scholarly journals Study of the influence of an external flow rate perturbation on the vortex structure and heat transfer in impinging jets

2021 ◽  
Vol 2057 (1) ◽  
pp. 012099
Author(s):  
M P Tokarev ◽  
M Yu Nichik ◽  
O A Gobyzov ◽  
S S Abdurakipov ◽  
V M Dulin
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Large Scale ◽  
Active Flow Control ◽  
Turbulent Jets ◽  
Impinging Jets ◽  
External Flow ◽  
Temperature Fields ◽  
Control Technique ◽  
Long Term Study

Abstract The study of physical processes dominating in submerged turbulent jets impinging on a wall is an important task because this configuration is utilized in various applications. The efficiency of heat transfer in this configuration has been a subject of a long-term study. Active flow control technique and the optimization of the control signal can be applied to exploit inherent flow properties to further improve the heat transfer from the wall in impingent jets. In this paper, IR-thermography and time-resolved PIV measurements are used for the diagnostics of wall temperature fields and large-scale vortex dynamics under external flow rate forcing control. It is found that the low-frequency forcing (for the Strouhal number St = 0.6) increases integral temperature on the wall as compared to the unforced case and the high-frequency forcing (St = 0.9).

Large Eddy Simulations of Flow and Heat Transfer in Rotating Ribbed Duct Flows

2005 ◽  
Vol 127 (5) ◽  
pp. 486-498 ◽  
Author(s):  
Mayank Tyagi ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Large Scale ◽  
Density Ratio ◽  
Low Frequency ◽  
Turbulent Energy ◽  
Large Eddy Simulations ◽  
Temperature Fields ◽  
Periodic Domain ◽  
Large Eddy

Large eddy simulations are performed in a periodic domain of a rotating square duct with normal rib turbulators. Both the Coriolis force as well as the centrifugal buoyancy forces are included in this study. A direct approach is presented for the unsteady calculation of the nondimensional temperature field in the periodic domain. The calculations are performed at a Reynolds number (Re) of 12,500, a rotation number (Ro) of 0.12, and an inlet coolant-to-wall density ratio Δρ/ρ of 0.13. The predicted time and space-averaged Nusselt numbers are shown to compare satisfactorily with the published experimental data. Time sequences of the vorticity components and the temperature fields are presented to understand the flow physics and the unsteady heat transfer behavior. Large scale coherent structures are seen to play an important role in the mixing and heat transfer. The temperature field appears to contain a low frequency mode that extends beyond a single inter-rib geometric module, and indicates the necessity of using at least two inter-rib modules for streamwise periodicity to be satisfied. Proper orthogonal decomposition (POD) of the flowfield indicates a low dimensionality of this system with almost 99% of turbulent energy in the first 80 POD modes.

Large Eddy Simulations of Flow and Heat Transfer in Rotating Ribbed Duct Flows

2004 ◽  
Author(s):  
Mayank Tyagi ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Large Scale ◽  
Density Ratio ◽  
Low Frequency ◽  
Turbulent Energy ◽  
Large Eddy Simulations ◽  
Temperature Fields ◽  
Periodic Domain ◽  
Large Eddy

Large eddy simulations are performed in a periodic domain of a rotating square duct with normal rib turbulators. Both the Coriolis force as well as the centrifugal buoyancy force are included in this study. A direct approach is presented for the unsteady calculation of the non-dimensional temperature field in the periodic domain. The calculations are performed at a Reynolds number (Re) of 12, 500, a Rotation number (Ro) of 0.12 and an inlet coolant-to-wall density ratio (Δρ/ρ) of 0.13. The time-averaged Nusselt numbers compare satisfactorily with the data of Wagner et al. (J. Turbomachinery, Vol. 114, pp. 847–857). Time-sequences of the vorticity components and the temperature fields are presented to understand the flow physics and the unsteady heat transfer processes. Large scale coherent structures are seen to play an important role in the mixing and heat transfer. The temperature field appears to contain a low frequency mode that extends beyond a single inter-rib geometric module, and indicates the necessity of using at least two inter-rib modules for streamwise periodicity to be satisfied. Proper orthogonal decomposition (POD) of 200 snapshots indicates a low dimensionality of this system with almost 99% of turbulent energy in the first 80 POD modes.

scholarly journals Impinging jets – a short review on strategies for heat transfer enhancement

2018 ◽  
Vol 32 ◽  
pp. 01013
Author(s):  
Ilinca Nastase ◽  
Florin Bode
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Short Review ◽  
Great Difficulty ◽  
Impinging Jets ◽  
Industrial Applications ◽  
Experimental Investigations ◽  
Small Scale ◽  
Strong Shear ◽  
Flow Phenomena

