scholarly journals Effect of Expansion Direction/Area Ratio on Loss Characteristics and Flow Rectification of Curve Diffuser

CFD Letters ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 52-68
Author(s):  
Teo Wen Yong ◽  
Normayati Nordin ◽  
Bukhari Manshoor ◽  
Zainal Ambri Abdul Karim ◽  
Shamsuri Mohamed Rasidi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aircraft Engine ◽  
Area Ratio ◽  
Pressure Recovery ◽  
Flow Uniformity ◽  
Cross Sectional ◽  
High Area ◽  
Overall Performance ◽  
Gas Turbine Cycle ◽  
Loss Characteristic

Curve diffuser is frequently used in applications such as HVAC, wind- tunnel, gas turbine cycle, aircraft engine etc. as an adapter to join the conduits of different cross-sectional areas or an ejector to decelerate the flow and raise the static pressure before discharging to the atmosphere. The performance of the curve diffuser is greatly affected by the abrupt expansion and inflection introduced, particularly when a sharp 90o curve diffuser is configured with a high area ratio (AR). Therefore, the paper aims to numerically investigate the effect of the expansion direction of AR=1.2 to 4.0 curve diffuser on loss characteristic and flow rectification. 90o curve diffuser operated at inflow Reynolds Number, Rein=5.934 × 104 to 1.783 × 105 was considered. Results show that pressure recovery improves when the area ratio increases from 1.2 to 2.16 for both 2D expansion (z- direction) and 3D expansion (x- and z- direction). On the other hand, the increase of inflow Reynolds number causes the flow uniformity to drop regardless of the expansion directions. 3D expansion (x- and z- direction) curve diffuser with AR=2.16, operated at Rein=8.163 × 104, is opted as the most optimum, producing the best pressure recovery up to 0.380. Meanwhile, 2D expansion (z-direction) curve diffuser of AR=2.16, , operated at Rein= 5.934 × 104, is chosen to provide the best flow uniformity of 2.330 m/s. 2D expansion (x- direction) should be as best avoided as it provides the worst overall performance of 90o curve diffuser.

Contraction/Expansion Effects in 90° Miter Bends in Rectangular Xurographic Microchannels

2011 ◽  
Author(s):  
Lam Nguyen ◽  
John Elsnab ◽  
Tim Ameel
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Area Ratio ◽  
Loss Coefficient ◽  
Sidewall Roughness ◽  
Cross Sectional ◽  
Loss Coefficients ◽  
Minor Losses ◽  
High Reynolds ◽  
Reported Data

Xurography is an inexpensive rapid prototyping technology for the development of microfluidic systems. Imprecision in the xurographic tape cutting process can result in undesired changes in channel dimensions near features that require a change in cutting direction, such as 90° miter bends. An experimental study of water flow in rectangular xurographic microchannels incorporating 90° miter bends with different channel widths in each leg is reported. A set of twelve microchannels, with channel depth approximately 105 micrometers and aspect ratio ranging from 0.071 to 0.435, were fabricated from double-sided adhesive Kapton® polyimide tape and two rectangular glass plates. The channels were reinforced with a mechanical clamping system, enabling high Reynolds number, Re, flows (up to Re = 3200) where Re was based upon hydraulic diameter and average velocity. Reported data include friction factor and critical Reynolds number for straight microchannels and loss coefficients for flow through 90° miter bends that contain either a contraction or expansion with cross-sectional area ratios of 0.5, 0.333 and 0.2. The critical Reynolds number, Recr, ranged from 1750 to 2300 and was found to be dependent on channel defects such as sidewall roughness, adhesive droplets, and corner imperfections. Loss coefficients through 90° miter bends with expansion decrease rapidly for Re < Recr. At the transition, the loss coefficient suddenly drops and approaches an asymptotic value for Re > Recr. For 90° miter bends with contractions, loss coefficients gradually decrease with increasing Re for 150 < Re < 1400. In addition, the loss coefficient decreases with decreasing area ratio through the contraction or expansion. The minor loss coefficient data were found to be dependent on Reynolds numbers and area ratio of contraction/expansion at the bend. The results suggest that the effect of the contraction/expansion was the dominant mechanism for minor losses in the 90° miter bend.

