Passive Leg Raising Research Articles

Magnetic Cavities in the Solar Wind, Their Influence on the Bow Shock Position and Geomagnetic Activity

Magnetic Cavities in the Solar Wind, Their Influence on the Bow Shock Position and Geomagnetic Activity

Changes of cardiac output and velocity time integral in blood return at the end of renal replacement therapy predict fluid responsiveness in critically Ill patients with acute circulatory failure

ObjectivesTo observe if blood return, also defined as the blood infusion test (BIT) could predict fluid responsiveness in critically ill patients with acute circulatory failure and renal replacement therapy (RRT).MethodsThis was a single-center, prospective, diagnostic accuracy study. Before BIT, the passive leg raise test (PLRT) was performed to record the change of cardiac output (ΔCO) by pulse contour analysis, and ΔCO > = 10% was defined as the fluid responder. Meanwhile, the change in velocity time integral (ΔVTI) was recorded by ultrasound. Later, the ΔCO and ΔVTI during BIT were recorded 5–10 min after PLRT. The receiver-operating characteristic curves of ΔCO and ΔVTI of BIT were performed in predicting the fluid responder defined by PLRT.ResultsA total of 43 patients with acute circulatory failure undergoing RRT were enrolled in the present study, and 25 patients (58.1%) were recognized as responders during PLRT. According to the receiver-operating characteristic curves, the cutoff value of ΔCO was 10% and ΔVTI was 9% during BIT with the area under curve of 0.96 and 0.94, respectively.ConclusionsBIT in RRT could identify fluid responsiveness in critically ill patients with shock.Trial registrationChiCTR-DDD-17010534. Registered on 30/01/2017 (retrospective registration).

End-expiratory Occlusion Test and Mini-fluid Challenge Test for Predicting Fluid Responsiveness in Acute Circulatory Failure.

Predicting which patients with acute circulatory failure will respond to the fluid by an increase in cardiac output is a daily challenge. End-expiratory occlusion test (EEOT) and mini-fluid challenge (MFC) can be used for assessing fluid responsiveness in patients with spontaneous breathing activity, cardiac arrhythmias, low-tidal volume and/or low lung compliance. The objective of the study is to evaluate the value of EEOT and MFC-induced rise in left ventricular outflow tract (LVOT) velocity time integral (VTI) in predicting fluid responsiveness in acute circulatory failure in comparison to the passive leg-raising (PLR) test. Hundred critically ill ventilated and sedated patients with acute circulatory failure were studied. LVOT VTI was measured by transthoracic echocardiography before and after EEOT (interrupting the ventilator at end-expiration over 15 s), and before and after MFC (100 ml of Ringer lactate was infused over 1 min). The variation of LVOT VTI after EEOT and the MFC was calculated from the baseline. Sensitivity, specificity, and area under the receiver-operating characteristic (AUROC) curve of LVOT VTI after EEOT and MFC to predict fluid responsiveness were determined. After PLR, stroke volume (SV) increased by ≥12% in 49 patients, who were defined as responders and 34 patients in whom the increase in SV <12% were defined as nonresponders. A cutoff of 9.1% Change in VTI after MFC (ΔVTIMFC) predicted fluid responsiveness with an AUROC of 0.96 (P < 0.001) with sensitivity and specificity of 91.5% and 88.9%, respectively. Change in VTI after EEOT (ΔVTIEEOT) >4.3% predicted fluid responsiveness with sensitivity and specificity 89.4% and 88.9%, respectively, with an AUROC of 0.97 (P < 0.001), but in 17 patients, EEOT was not possible because triggering of the ventilator by the patient's inspiratory effort. In conclusion, in mechanically ventilated patients with acute circulatory failure Δ VTIMFC and Δ VTI EEOT accurately predicts fluid responsiveness.

