| 1. |
- Jonnagiri, Raghuvir, et al.
(författare)
-
Influence of aortic valve morphology on vortical structures and wall shear stress
- 2023
-
Ingår i: Medical and Biological Engineering and Computing. - : Springer Nature. - 0140-0118 .- 1741-0444. ; 61:6, s. 1489-1506
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to assess the association between valve morphology and vortical structures quantitatively and to highlight the influence of valve morphology/orientation on aorta’s susceptibility to shear stress, both proximal and distal. Four-dimensional phase-contrast magnetic resonance imaging (4D PCMRI) data of 6 subjects, 3 with tricuspid aortic valve (TAV) and 3 with functionally bicuspid aortic values (BAV) with right-left coronary leaflet fusion, were processed and analyzed for vorticity and wall shear stress trends. Computational fluid dynamics (CFD) has been used with moving TAV and BAV valve designs in patient-specific aortae to compare with in vivo shear stress data. Vorticity from 4D PCMRI data about the aortic centerline demonstrated that TAVs had a higher number of vortical flow structures than BAVs at peak systole. Coalescing of flow structures was shown to be possible in the arch region of all subjects. Wall shear stress (WSS) distribution from CFD results at the aortic root is predominantly symmetric for TAVs but highly asymmetric for BAVs with the region opposite the raphe (fusion location of underdeveloped leaflets) being subjected to higher WSS. Asymmetry in the size and number of leaflets in BAVs and TAVs significantly influence vortical structures and WSS in the proximal aorta for all valve types and distal aorta for certain valve orientations of BAV. Graphical Abstract: Analysis of vortical structures using 4D PCMRI data (on the left side) and wall shear stress data using CFD (on the right side). [Figure not available: see fulltext.].
|
|
| 2. |
- Prahl-Wittberg, Lisa, et al.
(författare)
-
The Impact of Aortic Arch Geometry on Flow Characteristics
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Cardiovascular defects characterized by geometrical anomalies of the aorta and its eecton the blood ow is the focus of this study. Not only are the local ow characteristicsgeometry dependent, but they are also directly connected to the rheological properties ofblood. Flow characteristics such as wall shear stress are often postulated to play a centralrole in the development of vascular disease.In this study, blood is considered to be a non-Newtonian uid and modeled via theQuemada model, an empirical model that is valid for dierent red blood cell loading.Three patient-specic geometries of the aortic arch are investigated numerically. Thethree geometries investigated in this study all display malformations that are prevalent inpatients having the genetic disorder Turner syndrome. The results show a highly complexow with regions of secondary ow that are enhanced in two of the three aortas. Moreover,blood ow is clearly diverted due to the malformations, moving to a larger extent throughthe branches of the arch instead of through the descending aorta. The geometry havingan elongated transverse aorta is found to be subjected to larger areas of highly oscillatorylow wall shear stress.
|
|
| 3. |
|
|
| 4. |
- Ahn, MyeongHwan, et al.
(författare)
-
Large-eddy simulations of flow and aeroacoustics of twin square jets including turbulence tripping
- 2023
-
Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 35:6
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the flow and aeroacoustics of twin square (i.e., aspect ratio of 1.0) jets by implicit large-eddy simulations (LESs) under a nozzle pressure ratio of 3.0 and a temperature ratio of 1.0 conditions. A second-order central scheme coupled with a modified Jameson's artificial dissipation is used to resolve acoustics as well as to capture discontinuous solutions, e.g., shock waves. The flow boundary layer inside of the nozzle is tripped, using a small step in the convergent section of the nozzle. The time-averaged axial velocity and turbulent kinetic energy of LES with boundary layer tripping approaches better to particle image velocimetry experimental data than the LES without turbulence tripping case. A two-point space–time cross-correlation analysis suggests that the twin jets are screeching and are coupled to each other in a symmetrical flapping mode. Intense pressure fluctuations and standing waves are observed between the jets. Spectral proper orthogonal decomposition (SPOD) confirms the determined mode and the relevant wave propagation. The upstream propagating mode associated with the shock-cell structures is confined inside jets. Far-field noise obtained by solving Ffowcs Williams and Hawkings equation is in good agreement with the measured acoustic data. The symmetrical flapping mode of twin jets yields different levels of the screech tone depending on observation planes. The tonalities—the fundamental tone, second and third harmonics—appear clearly in the far-field, showing different contributions at angles corresponding to the directivities revealed by SPOD.
|
|
| 5. |
- Cuppoletti, Dan, et al.
(författare)
-
A Comprehensive Investigation of Pulsed Fluidic Injection for Active Control of Supersonic Jet Noise
- 2013
-
Ingår i: 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition. - Reston, Virigina : American Institute of Aeronautics and Astronautics. ; 2013
-
Konferensbidrag (refereegranskat)abstract
- Fluidic injection for noise control of high Reynolds number jets has shown promise and recent tests have demonstrated improved noise reduction while decreasing the injection mass flow required. This investigation was an experimental and numerical study on the capability of pulsed fluidic injection to reduce noise on a Md = 1.56 supersonic jet. The effect of pulse frequency, duty cycle, injector phasing, and injection angle on the noise components were studied. The pulsed injectors were characterized with hot-wire measurements. Far-fleld acoustics was used to survey the noise reduction of pulsed injection (up to 400 Hz) in comparison to the baseline and steady injection cases. Injection angles θinj = 30° to 90° with respect to the primary jet axis were investigated. High-speed shadowgraph was used to quantify the time scales involved in response of the shock train and screech instabilities with pulsed fluidic injection. LES and CAA were compared with measurements to evaluate the capability of numerical simulation of the pulsed injection configurations. It was shown that reduction of turbulent mixing noise generally scales with the actual duty cycle of applied injection. For 30 Hz injection at 20% mass flow up to up to 80% of the steady flow {increment}OASPL is achieved, demonstrating that low frequency injection is capable of enhanced noise reduction at certain conditions. The shocks in the jet potential core respond in 1 ms when injection is removed, while the jet column instability requires up to 7 ms to redevelop after injection is removed. The results demonstrate the feasibility of using active control with pulsed fluidic actuators to provide at least steady flow noise reduction with significantly reduced injection mass flow.
|
|
| 6. |
- Cuppoletti, Daniel, et al.
