Wall Static Pressure Research Articles

Experimental study of coherent wall-pressure fluctuations associated with the turbulent near wake of a cylinder

The objective of this work is to present a coherent detection method to determine relationships between pressure fluctuations and wake velocity in the case of the flow past a cylinder in a turbulent regime. We report experimental results and pressure–velocity statistics measured simultaneously on the surface boundary layer and the near wake in the range of Reynolds numbers (2×103<Re<3.5×104). The novelty of the analysis lies in the application of a coherent mean method to determine conditioned wall pressure statistics to velocity events observed in the turbulent cylinder wake. The method allows one to associate wake turbulent events with a corresponding wall-pressure signal profile on the cylinder surface performing discrete angular measurements with a minimum number of pressure sensors. Simultaneous measurements of both time series of wake velocity and wall pressure allow us to characterize the mutual influence of hydrodynamic perturbations from the boundary layer surface pressure with the near wake velocity fluctuations. Large scale turbulent vortex shedding is well correlated with surface pressure fluctuations as expected in the low frequency range. Near wake velocity signals were used as timing signals to determine the coherent influence of a representative velocity pattern on the statistical properties of wall pressure fluctuations. The dynamics of low-frequency large-scale structures is consistent with the presence of counter-rotating vortices and is well correlated with a great part of the pressure fluctuations of the boundary layer. Conditional statistics using the velocity pattern obtained from the coherent averaging method provided the instantaneous pressure fluctuating profile associated with the large-scale vortex shedding cycle, thus, enabling a coherent estimation of the fluctuating lift and drag forces. Conditional statistics on wake velocity are well influenced by the phase of the vortex life-cycle.

Simultaneous measurement of pressure and temperature in a supersonic ejector using FBG sensors

In this work, we have demonstrated the use of fiber Bragg grating (FBG) sensors for simultaneous measurement of wall static pressure and temperature in a supersonic ejector. Supersonic ejectors are ground-based high-speed aerodynamic test facilities characterized by harsh conditions, such as high pressure and temperature gradients. An FBG-based sensor setup was developed consisting of a pressure measuring bare FBG and a specially designed pressure-insensitive FBG temperature probe that can be mounted on the wall of the supersonic ejector. The FBG temperature probe was used for temperature measurement as well as temperature compensation of the pressure measuring FBG sensor. Wall static pressure measurements in the supersonic ejector were carried out at different tank pressures and Mach number flows. The FBG pressure measurements were validated with those of standard piezoresistive-based sensor measurements. Both responses were found to match closely, with FBG sensors having a faster response time and higher pressure resolution. Fluid structure interaction simulation was carried out in Comsol Multiphysics to understand the interaction of high-speed turbulent flow with FBG sensor. The FBG strain profile due to flow-induced stress and its dependence on flow pressure was studied. A detailed analysis of the effect of preceding fiber length on FBG pressure measurement was carried out. FBG sensors, due to their miniature size, ability to withstand harsh environments and multi-parameter sensing capability, can be used in ground-based aerodynamic test facilities with minimal intrusion into the flow.

Heat transfer characteristics of jet impingement onto the concave surface of a cone