Factors Affecting the Performance of the Supersonic Parallel Diffuser

1966 ◽  
Vol 8 (1) ◽  
pp. 62-69 ◽  
Author(s):  
B. W. Martin
Keyword(s):  
Static Pressure ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Stagnation Pressure ◽  
Pressure Recovery ◽  
Cross Sectional ◽  
Factors Affecting ◽  
Single Shock ◽  
Wide Range

Following the work of Baker and Martin (1), this paper provides further information about static pressure recovery in axi-symmetric supersonic parallel diffusers of fixed length and the same upstream generating nozzle when the diffuser cross-sectional area is varied over a wide range. Correlations based on these and associated experiments by Martin and Baker (2) indicate an area ratio for maximum possible static pressure recovery. At breakdown of the single shock, the diffuser stagnation pressure ratio corresponds to that for normal shock pressure recovery, while the outlet Mach number becomes independent of area ratio as the latter increases. The factors which influence the development and stability of the single shock regime are considered in some detail, from which the role of the boundary layer is shown to be predominant.

Systematic Approaches for Design of Distribution Manifolds Having the Same Per-Port Outflow

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Andrew W. Chen ◽  
Ephraim M. Sparrow
Keyword(s):  
Marked Effect ◽  
Reynolds Numbers ◽  
Area Ratio ◽  
Diameter Ratio ◽  
Sectional Area ◽  
Pressure Loading ◽  
Large Collection ◽  
Flow Uniformity ◽  
Cross Sectional ◽  
High Degree

Two geometric modalities were investigated to determine their effects on the degree of uniformity of the flow issuing from a manifold through a discrete set of exit ports. The goal of the investigation was to demonstrate how these geometric parameters can be used to achieve a high degree of exit-flow uniformity. The first investigated modality is the area ratio, which compares the total outflow area of all the exit ports with the cross-sectional area of the manifold. The second modality is the extent of pressure loading downstream of the exit ports of the manifold. The investigation was facilitated by numerical simulation for which an appropriate turbulence model was used. Three parameters were varied during the course of the research: (a) the area ratio, (b) the downstream pressure loading characterized by the length-to-diameter ratio of the outflow tubes that are attached to the exit ports, and (c) the Reynolds number. It was found that the area ratio parameter had a marked effect on the uniformity of the outflow from the manifold. Quantitative values of the area ratio corresponding to specified degrees of uniformity (i.e., 2%, 5%, and 10%) were identified. This information can be used as a guideline for manifold design. The imposition of the downstream pressure loading was also demonstrated to have a significant effect on the degree of uniformity, but that effect was not as strong as the effect of the area ratio. The manifold pressure was found to increase from the inlet of the manifold to the downstream end of the manifold. The direction of the jetlike discharge from the exit ports of the manifold into a large collection domain was found to vary along the length of the manifold, with inclined jets emanating from the upstream end and perpendicular jets at the downstream end. Over the range of investigated Reynolds numbers, from 40,000 to 200,000, the degree of uniformity of the mass effusion from the exit ports was found to be unaffected. The results of the numerical simulations were confirmed by experiments.

Effect of Varying Inflow Reynolds Number on Pressure Recovery and Flow Uniformity of 3-D Turning Diffuser

2014 ◽  
Vol 699 ◽  
pp. 422-428 ◽  
Author(s):  
Normayati Nordin ◽  
Zainal Ambri Abdul Karim ◽  
Safiah Othman ◽  
Vijay R. Raghavan
Keyword(s):  
Reynolds Number ◽  
Particle Image ◽  
Static Pressure ◽  
Flow Line ◽  
Pressure Recovery ◽  
Flow Uniformity ◽  
Subsonic Wind Tunnel ◽  
Image Velocimetry ◽  
Flow Quality ◽  
Experimental Rig

