate dampens the thermal response significantly. Therefore, only qualitative transient measurements are shown for the case of pulsating free-surface jet impingement, showing that the motion of the hydraulic jump coincides with thermal measurements. From these results, recommendations are made for coating/window combination in IR thermography.

  6. Thermal characteristics of air-water spray impingement cooling of hot metallic surface under controlled parametric conditions

    NASA Astrophysics Data System (ADS)

    Nayak, Santosh Kumar; Mishra, Purna Chandra

    2016-06-01

    Experimental results on the thermal characteristics of air-water spray impingement cooling of hot metallic surface are presented and discussed in this paper. The controlling input parameters investigated were the combined air and water pressures, plate thickness, water flow rate, nozzle height from the target surface and initial temperature of the hot surface. The effects of these input parameters on the important thermal characteristics such as heat transfer rate, heat transfer coefficient and wetting front movement were measured and examined. Hot flat plate samples of mild steel with dimension 120 mm in length, 120 mm breadth and thickness of 4 mm, 6 mm, and 8 mm respectively were tested. The air assisted water spray was found to be an effective cooling media and method to achieve very high heat transfer rate from the surface. Higher heat transfer rate and heat transfer coefficients were obtained for the lesser i.e, 4 mm thick plates. Increase in the nozzle height reduced the heat transfer efficiency of spray cooling. At an inlet water pressure of 4 bar and air pressure of 3 bar, maximum cooling rates 670°C/s and average cooling rate of 305.23°C/s were achieved for a temperature of 850°C of the steel plate.

  7. Morphology of an aluminum alloy eroded by a jet of angular particles impinging at normal incidence

    NASA Technical Reports Server (NTRS)

    Rao, P. V.; Young, S. G.; Buckley, D. H.

    1983-01-01

    The erosion of an aluminum alloy impinged by crushed glass particles at normal incidence was studied. The erosion patterns were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and surface profilometer measurements. From the analysis of specimens tested at various driving gas pressures and time intervals, four distinct erosion regions were identified. A study of pit morphology and its relationship to cumulative erosion was made. Cutting wear is believed to be the predominant material removal mechanism; some evidence of deformation wear was found during the incubation period.

  8. Spot cooling. Part 1: Human responses to cooling with air jets

    SciTech Connect

    Melikov, A.K.; Halkjaer, L.; Arakelian, R.S.; Fanger, P.O.

    1994-12-31

    Eight standing male subjects and a thermal manikin were studied for thermal, physiological, and subjective responses to cooling with an air jet at room temperatures of 28 C, 33 C, and 38 C and a constant relative humidity of 50%. The subjects wore a standard uniform and performed light work. A vertical jet and a horizontal jet were employed The target area of the jet, i.e., the cross section of the jet where it first met the subject, had a diameter of 0.4 m and was located 0.5 m from the outlet. Experiments were performed at average temperatures at the jet target area of 20 C, 24 C, and 28 C. Each experiment lasted 190 minutes and was performed with three average velocities at the target area: 1 and 2 m/s and the preferred velocity selected by the subjects. The impact of the relative humidity of the room air, the jet`s turbulence intensity, and the use of a helmet on the physiological and subjective responses of the eight subjects was also studied The responses of the eight subjects were compared with the responses of a group of 29 subjects. The spot cooling improved the thermal conditions of the occupants. The average general thermal sensation for the eight subjects was linearly correlated to the average mean skin temperature and the average sweat rate. An average mean skin temperature of 33 C and an average sweat rate of 33 g{center_dot}h{sup {minus}1} m{sup {minus}2} were found to correspond to a neutral thermal sensation. The local thermal sensation at the neck and at the arm exposed to the cooling jet was found to be a function of the room air temperature and the local air velocity and temperature of the jet. The turbulence intensity of the cooling jet and the humidity of the room air had no impact on the subjects` physiological and subjective responses. Large individual differences were observed in the evaluation of the environment and in the air velocity preferred by the subjects.

