An Approximate Theory for Developing Turbulent Free Shear Layers

1967 ◽  
Vol 89 (3) ◽  
pp. 633-640 ◽  
Author(s):  
J. P. Lamb
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Power Law ◽  
Flow Characteristics ◽  
Turbulent Shear ◽  
Transverse Motion ◽  
Approximate Theory ◽  
Mean Flow ◽  
Integral Forms ◽  
Position Parameter

The development of a two-dimensional, free turbulent shear layer from an arbitrary initial velocity profile is analyzed theoretically. Included in the analysis are effects of both compressibility and heat transfer with unit turbulent Prandtl number. The mean flow is described by approximate velocity profiles containing an unknown position parameter which is dependent upon the development distance. Integral forms of the continuity and momentum equations are utilized to specify the flow characteristics along the streamline which separates the primary and secondary flow regions. By integrating a simplified form of the transverse motion equation for this dividing streamline, one is able to calculate the position parameter and thus complete the description of the developing flow field. For initial profiles of a power law type, the theory shows that the development distance required for any flow field variable to achieve a specified percentage of its asymptotic value is proportional to the free-stream Crocco number, to the power law exponent, and to the ratio of the ambient to jet stagnation temperatures. The theory is also utilized to estimate the effects of heat transfer and compressibility on the variation of growth rates for fully developed mixing zones.

scholarly journals Analysis of temperature characteristics of ink fluid based on power law model in microchannel

2019 ◽  
Vol 11 (3) ◽  
pp. 168781401983358
Author(s):  
Hongyan Chu ◽  
Xuecong Lin ◽  
Ligang Cai
Keyword(s):  
Heat Transfer ◽  
Viscous Dissipation ◽  
Power Law ◽  
Flow Characteristics ◽  
Simulation Software ◽  
Fluid Simulation ◽  
Fluid Temperature ◽  
Power Law Model ◽  
Feature Size ◽  
Temperature Characteristics

In the offset press, ink flows in the microchannel made of two rotating rollers that are in the state of squeezing and contacting. The ink flow characteristics are not only influenced by the viscous dissipation effect, but also change with the heat transfer. First, by summarizing the common viscosity–shear rate models of non-Newtonian fluid, the power law model was chosen for describing offset ink through rheometer measuring. Combined with the experimental data, the viscosity–temperature relationship of the offset ink was described by the Arrhenius’s law. Then, the temperature characteristics of the offset ink fluid in the microchannel were studied using the fluid simulation software FLUENT. The ink fluid temperature field model considering viscous dissipation and heat transfer was established, and the temperature distributions of the ink fluid inside the microchannel and at the exit and entrance were obtained. The influence of the feature size on the ink temperature was also researched. Finally, the ink temperature and flow characteristics were compared with that under the condition without heat transfer. We got the influence of feature size and heat transfer on the ink temperature characteristics. As the feature size is smaller, the ink temperature increase from the microchannel entrance to the exit, increases first and then decreases, and keeps invariant at last. The heat transfer makes the viscous dissipation weaken relatively and then the ink temperature decreases. In a word, the heat transfer enhances as the feature size decreases. The results provide reference for improving the printing quality of offset press.

Flow and Heat Transfer Characteristics in Rectangular Channels With Staggered Transverse Ribs on Two Opposite Walls

2007 ◽  
Vol 129 (12) ◽  
pp. 1732-1736 ◽  
Author(s):  
Rong Fung Huang ◽  
Shyy Woei Chang ◽  
Kun-Hung Chen
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
Channel Height ◽  
Primary Concern ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Characteristic Flow ◽  
Rectangular Channels