Various diffuser types characterized by the geometry are introduced in the flow line to recover the energy. A 3-D turning diffuser is a type of diffuser that its cross-section diffuses in all 3 directions of axes, i.e. x, y and z. In terms of applicability, a 3-D turning diffuser offers compactness and more outlet-inlet configurations over a 2-D turning diffuser. However, the flow within a 3-D turning diffuser is expected to be more complex which susceptible to excessive losses. As yet there is no established guideline that can be referred to choose a 3-D turning diffuser with an optimum performance. This paper aims to investigate the effects of varying inflow Reynolds number (Rein) on the performance of 3-D turning diffuser with 90o angle of turn. The outlet pressure recovery (Cp) and flow uniformity (σu) of 3-D turning diffuser with an area ratio (AR = 2.16) and outlet-inlet configurations (W2/W1 = 1.44, X2/X1 = 1.5), operated at inflow Reynolds number of Rein = 5.786E+04 - 1.775E+05 have been experimentally tested. The experimental rig was developed by incorporating several features of low subsonic wind tunnel. This was mainly to produce a perfect fully developed and uniform flow entering diffuser. Particle image velocimetry (PIV) was used to examine the flow quality, and a digital manometer was used to measure the average static pressure of the inlet and outlet of turning diffuser. There is a promising improvement in terms of flow uniformity when a 3-D turning diffuser is used instead of a 2-D turning diffuser with the same AR. An unexpected trend found with a drop of pressure recovery at maximum operating condition of Rein = 1.775E+05 shall require further investigations. The results obtained from this study will be in future used to validate the numerical codes. Upon successful validation, several other configurations will be numerically tested in order to establish the guidelines in the form of mathematical models.

Investigation of Flow Uniformity and Pressure Recovery in a Turning Diffuser by Means of Baffles

2013 ◽  
Vol 465-466 ◽  
pp. 526-530 ◽  
Author(s):  
Nur Hazirah Nohseth ◽  
Normayati Nordin ◽  
Safiah Othman ◽  
Vijay R. Raghavan
Keyword(s):  
Reynolds Number ◽  
Particle Image Velocimetry ◽  
Flow Velocity ◽  
Particle Image ◽  
Static Pressure ◽  
The Other ◽  
Pressure Recovery ◽  
Flow Uniformity ◽  
Image Velocimetry ◽  
Work Done

Turning diffuser is an engineering device that is widely used in the industry to reduce the flow velocity as well as change the direction of the flow. Having a curvature shape causes its performance to decrease in terms of pressure recovery (Cp) and flow uniformity (σu). Therefore, this study presents the work done in designing baffles to be installed in the turning diffuser with ratio of AR=2.16 to improve the flow uniformity and pressure recovery. It also aims to investigate the mechanism of flow structure and pressure recovery in turning diffusers by means of turning baffles. The results with varying inflow Reynolds number (Rein) between 5.786E+04 1.775E+05 have been experimentally tested and compared with previous study. Particle image velocimetry (PIV) was used to determine the flow uniformity. On the other hand, a digital manometer provided the average static pressure of the inlet and outlet of turning diffuser. The best produced pressure recovery of Cp=0.526 were recorded when the system were operated at the highest Reynolds number tested Rein=1.775E+05. This result shows an improvement up to 54.625% deviation from previous study with Cp=0.239. The flow uniformity also shows an improvement of 47.127% deviation from previous study at the same Rein with σu=3.235 as compared to previous study σu=6.12.

High-Temperature Instability of A Cr2Nb-Nb(Cr) Microlaminate Composite

1996 ◽  
Vol 54 ◽  
pp. 374-375
Author(s):  
M. Larsen ◽  
R.G. Rowe ◽  
D.W. Skelly
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
High Temperature ◽  
Elevated Temperatures ◽  
Aircraft Engine ◽  
Lattice Parameter ◽  
Microstructural Stability ◽  
Elevated Temperature Strength ◽  
Cross Sectional ◽  
Bcc Structure