  9. Analysis of Material Sample Heated by Impinging Hot Hydrogen Jet in a Non-Nuclear Tester

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Foote, John; Litchford, Ron

    2006-01-01

    A computational conjugate heat transfer methodology was developed and anchored with data obtained from a hot-hydrogen jet heated, non-nuclear materials tester, as a first step towards developing an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective and thermal radiative, and conjugate heat transfers. Predicted hot hydrogen jet and material surface temperatures were compared with those of measurement. Predicted solid temperatures were compared with those obtained with a standard heat transfer code. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

  10. Numerical investigation on super-cooled large droplet icing of fan rotor blade in jet engine

    NASA Astrophysics Data System (ADS)

    Isobe, Keisuke; Suzuki, Masaya; Yamamoto, Makoto

    2014-10-01

    Icing (or ice accretion) is a phenomenon in which super-cooled water droplets impinge and accrete on a body. It is well known that ice accretion on blades and vanes leads to performance degradation and has caused severe accidents. Although various anti-icing and deicing systems have been developed, such accidents still occur. Therefore, it is important to clarify the phenomenon of ice accretion on an aircraft and in a jet engine. However, flight tests for ice accretion are very expensive, and in the wind tunnel it is difficult to reproduce all climate conditions where ice accretion can occur. Therefore, it is expected that computational fluid dynamics (CFD), which can estimate ice accretion in various climate conditions, will be a useful way to predict and understand the ice accretion phenomenon. On the other hand, although the icing caused by super-cooled large droplets (SLD) is very dangerous, the numerical method has not been established yet. This is why SLD icing is characterized by splash and bounce phenomena of droplets and they are very complex in nature. In the present study, we develop an ice accretion code considering the splash and bounce phenomena to predict SLD icing, and the code is applied to a fan rotor blade. The numerical results with and without the SLD icing model are compared. Through this study, the influence of the SLD icing model is numerically clarified.

  11. 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.

  12. Three-dimensional consideration of jet impingement onto the kerf in relation to laser cutting process: Effect of jet velocity on heat transfer rates

    NASA Astrophysics Data System (ADS)

    Melhem, Omar A.; Yilbas, Bekir S.; Shuja, Shahzada Z.

    2011-03-01

    In laser cutting process, an assisting gas is used to improve the mass removal rate from the cutting kerf and protect the kerf surfaces from the high temperature exothermic reactions, such as oxidation reactions, during the cutting process. Therefore, heat transfer rates from the kerf wall and the skin friction along the kerf surface are important for quality cutting. In the present study, jet emerging from a conical convergent nozzle and impinging onto the kerf surface is investigated in relation to the laser cutting process. The flow field in the kerf, the heat transfer rates from the kerf wall, and the skin friction along the kerf surface are computed for four average jet velocities at the nozzle exit and two kerf wall wedge angles. The ratio of the stand-off-distance (distance between the nozzle exit and the kerf top surface) to nozzle diameter is selected as H/ D=2.2., where H is the stand-off-distance and D is the nozzle exit diameter. The kerf wall temperature is kept at 1500 K to resemble the laser cutting process. It is found that the Nusselt number increases sharply at the kerf inlet and decreases towards the kerf exit for the kerf wall angle of 0°. However, it increases gradually in this region for the kerf wedge angle of 4°. The skin friction decreases along the kerf surface.

  13. Unsteady numerical simulation of a round jet with impinging microjets for noise suppression

    PubMed Central

    Lew, Phoi-Tack; Najafi-Yazdi, Alireza; Mongeau, Luc

    2013-01-01

    The objective of this study was to determine the feasibility of a lattice-Boltzmann method (LBM)-Large Eddy Simulation methodology for the prediction of sound radiation from a round jet-microjet combination. The distinct advantage of LBM over traditional computational fluid dynamics methods is its ease of handling problems with complex geometries. Numerical simulations of an isothermal Mach 0.5, ReD = 1 × 105 circular jet (Dj = 0.0508 m) with and without the presence of 18 microjets (Dmj = 1 mm) were performed. The presence of microjets resulted in a decrease in the axial turbulence intensity and turbulent kinetic energy. The associated decrease in radiated sound pressure level was around 1 dB. The far-field sound was computed using the porous Ffowcs Williams-Hawkings surface integral acoustic method. The trend obtained is in qualitative agreement with experimental observations. The results of this study support the accuracy of LBM based numerical simulations for predictions of the effects of noise suppression devices on the radiated sound power. PMID:23967931