Effect of Specific Verbal Instructions on the Identification of Pain Location during a Passive Straight Leg Raise Test

Effect of Specific Verbal Instructions on the Identification of Pain Location during a Passive Straight Leg Raise Test

Combination of genetic algorithm and CFD modelling to develop a new model for reliable prediction of normal shock wave in supersonic flows contributing to carbon capture

Carbon dioxide separation and capture using green and efficient methods is an important issue in studies related to climate change. The supersonic separator is one of the efficient and reliable methods that can be used to separate impurities, including carbon dioxide, from gas streams. Reliable estimation of normal shock wave position plays a vital role in the proper design and simulation of supersonic separators. Many studies have used a one-dimensional theoretical (ideal) model of a normal shock wave for the estimation of the shock position and pressure recovery, but the accuracy of the ideal model of normal shock may be insufficient in some situations, as reported in the literature. A novel approach is presented in this paper to provide new equations for normal shock waves by the combination of computational fluid dynamics (CFD) and genetic algorithm. The comparison of the proposed model with several experimental data and the ideal model of a normal shock wave indicate that the present model provides more accurate predictions than the traditional model of a normal shock wave. The present model showed an average absolute relative deviation (AARD) of 1.80%, which is about six times less than AARD of the ideal model, indicating the robustness of the proposed model. Consequently, the present model can be employed as an accurate and efficient tool for the prediction of shock position and design of converging–diverging nozzles.

A Unified Asymptotic Theory of Supersonic, Transonic, and Hypersonic Far Fields

The problems of steady, inviscid, isentropic, irrotational supersonic plane flow passing a body with a small thickness ratio was solved by the linearized theory, which is a first approximation at and near the surface but fails at far fields from the body. Such a problem with far fields was solved by W.D. Hayes’ “pseudo-transonic” nonlinear theory in 1954. This far field small disturbance theory is reexamined in this study first by using asymptotic expansion theory. A systematic approach is adopted to obtain the nonlinear Burgers’ equation for supersonic far fields. We also use the similarity method to solve this boundary value problem (BVP) of the inviscid Burgers’ equation and obtain the nonlinear flow patterns, including the jump condition for the shock wave. Secondly, the transonic and hypersonic far field equations were obtained from the supersonic Burgers’ equation by stretching the coordinate in the y direction and considering an expansion of the freestream Mach number in terms of the transonic and hypersonic similarity parameters. The mathematical structures of the far fields of the supersonic, transonic, and hypersonic flows are unified to be the same. The similar far field flow patterns including the shock positions of a parabolic airfoil for the supersonic, transonic, and hypersonic flow regimes are exemplified and discussed.

Nonlinear structural stability and linear dynamic instability of transonic steady-states to hydrodynamic model for semiconductors

For unipolar hydrodynamic model of semiconductor device represented by Euler-Poisson equations, when the doping profile is supersonic, and the boundary data are in subsonic region and supersonic region separately, the system possesses the shock transonic steady-states and the smooth transonic steady-states. In this paper we study the nonlinear structural stability and the linear dynamic instability of these steady transonic solutions. For any relaxation time: 0<τ≤+∞, by means of elaborate singularity analysis, we first investigate the structural stability of the C1-smooth transonic steady-states, once the perturbations of the initial data and the doping profiles are small enough. We note that, when the C1-smooth transonic steady-states pass through the sonic line, they produce singularities for the system, and cause some essential difficulty in the proof of structural stability. Moreover, when the relaxation time is large enough τ≫1, under the condition that the electric field is positive at the shock location, we prove that the transonic shock steady-states are structurally stable with respect to small perturbations of the supersonic doping profile. Furthermore, we show the linearly dynamic instability for these transonic shock steady-states provided that the electric field is suitable negative. The proofs for the structural stability results are based on singularity analysis, a monotonicity argument on the shock position and the downstream density, and the stability analysis of supersonic and subsonic solutions. The linear dynamic instability of the steady transonic shock for Euler-Poisson equations can be transformed to the ill-posedness of a free boundary problem for the Klein-Gordon equation. By using a nontrivial transformation and the shooting method, we prove that the linearized problem has a transonic shock solution with exponential growths. These results enrich and develop the existing studies.