ABSTRACT Heat transfer coefficient measurements for jet impingement onto the concave surface of a cone with apex angles equal to 30° and 70° are reported in this study. Static pressure measurements along the cone surface are also reported which aid in explaining the results from the heat transfer measurements. The conical geometry finds application for the heating of aircraft gas turbine engine nose bullet region which could experience ice formation whenever aircraft operates at higher altitudes. The concave surface of the cone is heated by impinging hot air tapped from the compressor. The heat transfer coefficients, which are significantly different compared to flat surface impingement, and are scarcely available, are reported in this study. The influence of the jet axis coincident with the cone axis and impinging into apex region was studied first. The methodology where a thin stainless-steel foil is heated with a known heat flux by passing electric current through it and then measuring the detailed surface temperature using an infrared thermal camera, was used to compute the wall Nusselt distribution. The Nusselt number variation is presented as a function of nondimensional apex to nozzle spacing (L/D) and the nondimensional axis displacement (O/D). Three different diameter (D equal to 10 mm,14 mm and 20 mm) pipes were used for the concentric impingement case and the Nusselt number distribution was observed not depend on the injection diameter. The jet Reynolds number was varied between 25000 and 82000. The peak Nusselt number values are similar to those for flat plate impingement and do not occur at the cone apex, but at a nondimensional distance between 3.2 and 3.9 for 4.25 < L/D < 10.25 for the 30° cone. The peak Nusselt number values increase by almost 30% with decrease in the L/D from 10.2 to 3.0. Wall static pressure measurements indicated that the peak Nusselt number values occur in regions where the interaction between the incoming and outgoing streams is strongest – these regions occur at distances downstream from the stagnation region toward cone exit. The peak heat transfer coefficient location could not be obtained for the 70° cone, but the measured maximum values are higher by 30–50% compared to those for the 30° case. The jet is able to penetrate further toward the apex of the cone for 70° cone compared to 30° cone shifting the peak heat transfer locations closer to the apex for larger apex angle case. There is insignificant influence of jet diameter on Nusselt number variation for the three diameter values investigated in this study. The influence of displacing the jet axis by a distance equal to half the jet diameter in a direction perpendicular to the cone axis was also studied but detailed measurements were possible only for the 30° cone. Two semi-circular regions, one close to the impingement tube and the other away from the tube, displaying similar heat transfer coefficient behavior were observed. A peak in the Nusselt number occurs in each semi-circular region and the magnitude of the peaks are nearly same and they lie on either side of the peak location observed for the concentric impingement case when the flow geometric parameters are similar for the two cases. The measurements for the 70° cone exhibited all features of the 30° cone but the maximum values were higher by nearly 40% for this case.

Enhancement of blowout limit in a Mach 2.92 cavity-based scramjet combustor by a gliding arc discharge

Plasma-assisted combustion (PAC) has shown excellent performance in the ignition and combustion enhancement of scramjet combustors. A multi-channel gliding arc (MCGA) plasma placed on the sidewall surface of a scramjet combustor was employed to enhance combustion near the flame blowout limit (BL) in a C2H4-fueled and cavity-based model scramjet combustor. Wall static pressure measurements, simultaneous 10 kHz CH* chemiluminescence imaging from the top and side views, optical emission spectroscopy, and discharge waveform measurements were used to elucidate the combustion physics throughout the PAC events. For the current cavity configuration and fueling condition, a general estimate of the flame BL in a rich-fuel environment was provided, in which a fuel flow rate (FFR) was 7.5 g/s. Once the FFR was exceeded, the flame was unstable and blown out, whereas the MCGA plasma demonstrated an excellent flame stabilization ability. The flame BL of the scramjet combustor in the presence of the MCGA plasma has an increase of ∼29%. Two PAC processes, including enhancement mode and re-ignition mode, were distinguished to play a vital role in extending the flame BL. The two PAC processes showed that the spark-type discharge generated by the MCGA could ignite the local fuel-rich mixture and increase the flame BL. The local ignition is dominated by the continuous accumulation of the massive flame kernels with the local fuel-rich mixture, as well as more heat and species exchanges.

Effect of Flap Deflection on Single-Expansion-Ramp Nozzles Performance at Different Pressure Ratios