  14. Unsteady numerical simulation of a round jet with impinging microjets for noise suppression.

    PubMed

    Lew, Phoi-Tack; Najafi-Yazdi, Alireza; Mongeau, Luc

    2013-09-01

    The objective of this study was to determine the feasibility of a lattice-Boltzmann method (LBM)-Large Eddy Simulation methodology for the prediction of sound radiation from a round jet-microjet combination. The distinct advantage of LBM over traditional computational fluid dynamics methods is its ease of handling problems with complex geometries. Numerical simulations of an isothermal Mach 0.5, Re(D) = 1 × 10(5) circular jet (D(j) = 0.0508 m) with and without the presence of 18 microjets (D(mj) = 1 mm) were performed. The presence of microjets resulted in a decrease in the axial turbulence intensity and turbulent kinetic energy. The associated decrease in radiated sound pressure level was around 1 dB. The far-field sound was computed using the porous Ffowcs Williams-Hawkings surface integral acoustic method. The trend obtained is in qualitative agreement with experimental observations. The results of this study support the accuracy of LBM based numerical simulations for predictions of the effects of noise suppression devices on the radiated sound power. PMID:23967931

  15. Conjugate heat transfer from a heated disk to a thin liquid film formed by a controlled impinging jet

    NASA Technical Reports Server (NTRS)

    Faghri, A.; Thomas, S.; Rahman, M. M.

    1993-01-01

    An experimental and numerical study of the heat transfer from a heated horizontal disk to a thin film of liquid is described. The liquid was delivered to the disk by a collar arrangement such that the film thickness and radial velocity were known at the outer radius of the collar. This method of delivery is termed as a controlled impinging jet. Flow visualization tests were performed and heat transfer data were collected along the radius of the disk for different volumetric flow rates and inlet temperatures in the supercritical and subcritical regions. The heat transfer coefficient was found to increase with flow rate when both supercritical and subcritical regions were present on the heated surface. A numerical simulation of this free surface problem was performed, which included the effects of conjugate heat transfer within the heated disk and the liquid. The numerical predictions agree with the experimental results and show that conjugate heat transfer has a significant effect on the local wail temperature and heat transfer coefficient.

  16. Preparation of poly(MePEGCA-co-HDCA) nanoparticles with confined impinging jets reactor: experimental and modeling study.

    PubMed

    Lince, Federica; Bolognesi, Sara; Marchisio, Daniele L; Stella, Barbara; Dosio, Franco; Barresi, Antonello A; Cattel, Luigi

    2011-06-01

    In this work, the biodegradable copolymer poly(methoxypolyethyleneglycolcyanoacrylate-co-hexadecylcyanoacrylate) is used to prepare nanoparticles via solvent displacement in a confined impinging jets reactor (CIJR). For comparison, nanoparticles constituted by the homopolymer counterpart are also investigated. The CIJR is a small passive mixer in which very fast turbulent mixing of the solvent (i.e., acetone and tetrahydrofuran) and of the antisolvent (i.e., water) solutions occurs under controlled conditions. The effect of the initial copolymer concentration, solvent type, antisolvent-to-solvent ratio, and mixing rate inside the mixer on the final nanoparticle size distribution, surface properties, and morphology is investigated from the experimental point of view. The effect of some of these parameters is studied by means of a computational fluid dynamics (CFD) model, capable of quantifying the mixing conditions inside the CIJR. Results show that the CIJR can be profitably used for producing nanoparticles with controlled characteristics, that there is a clear correlation between the mixing rate calculated by CFD and the mean nanoparticle size, and therefore that CFD can be used to design, optimize, and scale-up these processes. PMID:21259236

  17. Stimulated emission pumping spectroscopy of jet-cooled C3

    NASA Astrophysics Data System (ADS)

    Rohlfing, Eric A.; Goldsmith, J. E. M.

    1989-06-01

    We report a dispersed fluorescence spectrum obtained for excitation of a ∑+u-∑+g vibronic band of C3 at 33 588 cm-1, part of a newly discovered electronic system. Rotationally resolved stimulated-emission-pumping spectra of jet-cooled C3 using this ∑+u intermediate state are presented for dumping to the 0v121 (1≤v2≤13) and 6v121 (1≤v2≤5) levels in the 1Σ+g ground state. Vibrational term energies, rotational constants, and l-type doubling parameters are determined for each level.