Microlaminate composites consisting of alternating layers of a high temperature intermetallic compound for elevated temperature strength and a ductile refractory metal for toughening may have uses in aircraft engine turbines. Microstructural stability at elevated temperatures is a crucial requirement for these composites. A microlaminate composite consisting of alternating layers of Cr2Nb and Nb(Cr) was produced by vapor phase deposition. The stability of the layers at elevated temperatures was investigated by cross-sectional TEM.The as-deposited composite consists of layers of a Nb(Cr) solid solution with a composition in atomic percent of 91% Nb and 9% Cr. It has a bcc structure with highly elongated grains. Alternating with this Nb(Cr) layer is the Cr2Nb layer. However, this layer has deposited as a fine grain Cr(Nb) solid solution with a metastable bcc structure and a lattice parameter about half way between that of pure Nb and pure Cr. The atomic composition of this layer is 60% Cr and 40% Nb. The interface between the layers in the as-deposited condition appears very flat (figure 1). After a two hour, 1200 °C heat treatment, the metastable Cr(Nb) layer transforms to the Cr2Nb phase with the C15 cubic structure. Grain coarsening occurs in the Nb(Cr) layer and the interface between the layers roughen. The roughening of the interface is a prelude to an instability of the interface at higher heat treatment temperatures with perturbations of the Cr2Nb grains penetrating into the Nb(Cr) layer.

Performance Evaluation of Divided Intake Ducts: Effect of Area Ratio and Inlet Reynolds Number

2003 ◽  
Vol 30 (5) ◽  
pp. 525-541 ◽  
Author(s):  
Sanjeev Bharani ◽  
S.N. Singh ◽  
V. Seshadri ◽  
R. Chandramouli
Keyword(s):  
Reynolds Number ◽  
Performance Evaluation ◽  
Area Ratio

scholarly journals Atrophy patterns in isolated subscapularis lesions

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Gernot Seppel ◽  
Andreas Voss ◽  
Daniel J. H. Henderson ◽  
Simone Waldt ◽  
Bernhard Haller ◽  
...  
Keyword(s):  
Muscle Atrophy ◽  
Area Ratio ◽  
Cross Sectional Area ◽  
Control Group ◽  
Sectional Area ◽  
Cross Sectional ◽  
Subscapularis Muscle ◽  
Mri Scans ◽  
The Mean ◽  
The Cross

Abstract Background While supraspinatus atrophy can be described according to the system of Zanetti or Thomazeau there is still a lack of characterization of isolated subscapularis muscle atrophy. The aim of this study was to describe patterns of muscle atrophy following repair of isolated subscapularis (SSC) tendon. Methods Forty-nine control shoulder MRI scans, without rotator cuff pathology, atrophy or fatty infiltration, were prospectively evaluated and subscapularis diameters as well as cross sectional areas (complete and upper half) were assessed in a standardized oblique sagittal plane. Calculation of the ratio between the upper half of the cross sectional area (CSA) and the total CSA was performed. Eleven MRI scans of patients with subscapularis atrophy following isolated subscapularis tendon tears were analysed and cross sectional area ratio (upper half /total) determined. To guarantee reliable measurement of the CSA and its ratio, bony landmarks were also defined. All parameters were statistically compared for inter-rater reliability, reproducibility and capacity to quantify subscapularis atrophy. Results The mean age in the control group was 49.7 years (± 15.0). The mean cross sectional area (CSA) was 2367.0 mm2 (± 741.4) for the complete subscapularis muscle and 1048.2 mm2 (± 313.3) for the upper half, giving a mean ratio of 0.446 (± 0.046). In the subscapularis repair group the mean age was 56.7 years (± 9.3). With a mean cross sectional area of 1554.7 mm2 (± 419.9) for the complete and of 422.9 mm2 (± 173.6) for the upper half of the subscapularis muscle, giving a mean CSA ratio of 0.269 (± 0.065) which was seen to be significantly lower than that of the control group (p < 0.05). Conclusion Analysis of typical atrophy patterns of the subscapularis muscle demonstrates that the CSA ratio represents a reliable and reproducible assessment tool in quantifying subscapularis atrophy. We propose the classification of subscapularis atrophy as Stage I (mild atrophy) in case of reduction of the cross sectional area ratio < 0.4, Stage II (moderate atrophy) in case of < 0.35 and Stage III (severe atrophy) if < 0.3.

