Turbulent Flows in a Model SDR Combustor

1993 ◽  
Vol 115 (3) ◽  
pp. 468-473 ◽  
Author(s):  
T.-M. Liou ◽  
Y.-Y. Wu
Keyword(s):  
Turbulent Flows ◽  
Computational Models ◽  
Fluid Dynamic ◽  
Flow Characteristics ◽  
Joint Probability ◽  
Spreading Rate ◽  
Point Of View ◽  
Laser Doppler Velocimeter ◽  
Mean Velocity ◽  
Ducted Rocket

An experimental study is reported on the isothermal flow fields in a model solid-propellant ducted rocket combustor with two opposing side inlets. The measurements were made by using a four-beam two-color laser-Doppler velocimeter (LDV). Three values of momentum ratio (Ma/Ms) of the axial- to side-inlet jet—0.025, 0.11, and 1.28—were selected to investigate their effects on the flow characteristics. The Reynolds number, based on the air density, combustor height, and bulk velocity, was 4.56 × 104. The flow field was characterized in terms of the mean-velocity vectors and contours, joint probability functions, mean reattachment lengths, spreading rate of the axial-jet width, and Reynolds stress and turbulence kinetic energy contours. The LDV measured mean reattachment lengths were found to well agree with the corresponding flow-visualization photograph. In addition, the three Ma/Ms values provided three characteristic flows which are useful in testing the computational models. Further, correlations between the present cold-flow and previous reading-flow studies were documented in detail. It was found that from the fluid dynamic point of view Ma/Ms = 0.11 was preferable to the other two values of Ma/Ms.

Laser Velocimeter Measurements in Highly Turbulent Recirculating Flows

1984 ◽  
Vol 106 (2) ◽  
pp. 173-180 ◽  
Author(s):  
W. H. Stevenson ◽  
H. D. Thompson ◽  
R. R. Craig
Keyword(s):  
Turbulent Flows ◽  
Turbulence Model ◽  
Quantitative Description ◽  
Sudden Expansion ◽  
Laser Doppler Velocimeter ◽  
Bias Error ◽  
Mean Velocity ◽  
One Dimensional ◽  
Numerical Predictions ◽  
Velocity Bias

This paper presents the results of an extensive study of subsonic separated flows using a laser Doppler velocimeter. Both a rectangular rearward facing step and cylindrical (axisymmetric) sudden expansion geometry were studied. The basic objectives were to resolve the question of whether a velocity bias error does, in fact, occur in LDV measurements in highly turbulent flows of this type and, if so, how it may be eliminated; map the velocity field (mean velocity, turbulence intensity, Reynolds stress, etc.) including the entire recirculation zone; and compare experimental results with numerical predictions based on the k-ε turbulence model. Measurements were carried out using a one-dimensional LDV operating in forward scatter with signal processing by means of a commercial counter-type processor. Results obtained show that velocity bias does occur in turbulent flows and that it can be overcome by proper data acquisition procedures. The results also indicate that the important mean velocity and turbulence quantities can be obtained with reasonable accuracy using a one-dimensional LDV system. Although the k-ε turbulence model provides a good qualitative picture of the flow field, it does not yield a completely adequate quantitative description. Results obtained here illustrate the discrepancies to be expected and provide a basis for further model development.

LDV and PIV Velocity Results in a Thermosiphon

2003 ◽  
Author(s):  
J. Kulman ◽  
D. Gray ◽  
S. Sivanagere ◽  
S. Guffey
Keyword(s):  
Large Scale ◽  
Single Phase ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Laser Doppler Velocimeter ◽  
Mean Velocity ◽  
Developed Turbulence ◽  
The Mean ◽  
Good Agreement

Heat transfer and flow characteristics have been determined for a single-phase rectangular loop thermosiphon. The plane of the loop was vertical, and tests were performed with in-plane tilt angles ranging from 3.6° CW to 4.2° CCW. Velocity profiles were measured in one vertical leg of the loop using both a single-component Laser Doppler Velocimeter (LDV), and a commercial Particle Image Velocimeter (PIV) system. The LDV data and PIV data were found to be in good agreement. The measured average velocities were approximately 2–2.5 cm/s at an average heating rate of 70 W, and were independent of tilt angle. Significant RMS fluctuations of 10–20% of the mean velocity were observed in the test section, in spite of the laminar or transitional Reynolds numbers (order of 700, based on the hydraulic diameter). These fluctuations have been attributed to vortex shedding from the upstream temperature probes and mitre bends, rather than to fully developed turbulence. Animations of the PIV data clearly show these large scale unsteady flow patterns. Multiple steady state flow patterns were not observed.