  18. Cratering Soil by Impinging Jets of Gas, with Application to Landing Rockets on Planetary Surfaces

    NASA Technical Reports Server (NTRS)

    Metzger, Philip T.; Vu, B. T.; Taylor, D. E.; Kromann, M. J.; Fuchs, M.; Yutko, B.; Dokos, A.; Immer, Christopher D.; Lane, J. E.; Dunkel, Michael B.; Donahue, Carly M.; Latta, R. C., III

    2007-01-01

    Several physical mechanisms are involved in excavating granular materials beneath a vertical jet of gas. These occur, for example, beneath the exhaust plume of a rocket landing on the soil of the Moon or Mars. A series of experiments and simulations have been performed to provide a detailed view of the complex gas/soil interactions. Measurements have also been taken from the Apollo lunar landing videos and from photographs of the resulting terrain, and these help to demonstrate how the interactions extrapolate into the lunar environment. It is important to understand these processes at a fundamental level to support the ongoing design of higher-fidelity numerical simulations and larger-scale experiments. These are needed to enable future lunar exploration wherein multiple hardware assets will be placed on the Moon within short distances of one another. The high-velocity spray of soil from landing spacecraft must be accurately predicted and controlled lest it erosively damage the surrounding hardware.

  19. Direct Flame Impingement

    SciTech Connect

    2005-09-01

    During the DFI process, high velocity flame jets impinge upon the material being heated, creating a high heat transfer rate. As a result, refractory walls and exhaust gases are cooler, which increases thermal efficiency and lowers NOx emissions. Because the jet nozzles are located a few inches from the load, furnace size can be reduced significantly.

  20. Adiabatic cooling of the artificial Porcupine plasma jet

    NASA Astrophysics Data System (ADS)

    Ruizhin, Iu. Ia.; Treumann, R. A.; Bauer, O. H.; Moskalenko, A. M.

    1987-01-01

    Measurements of the plasma density obtained during the interaction of the artificial plasma jet, fired into the ionosphere with the body of the Porcupine main payload, have been analyzed for times when there was a well-developed wake effect. Using wake theory, the maximum temperature of the quasi-neutral xenon ion beam has been determined for an intermediate distance from the ion beam source when the beam has left the diamagnetic region but is still much denser than the ionospheric background plasma. The beam temperature is found to be about 4 times less than the temperature at injection. This observation is very well explained by adiabatic cooling of the beam during its initial diamagnetic and current-buildup phases at distances r smaller than 10 m. Outside this region, the beam conserves the temperature achieved. The observation proves that the artificial plasma jet passes through an initial gas-like diamagnetic phase restricted to the vicinity of the beam source, where it expands adiabatically. Partial cooling also takes place outside the diamagnetic region where the beam current still builds up. The observations also support a recently developed current-closure model of the quasi-neutral ion beam.

  1. Comparison of central axis and jet ring coolant supply for turbine disk cooling on a SSME-HPOTP model

    NASA Technical Reports Server (NTRS)

    Kim, Y. W.; Metzger, D. E.

    1992-01-01

    The test facility, test methods and results are presented for an experimental study modeling the cooling of turbine disks in the blade attachment regions with multiple impinging jets, in a configuration simulating the disk cooling method employed on the Space Shuttle Main Engine oxygen turbopump. The study's objective was to provide a comparison of detailed local convection heat transfer rates obtained for a single center-supply of disk coolant with those obtained with the present flight configuration where disk coolant is supplied through an array of 19 jets located near the disk outer radius. Specially constructed disk models were used in a program designed to evaluate possible benefits and identify any possible detrimental effects involved in employing an alternate disk cooling scheme. The study involved the design, construction and testing of two full scale rotating model disks, one plane and smooth for baseline testing and the second contoured to the present flight configuration, together with the corresponding plane and contoured stator disks. Local heat transfer rates are determined from the color display of encapsulated liquid crystals coated on the disk in conjunction with use of a computer vision system. The test program was composed of a wide variety of disk speeds, flowrates, and geometrical configurations, including testing for the effects of disk boltheads and gas ingestion from the gas path region radially outboard of the disk-cavity.