The flow characteristics and the heat transfer properties of the rectangular channels with staggered transverse ribs on two opposite walls are experimentally studied. The rib height to channel height ratio ranges from 0.15 to 0.61 (rib height to channel hydraulic diameter ratio from 0.09 to 0.38). The pitch to rib height ratio covers from 2.5 to 26. The aspect ratio of the rectangular channel is 4. The flow characteristics are studied in a water channel, while the heat transfer experiments are performed in a wind tunnel. Particle image velocimetry (PIV) is employed to obtain the quantitative flow field characteristics. Fine-wire thermocouples imbedded near the inner surface of the bottom channel wall are used to measure the temperature distributions of the wall and to calculate the local and average Nusselt numbers. Using the PIV measured streamline patterns, various characteristic flow modes, thru flow, oscillating flow, and cell flow, are identified in different regimes of the domain of the rib height to channel height ratio and pitch to rib height ratio. The vorticity, turbulence intensity, and wall shear stress of the cell flow are found to be particularly larger than those of other characteristic flow modes. The measured local and average Nusselt numbers of the cell flow are also particularly higher than those of other characteristic flow modes. The distinctive flow properties are responsible for the drastic increase of the heat transfer due to the enhancement of the momentum, heat, and mass exchanges within the flow field induced by the large values of the vorticity and turbulence intensity. Although the thru flow mode is conventionally used in the ribbed channel for industrial application, the cell flow could become the choice if the heat transfer rate, instead of the pressure loss, is the primary concern.

scholarly journals Experimental Study of Mean Flow Characteristics in the Near Field of Wedge-Shaped Swirling Jets

2020 ◽  
Vol 5 (10) ◽  
pp. 1199-1203
Author(s):  
Md. Mosharrof Hossain ◽  
Muhammed Hasnain Kabir Nayeem ◽  
Dr. Md Abu Taher Ali
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Mean Flow ◽  
Mean Velocity ◽  
Potential Core ◽  
Swirling Jets ◽  
The Mean ◽  
Sinusoidal Flow

In this investigation experiment was carried out in 80 mm diameter swirling pipe jet, where swirl was generated by attaching wedge-shaped helixes in the pipe. All measurements were taken at Re 5.3e4. In the plain pipe jet the potential core was found to exist up to x/D=5 but in the swirling jet there was no existence of potential core. The mean velocity profiles were found to be influenced by the presence of wedge-shaped helixes in the pipe. The velocity profiles indicated the presence of sinusoidal flow field in the radial direction existed only in the near field of the jet. This flow field died out after x/D=3 and the existence of jet flow diminished after x/D=5.

Flow and Heat Transfer Analysis in a Single Row Narrow Impingement Channel: Comparison of PIV, LES, and RANS to Identify RANS Limitations

2017 ◽  
Author(s):  
Jahed Hossain ◽  
Erik Fernandez ◽  
Christian Garrett ◽  
Jay Kapat
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Flow Field ◽  
Mean Flow ◽  
Single Row ◽  
Flow And Heat Transfer ◽  
Turbulent Statistics ◽  
Flow Phenomena ◽  
The Mean ◽  
Channel Configuration

The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall cooling schemes have become more practical. In this study, the Reynolds number based on jet diameter was ≃15,000, with the jet plate having fixed jet hole diameters and hole spacing. The height of the channel is 3 times the impingement jet diameter. The channel width is 4 times the jet diameter of the impingement hole. The channel configuration was chosen such that the crossflow air is drawn out in the streamwise direction (maximum crossflow configuration). The impinging jets and the wall jets play a substantial role in removing heat in this kind of configuration. Hence, it is important to understand the evolution of flow and heat transfer in a channel of this configuration. The dynamics of flow and heat transfer in a single row narrow impingement channel are experimentally and numerically investigated. Particle Image Velocimetry (PIV) was used to reveal the detailed information of flow phenomena. The detailed PIV experiment was performed on this kind of impingement channel to satisfy the need for experimental data for this kind of impingement configuration, in order to validate turbulence models. PIV measurements were taken at a plane normal to the target wall along the jet centerline. The mean velocity field and turbulent statistics generated from the mean flow field were analyzed. The experimental data from the PIV reveals that flow is highly anisotropic in a narrow impingement channel. To support experimental data, wall-modeled Large Eddy Simulation (LES), and Reynolds Averaged Navier-Stokes (RANS) simulations (SST k-ω, v2–f, and Reynolds Stress Model (RSM)) were performed in the same channel geometry. The Wall-Adapting Local Eddy-viscosity SGS mdoel (WALE) [1] is used for the LES calculation. Mean velocities calculated from the RANS and LES were compared with the PIV data. Turbulent kinetic energy budgets were calculated from the experiment, and were compared with the LES and RSM model, highlighting the major shortcomings of RANS models to predict correct heat transfer behavior for the impingement problem. Temperature Sensitive Paint (TSP) was also used to experimentally obtain a local heat transfer distribution at the target and the side walls. An attempt was made to connect the complex aerodynamic flow behavior with results obtained from heat transfer, indicating heat transfer is a manifestation of flow phenomena. The accuracy of LES in predicting the mean flow field, turbulent statistics, and heat transfer is shown in the current work as it is validated against the experimental data through PIV and TSP.