Experimental and Computational Study of Turbulent Flows in a Channel With Two Pairs of Turbulence Promoters in Tandem

1990 ◽  
Vol 112 (3) ◽  
pp. 302-310 ◽  
Author(s):  
T.-M. Liou ◽  
Y. Chang ◽  
D.-W. Hwang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flows ◽  
Turbulence Intensity ◽  
Computational Models ◽  
Computational Study ◽  
Reattachment Length ◽  
Transfer Enhancement ◽  
Mean Velocity ◽  
Pitch Ratio

Measurements and computations are presented of mean velocity and turbulence intensity for an arrangement of two pairs of turbulence promoters mounted in tandem in developing channel flow. The Reynolds number (ReD) and the pitch ratio (PR) were varied in the range of 1.2 × 104 to 1.2 × 105 and 1 to 100, respectively. The three pitch ratios 5, 10, 15 were found to provide three characteristic flows which are a useful test of the computational models. The effects of PR on the reattachment lengths and the pressure loss as well as the influence of ReD on the reattachment length were documented in detail. It was found that PR=10 was preferable to PR = 5 and PR = 15 from the standpoint of heat transfer enhancement.

Pressure and Flow Characteristics in a Rotating Two-Pass Square Duct With 45° Angled Ribs

2003 ◽  
Author(s):  
Tong-Miin Liou ◽  
Guang-Yuan Dai
Keyword(s):  
Secondary Flow ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Laser Doppler Velocimeter ◽  
Main Stream ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct ◽  
Pressure Transducers

Measurements are presented of the local velocity and wall static-pressure distributions by using laser-Doppler velocimeter and pressure transducers, respectively, in a rotating two-pass square duct with ribs placed on the leading and trailing walls at an angle of 45° to the main stream. The ribs were square in cross-section and in a parallel mode of arrangement. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are addressed in terms of the evolutions of both main flow and cross-stream secondary flow and the distributions of the pressure coefficient, which are lacking in the published literature for ducts ribbed with 45° ribs and under rotation. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are documented. The 45° ribs are found to reduce the pressure loss to 60% of the 90° ribs for rotating duct under same operating conditions. For CFD reference, the fully developed flow condition is absent for the rotating ducts investigated. The measured evolution of complex secondary flow vortices is believed to be a challenge to numerical simulations.

Thermal Mixing Downstream of a 90-Degree T-Junction: Laminar and Turbulent Flows

2019 ◽  
Author(s):  
Bakhtier Farouk
Keyword(s):  
Turbulent Flows ◽  
Thermophysical Properties ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Inlet Temperature ◽  
Horizontal Pipe ◽  
Thermal Mixing ◽  
Large Eddy ◽  
Inlet Conditions

Abstract A three-dimensional time dependent computational fluid dynamic (CFD) study of laminar and turbulent thermal mixing of two flows entering a 90° T-junction pipe is presented. The two incoming flows (both liquids) in the T-junction enter the flow domain with different inlet velocities, and temperatures. Water flow is considered in both the horizontal pipe and the vertical pipe. Inlet temperature differences and temperature dependent thermophysical properties are considered. Large eddy simulations (LES) with sub-grid scale (SGS) modeling were considered for the simulation of the turbulent cases. The flow characteristics, and thermal mixing behaviors and detailed mixing structures were simulated, and they showed that thermal mixing of the two streams are closely affected by the inlet conditions of the two streams and the inlet thermophysical properties of the two streams.