  2. Effects of geometry on slot-jet film cooling performance

    SciTech Connect

    Hyams, D.G.; McGovern, K.T.; Leylek, J.H.

    1995-10-01

    The physics of the film cooling process for shaped, inclined slot-jets with realistic slot-length-to-width ratios (L/s) is studied for a range of blowing ratio (M) and density ratio (DR) parameters typical of gas turbine operations. For the first time in the open literature, the effect of inlet and exit shaping of the slot-jet on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. A previously documented computational methodology was applied for the study of four distinct configurations: (1) slot with straight edges and sharp corners (reference case); (2) slot with shaped inlet region; (3) slot with shaped exit region; and (4) slot with both shaped inlet and exit regions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness ({eta}) and heat transfer coefficient (h) are presented. It is demonstrated that both {eta} and h results are vital in the proper assessment of film cooling performance. All simulations were carried out using a multi-block, unstructured/adaptive grid, fully explicit, time-marching solver with multi-grid, local time stepping, and residual smoothing type acceleration techniques. Special attention was paid to and full documentation provided for: (1) proper modeling of the physical phenomena; (2) exact geometry and high quality grid generation techniques; (3) discretization schemes; and (4) turbulence modeling issues. The key parameters M and DR were varied from 1.0 to 2.0 and 1.5 to 2.0, respectively, to show their influence. Simulations were repeated for slot length-to-width ratio (L/s) of 3.0 and 4.5 in order to explain the effects of this important parameter. Additionally, the performance of two popular turbulence models, standard k-F, and RNG k-E, were studied to establish their ability to handle highly elliptic jet/crossflow interaction type processes.

  3. Laboratory Studies of Magnetically Driven, Radiatively Cooled Supersonic Plasma Jets

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergey V.

    2010-05-01

    Results of the recent experiments with radiatively cooled jets performed on the pulsed power MAGPIE facility (1.5MA, 250ns) at Imperial College will be presented. The experiments are scalable to astrophysical flows in that critical dimensionless numbers such as the plasma collisionality, the plasma beta, Reynolds number and the magnetic Reynolds number are all in the astrophysically appropriate ranges. The experimental results will be compared with computer simulations performed with laboratory plasma codes and with astrophysical codes. The main part of the presentation will concentrate on the dynamics of magnetically driven jets, in particular on formation of episodic outflows [1]. The experimental results show the periodic ejections of magnetic bubbles naturally evolving into a heterogeneous jet propagating inside a channel made of self-collimated magnetic cavities. Experimental data on the energy balance in the magnetically driven jets, the conversion of the Poynting flux energy into kinetic energy of the outflow, will be also presented. *) In collaboration with A. CIARDI, F.A. SUZUKI-VIDAL, S.N. BLAND, M. BOCCHI, G. BURDIAK, J.P. CHITTENDEN, P. de GROUCHY, G. HALL, A. HARVEY-THOMSON, A. MAROCCHINO, G. SWADLING, A. FRANK, E. G. BLACKMAN, C. STEHLE, M. CAMENZIND. This research was sponsored by EPSRC, by the OFES DOE, by the NNSA under DOE Cooperative Agreement No. DE-FC03-02NA00057 and by the European Community's Marie Curie Actions within the JETSET network under Contract No. MRTNCT- 2004 005592. References [1] A. Ciardi, S.V. Lebedev, A. Frank et al., The Astrophysical Journal, 691: L147-L150 (2009).

  4. Large area impingement spray cooling from multiple normal and inclined spray nozzles

    NASA Astrophysics Data System (ADS)

    Yan, Z. B.; Duan, F.; Wong, T. N.; Toh, K. C.; Choo, K. F.; Chan, P. K.; Chua, Y. S.; Lee, L. W.

    2013-07-01

    An inclined spray chamber with four multiple nozzles to cool a 1 kW 6U electronic test card has been designed and tested in this study. The multiple inclined sprays can cover the same heated surface area as that with the multiple normal sprays but halve the volume of the spray chamber. The spray cooling system used R134a as a working fluid in a modified refrigeration cycle. It is observed that increasing mass flow rate and pressure drop across the nozzles improved the heat transfer coefficient with a maximum enhancement of 117 %, and reduced the maximum temperature difference at the heated surface from 13.8 to 8.4 °C in the inclined spray chamber with a heat flux of 5.25 W/cm2, while the heat transfer coefficient of the normal spray increased with a maximum enhancement of 215 % and the maximum temperature difference decreased from 10.8 to 5.4 °C under similar operating conditions. We conclude that the multiple inclined sprays could produce a higher heat transfer coefficient but with an increase in non-uniformity of the surface temperature compared with the multiple normal sprays.