Measurement of the Reynolds stresses and the mean-flow field in a three-dimensional pressure-driven boundary layer

1982 ◽  
Vol 119 ◽  
pp. 121-153 ◽  
Author(s):  
Udo R. Müller
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Flow Field ◽  
Three Dimensional ◽  
Turbulent Shear ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Acceleration ◽  
The Mean

An experimental study of a steady, incompressible, three-dimensional turbulent boundary layer approaching separation is reported. The flow field external to the boundary layer was deflected laterally by turning vanes so that streamwise flow deceleration occurred simultaneous with cross-flow acceleration. At 21 stations profiles of the mean-velocity components and of the six Reynolds stresses were measured with single- and X-hot-wire probes, which were rotatable around their longitudinal axes. The calibration of the hot wires with respect to magnitude and direction of the velocity vector as well as the method of evaluating the Reynolds stresses from the measured data are described in a separate paper (Müller 1982, hereinafter referred to as II). At each measuring station the wall shear stress was inferred from a Preston-tube measurement as well as from a Clauser chart. With the measured profiles of the mean velocities and of the Reynolds stresses several assumptions used for turbulence modelling were checked for their validity in this flow. For example, eddy viscosities for both tangential directions and the corresponding mixing lengths as well as the ratio of resultant turbulent shear stress to turbulent kinetic energy were derived from the data.

The Dynamics of the Horseshoe Vortex and Associated Endwall Heat Transfer—Part II: Time-Mean Results

2005 ◽  
Vol 128 (4) ◽  
pp. 755-762 ◽  
Author(s):  
T. J. Praisner ◽  
C. R. Smith
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Field Data ◽  
Bluff Body ◽  
Symmetry Plane ◽  
Horseshoe Vortex ◽  
High Heat ◽  
Thermochromic Liquid Crystal ◽  
Mean Flow ◽  
High Heat Transfer

Time-mean endwall heat transfer and flow-field data in the endwall region are presented for a turbulent juncture flow formed with a symmetric bluff body. The experimental technique employed allowed the simultaneous recording of instantaneous particle image velocimetry flow field data, and thermochromic liquid-crystal-based endwall heat transfer data. The time-mean flow field on the symmetry plane is characterized by the presence of primary (horseshoe), secondary, tertiary, and corner vortices. On the symmetry plane the time-mean horseshoe vortex displays a bimodal vorticity distribution and a stable-focus streamline topology indicative of vortex stretching. Off the symmetry plane, the horseshoe vortex grows in scale, and ultimately experiences a bursting, or breakdown, upon experiencing an adverse pressure gradient. The time-mean endwall heat transfer is dominated by two bands of high heat transfer, which circumscribe the leading edge of the bluff body. The band of highest heat transfer occurs in the corner region of the juncture, reflecting a 350% increase over the impinging turbulent boundary layer. A secondary high heat-transfer band develops upstream of the primary band, reflecting a 250% heat transfer increase, and is characterized by high levels of fluctuating heat load. The mean upstream position of the horseshoe vortex is coincident with a region of relatively low heat transfer that separates the two bands of high heat transfer.