Flowfield Investigation of the Effect of Rib Open Area Ratio in a Rectangular Duct

1998 ◽  
Vol 120 (3) ◽  
pp. 504-512 ◽  
Author(s):  
Tong-Miin Liou ◽  
Chih-Wen Kao ◽  
Shih-Hui Chen
Keyword(s):  
Computational Models ◽  
Fluid Dynamic ◽  
Fluid Flows ◽  
Area Ratio ◽  
Open Area ◽  
Height Ratio ◽  
Mean Velocity ◽  
Dynamic Factors ◽  
Nusselt Number Distribution ◽  
Spatially Periodic

The spatially periodic turbulent fluid flows and friction in a rectangular passage of width-to-height ratio of 4:1 with perforated rectangular ribs mounted on one wall have been studied using laser Doppler velocimetry and pressure probing. The parameters fixed were rib height to duct hydraulic diameter ratio of 0.106, rib width-to-height ratio of 0.76, rib pitch-to-height ratio of 10, and Reynolds number of 2 × 104, while the main parameter investigated was the rib open-area ratio (β) with values of 0%, 10%, 22%, 38%, and 44%. Two critical ranges of β and three characteristic flow regimes were identified, which provides useful references of practical tests of computational models. The results also showed that the dominant fluid dynamic factors responsible for the reported peak values of local Nusselt number distribution could be recognized. Moreover, the secondary-flow mean velocity components were found to be one to two orders of magnitude smaller than the bulk mean velocity.

Heat Transfer and Fluid Flow in a Square Duct With 12 Different Shaped Vortex Generators

1999 ◽  
Vol 122 (2) ◽  
pp. 327-335 ◽  
Author(s):  
T.-M. Liou ◽  
C.-C. Chen ◽  
T.-W. Tsai
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Delta Wing ◽  
Fluid Dynamic ◽  
Vortex Generator ◽  
Hydraulic Diameter ◽  
Longitudinal Vortex ◽  
Laser Doppler Velocimeter ◽  
Mean Velocity ◽  
Single Vortex

Detailed local Nusselt number distributions in the first pass of a sharp turning two-pass square channel with various configurations of longitudinal vortex generator arranged on one wall were measured using transient liquid crystal thermography. Flow patterns and friction factors were measured by the use of laser-Doppler velocimeter and pressure transducer, respectively. The Reynolds number, based on channel hydraulic diameter and bulk mean velocity, was fixed at 1.2×104. The vortex generator height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.12 and 10, respectively. Comparisons in terms of heat transfer augmentation and uniformity and friction loss are first performed on 12 configurations of single longitudinal vortex generator. The fluid dynamic mechanisms and wall confinement relevant to heat transfer enhancement are then documented for three-selected vortex generator models. In addition, the differences in fluid flow and heat transfer characteristics between a single vortex generator and a vortex generator array are addressed for the delta wing I and 45 deg V (with tips facing upstream) models which provide better thermal performance among the 12 configurations examined. The direction and strength of the secondary flow with respect to the heat transfer wall are found to be the most important fluid dynamic factors affecting the heat transfer promotion through the channel wall, followed by the convective mean velocity, and then the turbulent kinetic energy. [S0022-1481(00)01202-0]

Pressure and Flow Characteristics in a Rotating Two-Pass Square Duct With 45-Deg Angled Ribs

2004 ◽  
Vol 126 (1) ◽  
pp. 212-219 ◽  
Author(s):  
Tong-Miin Liou ◽  
Guang-Yuan Dai
Keyword(s):  
Secondary Flow ◽  
Friction Factor ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Laser Doppler Velocimeter ◽  
Main Stream ◽  
Height Ratio ◽  
Mean Velocity ◽  
Square Duct

