scholarly journals TR-PIV in highly pulsatile flow: pulsation frequency and wake dynamics case study

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Ian A. Carr ◽  
Michael W. Plesniak
Keyword(s):  
Pulsatile Flow ◽  
High Frequency ◽  
Dynamic Range ◽  
Low Frequency ◽  
Pulsation Frequency ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Pulsatile Flows ◽  
Conceptual Overview

Experimental study of highly pulsatile flows presents a number of challenges, primarily the inherently large dynamic range of velocities. Herein, we use time-resolved particle image velocimetry processed with a technique known as pyramid sum-of-correlation to study highly pulsatile flow around a surface-mounted hemisphere. The frequency of pulsation is varied from low- frequency, quasi-steady pulsation to high frequency pulsation. We present a conceptual overview of the wake regimes observed and compare the flow physics of the high-frequency case to that of a vortex ring produced by a single impulse of fluid.

scholarly journals Vortex dynamics under pulsatile flow in axisymmetric constricted tubes

2020 ◽  
Vol 12 ◽  
pp. 120002
Author(s):  
Nicasio Barrere ◽  
Javier Brum ◽  
Alexandre L'her ◽  
Gustavo L. Sarasúa ◽  
Cecilia Cabeza
Keyword(s):  
Flow Pattern ◽  
Pulsatile Flow ◽  
Scaling Law ◽  
Transport Processes ◽  
Turbulent Regime ◽  
Dimensionless Variable ◽  
Image Velocimetry ◽  
Pulsatile Flows ◽  
Rigid Model

Improved understanding of how vortices develop and propagate under pulsatile flow can shed important light on the mixing and transport processes occurring in such systems, including the transition to turbulent regime. For example, the characterization of pulsatile flows in obstructed artery models serves to encourage research into flow-induced phenomena associated with changes in morphology, blood viscosity, wall elasticity and flow rate. In this work, an axisymmetric rigid model was used to study the behaviour of the flow pattern with varying degrees constriction  ($d_0$) and mean Reynolds ($\bar{Re}$) and Womersley numbers ($\alpha$). Velocity fields were obtained experimentally using Digital Particle Image Velocimetry and generated numerically. For the acquisition of data, $\bar{Re}$ was varied from 385 to 2044, $d_0$ was 1.0 cm and 1.6 cm, and $\alpha$ was varied from 17 to 33 in the experiments and from 24 to 50 in the numerical simulations. Results for the Reynolds number considered showed that the flow pattern consisted of two main structures: a central jet around the tube axis and a recirculation zone adjacent to the inner wall of the tube, where vortices shed. Using the vorticity fields, the trajectory of vortices was tracked and their displacement over their lifetime calculated. The analysis led to a scaling law equation for maximum vortex displacement as a function of a dimensionless variable dependent on the system parameters Re and $\alpha$.

Combustion Instability and Emission Control by Pulsating Fuel Injection

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Christian Oliver Paschereit ◽  
Ephraim Gutmark
Keyword(s):  
High Frequency ◽  
Fuel Injection ◽  
Low Frequency ◽  
Nox Emissions ◽  
Modulation Amplitude ◽  
Pulsation Frequency ◽  
Symmetric Mode ◽  
Instability Mode ◽  
Secondary Fuel ◽  
Symmetric Instability

Open-loop control methodologies were used to suppress symmetric and helical thermoacoustic instabilities in an experimental low-emission swirl-stabilized gas-turbine combustor. The controllers were based on fuel (or equivalence ratio) modulations in the main premixed combustion (premixed fuel injection (PMI)) or, alternatively, in the secondary pilot fuel. PMI included symmetric and asymmetric fuel injection. The symmetric instability mode responded to symmetric excitation only when the two frequencies matched. The helical fuel injection affected the symmetric mode only at frequencies that were much higher than that of the instability mode. The asymmetric excitation required more power to obtain the same amount of reduction as that required by symmetric excitation. Unlike the symmetric excitation, which destabilized the combustion when the modulation amplitude was excessive, the asymmetric excitation yielded additional suppression as the modulation level increased. The NOx emissions were reduced to a greater extent by the asymmetric modulation. The second part of the investigation dealt with the control of low frequency symmetric instability and high frequency helical instability by the secondary fuel injection in a pilot flame. Adding a continuous flow of fuel into the pilot flame controlled both instabilities. However, modulating the fuel injection significantly decreased the amount of necessary fuel. The reduced secondary fuel resulted in a reduced heat generation by the pilot diffusion flame and therefore yielded lower NOx emissions. The secondary fuel pulsation frequency was chosen to match the time scales typical to the central flow recirculation zone, which stabilizes the flame in the burner. Suppression of the symmetric mode pressure oscillations by up to 20dB was recorded. High frequency instabilities were suppressed by 38dB, and CO emissions reduced by using low frequency modulations with 10% duty cycle.