  5. Jet-Cooled Emission Spectra of the Xylyl Radicals

    NASA Astrophysics Data System (ADS)

    Selco, J. I.; Carrick, P. G.

    1995-09-01

    Jet-cooled electronic emission spectra from ortho-, meta-, and para-xylyl (methylbenzyl) radicals have been recorded with a corona excited supersonic expansion (CESE) apparatus. A full vibronic analysis of the D1 → D0 transitions for all three isomers has been carried out, allowing for unambiguous assignments of the gas-phase ground state vibrational frequencies. For modes exhibiting progressions (numbering according to Green and Wilson) (11 (18a), 29 (6b), 10 (6a), 9 (1), 25 (3) and 5 (14) in ortho-xylyl; 10 (6b) in meta-xylyl; and 5 (1), 6 (6a), 3 (7a), and 17 (10a) in para-xylyl), anharmonicity constants are calculated and reported. Although CESE excitation of the xylenes (used in this study as precursors) did not result in the interconversion of isomers, it does occur along with homolytic methyl C-H bond dissociation during the formation of the radicals.

  6. Transpiring Cooling of a Scram-Jet Engine Combustion Chamber

    NASA Technical Reports Server (NTRS)

    Choi, Sang H.; Scotti, Stephen J.; Song, Kyo D.; Ries,Heidi

    1997-01-01

    The peak cold-wall heating rate generated in a combustion chamber of a scram-jet engine can exceed 2000 Btu/sq ft sec (approx. 2344 W/sq cm). Therefore, a very effective heat dissipation mechanism is required to sustain such a high heating load. This research focused on the transpiration cooling mechanism that appears to be a promising approach to remove a large amount of heat from the engine wall. The transpiration cooling mechanism has two aspects. First, initial computations suggest that there is a reduction, as much as 75%, in the heat flux incident on the combustion chamber wall due to the transpirant modifying the combustor boundary layer. Secondly, the heat reaching the combustor wall is removed from the structure in a very effective manner by the transpirant. It is the second of these two mechanisms that is investigated experimentally in the subject paper. A transpiration cooling experiment using a radiant heating method, that provided a heat flux as high as 200 Btu/sq ft sec ( approx. 234 W/sq cm) on the surface of a specimen, was performed. The experiment utilized an arc-lamp facility (60-kW radiant power output) to provide a uniform heat flux to a test specimen. For safety reasons, helium gas was used as the transpirant in the experiments. The specimens were 1.9-cm diameter sintered, powdered-stainless-steel tubes of various porosities and a 2.54cm square tube with perforated multi-layered walls. A 15-cm portion of each specimen was heated. The cooling effectivenes and efficiencies by transpiration for each specimen were obtained using the experimental results. During the testing, various test specimens displayed a choking phenomenon in which the transpirant flow was limited as the heat flux was increased. The paper includes a preliminary analysis of the transpiration cooling mechanism and a scaling conversion study that translates the results from helium tests into the case when a hydrogen medium is used.

  7. Combustion of LOX with H2(sub g) under subcritical, critical, and supercritical conditions and experimental observation of dense spray and mixing of impinging jets

    NASA Technical Reports Server (NTRS)

    Kuo, Kenneth K.; Hsieh, W. H.; Yang, A. S.; Brown, J. J.; Cheung, F. B.; Woodward, R. D.; Kline, M. C.

