scholarly journals Simulation of Single and Twin Impinging Jets in Cross-flow of VTOL Aircrafts (Review)

2020 ◽  
pp. 338-349
Author(s):  
César A. Cárdenas R ◽  
Carlos Andrés Collazos Morales ◽  
Juan Carlos Amaya ◽  
Yaneth Patricia Caviativa Castro ◽  
Emiro De-la-Hoz-Franco
Keyword(s):  
Cross Flow ◽  
Impinging Jets

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

Heat Transfer Study of a Novel Low-Crossflow Design for Jet Impingement

2004 ◽  
Author(s):  
Ryan Hebert ◽  
Srinath V. Ekkad ◽  
Vivek Khanna ◽  
Mario Abreu ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Impingement Heat Transfer ◽  
Hole Arrays ◽  
Transient Liquid Crystal Technique ◽  
Rate Requirement ◽  
Transfer Study

Impingement heat transfer is significantly affected by initial cross-flow or by the presence of cross-flow from upstream spent jets. In this study, a zero cross-flow design is presented. The zero-crossflow design creates spacing between hole arrays to allow for spent flow to be directed away from impinging jets. Three configurations with different impingement holes placements are studied and compared with pure impingement with spent crossflow cases for the same jet Reynolds number. Three jet Reynolds numbers are studied for Rej = 10000, 20000, and 30000. Detailed heat transfer distributions are obtained using the transient liquid crystal technique. The zero-cross flow design clearly shows minimal degradation of impingement heat transfer due to crossflow compared to conventional design with lower mass flow rate requirement and lesser number of overall impingement holes due to the reduced cross-flow effect on the impingement region.

scholarly journals An Experimental and Numerical Study of Heat Transfer From Arrays of Impinging Jets With Surface Ribs

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
Sebastian Spring ◽  
Yunfei Xing ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Cross Flow ◽  
Impinging Jets ◽  
Separation Distance ◽  
Distance Measures ◽  
Impingement Plate ◽  
Roughness Elements ◽  
Staggered Arrangement ◽  
The Heat Transfer Coefficient

A combined experimental and numerical investigation of the heat transfer characteristics within arrays of impinging jets with rib-roughened surfaces is presented. Two configurations are considered: One with an inline arrangement of jets and ribs oriented perpendicular to the direction of cross-flow and one with a staggered arrangement of jets and broken ribs aligned with the direction of cross-flow. For both cases, the jet Reynolds number is 35,000, the separation distance measures H/D = 3, the spent air is routed through one exit contributing to the maximum cross-flow condition, and the rib height and width is both 1 D. The experiments are carried out in perspex models using the transient liquid crystal method. Local jet temperatures are measured at several positions on the impingement plate to account for an exact evaluation of the heat transfer coefficient. In addition to the measurements, a numerical analysis using the commercial CFD software package ANSYSCFX is conducted. Heat transfer predictions are compared with those obtained from experiments with regards to local distributions as well as averaged quantities. A good overall agreement is found but discrepancies for local values need to be accepted. The present investigation also emphasizes that configurations including rib roughness elements should be compared based on the amount of transferred heat flux in order to account for the area enlarging effect. This allows a correct evaluation of the thermal performance.

Large Eddy Simulation of Impinging Jets in Crossflow

2003 ◽  
Author(s):  
Adrian Spencer ◽  
Virgil Adumitroaie
Keyword(s):  
Experimental Data ◽  
Cross Flow ◽  
Impinging Jets ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Primary Zone ◽  
Large Eddy ◽  
Mixing Rates ◽  
Time Average ◽  
Set Up

Large Eddy Simulations and RANS predictions have been carried out for a generic primary zone type jet configuration, for which significant LDA experimental data is available. It consists of an annular passage feeding a row of ports that issue jets into a confined crossflow. A bleed flow of 50% past the ports in the feed annulus and a jet to cross flow ratio of 5 are set-up in order to be representative of annulus fed primary jets. Time averaged inlet boundary conditions have been taken from experimental data and have had time-correlated fluctuations with the correct RMS values and time scales imposed on them. Calculations have been performed on a modest PC cluster using the CFD-ACE+ flow solver package. Results show that LES is able to surpass RANS quantitatively and qualitatively. At the time-average impingement point of the jets the LES predicted normal stresses are in considerably better agreement with experimental data than is RANS, which is to be expected considering the limitations of k-ε models relying upon linear stress-strain relationships. Phenomena impossible to capture using RANS are also well predicted by LES, such as bimodal pdf’s that have been witnessed at the time average stagnation point where the cross flow and jet back flow meet. By solving for a conserved scalar it has also been possible to examine mixing rates within the recirculation zone.