scholarly journals Pre-Emption of Affliction Severity Using HRV Measurements from a Smart Wearable; Case-Study on SARS-Cov-2 Symptoms

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7068
Author(s):  
Gatha Tanwar ◽  
Ritu Chauhan ◽  
Madhusudan Singh ◽  
Dhananjay Singh
Keyword(s):  
High Frequency ◽  
Viterbi Algorithm ◽  
Low Frequency ◽  
Very Low Frequency ◽  
Internal States ◽  
Hidden States ◽  
Complications And Mortality ◽  
Smart Wearable

Smart wristbands and watches have become an important accessory to fitness, but their application to healthcare is still in a fledgling state. Their long-term wear facilitates extensive data collection and evolving sensitivity of smart wristbands allows them to read various body vitals. In this paper, we hypothesized the use of heart rate variability (HRV) measurements to drive an algorithm that can pre-empt the onset or worsening of an affliction. Due to its significance during the time of the study, SARS-Cov-2 was taken as the case study, and a hidden Markov model (HMM) was trained over its observed symptoms. The data used for the analysis was the outcome of a study hosted by Welltory. It involved the collection of SAR-Cov-2 symptoms and reading of body vitals using Apple Watch, Fitbit, and Garmin smart bands. The internal states of the HMM were made up of the absence and presence of a consistent decline in standard deviation of NN intervals (SSDN), the root mean square of the successive differences (rMSSD) in R-R intervals, and low frequency (LF), high frequency (HF), and very low frequency (VLF) components of the HRV measurements. The emission probabilities of the trained HMM instance confirmed that the onset or worsening of the symptoms had a higher probability if the HRV components displayed a consistent decline state. The results were further confirmed through the generation of probable hidden states sequences using the Viterbi algorithm. The ability to pre-empt the exigent state of an affliction would not only lower the chances of complications and mortality but may also help in curbing its spread through intelligence-backed decisions.

Dynamic Range for Speech Materials in Korean, English, and Mandarin: A Cross-Language Comparison

2014 ◽  
Vol 57 (5) ◽  
pp. 2024-2030 ◽  
Author(s):  
In-Ki Jin ◽  
James M. Kates ◽  
Kathryn H. Arehart
Keyword(s):  
High Frequency ◽  
Dynamic Range ◽  
Low Frequency ◽  
Integration Time ◽  
Language Differences ◽  
Frequency Bands ◽  
Sentence Level ◽  
Cross Language ◽  
Best Fit ◽  
Signal Intensities

Purpose The purpose of this study was to identify whether differences in dynamic range (DR) are evident across the spoken languages of Korean, English, and Mandarin. Method Recorded sentence-level speech materials were used as stimuli. DR was quantified using different definitions of DR (defined as the range in decibels from the highest to the lowest signal intensities), for several integration times (from 1 to 512 ms) and in different frequency bands (center frequencies [CFs] ranging from 150 to 8600 Hz). Results Across the 3 languages, DR was affected in similar ways with regard to changes in DR definition and integration time. In contrast, across-language differences in DR were evident when considering frequency-band effects. Specifically, the DR for Korean was smaller than the English DR and the Mandarin DR in low-frequency bands (less than the CF of 455 Hz). Compared with Korean and Mandarin, the DR for English was smallest in mid-frequency bands (between the CF of 455 Hz and 4050 Hz) and was greatest in high-frequency bands (above the CF of 4050 Hz). Conclusion The observed differences in DR across languages suggest that the best-fit DR for Korean and Mandarin may be different than the best fit for English.

