An Experimental and Numerical Investigation on the Effects of Aerothermal Mixing in a Confined Oblique Jet Impingement Configuration

2015 ◽  
Author(s):  
Sebastian Schulz ◽  
Alexander Schindler ◽  
Jens von Wolfersdorf
Keyword(s):  
Reynolds Number ◽  
Jet Impingement ◽  
Field Measurements ◽  
Fluid Temperature ◽  
Number Range ◽  
Ansys Cfx ◽  
Image Velocimetry ◽  
Flow Features ◽  
Sst Turbulence Model ◽  
Good Agreement

An investigation to characterize the effect of entrainment in a confined jet impingement arrangement is presented. The investigated configuration models an impingement cooled turbine blade passage and holds two staggered rows of inclined impingement jets. In order to distinctly promote thermal entrainment phenomena the jets were heated separately. A steady-state liquid crystal technique was used to obtain near-wall fluid temperature distributions for the impingement surfaces at adiabatic conditions. Additionally, flow field measurements were undertaken using Particle Image Velocimetry (PIV). Furthermore, compressible RANS simulations were carried out with ANSYS CFX using Menter’s SST turbulence model to accompany the experiments. Distributions of effectiveness, velocity, and turbulent kinetic energy detail the complexity of the aerothermal situation. The study was conducted for a jet Reynolds number range from 10,000 to 45,000. The experimental and numerical results are generally in good agreement. Nevertheless, the simulations predict flow features in particular regions of the geometry that are not as prominent in the experiments. These affect the effectiveness distributions, locally. The investigations revealed that the effectiveness is independent of the temperature difference between the heated and cold jet as well as the jet Reynolds number.

An Experimental and Numerical Investigation on the Effects of Aerothermal Mixing in a Confined Oblique Jet Impingement Configuration

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Sebastian Schulz ◽  
Alexander Schindler ◽  
Jens von Wolfersdorf
Keyword(s):  
Reynolds Number ◽  
Jet Impingement ◽  
Field Measurements ◽  
Navier Stokes ◽  
Fluid Temperature ◽  
Number Range ◽  
Ansys Cfx ◽  
Image Velocimetry ◽  
Flow Features ◽  
Sst Turbulence Model

An investigation to characterize the effect of entrainment in a confined jet impingement arrangement is presented. The investigated configuration shows an impingement-cooled turbine blade passage and holds two staggered rows of inclined impingement jets. In order to distinctly promote thermal entrainment phenomena, the jets were heated separately. A steady-state liquid crystal technique was used to obtain near-wall fluid temperature distributions for the impingement surfaces under adiabatic conditions. Additionally, flow field measurements were undertaken using particle image velocimetry (PIV). Furthermore, compressible Reynolds-averaged Navier–Stokes (RANS) simulations carried out with ansys cfx using Menter's shear stress transport (SST) turbulence model accompany the experiments. Distributions of effectiveness, velocity, and turbulent kinetic energy detail the complexity of the aerothermal situation. The study was conducted for a jet Reynolds number range from 10,000 to 45,000. The experimental and numerical results are generally in good agreement. Nevertheless, the simulations predict flow features in particular regions of the geometry that are not as prominent in the experiments. These affect the effectiveness distributions, locally. The investigations reveal that the effectiveness is independent of the temperature difference between the heated and cold jet as well as the jet Reynolds number.

Velocity Field Measurements in Leading Edge Wing Compartments

2008 ◽  
Author(s):  
V. Egan ◽  
D. T. Newport ◽  
V. Larcarac ◽  
B. Estebe
Keyword(s):  
Natural Convection ◽  
Leading Edge ◽  
Field Measurements ◽  
Dominant Mode ◽  
Fluid Temperature ◽  
Velocity Measurements ◽  
Thermal Boundary Conditions ◽  
Single Compartment ◽  
Image Velocimetry ◽  
Convection Cooling

For many applications the optimisation of natural convection cooling is a major design consideration due to factors such as weight, accessibility, cost and power consumption. In aircraft wing compartments, natural convection is the dominant mode of heat transfer due to high wall temperatures resulting from solar loading and heat dissipating internal electronics. This paper investigates the flow structures in a leading edge compartment subject to various thermal boundary conditions. The experimental configuration consisted of two leading edge enclosures; the first is a single compartment while the second has an attached wing box. Particle image velocimetry (PIV) was employed to obtain velocity measurements of the flow in both leading edge enclosures. The second compartment investigated the effect of an adjacent fluid filled enclosure on the flow regime in the leading edge compartment. Higher local velocities were found in the second compartment due to an increase in buoyancy forces resulting from a lower of the average fluid temperature within the compartment. The introduction of a heat dissipating component gave rise to two separate convection structures and in general increased the fluctuations in the both temperature and velocities within the compartment.