    1992-01-01

    Progress made during the period of February 1 to October 15, 1992 is reported. The overall objective of Task 1 of the investigation is to achieve a better understanding of the combustion processes of liquid oxygen and gaseous hydrogen under subcritical, critical, and supercritical conditions. Specific objectives of the research program are: (1) to determine the evaporation- and burning-rate characteristics of LOX in hydrogen/helium environments under broad ranges of operating conditions; (2) to measure species concentration profile and surface temperature of LOX employing the gas chromatography and fine-wire thermocouples under non-reacting flow situations; (3) to perform a fugacity-based multicomponent thermodynamic phase equilibrium analysis for examining the high-pressure vapor-liquid equilibrium behavior at the liquid surface of LOX; (4) to formulate and solve a theoretical model for simulating the evaporation and combustion processes in a LOX/H2/He system; and (5) to validate the theoretical model with the measured experimental data. Task 2 of the investigation is described. Observation of a like-on-like injector element in the near-injector region performed in the previous phase of this project has identified the existence of a high Reynolds number regime in which the pre-impingement jets are fully turbulent and undergoing surface breakup. The new spray regime, which has not been observed by previous investigators, is characterized by the presence of many fine droplets and the disappearance of the well-defined liquid breakup wave pattern in the post-impingement region. It is speculated that a cavitating region may be present within the orifice so that it could induce strong turbulence, leading to an onset of atomization of the jets prior to impingement. To further investigate the dense spray behavior of the impinging jets in the high Reynolds number region, experiments were conducted using Plexiglas injector components for direct internal flow observation

  8. Modeling studies of an impinging jet reactor design for hybrid physical-chemical vapor deposition of superconducting MgB 2 films

    NASA Astrophysics Data System (ADS)

    Lamborn, Daniel R.; Wilke, Rudeger H. T.; Li, Qi; Xi, X. X.; Snyder, David W.; Redwing, Joan M.

    2009-03-01

    An impinging jet reactor was developed for the deposition of superconducting MgB 2 thin films by hybrid physical-chemical vapor deposition, a technique that combines Mg evaporation with the thermal decomposition of B 2H 6 gas. A transport and chemistry model for boron film deposition from B 2H 6 was initially used to investigate the effect of carrier gas, Mg crucible temperature and gas flow rates on boron film growth rate and uniformity. The modeling studies, which were validated experimentally, demonstrated a reduction in B 2H 6 gas-phase depletion and an increased boron film growth rate using an argon carrier gas compared to hydrogen. The results were used to identify a suitable set of process conditions for MgB 2 deposition in the impinging jet reactor. The deposition of polycrystalline MgB 2 thin films that exhibited a transition temperature of 39.5 K was demonstrated at growth rates up to ˜50 μm/h.

  9. High-resolution photoabsorption spectrum of jet-cooled propyne

    SciTech Connect

    Jacovella, U.; Holland, D. M. P.; Boyé-Péronne, S.; Joyeux, D.; Archer, L. E.; Oliveira, N. de; Nahon, L.; Lucchese, R. R.; Xu, Hong; Pratt, S. T.

    2014-09-21

    The absolute photoabsorption cross section of propyne was recorded between 62 000 and 88 000 cm{sup −1} by using the vacuum-ultraviolet, Fourier-transform spectrometer at the Synchrotron Soleil. This cross section spans the region including the lowest Rydberg bands and extends above the Franck-Condon envelope for ionization to the ground electronic state of the propyne cation, X{sup ~+}. Room-temperature spectra were recorded in a flowing cell at 0.9 cm{sup −1} resolution, and jet-cooled spectra were recorded at 1.8 cm{sup −1} resolution and a rotational temperature of ∼100 K. The reduced widths of the rotational band envelopes in the latter spectra reveal new structure and simplify a number of assignments. Although nf Rydberg series have not been assigned previously in the photoabsorption spectrum of propyne, arguments are presented for their potential importance, and the assignment of one nf series is proposed. As expected from previous photoelectron spectra, Rydberg series are also observed above the adiabatic ionization threshold that converge to the v{sub 3}{sup +} = 1 and 2 levels of the C≡C stretching vibration.

  10. Liquid film target impingement scrubber

    DOEpatents

    McDowell, William J.; Coleman, Charles F.

    1977-03-15

    An improved liquid film impingement scrubber is provided wherein particulates suspended in a gas are removed by jetting the particle-containing gas onto a relatively small thin liquid layer impingement target surface. The impingement target is in the form of a porous material which allows a suitable contacting liquid from a pressurized chamber to exude therethrough to form a thin liquid film target surface. The gas-supported particles collected by impingement of the gas on the target are continuously removed and flushed from the system by the liquid flow through each of a number of pores in the target.