In industrial applications, heat and mass transfer can be considerably increased using impinging jets. A large number of flow phenomena will be generated by the impinging flow, such as: large scale structures, large curvature involving strong shear and normal stresses, stagnation in the wall boundary layers, heat transfer with the impinged wall, small scale turbulent mixing. All these phenomena are highly unsteady and even if nowadays a substantial number of studies in the literature are dedicated, the impinging jets are still not fully understood due to the highly unsteady nature and more over due to great difficulty of performing detailed numerical and experimental investigations.

scholarly journals Experimental study of the heat transfer of two parallel impinging jets

2021 ◽  
Vol 2119 (1) ◽  
pp. 012029
Author(s):  
M V Philippov ◽  
I A Chokhar ◽  
V V Terekhov ◽  
V I Terekhov
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Local Heat Transfer ◽  
Turbulent Jets ◽  
Local Heat ◽  
Impinging Jets ◽  
Jet Interaction ◽  
Flow Parameters ◽  
Integral Characteristics ◽  
Integral Heat

Abstract Local and integral characteristics of heat transfer are obtained at varying the Reynolds number Re = 5500, 11000, the distance between the jets y/D = 1.8, and the distance from the jets to the surface z/D = 0.5-10 for the system of two identical impinging jets. It is found in experiments that the effect of an adjacent jet leads to enhancement of local heat transfer at large distances between the nozzles and the barrier. It is also shown that an increase in the Re number increases integral heat transfer, and, at the same time, weakens the inter-jet interaction. The paper analyzes the scenarios of the behavior of local and integral heat transfer depending on the geometric and flow parameters of the system of two circular turbulent jets.

scholarly journals Heat and mass transfer enhancement strategies by impinging jets: A literature review

2020 ◽  
pp. 227-227
Author(s):  
Florin Bode ◽  
Claudiu Patrascu ◽  
Ilinca Nastase
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Large Scale ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Nozzle Geometry ◽  
Small Scale ◽  
Mixing Enhancement ◽  
Transfer Enhancement

Heat and mass transfer can be greatly increased when using impinging jets, regardless the application. The reason behind this is the complex behavior of the impinging jet flow which is leading to the generation of a multitude of flow phenomena, like: large-scale structures, small scale turbulent mixing, large curvature involving strong normal stresses and strong shear, stagnation, separation and re-attachment of the wall boundary layers, increased heat transfer at the impinged plate. All these phenomena listed above have highly unsteady nature and even though a lot of scientific studies have approached this subject, the impinging jet is not fully understood due to the difficulties of carrying out detailed experimental and numerically investigations. Nevertheless, for heat transfer enhancement in impinging jet applications, both passive and active strategies are employed. The effect of nozzle geometry and the impinging surface macrostructure modification are some of the most prominent passive strategies. On the other side, the most used active strategies utilize acoustical and mechanical oscillations in the exit plane of the flow, which in certain situations favors mixing enhancement. This is favored by the intensification of some instabilities and by the onset of large scale vortices with important levels of energy.

An Annular Impinging Jet Alternated by Pulse-Modulated Synthetic Jets

2011 ◽  
Author(s):  
Zdeneˇk Tra´vni´cˇek ◽  
Va´clav Tesarˇ
Keyword(s):  
Heat Transfer ◽  
Active Flow Control ◽  
Substantial Reduction ◽  
Central Area ◽  
Impinging Jets ◽  
Synthetic Jets ◽  
Working Fluid ◽  
Flow Control System ◽  
And Control ◽  
Active Flow

The present experimental study focuses on a generation and control of annular impinging jets. The used working fluid is air. An active flow control system is designed with six radial synthetic jets, which are generated by a common actuator located in the central body of the annular nozzle. The synthetic jets are pulse-modulated. Flow visualization and measurements of the wall pressure and wall heat transfer have been performed. Two flowfield steady patterns A and B (small or large recirculation bubbles, respectively) are recognized. The pattern B exists without the actuation, the unmodulated actuation causes the flowfield switching into the pattern A, and the pulse-modulated actuation generates an alternating flowfield. The present results indicate that the area of higher heat transfer can be slightly spread by means of flow alternation. However, the penalty for this slight gain is a substantial reduction of the heat transfer in the central area.

scholarly journals Maximal heat transfer between two parallel plates

2018 ◽  
Vol 851 ◽  
Author(s):  
Shingo Motoki ◽  
Genta Kawahara ◽  
Masaki Shimizu
Keyword(s):  
Heat Transfer ◽  
Velocity Field ◽  
Large Scale ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Two Dimensional ◽  
Parallel Plates ◽  
Solution Branch ◽  
Search Range ◽  
Dimensional Solution