Experimental Analysis of Microchannel Entrance Length Characteristics Using Microparticle Image Velocimetry

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Tariq Ahmad ◽  
Ibrahim Hassan
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Entrance Region ◽  
Working Fluid ◽  
Parallel Plates ◽  
Entrance Length ◽  
Number Range ◽  
Micro Piv ◽  
Image Velocimetry ◽  
Microparticle Image Velocimetry

The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500 μm, 200 μm, and 100 μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices.

Inspiratory and Expiratory Steady Flow Analysis in a Model Symmetrically Bifurcating Airway

1997 ◽  
Vol 119 (1) ◽  
pp. 52-58 ◽  
Author(s):  
Y. Zhao ◽  
C. T. Brunskill ◽  
B. B. Lieber
Keyword(s):  
Reynolds Number ◽  
Flow Analysis ◽  
Experimental Studies ◽  
Velocity Profiles ◽  
The Finite Element Method ◽  
Velocity Peak ◽  
Flow Features ◽  
Experimental Findings ◽  
Parent Tube ◽  
Good Agreement

Steady inspiratory and expiratory flow in a symmetrically bifurcating airway model was studied numerically using the finite element method (FIDAP). Flows of Reynolds number of 500 and 1000 during inspiration and a flow of Reynolds number of 500 during expiration were analyzed. Since the geometry of the bifurcation model used in this study is exactly the same as the model used in the experimental studies, the computed results were compared to the experimental findings. Results show that most of the important flow features that were observed in the experiment, such as the skewed velocity profiles in the daughter branches during inspiration and velocity peak in the parent tube during expiration, were captured in the numerical simulation. Quantitatively, the computed velocity profiles are in good agreement with the measured profiles. This comparison validates the computational simulations.

Experimental and Numerical Investigations on Turbine Airfoil Cooling Designs: Part I—An Investigation on Flow Features by Particle Image Velocimetry

2008 ◽  
Author(s):  
J. H. Wang ◽  
H. Z. Xu ◽  
Y. L. Liu ◽  
Z. N. Du ◽  
S. J. Yang
Keyword(s):  
Reynolds Number ◽  
Particle Image ◽  
Turbulence Models ◽  
Velocity Fields ◽  
Numerical Investigations ◽  
Wall Film ◽  
Image Velocimetry ◽  
Flow Features ◽  
Numerical Grid ◽  
Double Wall

Experimental and numerical investigations are conducted to understand the features of the fluid dynamics within double-wall film-cooled configurations. Based on the similarity principle of the Reynolds number, a large-scale similar configuration made of transparent material is used as specimen, and the fluid velocity distributions over several typical cross sections within the specimen channel are captured by a particle image velocimetry (PIV) system. The experiments are carried out at a density ratio of fluid medium to tracer particle 1.05. The flow features are respectively calculated by different turbulence models and numerical grids. To confirm turbulence models and numerical grids, the numerical results are compared with the experimental data obtained by the PIV system. Through the comparisons, recommendations have been made with regard to the best model and numerical grid which best predict such velocity fields. The influences of inlet Reynolds numbers and the geometrical device of the double-wall film-cooled configurations on the features of flow field are numerically simulated by the recommended model and grid. The simulation results predicate that the flow features are mainly dominated by the geometrical device, the inlet Reynolds number can only result in a magnitude change of velocity fields, and this change is almost linear. This is the first part of the entire investigations on the double-wall film-cooled configurations, and the objective of this part is to confirm a suitable mathematical model and numerical grid for describing the flow features. In the next part, the overall heat transfer characteristics of these configurations will be studied.

Full-Field Flow Measurements and Heat Transfer of a Compact Jet Impingement Array With Local Extraction of Spent Fluid

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Andrew J. Onstad ◽  
Christopher J. Elkins ◽  
Robert J. Moffat ◽  
John K. Eaton
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Smooth Transition ◽  
Transfer Coefficients ◽  
Flow Measurements ◽  
Extraction Area ◽  
Number Range ◽  
Full Field ◽  
High Heat Transfer

Jet impingement cooling is widely used due to the very high heat transfer coefficients that are attainable. Both single and multiple jet systems can be used, however, multiple jet systems offer higher and more uniform heat transfer. A staggered array of 8.46 mm diameter impingement jets with jet-to-jet spacing of 2.34 D was examined where the spent fluid is extracted through one of six 7.36 mm diameter extraction holes regularly located around each jet. The array had an extraction area ratio (Ae/Ajet) of 2.23 locally and was tested with a jet-to-target spacing (H/D) of 1.18 jet diameters. Magnetic resonance velocimetry was used to both quantify and visualize the three dimensional flow field inside the cooling cavity at jet Reynolds numbers of 2600 and 5300. The spatially averaged velocity measurements showed a smooth transition is possible from the impingement jet to the extraction hole without the presence of large vortical structures. Mean Nusselt number measurements were made over a jet Reynolds number range of 2000–10,000. Nusselt numbers near 75 were measured at the highest Reynolds number with an estimated uncertainty of 7%. Large mass flow rate per unit heat transfer area ratios were required because of the small jet-to-jet spacing.

