Coolant Jets Interaction in Effusion Cooling System: Experimental and Numerical Study

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Y. Jiang ◽  
A. V. Murray ◽  
P.T. Ireland ◽  
L. di Mare
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Cooling System ◽  
Numerical Study ◽  
Mesh Size ◽  
Cooling Flow ◽  
Fine Mesh ◽  
Flow Features ◽  
Single Jet

Abstract The interaction of coolant jets is significant in effusion settings as a result of the short streamwise and spanwise distance between films. This complicates the design of effusion cooling devices because computing the interaction between numerous, closely spaced rows of films is a challenging task. A flat plate effusion cooling model is investigated at both low and high blowing ratios. Pressure-sensitive paint (PSP) is used to measure film effectiveness. Computational fluid dynamics (CFD) calculations are performed to examine the cooling flow features in detail. The mesh sensitivity is studied to demonstrate the effect of mesh size on film effectiveness. The solution obtained by coarse mesh may not capture the correct trend with blowing ratio variation. Results of the computational work by fine mesh demonstrate good agreement with the measured effectiveness. Coolant jets interaction is also investigated. The profile of quantities such as velocity, temperature, kinetic energy, and Reynolds stress at several locations in the flow field is compared. The boundary layer profiles are scaled by the thermal boundary layer thickness to study the feature of heat transfer. It is observed that profiles of the flow quantities are self-similar. Two distinct scalings are found: an outer scaling based on boundary layer thickness which collapses the upper part of the profiles; an inner scaling which collapses the profiles at distances from the wall comparable to the penetration depth of a single jet. The latter scaling is based on the distance from the wall to the minimum temperature profile. This distance identifies the location of the coolant leaving the effusion cooling device.

Coolant Jets Interaction in Effusion Cooling System: Experimental and Numerical Study

2019 ◽  
Author(s):  
Y. Jiang ◽  
A. V. Murray ◽  
P. T. Ireland ◽  
L. di Mare
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Cooling System ◽  
Numerical Study ◽  
Mesh Size ◽  
Cooling Flow ◽  
Fine Mesh ◽  
Flow Features ◽  
Single Jet

Abstract The interaction of coolant jets is significant in effusion settings as a result of the short streamwise and spanwise distance between films. This complicates the design of effusion cooling devices because computing the interaction between numerous, closely spaced rows of films is a challenging task. A flat plate effusion cooling model is investigated at both low and high blowing ratios. Pressure sensitive paint (PSP) is used to measure film effectiveness. Computational fluid dynamics (CFD) calculations are performed to examine the cooling flow features in detail. The mesh sensitivity is studied to demonstrate the effect of mesh size on film effectiveness. The solution obtained by coarse mesh may not capture the correct trend with blowing ratio variation. Results of the computational work by fine mesh demonstrate good agreement with the measured effectiveness. Coolant jets interaction is also investigated. The profile of quantities such as velocity, temperature, kinetic energy and Reynolds stress at several locations in the flow field is compared. The boundary layer profiles are scaled by the thermal boundary layer thickness to study the feature of heat transfer. It is observed that profiles of the flow quantities are self-similar. Two distinct scalings are found: an outer scaling based on boundary layer thickness which collapses the upper part of the profiles; an inner scaling which collapses the profiles at distances from the wall comparable to the penetration depth of a single jet. The latter scaling is based on the distance from the wall to the minimum temperature profile. This distance identifies the location of the coolant leaving the effusion cooling device.

scholarly journals Oblique stagnation point flow of a non-Newtonian nanofluid over stretching surface with radiation: A numerical study

2017 ◽  
Vol 21 (5) ◽  
pp. 2139-2153 ◽  
Author(s):  
Abuzar Ghaffari ◽  
Tariq Javed ◽  
Fotini Labropulu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Layer Thickness ◽  
Stagnation Point ◽  
Boundary Layer Thickness ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Stretching Surface ◽  
Convective Boundary

In this study, we discussed the enhancement of thermal conductivity of elasticoviscous fluid filled with nanoparticles, due to the implementation of radiation and convective boundary condition. The flow is considered impinging obliquely in the region of oblique stagnation point on the stretching surface. The obtained governing partial differential equations are transformed into a system of ordinary differential equations by employing a suitable transformation. The solution of the resulting equations is computed numerically using Chebyshev spectral newton iterative scheme. An excellent agreement with the results available in literature is obtained and shown through tables. The effects of involving parameters on the fluid flow and heat transfer are observed and shown through graphs. It is importantly noted that the larger values of Biot number imply the enhancement in heat transfer, thermal boundary layer thickness, and concentration boundary layer thickness.