Effect of Mach Number and Pitching Eigenfrequency on Transonic Buffet Onset

The transonic flow around an elastically suspended supercritical airfoil was experimentally investigated in order to enhance knowledge of buffet boundary dependencies and the corresponding self-excited fluid–structure interaction (buffeting). For that purpose, an experimental setup was designed, manufactured, and integrated in the Trisonic Wind Tunnel Munich. The design consisted of a rigid, two-dimensional, supercritical airfoil (OAT15A) with optional pitching degree of freedom and variable torsional spring stiffness. High-speed background-oriented schlieren measurements were used to observe the shock with its dynamics, while a high-speed stereo camera setup for correlation-based deformation measurements was implemented to track the dynamics of the structural motion. Pre-buffet and buffet flows were analyzed by a continuous increase of the angle of attack. The detailed observation of the shock position with increasing angle of attack exhibited a clear effect of Mach number and pitch eigenfrequency on the buffet phenomenon. The corresponding onset boundary clearly shifted into the “pre-buffet” regime given specific structural settings. Furthermore, the resulting fluid–structure interaction of shock and coupled pitch–heave motion showed characteristics of structural frequency lock-in for the pitch-to-buffet frequency ratios of 1.2 and the mode veering region for ratios of 1 and 0.9, indicating the transition region from fluid mode flutter to structural mode flutter.

Calibration of the k-ω shear stress transport turbulence model for shock wave boundary layer interaction in a SERN using machine learning

The Single Expansion Ramp Nozzle, which is called SERN, is commonly used in supersonic and hypersonic aircraft, taking into account the design of integrated aircraft/propulsion systems/nozzles. Under the conditions of low Mach number and low nozzle pressure ratio, the flow in this device became severely over-expanded, internal resistance was clearly enhanced, and the quality and performance of the flow deteriorated sharply. In general, the exact prediction of shock wave structure and its interaction with the boundary layer in operating conditions plays an important role in the design of the protective structures. To this end, this paper uses machine learning techniques to calibrate the constant coefficient of the k-ω SST turbulence model. Furthermore, recognizing the effective factors in the performance reduction of the SERNs in different working conditions can be very helpful in optimizing them. Therefore, the second aim of this work is to investigate the effects of the main working parameters on the behavior of the supersonic flow of a SERN. It was shown that using the calibrated k-ω SST turbulence model improved the accuracy of computations by 4.5% when compared to using the model with its default constant coefficients. After that, the effects of inlet temperature on the flow behavior in the SERN have been studied. The results showed that The shock position shifts by 0.33% away from the throat and 0.17% closer to the SERN center when the inlet flow temperature is raised from 250 to 325 K.

Analysis of stagger effects on Busemann supersonic biplane airfoil in shock tube tests by point diffraction interferometer method

The Busemann biplane concept is proposed for low-boom low-drag supersonic aircraft. Studies on the supersonic biplane have been focused on supersonic flow, whereas the understanding of transonic aerodynamic characteristics is essential for aircraft design. Significantly, the complicated flow field with a shock and boundary layer interaction between Busemann biplane elements in transonic flow remains unclear. In the present study, the transonic aerodynamic characteristics of the two-dimensional Busemann biplane are investigated by shock tube tests and numerical simulations, focusing on the flow field between the biplane elements. In addition, the stagger effects, which change the relative position of the lower and upper elements in the freestream direction to avoid the choked flow between the biplane elements, are also analyzed. A shock tube system creates a test flow at Mach numbers of 0.6 to 0.8, and the Reynolds number is set at 2.85 × 105. The Point Diffraction Interferometer (PDI) method is applied to determine the density distribution around the model and the pressure coefficient on the surfaces of the biplane elements. Symmetrical density distribution is confirmed in the Busemann biplane (the baseline model, or the biplane with no stagger). A normal shock wave is generated between the biplane elements. When the Mach number increases, the normal shock wave moves downstream. The normal shock position is quantitatively stable with small fluctuation amplitudes. The fringes are strongly curved near the surfaces of the biplane elements due to the flow separation near the airfoil surfaces. When the Mach number increases, the separation area increases. When the Mach number increases, the peak value of the pressure coefficient on the surfaces of the biplane elements increases. On the other hand, the normal shock wave between the biplane elements is eliminated in the staggered models. The changes in density distribution between the biplane elements are minor compared to the case of the baseline model, which indicates that the stagger reduces the choked flow between the biplane elements. The peak value of the pressure coefficient on the wing surface increases when the stagger value increases. The stagger effects on reducing the total drag coefficient of the biplane models are confirmed.