Use of Cardiac Magnetic Resonance Imaging Based Measurements of Inferior Vena Cava Cross-Sectional Area in the Diagnosis of Pericardial Constriction

2015 ◽  
Vol 66 (3) ◽  
pp. 231-237 ◽  
Author(s):  
Kate Hanneman ◽  
Paaladinesh Thavendiranathan ◽  
Elsie T. Nguyen ◽  
Hadas Moshonov ◽  
Rachel Wald ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Cardiac Magnetic Resonance ◽  
Inferior Vena ◽  
Vena Cava ◽  
Area Ratio ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Resonance Imaging ◽  
Cross Sectional ◽  
Aortic Area

Purpose To evaluate the value of cardiac magnetic resonance imaging (MRI)–based measurements of inferior vena cava (IVC) cross-sectional area in the diagnosis of pericardial constriction. Methods Patients who had undergone cardiac MRI for evaluation of clinically suspected pericardial constriction were identified retrospectively. The diagnosis of pericardial constriction was established by clinical history, echocardiography, cardiac catheterization, intraoperative findings, and/or histopathology. Cross-sectional areas of the suprahepatic IVC and descending aorta were measured on a single axial steady-state free-precession (SSFP) image at the level of the esophageal hiatus in end-systole. Logistic regression and receiver-operating curve (ROC) analyses were performed. Results Thirty-six patients were included; 50% (n = 18) had pericardial constriction. Mean age was 53.9 ± 15.3 years, and 72% (n = 26) were male. IVC area, ratio of IVC to aortic area, pericardial thickness, and presence of respirophasic septal shift were all significantly different between patients with constriction and those without ( P < .001 for all). IVC to aortic area ratio had the highest odds ratio for the prediction of constriction (1070, 95% confidence interval [8.0-143051], P = .005). ROC analysis illustrated that IVC to aortic area ratio discriminated between those with and without constriction with an area under the curve of 0.96 (95% confidence interval [0.91-1.00]). Conclusions In patients referred for cardiac MRI assessment of suspected pericardial constriction, measurement of suprahepatic IVC cross-sectional area may be useful in confirming the diagnosis of constriction when used in combination with other imaging findings, including pericardial thickness and respirophasic septal shift.

Effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers

2003 ◽  
Vol 217 (1) ◽  
pp. 29-41 ◽  
Author(s):  
R B Anand ◽  
L Rai ◽  
S N Singh
Keyword(s):  
Total Pressure ◽  
Static Pressure ◽  
Area Ratio ◽  
Secondary Flows ◽  
Performance Characteristics ◽  
Pressure Recovery ◽  
Recovery Coefficient ◽  
Turning Angle ◽  
And Performance ◽  
Pressure Recovery Coefficient

The effect of the turning angle on the flow and performance characteristics of long S-shaped circular diffusers (length-inlet diameter ratio, L/Di = 11:4) having an area ratio of 1.9 and centre-line length of 600 mm has been established. The experiments are carried out for three S-shaped circular diffusers having angles of turn of 15°/15°, 22.5°/22.5° and 30°/30°. Velocity, static pressure and total pressure distributions at different planes along the length of the diffusers are measured using a five-hole impact probe. The turbulence intensity distribution at the same planes is also measured using a normal hot-wire probe. The static pressure recovery coefficients for 15°/15°, 22.5°/22.5° and 30°/30° diffusers are evaluated as 0.45, 0.40 and 0.35 respectively, whereas the ideal static pressure recovery coefficient is 0.72. The low performance is attributed to the generation of secondary flows due to geometrical curvature and additional losses as a result of the high surface roughness (~0.5 mm) of the diffusers. The pressure recovery coefficient of these circular test diffusers is comparatively lower than that of an S-shaped rectangular diffuser of nearly the same area ratio, even with a larger turning angle (90°/90°), i.e. 0.53. The total pressure loss coefficient for all the diffusers is nearly the same and seems to be independent of the angle of turn. The flow distribution is more uniform at the exit for the higher angle of turn diffusers.

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