scholarly journals KARAKTERISASI TEBAL LAPISAN BATAS FLUIDA NANO ZrO2 DI PERMUKAAN PEMANAS PADA PROSES KONVEKSI ALAMIAH

2015 ◽  
Vol 17 (3) ◽  
pp. 167
Author(s):  
V. Indriati Sri Wardhani ◽  
Henky P. Rahardjo
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Heat Source ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Thermal Boundary Layer ◽  
Cooling System ◽  
Thermal Boundary Layer Thickness ◽  
Cooling Fluid ◽  
Nano Fluid

ABSTRAK KARAKTERISASI Tebal Lapisan Batas Fluida Nano ZrO2 di permukaan pemanas pada Proses Konveksi Alamiah. Pendinginan sistem sangat dipengaruhi oleh proses perpindahan panas konveksi dari sumber panas ke fluida pendingin. Biasanya sebagai fluida pendingin digunakan fluida konvensional seperti air. Pendinginan suatu sistem dengan air tersebut dapat ditingkatkan dengan menggunakan fluida lain seperti fluida nano, yaitu fluida yang dibuat dari campuran air ditambah partikel dengan ukuran nano. Peneliti Batan Bandung telah membuat fluida nano ZrO2 dari bahan local. Telah dibuat pula peralatan eksperimen untuk mempelajari sifat-sifat termohidrolik fluida nano tersebut. Hal ini dilakukan untuk mendapatkan fluida nano yang tepat jika digunakan sebagai fluida pendingin sistem. Dalam penelitian ini dilakukan eksperimen untuk mempelajari sifat-sifat termohidrolik fluida nano ZrO2 yang terbuat dari campuran air dengan partikel nano ZrO2 yang berukuran 10-7-10-９nm dengan konsentrasi 1 gr/lt yang digunakan sebagai pendingin pada proses pendinginan konveksi alamiah. Proses tersebut sangat bergantung pada perubahan temperatur dari sumber panas ke fluida pendingin. Dalam pendinginan konveksi alamiah perubahan temperatur itu akan terjadi di dalam tebal lapisan batas termalnya. Oleh karena itu perlu diteliti tebal lapisan batas termal dari fluida nano ZrO2 yang selanjutnya juga dapat untuk menentukan kecepatan aliran lokalnya. Eksperimen dilakukan melalui proses perpindahan panas konveksi alamiah dengan memasukkan beberapa variasi daya pemanas, kemudian dilakukan pengukuran temperatur di beberapa titik secara horizontal untuk melihat distribusi temperaturnya. Hasil pengukuran distribusi temperatur tersebut dapat digunakan untuk menentukan tebal lapisan batas dan kecepatan alirannya. Diperoleh bahwa tebal lapisan batas termal dan kecepatan konveksi alamiah fluida nano ZrO2 tidak jauh berbeda dari fluida konvensional air. Kata kunci: Lapisan batas, fluida nano ZrO2, konveksi alamiah.  ABSTRACT CHARACTERIZATION of boundary layer thickness OF nano FLUID ZrO2 on natural convection process. Cooling system is highly influenced by the process of convection heat transfer from the heat source to the cooling fluid. The cooling fluid usually used conventional fluid such as water. Cooling system performance can be improved by using fluids other than water such as nano fluid that is made from a mixture of water and nano-sized particles. Researchers at Batan Bandung have made nano fluid ZrO2 from local materials, as well as experimental equipment for studying the thermohidraulic characteristics of nano fluid as the cooling fluid. In this study, thermohidraulic characteristics of nano fluid ZrO2 are observed through experimentation.  Nano fluid ZrO2 is made from a mixture of water with ZrO2 nano-sized particles of 10-7-10-9 nm whose concentration is 1 g/ltr. This nano fluid is used as coolant in the cooling process of natural convection. The natural convection process depends on the temperature difference between heat source and the cooling fluid, which occur in the thermal boundary layer. Therefore it is necessary to study the thermal boundary layer thickness of nano fluid ZrO2, which is also able to determine the local velocity. Experimentations are done with several variation of the heater power and then the temperature are measured at several horizontal points to see the distribution of the temperatures. The temperature distribution measurement results can be used to determine the boundary layer thickness and flow rate. It is obtained that thermal boundary layer thickness and velocity of nano fluid ZrO2 is not much different from the conventional fluid water. Keywords: Boundary layer, nanofluid ZrO2, natural convection.