Changes in carotid corrected flow time in guiding fluid resuscitation in septic patients

Introduction Accurate estimation of intravascular volume status is important in the resuscitation of patients in ICUs. Although intensive fluid therapy in patients with life-threatening volume depletion can prevent death and end-organ damage, volume overload is known to result in increased mortality, morbidity, and duration of hospital stay. Ultrasonography has become a common diagnostic choice in assessment of fluid status in septic patients. This method is noninvasive, easy to learn, and provides real-time assessment at the patient’s bedside. Various ultrasound modalities have been developed to provide accurate and minimally invasive assessment of volume status. In this regard, one of the most promising methods is the evaluation of the blood flow velocity waveform in the descending thoracic aorta via a nonimaging Doppler probe. This modality is based on calculating the systolic flow time with cycle time correction [corrected flow time (FTc)]. FTc is known to be directly associated with volume status. FTc measurement in carotid artery is a completely noninvasive and much more feasible approach. Aim To compare the use of ultrasonography in the measurement of the changes in carotid FTc with echocardiography in the assessment of changes in heart dynamics to assess changes in volume status before and after passive leg raising (PLR) in septic patients. Patients and methods A total of 40 septic patients, including 18 (45.5%) patients as fluid responders and 22 (54.5%) patients as nonfluid responders, were included. Increased FTc by 7 ms, as well as 10% increase in stroke volume was considered to be fluid responsive. Results Our study results showed that 45.5% (n=18) of study population were fluid responders. The PLR test could assess fluid responsiveness with a specificity of 100% and sensitivity of 95% at a cutoff of 10.6% change in CO to predict fluid responsiveness. The study showed a statistically significant moderate positive correlation between CCA FTc and the percent of change in CO measured by echocardiography. An agreement analysis was formed. We concluded that there was a strong relation between change in carotid corrected blood flow and change in COP before and after PLR, with P value less than 0.001. Therefore, we can use this parameter to predict fluid responsiveness after PLR. Conclusions Carotid artery blood flow is a promising noninvasive and easy-to-perform tool for the evaluation of fluid responsiveness in critically ill septic patients. The PLR maneuver has demonstrated excellent performance for predicting fluid responsiveness. It is simple to perform but requires a reliable system of carotid corrected blood flow (COP) monitoring able to quantify the short-term changes.

The 3D X-Ray Ejecta Structure of Tycho's Supernova Remnant

We present our velocity measurements of 59 clumpy, metal-rich ejecta knots in the supernova remnant (SNR) of SN 1572 (Tycho). We use our 450 ks Chandra High Energy Transmission Grating Spectrometer observation to measure the Doppler shift of the He-like Si Kα line-center wavelength emitted from these knots to find their line-of-sight (radial) velocities (v r ). We find v r up to ∼5500 km s−1, with roughly consistent speeds between blueshifted and redshifted ejecta knots. We also measure the proper motions (PMs) for our sample based on archival Chandra Advanced CCD Imaging Spectrometer data taken from 2003, 2009, and 2015. We estimate PMs up to 0.″35 yr−1, which corresponds to a transverse velocity of about 5800 km s−1 for the distance of 3.5 kpc to Tycho. Our v r and transverse velocity measurements imply space velocities of ∼1900–6000 km s−1 for the ejecta knots in Tycho. We estimate a new expansion center of R.A.(J2000) = 00h25m18s.725 ± 1.ˢ157 and decl.(J2000) = +64°08′02.″5 ± 11.″2 from our PM measurements, consistent to within ∼13″ of the geometric center. The distribution of space velocities throughout the remnant suggests that the southeast quadrant generally expands faster than the rest of the SNR. We find that blueshifted knots are projected more in the northern shell, while redshifted knots are more in the southern shell. The previously estimated reverse shock position is consistent with most of our estimated ejecta distribution; however, some ejecta show deviations from the 1D picture of the reverse shock.