Measurements are presented of the local velocity and wall static-pressure distributions by using laser-Doppler velocimeter and pressure transducers, respectively, in a rotating two-pass square duct with ribs placed on the leading and trailing walls at an angle of 45 deg to the main stream. The ribs were square in cross section and in a parallel mode of arrangement. The rib-height/duct-height ratio and the pitch/rib-height ratio were 0.136 and 10, respectively. The duct Reynolds number was 1×104 and rotation number Ro ranged from 0 to 0.2. Results are addressed in terms of the evolutions of both main flow and cross-stream secondary flow, the distributions of the pressure coefficient, and the variation of friction factor with Ro. In addition, the relationships between the regional averaged Nusselt number, transverse and convective mean velocity component, and turbulent kinetic energy are documented. Simple expressions are obtained to correlate friction factor with Ro, which are lacking in the published literature for ducts ribbed with 45- deg ribs. The 45-deg ribs are found to reduce the friction loss to 60% of the 90-deg ribs for rotating duct under the same operating conditions. For CFD reference, the fully developed flow condition is absent for the rotating ribbed duct investigated. The measured evolution of complex secondary flow vortices is believed to be a challenge to numerical simulations.

scholarly journals Variable-Order Fractional Models for Wall-Bounded Turbulent Flows

Entropy ◽  
2021 ◽  
Vol 23 (6) ◽  
pp. 782
Author(s):  
Fangying Song ◽  
George Em Karniadakis
Keyword(s):  
Fractional Derivative ◽  
Turbulent Flows ◽  
Fractional Order ◽  
Variable Order ◽  
Universal Curve ◽  
Reynolds Stresses ◽  
Continuous Change ◽  
Mean Velocity ◽  
Symmetric Variable ◽  
Fractional Models

Modeling of wall-bounded turbulent flows is still an open problem in classical physics, with relatively slow progress in the last few decades beyond the log law, which only describes the intermediate region in wall-bounded turbulence, i.e., 30–50 y+ to 0.1–0.2 R+ in a pipe of radius R. Here, we propose a fundamentally new approach based on fractional calculus to model the entire mean velocity profile from the wall to the centerline of the pipe. Specifically, we represent the Reynolds stresses with a non-local fractional derivative of variable-order that decays with the distance from the wall. Surprisingly, we find that this variable fractional order has a universal form for all Reynolds numbers and for three different flow types, i.e., channel flow, Couette flow, and pipe flow. We first use existing databases from direct numerical simulations (DNSs) to lean the variable-order function and subsequently we test it against other DNS data and experimental measurements, including the Princeton superpipe experiments. Taken together, our findings reveal the continuous change in rate of turbulent diffusion from the wall as well as the strong nonlocality of turbulent interactions that intensify away from the wall. Moreover, we propose alternative formulations, including a divergence variable fractional (two-sided) model for turbulent flows. The total shear stress is represented by a two-sided symmetric variable fractional derivative. The numerical results show that this formulation can lead to smooth fractional-order profiles in the whole domain. This new model improves the one-sided model, which is considered in the half domain (wall to centerline) only. We use a finite difference method for solving the inverse problem, but we also introduce the fractional physics-informed neural network (fPINN) for solving the inverse and forward problems much more efficiently. In addition to the aforementioned fully-developed flows, we model turbulent boundary layers and discuss how the streamwise variation affects the universal curve.

Non-invasive temperature measurement of turbulent flows of aqueous solutions and gases in pipes

2020 ◽  
Vol 87 (9) ◽  
pp. 553-563
Author(s):  
Jörg Gebhardt ◽  
Guruprasad Sosale ◽  
Subhashish Dasgupta
Keyword(s):  
Surface Temperature ◽  
Temperature Measurement ◽  
Turbulent Flows ◽  
Fluid Dynamic ◽  
Industrial Applications ◽  
Static Case ◽  
Pipe Surface ◽  
Non Invasive ◽  
Step Model ◽  
Plant Optimization

AbstractAccurate and responsive non-invasive temperature measurements are enablers for process monitoring and plant optimization use cases in the context of Industry 4.0. If their performance is proven for large classes of applications, such measurement principles can replace traditional invasive measurements. In this paper we describe a two-step model to estimate the process temperature from a pipe surface temperature measurement. This static case model is compared to and enhanced by computational fluid dynamic (CFD) calculations to predict transient situations. The predictions of the approach are validated by means of controlled experiments in a laboratory environment. The experimental results demonstrate the efficacy of the model, the responsiveness of the pipe surface temperature, and that state of the art industrial non-invasive sensors can achieve the performance of invasive thermowells. The non-invasive sensors are then used to demonstrate the performance of the model in industrial applications for cooling fluids and steam.

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