EFFECTS OF BOUNDARY-LAYER THICKNESS ON UNSTEADY FLOW CHARACTERISTICS INSIDE OPEN CAVITIES AT SUBSONIC AND TRANSONIC SPEEDS

2012 ◽  
Vol 19 ◽  
pp. 206-213
Author(s):  
DANG-GUO YANG ◽  
JIAN-QIANG LI ◽  
ZHAO-LIN FAN ◽  
XIN-FU LUO
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Sound Pressure ◽  
Flow Characteristics ◽  
Open Cavity ◽  
Aerodynamic Noise ◽  
Sustained Oscillation ◽  
Cavity Depth

An experimental study was conducted in a 0.6m by 0.6m wind-tunnel to analyze effects of boundary-layer thickness on unsteady flow characteristics inside a rectangular open cavity at subsonic and transonic speeds. The sound pressure level (SPL) distributions at the centerline of the cavity floor and Sound pressure frequency spectrum (SPFS) characteristics on some measurement positions presented herein was obtained with cavity length-to-depth ratio (L/D) of 8 over Mach numbers (Ma) of 0.6 and 1.2 at a Reynolds numbers (Re) of 1.23 × 107 and 2.02 × 107 per meter under different boundary-layer thickness to cavity-depth ratios (δ/D). The experimental angle of attack, yawing and rolling angles were 0°. The results indicate that decrease in δ/D leads to severe flow separation and unsteady pressure fluctuation, which induces increase in SPL at same measurement points inside the cavity at Ma of 0.6. At Ma of 1.2, decrease in δ/D results in enhancing compressible waves. Generally, decrease in δ/D induces more flow self-sustained oscillation frequencies. It also makes severer aerodynamic noise inside the open cavity.

Boundary Layer Closure and Heat Transfer in Constant Base Pressure and Simple Wave Guns

1978 ◽  
Vol 100 (4) ◽  
pp. 690-696 ◽  
Author(s):  
A. D. Anderson ◽  
T. J. Dahm
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Method Of Characteristics ◽  
Simple Wave ◽  
Momentum Equation ◽  
Base Pressure ◽  
Two Dimensional ◽  
The Method Of Characteristics

Solutions of the two-dimensional, unsteady integral momentum equation are obtained via the method of characteristics for two limiting modes of light gas launcher operation, the “constant base pressure gun” and the “simple wave gun”. Example predictions of boundary layer thickness and heat transfer are presented for a particular 1 in. hydrogen gun operated in each of these modes. Results for the constant base pressure gun are also presented in an approximate, more general form.

The structure of a highly decelerated axisymmetric turbulent boundary layer

2021 ◽  
Vol 929 ◽  
Author(s):  
N. Agastya Balantrapu ◽  
Christopher Hickling ◽  
W. Nathan Alexander ◽  
William Devenport
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Convection Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Experiments were performed over a body of revolution at a length-based Reynolds number of 1.9 million. While the lateral curvature parameters are moderate ( $\delta /r_s < 2, r_s^+>500$ , where $\delta$ is the boundary layer thickness and r s is the radius of curvature), the pressure gradient is increasingly adverse ( $\beta _{C} \in [5 \text {--} 18]$ where $\beta_{C}$ is Clauser’s pressure gradient parameter), representative of vehicle-relevant conditions. The mean flow in the outer regions of this fully attached boundary layer displays some properties of a free-shear layer, with the mean-velocity and turbulence intensity profiles attaining self-similarity with the ‘embedded shear layer’ scaling (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592–642). Spectral analysis of the streamwise turbulence revealed that, as the mean flow decelerates, the large-scale motions energize across the boundary layer, growing proportionally with the boundary layer thickness. When scaled with the shear layer parameters, the distribution of the energy in the low-frequency region is approximately self-similar, emphasizing the role of the embedded shear layer in the large-scale motions. The correlation structure of the boundary layer is discussed at length to supply information towards the development of turbulence and aeroacoustic models. One major finding is that the estimation of integral turbulence length scales from single-point measurements, via Taylor's hypothesis, requires significant corrections to the convection velocity in the inner 50 % of the boundary layer. The apparent convection velocity (estimated from the ratio of integral length scale to the time scale), is approximately 40 % greater than the local mean velocity, suggesting the turbulence is convected much faster than previously thought. Closer to the wall even higher corrections are required.

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