Numerical modeling of imposed magnetohydrodynamic effects in hypersonic flows

Weakly ionized plasmas, formed in high enthalpy hypersonic flows, can be actively manipulated via imposed magnetic fields—a concept termed magnetohydrodynamic (MHD) flow control. Imposed MHD effects, within flows that exhibit multiple shock interactions, are consequential for emerging aerospace technologies, including the possibility of replacing mechanical control surfaces with magnetic actuation. However, numerical modeling of this flow type remains challenging due to the sensitivity of feature formation and the real gas modeling of weakly ionized, electrically conductive, air plasma. In this work, numerical simulation capabilities have been developed for the study of MHD affected, hypersonic flows, around two-dimensional axisymmetric non-simple geometries. The validated numerical methodology, combined with an advanced 19 species equation of state for air plasma, permits the realistic and efficient simulation of air plasmas in the equilibrium regime. Quantitative agreement is achieved between simulation and experiment for a Mach 5.6 double cone geometry with applied magnetic field. In the context of the magnetic actuation concept, numerical studies are conducted for varied conical surface angle and magnetic field configuration. For simple geometries with an elemental shock type, the MHD enhancement effect produces a self-similar shock structure. This paper demonstrates how, for hypersonic flows with complex shock interactions, the MHD affected flow is not only augmented in terms of shock position but may exhibit topological adaptations in the fundamental flow structure. A classification system is introduced for the emergent flow topologies identified in this work. Fluid-magnetic interactions are explored and explained in terms of the coupled mechanisms leading to (1) differences in magnitude of MHD enhancement effect and (2) structural adaptations of the flow topology. The applied numerical studies examine why increased conical surface angle does not amplify the MHD enhancement effect as expected from the base flow conditions, and the mechanisms by which the magnetic field configuration influences the MHD augmented shock structure. Most critically, classes of conditions are identified that produce topological equivalence between the magnetic interaction effects and a generalized mechanical control surface.

Refilling and preload dependence failed to predict cardiac index decrease during fluid removal with continuous renal replacement therapy.

Fluid removal can reduce the burden of fluid overload after initial resuscitation. According to the Frank-Starling model, iatrogenic hypovolemia should induce a decrease in cardiac index. We hypothesized that inadequate refilling detected by haemoconcentration during fluid removal or an increase in cardiac index (CI) during passive leg raising (PLR) could predict CI decrease during mechanical fluid removal with continuous renal replacement therapy (CRRT). We conducted a single-centre prospective diagnostic accuracy study. The primary objective was to investigate the diagnostic performance of plasma protein concentration variations in detecting a CI decrease ≥ 12% during mechanical fluid removal. Secondary objective was to assess other predictive factors of CI change. The attending physician prescribed a fluid removal challenge consisting of a mechanical fluid removal challenge of 500mL for one hour. Plasma protein concentration, haemoglobin level, PLR and transpulmonary thermodilution were done before and after the fluid removal challenge. We included 69 adult patients between December 2016 and April 2020. Sixteen patients had a significant CI decrease (23% [95% CI 14-35]). Haemoconcentration and PLR before fluid removal challenge or CI trending failed to predict CI decrease. Haemoconcentration variables, preload dependence status and CI trending failed to predict CI decrease during fluid removal challenge.

Dynamic changes of pulse pressure but not of pulse pressure variation during passive leg raising predict preload responsiveness in critically ill patients with spontaneous breathing activity