Mechanisms of instability growth, interaction and breakdown induced by a backward-facing step in a swept-wing flow

2021 ◽  
Vol 931 ◽  
Author(s):  
Jenna L. Eppink
Keyword(s):  
Particle Image ◽  
Low Frequency ◽  
Streamwise Velocity ◽  
Swept Wing ◽  
Backward Facing Step ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Large Velocity ◽  
Instability Growth ◽  
Constructive Interaction

Time-resolved particle image velocimetry measurements were performed downstream of a swept backward-facing step. The measurements allow detailed analysis of the interactions between the unsteady instabilities and the stationary crossflow vortices. Different mechanisms are identified that lead to the modulation of the different families of unsteady instabilities that occur downstream of the step. For the low-frequency spanwise-travelling mode, the modulation occurs due to a redistribution of momentum when the instability encounters regions of large spanwise shear of the wall-normal and streamwise velocity. However, the higher-frequency streamwise-travelling instabilities undergo the familiar ‘lift-up’ mechanism when they encounter the regions of large vertical velocity due to the presence of the stationary crossflow vortices. The process leading to large velocity spikes, and ultimately to a laminar breakdown to turbulence, is identified as a constructive interaction between the different unsteady instabilities, coupled with an interaction with the stationary crossflow vortices when the phases align properly.

scholarly journals ANALISIS SUSEPTIBILITAS MAGNETIK TANAH LAPISAN ATAS SEBAGAI INDIKATOR BENCANA LONGSOR DI BUKIT SULA KECAMATAN TALAWI KOTA SAWAHLUNTO

2018 ◽  
Vol 15 (2) ◽  
pp. 112
Author(s):  
Arif Budiman ◽  
Dwi Puryanti ◽  
Febri Naldi
Keyword(s):  
Magnetic Susceptibility ◽  
High Frequency ◽  
Low Frequency ◽  
Magnetic Minerals ◽  
Average Value ◽  
Rain Drop ◽  
Space Range ◽  
Test Result ◽  
Scanning Electron

Landslide is a disaster that can harm properties and souls. Losses due to landslide can be minimized if there are known signs of landslide.. In this research, the landslide indicator is known through the analysis of the magnetic susceptibility of topsoil. This research is a case study conducted at Bukit Sula, Talawi District, Sawahlunto City.Soil samples were taken from two locations in Sula Hill, which are vegetated location (location A) and unvegetated location (location B). This research’s samples took with downward vertical  of each 100 m was taken with a space range of 5 m, so that is obtained 21 sampling points at each of these locations. Measurement of magnetic susceptibility value using Bartington Magnetic Susceptibility Meter measured at two frequencies, namely low frequency of 0.465 kHz (χLF) and high frequency of 4.65 kHz (χHF). At location A the obtained average value of χLF is 804.05×10-8 m3kg-1while the average value of χHF is 804.25×10-8 m3kg-1. At location B the obtained average value of χLF is 9.85×10-8 m3kg-1, while the average value of χHF is 9.64×10-8 m3kg-1. XRF test result showed that magnetic minerals in samples at both locations a hematit (Fe2O3). Based on the comparison of susceptibility value and concentration of hematite and quartz minerals between sample of location A and location B, it can be said that location B has been eroded. Based on the presence of superparamagnetic grain, the samples taken from location B have finer grains than the samples at location A. Scanning Electron Microscope (SEM) also shows that sample B has finer grains than the sample B.  These are because location B is an area without vegetation, causing rain drop directly into the soil and can decrease the level of soil grain attachment. Therefore, location B more likely occurred landslide than location A.

scholarly journals How useful is eap vocabulary for esp? a corpus based case study

2020 ◽  
Author(s):  
C Sutarsyah ◽  
Paul Nation ◽  
G Kennedy
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Word List ◽  
Academic Vocabulary ◽  
Very High Frequency ◽  
Academic Texts ◽  
The University ◽  
General Service ◽  
Very High

This study compares the vocabulary of a single Economics text of almost 300,000 running words with the vocabulary of a corpus of similar length made up of a variety of academic texts. It was found that the general academic corpus used a very much larger vocabulary than the more focused Economics text. A small number of words that were closely related to the topic of the text occurred with very high frequency in the Economics text. The general academic corpus had a very large number of low frequency words. Beyond the words in West's General Service List and the University Word List, there was little overlap between the vocabulary of the two corpora. This indicates that as far as vocabulary is concerned, EAP courses that go beyond the high frequency academic vocabulary are of little value for learners with specific purposes. © 1994, Sage Publications. All rights reserved.

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