(författare)
-
Analysis of Supersonic Jet Thrust with Fluidic Injection
- 2014
-
Ingår i: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014; National Harbor, MD; United States; 13 January 2014 through 17 January 2014. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102561
-
Konferensbidrag (refereegranskat)abstract
- Considerable focus on noise abatement for aircraft has spawned various noise control devices, passive and active. Aircraft and propulsion system design now has the additional criteria of acoustic performance to consider among many other criteria in advanced flight vehicle design. It is essential to consider the effect that noise control methods have on the performance of the propulsion device and overall effect on system performance. Thrust calculated from measurements and LES are compared for a Md = 1.56 jet at various operating conditions for validation. Experimental measurements on the baseline supersonic jet are used to validate computational results for the pressure and momentum thrust components. Thrust for various fluidic injection configurations are evaluated using computational results from the highly three dimensional flowfield. Analysis and discussion of requirements for fluidic injection air are provided to develop a complete system approach to aid design of fluidic injection systems. Fluidic injection decreases momentum thrust by creating axial velocity deficits in the region of injection. Pressure thrust is increased from local pressure rise from the injectors and area control at the nozzle exit. Fluidic injection increases total thrust as the pressure thrust gains are greater than the momentum thrust deficits. Specific thrust is reduced slightly with 6 injectors being a more efficient use of the injection air with greater noise reduction.
|
|
| 7. |
- Cuppoletti, Daniel, et al.
(författare)
-
Elimination of shock associated noise in supersonic jets by destructive wave interference
- 2018
-
Ingår i: AIAA Aerospace Sciences Meeting, 2018. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied resulting in unique acoustic behavior and flow field modifications. For most conditions the acoustics are relatively unaffected or increased, but for very specific conditions noise was drastically decreased. For optimized conditions the shock noise was completely eliminated and in other cases a jet instability was generated that significantly decreased high frequency noise. Measurements of the velocity field indicated that shock interaction due to shocks from the injection jet interact with the primary jet shocks, and significantly reduce the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with LES, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of OASPL of -7 dB at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction, destructive interference of the shock structure in the jet is reported.
|
|
| 8. |
- Cuppoletti, Daniel, et al.
(författare)
-
Elimination of Shock-Associated Noise in Supersonic Jets by Destructive Wave Interference
- 2019
-
Ingår i: AIAA Journal. - 1533-385X .- 0001-1452. ; 57:2, s. 720-734
-
Tidskriftsartikel (refereegranskat)abstract
- A novel application of fluidic injection was developed to investigate and understand the effects of discrete fluidic injection internal to the jet nozzle. Various injection locations, angles, and conditions were studied, resulting in unique acoustic behavior and flowfield modifications. For most conditions, the acoustics are relatively unaffected or increased, but for very specific conditions, noise was drastically decreased. For optimized conditions, the shock noise was completely eliminated, and in other cases, a jet instability was generated that significantly decreased high-frequency noise. Measurements of the velocity field indicated that shock interaction, due to shocks from the injection jets, interacts with the primary jet shocks and significantly reduces the shock strength, attributing massive shock noise reduction. Validation of the experimental results was achieved with large-eddy simulation, which provided additional insight into the shock suppression due to resolution of the flowfield internal to the nozzle. Optimal injection parameters resulted in reduction of overall sound pressure level of -7 d B at the upstream and downstream angles simultaneously through a combination of shock disruption and streamwise vorticity introduction. A new mechanism of supersonic jet noise reduction and destructive interference of the shock structure in the jet is reported.
|
|
| 9. |
|
|
| 10. |
- Cuppoletti, Daniel, et al.
(författare)
-
The Role of Nozzle Contour on Supersonic Jet Thrust and Acoustics
- 2014
-
Ingår i: AIAA Journal. - : American Institute of Aeronautics and Astronautics (AIAA). - 1533-385X .- 0001-1452. ; 52:11, s. 2594-2614
-
Tidskriftsartikel (refereegranskat)abstract
- This work is an experimental and computational investigation of acoustics and performance of a biconical and splined supersonic nozzle to identify the dependencies of noise components on the nozzle design. The convergent section and throat of a biconical supersonic nozzle were optimized with a Reynolds-averaged Navier-Stokes solver to optimize thrust and minimize internal losses. Far-field acoustics and the jet flowfield were measured and studied using large-eddy simulations at design, overexpanded, and underexpanded conditions. The biconical and splined nozzles are designed to be thrust matched at fully expanded conditions. The convergent section and throat contour do not significantly affect the turbulent mixing noise or shock-associated noise at most conditions. Analysis of the jet flowfield shows differences in shock structure, although the "global" shock strength remains relatively unchanged. A comparison of measurements and computations of mean velocity and turbulence shows minor differences in the shear-layer region and near strong shocks. Momentum thrust and pressure thrust were measured and compared with computational results. The contoured throat nozzle provides equivalent thrust with a 4% lower nozzle pressure ratio at the design condition with no acoustic penalty. At equivalent nozzle pressure ratios, the contoured nozzle provides 10% higher thrust with no increase in mixing noise or shock noise.
|
|