Heat Transfer Enhancement of Impinging Row Jets in Cross-Flow with Mounting Baffles on Surface

2014 ◽  
Vol 931-932 ◽  
pp. 1218-1222
Author(s):  
Rattanakorn Pansang ◽  
Makatar Wae-Hayee ◽  
Passakorn Vessakosol ◽  
Chayut Nuntadusit
Keyword(s):  
Heat Transfer ◽  
Cross Flow ◽  
Jet Impingement ◽  
Transfer Characteristic ◽  
Impinging Jets ◽  
Upstream Region ◽  
Orifice Diameter ◽  
Thermochromic Liquid Crystal ◽  
Cross Flow Velocity ◽  
Jet Velocity

The aim of this research is to enhance heat transfer on a surface of row of impinging jets in cross-flow by mounting some baffles on the surface. A row of 4 jets with inline arrangement discharging from round orifices impinged normally on inner surface of wind tunnel with simulated cross-flow. The orifice diameter (D) was 13.2 mm. The jet-to-surface distance and jet-to-jet distance were fixed at H=2D and S=3D, respectively. Four couples of baffles with V-shaped arrangement at attack angle, θ=30o, were mounted on surface in upstream or downstream of impinging jets and the location of baffles attachment is L=1.5D apart from the jet impingement region. The velocity ratios (Jet velocity/cross-flow velocity) were varied from VR=3, 5 and 7 while the jet velocity was kept constant corresponding to Re=13,400. The experimental investigation was carried out for heat transfer characteristic by using Thermochromic Liquid Crystal sheet, and heat transfer coefficient distributions were evaluated using an image processing method. The results show that the impinging jets with mounting the baffles in the upstream region of jet impingement region can enhance the heat transfer rate throughout VR.

scholarly journals Numerical Investigation of Parameters Affecting the Thermal and Hydrodynamic Characteristics of Impinging Jets in Cross Flow

1970 ◽  
Vol 1 (1) ◽  
Author(s):  
B. M. Suloiman ◽  
B. A. Jubran
Keyword(s):  
Numerical Investigation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Impinging Jets ◽  
Minor Effect ◽  
Vortex Strength ◽  
Effective Velocity

In this investigation the hydrodynamic and the thermal fields due to a single impinging jet in cross-flow have been investigated numerically, using a 2-D axisymmetric model in order to predict the ground vortex characteristics. The parameters investigated include the effective velocity ratio, the nozzle height, the nozzle pressure ratio, the intake location, the intake mass flow rate and the jet temperature ratio. It is interesting to note that even with the 2-D modeling limitations it was possible to capture most of the thermal and fluid field characteristics of the ground vortex. It was found that the temperature distribution in the flow field is greatly affected by the effective velocity, and the maximum penetration point of the ground vortex is equal to the hot gas penetration. The ground vortex strength increases slightly with increasing the intake mass flow rate but has a minor effect on the ground vortex geometry and on the penetration of the hot gases. The intake location has a significant effect on the ground vortex strength when it is located upstream of the ground vortex core. Key Words: Numerical investigation, Turbulence Models, Impinging jets, Cross-flow.

scholarly journals Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Experimental Investigation

2016 ◽  
Author(s):  
Daniele Massini ◽  
Emanuele Burberi ◽  
Carlo Carcasci ◽  
Lorenzo Cocchi ◽  
Bruno Facchini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Cooling System ◽  
Cross Flow ◽  
Leading Edge ◽  
Impinging Jets ◽  
Internal Cooling ◽  
Transfer Pattern

A detailed aerothermal characterization of an advanced leading edge cooling system has been performed by means of experimental measurements. Heat transfer coefficient distribution has been evaluated exploiting a steady-state technique using Thermocromic Liquid Crystals (TLC), while flow field has been investigated by means of Particle Image Velocimetry (PIV). The geometry key features are the multiple impinging jets and the four rows of coolant extraction holes, which mass flow rate distribution is representative of real engine working conditions. Tests have been performed in both static and rotating conditions, replicating a typical range of jet Reynolds number (Rej), from 10000 to 40000, and Rotation number (Roj) up to 0.05. Different cross-flow conditions (CR) have been used to simulate the three main blade regions (i.e. tip, mid and hub). The aerothermal field turned out to be rather complex, but a good agreement between heat transfer coefficient and flow field measurement has been found. In particular, jet bending strongly depends on crossflow intensity, while rotation has a weak effect on both jet velocity core and area-averaged Nusselt number. Rotational effects increase for the lower cross-flow tests. Heat transfer pattern shape has been found to be substantially Reynolds-independent.

Unsteady Structure and Development of a Row of Impingement Jets, Including Shear Layer and Vortex Development: Part 2 — Laminar Jets

2015 ◽  
Author(s):  
L. Yang ◽  
J. Ren ◽  
H. Jiang ◽  
P. M. Ligrani
Keyword(s):  
Broad Band ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Axial Direction ◽  
Impinging Jets ◽  
Laminar Jet ◽  
Laminar Jets ◽  
Spectral Peaks ◽  
Unsteady Rans ◽  
Band Mixing

Considered is a cylinder channel with a single row of 10 aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, each jet is laminar with a Reynolds number of 200. An unsteady RANS solver is employed for predictions of flow characteristics within and nearby the 10 impingement jets. Spectrum analysis of different flow quantities shows frequencies associated with laminar jet and vortex oscillations, and evidence more orderly flow for Re=200, without the chaos and broad-band mixing associated with the turbulent flow when Re=15,000. Laminar flow spectra also evidence increased flow unsteadiness as cross-flows accumulate within the impingement channel with streamwise development as Z/D increases. In some cases, this increased unsteadiness manifests itself through the formation of multiple spectral peaks, in place of single peak spectra. As for the turbulent jet arrangements, unsteady, local static pressure gradient variations along interfaces between laminar jets and cross flow are also a key flow feature, which is connected to the initiation and development of the Kelvin-Helmholtz instability induced vortices.

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