PurposeTo evaluate whether the changes in arterial pulse pressure (PP) and/or pulse pressure variation (PPV) during passive leg raising (PLR) can be used to evaluate preload responsiveness in patients with spontaneous breathing activity. Materials and methodsPatients ventilated with pressure support mode or totally spontaneously breathing were prospectively included. The values of PP and PPV were recorded before and at the end of PLR. The changes in cardiac index (CI) or the velocity-time integral (VTI) of the left ventricular outflow tract during PLR were tracked by the pulse contour analysis or transthoracic echocardiography. Patients exhibiting an increase in CI ≥ 10% or VTI ≥ 12% during PLR were defined as preload responders. ResultsAmong 33 patients included, 28 (80%) received norepinephrine and 14 were preload responders. The increase in PP > 2 mmHg in absolute value (4% in percentage) during PLR (PLRPP) predicted preload responsiveness with an area under the receiver operating characteristic (AUROC) of 0.76 ± 0.09 (p = 0.003 vs. AUROC of 0.5). The changes in PPV during PLR, however, failed to predict preload responsiveness (p = 0.82 vs. AUROC of 0.5). ConclusionIn patients with full spontaneous breathing activity, PLR-induced changes in PP had a fair ability to assess preload responsiveness even when norepinephrine was administered.Registration number:ClinicalTrials.gov (NCT04369027).

Inferring the temperature profile of the radiative shock in the COAX experiment with shock radiography, Dante, and spectral temperature diagnostics

Predicting and modeling the behavior of experiments with radiation waves propagating through low-density foams require a detailed quantification of the numerous uncertainties present. In regimes where a prominent radiative shock is produced, key dynamical features include the shock position, temperature, and curvature and the spatial distribution and temperature of the corresponding supersonic radiation wave. The COAX experimental platform is designed to constrain numerical models of such a radiative shock propagating through a low-density foam by employing radiography for spatial and shock information, Dante for characterizing the x-ray flux from the indirectly driven target, and a novel spectral diagnostic designed to probe the temperature profile of the wave. In this work, we model COAX with parameterized 2D simulations and a Hohlraum-laser modeling package to study uncertainties in diagnosing the experiment. The inferred temperature profile of the COAX radiation transport experiments has been shown to differ from simulations more than expected from drive uncertainties that have been constrained by simultaneous soft x-ray flux and radiography measurements.

A High-Order Residual-Based Viscosity Finite Element Method for the Ideal MHD Equations

We present a high order, robust, and stable shock-capturing technique for finite element approximations of ideal MHD. The method uses continuous Lagrange polynomials in space and explicit Runge-Kutta schemes in time. The shock-capturing term is based on the residual of MHD which tracks the shock and discontinuity positions, and adds sufficient amount of viscosity to stabilize them. The method is tested up to third order polynomial spaces and an expected fourth-order convergence rate is obtained for smooth problems. Several discontinuous benchmarks such as Orszag-Tang, MHD rotor, Brio-Wu problems are solved in one, two, and three spacial dimensions. Sharp shocks and discontinuity resolutions are obtained.

Passive Leg Raise Stress Echocardiography in Severe Paradoxical Low-Flow, Low-Gradient Aortic Stenosis