The divergence-free time-independent velocity field has been determined so as to maximise heat transfer between two parallel plates with a constant temperature difference under the constraint of fixed total enstrophy. The present variational problem is the same as that first formulated by Hassanzadeh et al. (J. Fluid Mech., vol. 751, 2014, pp. 627–662); however, the search range for optimal states has been extended to a three-dimensional velocity field. A scaling of the Nusselt number $Nu$ with the Péclet number $Pe$ (i.e., the square root of the non-dimensionalised enstrophy with thermal diffusion time scale), $Nu\sim Pe^{2/3}$, has been found in the three-dimensional optimal states, corresponding to the asymptotic scaling with the Rayleigh number $Ra$, $Nu\sim Ra^{1/2}$, expected to appear in an ultimate state, and thus to the Taylor energy dissipation law in high-Reynolds-number turbulence. At $Pe\sim 10^{0}$, a two-dimensional array of large-scale convection rolls provides maximal heat transfer. A three-dimensional optimal solution emerges from bifurcation on the two-dimensional solution branch at $Pe\sim 10^{1}$, and the three-dimensional solution branch has been tracked up to $Pe\sim 10^{4}$ (corresponding to $Ra\approx 2.7\times 10^{6}$). At $Pe\gtrsim 10^{3}$, the optimised velocity fields consist of convection cells with hierarchical self-similar vortical structures, and the temperature fields exhibit a logarithmic-like mean profile near the walls.

Two Dimensional Simulation of Flow and Heat Transfer Characteristics of Turbulent Jets

2010 ◽  
Author(s):  
Tarek Abdel-Salam
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Jets ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Dimensional Simulation

In this study, flow and heat transfer characteristics of two-dimensional impinging jets are investigated numerically. Flow geometries under consideration are single and multiple impinging jets issued from a plane wall. Both confined and unconfined configurations are simulated. Effects of Reynolds number and the distance between the jets are investigated. Results are obtained with a finite volume CFD code. Structured grids are used in all cases of the present study. Turbulence is treated with a two equation k-ε model. Different jet velocities have been examined corresponding to Reynolds numbers of 5,000 to 20,000. Results show that the Reynolds number has significant effect on the heat transfer rate and has no effect on the location of the maximum Nusselt number.

Heat Transfer From Arrays of Impinging Jets with Large Jet-to-Jet Spacing

1978 ◽  
Vol 100 (2) ◽  
pp. 352-357 ◽  
Author(s):  
B. R. Hollworth ◽  
R. D. Berry
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Turbulent Jets ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Turbine Cooling ◽  
Heat Transfer Coefficients

Local and average convective heat transfer coefficients were measured for arrays of widely spaced impinging air jets and correlated in terms of system geometry, air flow, and fluid properties. The configurations were square arrays of circular turbulent jets (spaced from 10–25 diameters apart) incident upon a flat isothermal target surface. Independent parameters were varied over ranges generally corresponding to gas turbine cooling applications. Local heat transfer coefficients were influenced by interference from neighboring jets only when the target plate and the jet orifice plate were less than five jet diameters apart. Average heat transfer coefficients were nearly equal for all the arrays tested as long as the coolant flow per unit area of target surface was held constant. In fact, there was a tendency for the more widely spaced configurations to produce slightly higher average heat transfer under such conditions.

A Comparison of Full Surface Local Heat Transfer Coefficient and Flow Field Studies Beneath Sharp-Edged and Radiused Entry Impinging Jets

1996 ◽  
Author(s):  
D. R. H. Gillespie ◽  
S. M. Guo ◽  
Z. Wang ◽  
P. T. Ireland ◽  
S. T. Kohler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Large Scale ◽  
Static Pressure ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Impinging Jets ◽  
Velocity Variation

Full heat transfer coefficient and static pressure distributions have been measured on the target surface under impinging jets formed by sharp-edged and large entry radius holes. These geometries are representative of impingement holes in a gas turbine blade manufactured by laser cutting and by casting, respectively. Target surface heat transfer has been measured in a large scale perspex rig using both the transient liquid crystal technique and hot thin film gauges. A range of jet Reynolds numbers, representative of engine conditions, has been investigated. The velocity variation has been calculated from static pressure measurements on the impingement target surface. The heat transfer to the target surface is discussed in terms of the interpreted flow field.

Sign in / Sign up

Export Citation Format

Share Document