An Experimental Investigation of Liquid Jet Array and Single Phase Spray Impingement Cooling Using Polyalphaolefin

2003 ◽  
Author(s):  
Ahmad K. Sleiti ◽  
J. S. Kapat
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Single Phase ◽  
Jet Impingement ◽  
Spray Cooling ◽  
Rectangular Array ◽  
Number Range

Experiments on triangular and rectangular array jet impingement and single phase spray cooling have been performed to determine the effect of both cooling techniques on heat transfer coefficient and the coolant mass flux required for a given cooling load. Experiments were performed with circular orifices and nozzles for different H/D values from 1.5 to 26 and Reynolds number range of 219 to 837, which is quite lower than the ranges used in widely used correlations. The coolant used was polyalphaolefin. For the custom fabricated orifices, commercial nozzles and conditions used in this study, both cooling techniques showed enhancement of heat transfer coefficient as H/D increases to a certain limit after which it starts to decrease. The heat transfer coefficient always increases with Reynolds number. In keeping with previous studies, single-phase spray cooling technique can provide the same heat transfer coefficient as jets at a slightly lower mass flux, but with a higher pressure head.

Turbulent Lubrication Flow in an Annular Channel

1986 ◽  
Vol 108 (2) ◽  
pp. 185-192 ◽  
Author(s):  
H. G. Polderman ◽  
G. Velraeds ◽  
W. Knol
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Diffusion Model ◽  
Annular Channel ◽  
Velocity Profiles ◽  
Experimental Results ◽  
Wall Friction ◽  
Number Range ◽  
Gradient Diffusion ◽  
Good Agreement

An analytical and experimental study is presented of the lubrication flow in an annular channel with a moving core. Velocity profiles and wall friction were determined over a Reynolds number range up to 3 × 104 and radius ratios of 0.6 and 0.85. The experimental results are shown to be in good agreement with the predictions of a three-layer gradient-diffusion model.

Wall Roughness Effects on Stagnation-Point Heat Transfer Beneath an Impinging Liquid Jet

1994 ◽  
Vol 116 (1) ◽  
pp. 81-87 ◽  
Author(s):  
L. A. Gabour ◽  
J. H. Lienhard
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Stagnation Point ◽  
Rough Surfaces ◽  
Roughness Parameter ◽  
Jet Impingement ◽  
Liquid Jet ◽  
Wall Roughness ◽  
Smooth Wall ◽  
Number Range

Jet impingement cooling applications often involve rough surfaces, yet few studies have examined the role of wall roughness. Surface protrusions can pierce the thermal sublayer in the stagnation region and increase the heat transfer. In this paper, the effect of surface roughness on the stagnation-point heat transfer of an impinging unsubmerged liquid jet is investigated. Experiments were performed in which a fully developed turbulent water jet struck a uniformly heated rough surface. Heat transfer measurements were made for jets of diameters 4.4–9.0 mm over a Reynolds number range of 20,000–84,000. The Prandtl number was held nearly constant at 8.2–9.1. Results are presented for nine well-characterized rough surfaces with root-mean-square average roughness heights ranging from 4.7 to 28.2 μm. Measured values of the local Nusselt number for the rough plates are compared with those for a smooth wall, and increases of as much as 50 percent are observed. Heat transfer in the stagnation zone is scaled with Reynolds number and a roughness parameter. For a given roughness height and jet diameter, the minimum Reynolds number required to increase heat transfer above that of a smooth plate is established. A correlation for smooth wall heat transfer is also given.

scholarly journals RANS Simulations of Flow Past an DU-91-W2-250 Airfoil at High Reynolds Number

2018 ◽  
Vol 44 ◽  
pp. 00150
Author(s):  
Krzysztof Rogowski ◽  
Martin O.L. Hansen
Keyword(s):  
Reynolds Number ◽  
Navier Stokes ◽  
Transient Model ◽  
Drag Coefficients ◽  
Pressure Distributions ◽  
Sst Turbulence Model ◽  
Rans Simulations ◽  
High Reynolds ◽  
Lift And Drag ◽  
Good Agreement

This paper presents numerical results of the DU-91-W2-250 airfoil. Reynolds-averaged Navier–Stokes (RANS) simulations of the 2D profile are performed employing the Transient SST turbulence model. The airfoil was investigated for the Reynolds number of 6 106. Lift and drag coefficients are compared with the experimental data from LM Low Speed Wind Tunnel (LSWT). The results of lift and drag coefficients obtained using the SST Transient model are in a good agreement in comparison with the experiment in the angle of attack range from -10° to 10°. The static pressure distributions calculated by the SST Transition model are also in good agreement with the experiment.

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