Dobutamine stress echocardiography is used to increase transvalvular flow in patients with low-flow, low-gradient aortic stenosis (AS). Dobutamine fails to increase the stroke volume index (SVI) in one third of patients. The aim of this study was to test whether passive leg raise (PLR) added to dobutamine could increase SVI and transvalvular flow in patients with severe paradoxical low-flow, low-gradient AS. Forty-five patients with apparent severe low-flow, low-gradient AS on the basis of traditional measurements were included. Twenty-five were categorized as belonging to the paradox group (left ventricular ejection fraction [EF]≥50%) and 20 to the low EF group (left ventricular EF&lt;50% or "classical" low-flow, low-gradient AS) for comparison. A four-step stress echocardiographic examination was performed: resting conditions (rest), PLR alone (PLR), maximal dobutamine infusion rate (Dmax), and a combination of Dmax and PLR (Dmax+PLR). Aortic valve area, SVI, and mean transvalvular flow were calculated using both the velocity-time integral (VTI) of left ventricular outflow tract and the Simpson method. Changes compared with rest and between the stress maneuvers were analyzed. In the paradox group, compared with rest, left ventricular end-diastolic volume was significantly decreased with Dmax but was completely restored with Dmax+PLR (rest vs Dmax vs Dmax+PLR: 61±15 vs 49±18mL [P&lt;.001] vs 61±18mL [P= NS]). The smallest increase in SVI in the paradox group was observed during Dmax (PLR vs Dmax vs Dmax+PLR: VTI, 38±4mL/m² [P&lt;.001] vs 36±7mL/m² [P=.019] vs 41±7mL/m² [P&lt;.001]; Simpson, 28±6mL/m² [P&lt;.001], 21±7mL/m² [P= NS], 27±7mL/m² [P= NS]). Compared with Dmax, Dmax+PLR was able to achieve a higher SVI (VTI, 36±7 vs 41±7mL/m² [P&lt;.001]; Simpson, 21±7 vs 27±7mL/m² [P&lt;.001]) and transvalvular flow with the Simpson method only (179±56 vs 219±56mL/sec, P&lt;.001), as well as a higher mean gradient (34±10 vs 39±12mm Hg, P=.003) and AVA with the Simpson method (0.64±0.21 vs 0.73±0.21cm², P=.026). In the low EF group, only SVI VTI (31±8 vs 35±7mL/m², P=.034) and mean gradient (29±12 vs 34±14mm Hg, P=.003) were higher with Dmax+PLR. The proportion of patients with SVI VTI ≥ 35mL/m² and increases of SVI VTI of &gt;20% compared with rest was highest with Dmax+PLR in both groups. Dobutamine decreases preload in paradoxical low-flow, low-gradient AS. Adding PLR counteracts this effect, resulting in increased SVI and flow (in one method). The combined stress maneuver allowed reclassification of some patients from severe to moderate AS and may therefore be useful in selected cases in this population in which severity is uncertain.

PIV investigations of shock-buffet dynamics on a supercritical airfoil with a pitching degree of freedom

The interaction between the transonic flow around a spring mounted OAT15A airfoil model and the resulting pitching motion of the model was investigated with the goal of understanding the dynamics of the occurring phenomena. The experiments were performed at free-stream Mach numbers from 0.70 to 0.77 and at a Reynolds number of Rec ≈ 3 × 10^6. The dominant structural frequency of the airfoil’s pitch motion was adjusted to be in the range of the natural buffet frequency of the flow with inhibited pitching motion of the model. The variation of the Mach number allowed for an investigation in the pre-buffet, buffet and post-buffet regime. A periodic pitch motion with an amplitude of the angle of attack of up to ±1.17° was observed for buffeting flow conditions while it was significantly less in pre-buffet and post-buffet conditions. Velocity field measurements by means of high repetition rate particle image velocimetry (PIV) were used to capture the motion of the shock and to determine the state of the boundary layer flow for the different phases of the model motion. For the Mach number range Ma = 0.72 − 0.75 the change of the angle of attack and the shock position correlate strongly with each other. From the measurements, the delay of both quantities during the coupled motion could be determined.

Experimental Investigation of Fluid-Structure Interaction in Mach 2 Flow Using Simultaneous High-Speed PIV and DIC

The fluid-structure interaction (FSI) of a compliant panel under a compression-ramp-induced shock-wave/boundary-layer interaction (SBLI) has been studied in Mach 2 flow. Simultaneous high-speed measurements of the velocity field and the panel displacement were conducted using 50 kHz particle image velocimetry (PIV) and 5 kHz stereoscopic digital image correlation (DIC). The mean effect of the panel displacement has been evaluated by monitoring the change in velocity profiles along the streamwise direction (x), upstream of the separated flow region. Streamwise (u) velocity near the panel surface has been shown to change its magnitude in response to the wall shape. Furthermore, the strong cross-correlation between fluctuations of the wall-normal panel displacement and the transverse (v) velocity can be explained by the flow remaining tangent to the wall surface as the panel deforms. This latter result is consistent with the panel motion being sufficiently low frequency compared to flow convective time scales that the flow is quasi-steady. In addition, assessment of the correlation between the separation shock position and panel displacement seems to suggest that when the panel is bulged down (concave up) at the downstream end of the panel, a larger separated flow is generated and the shock moves upstream. This observation remains speculative, but is consistent with the flow undergoing greater compression for the bulged down case.