Heat Transfer and Flow Characteristics of Two-Pass Parallelogram Channels With Attached and Detached Transverse Ribs

2016 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shyy-Woei Chang ◽  
Yi-An Lan ◽  
Shu-Po Chan ◽  
Yu-Shuai Liu
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Flow Characteristics ◽  
Height Ratio ◽  
Differential Heat ◽  
Flow Measurements ◽  
Full Field ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Design Activities

The full-field endwall Nusselt number (Nu) distributions and flow field are presented respectively using steady-state infrared thermography and particle image velocimetry (PIV) for the two-pass parallelogram channels with attached and detached transverse ribs. These square transverse ribs on two opposite channel endwalls are in-line arranged with rib-height to duct-height ratio of 0.1 and rib-pitch to rib-height ratio of 10. For the detached ribs, the detached distance between rib and channel endwall is 0.38 rib height. With the measurements of Fanning friction factor (f), heat transfer distributions and flow field features, the thermal performance factors (TPF) for the attached and detached rib cases are comparatively examined. A set of Nu, f and TPF results with the associated flow measurements at the test conditions of 5,000≤Re≤20,000 is selected to disclose the differential heat transfer enhancement mechanisms and heat transfer efficiencies between the attached and detached ribbed channels. Empirical correlations evaluating the endwall area-averaged Nusselt numbers (Nu) and f factors are devised to assist the relevant design activities.

Flow Field Analysis of the Reactor Coolant Pump Internal Cooling Circulation

2017 ◽  
Author(s):  
Jie Qin ◽  
Qingmu Xu ◽  
Junkai Yuan ◽  
Kun Cai
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Distribution ◽  
Internal Cooling ◽  
Shaft Seal ◽  
Flow Area ◽  
Coolant Pump ◽  
Reactor Coolant

Reactor coolant pump (RCP) is one of the most critical devices in third generation of pressurized water reactor nuclear power plant. EMD shield pump and KSB wet winding pump are two representative kinds of RCPs without complex shaft seal system. Due to cancellation of shaft seal system, the entire rotors (including the flywheel) are immersed in the coolant. The losses in RCPs take one third of the total power including rotation loss caused by rotor in the water, electromagnetic loss in the shielding sleeve,the heat transferred through high temperature coolant, and heat generated by bearing.Because of the losses listed above, bearing and winding are heated,and the losses make temperature rise. in order to ensure that the motor is working properly at low temperatures, the company EMD and KSB design the RCP internal cooling circulation which brings the heat out to ensure the normal operation of the RCPs. The RCP internal cooling circulation includes inlet flow area, auxiliary impeller, thrust bearing, the lower flywheel, motor can, upper radial bearing, upper flywheel, outlet flow area, and external heat exchanger,etc. Flow characteristics in every flow path determine the flow distribution and heat transfer, and the flow distribution determines whether the cooling performance of RCP internal cooling circulation meets the requirements. In order to control operating temperature of motor and bearing, and to optimize heat transfer, adjusting the size of flow area and changing the flow characteristics arecritical. flow field and temperature field in RCP internal cooling circulation need overall analysis. Flow distribution can be obtained theoretically through the calculation of an overall three-dimensional model.But on the one hand, the calculation time is long due to a complex three-dimensional model with a large quantity of grids, on the other hand, it is easier to casue errors in local processing and the errors are difficult to find or correct. For rapid analysis and optimization of flow and heat transfer in RCP internal cooling circulation, ensure the motor winding and bearing operate at an appropriate temperature, the local characteristics of RCP internal cooling circulation are studied, one-dimensionalanalysis method of RCP internal cooling circulation is developed. This one-dimensional analysis method can be used to predict the flow distribution of each part of RCP internal cooling circulation according to change of the channel geometry parameters, key dimensions, boundary conditions and rotor speed. The geometric parameters are optimized by analyzing the flow distribution, and the purpose of design guidance are achieved.

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