Experiments have been carried out to investigate the various performance characteristics of single-expansion-ramp nozzle with straight and deflected flap conditions for two different flap lengths. Experiments were performed at different nozzle pressure ratios (NPRs) ranging between 1.5 and 9. Wall static pressure measurements were made to estimate the various performance parameters, such as surface axial force, normal force, overall axial force, pitching moment, and thrust vectoring angles. Schlieren flow visualization technique was adopted to understand the internal shock-induced flow separation and shock patterns inside the nozzle under various NPRs. Flap deflection and NPR control the shock location through area variation, and thus the pressure distribution on the walls. At low NPRs, the internal drag force generated by deflected flap is lesser than that by straight flap, whereas at high NPRs the straight flap produces significantly higher surface axial thrust over the deflected flap. Behavior of normal force and pitching moment was affected by two factors: flap length and shock location. The straight flap shows significantly higher normal force than deflected flap. Hence, the thrust vectoring was better for straight flap nozzles compared to deflected flap nozzles, over the full range of NPRs tested. On the other hand, the gross thrust force performance is better for the straight flap for low NPRs and for the deflected flap for high NPRs. Overall, at high speeds, longer deflected flap appears to give better performance considering all the parameters, but will lead to heavier nozzle.

Characterizing the respiratory-induced mechanical stimulation at the maxillary sinus floor following sinus augmentation by computational fluid dynamics

Background: The relationship between maxillary sinus pneumatization and respiratory-induced fluid mechanics remains unclear. The purpose of this study was to simulate and measure the respiratory-induced mechanical stimulation at the sinus floor under different respiratory conditions and to investigate its potential effect on the elevated sinus following sinus-lifting procedures. Methods: The nasal airway together with the bilateral maxillary sinuses of the selected patient was segmented and digitally modeled from a computed tomographic image. The sinus floors of the models were elevated by simulated sinus augmentations using computer-aided design. The numerical simulations of sinus fluid motion under different respiratory conditions were performed using a computational fluid dynamics (CFD) algorithm. Sinus wall shear stress and static pressure on the pre-surgical and altered sinus floors were examined and quantitatively compared. Results: Streamlines with minimum airflow velocity were visualized in the sinus. The sinus floor pressure and the wall shear stress increased with the elevated inlet flow rate, but the magnitude of these mechanical stimulations remained at a negligible level. The surgical technique and elevated height had no significant influence on the wall pressure and the fluid mechanics. Conclusion: This study shows that respiratory-induced mechanical stimulation in the sinus floor is negligible before and after sinus augmentation.

Unsteady Interaction Mechanisms of Axial-Slot Casing Treatment With Tip Region Flow in a Highly-Loaded Mixed-Flow Compressor

Abstract The influences of axial-slot casing treatment (ASCT) on the performance and unsteady tip region flow are experimentally and numerically investigated in a highly-loaded mixed-flow compressor. The total pressure ratio, stall margin, and efficiency of the compressor are improved with ASCT. Static wall pressure was measured using unsteady pressure taps installed on the casing to identify the stall inception and resolve the tip region flow. The compressor stalls through spike-stall inception with the spillage of tip leakage flow (TLF). FFT analysis of dynamic pressure data shows that unsteady tip clearance flow (TCF) characterized by a frequency band of 0.4–0.6 blade passing frequency exists for both cases with and without ASCT. The addition of ASCT alleviates fluctuating amplitude of TCF in the blade passage but enhances oscillating strength of the main flow located upstream of blade leading-edge. Time-averaged solutions of unsteady simulations indicate that ASCT suppresses the spillage of TLF through suction and injection effects. However, flow separation located downstream of slots is enlarged by ASCT, which is attributed to the increased blade tip load. To reveal the underlying mechanisms, the tip flow field was further studied at various time instants. The fluids with high enthalpy are injected from slots and then divided into two parts by the rotor blade. One part of the fluids attaches on blade pressure side causing the local high static pressure spot, which leads to the increment of pressure loading at blade tip. The other part interacts with TLF periodically, thus pushing it into passage and delaying rotating stall.

Computation of viscous flow characteristics of a supersonic intake using eddy-viscosity turbulence models

Results of numerical investigation of flow and performance characteristics of a rectangular supersonic intake experimentally tested at Mach number of 4.03 are presented. The viscous flowfield has been obtained by solving Favre averaged Navier–Stokes equations with two eddy viscosity turbulence models, namely, Mentor’s baseline (BSL) k-ω and shear stress transport (SST) k-ω models. In addition, the effect of wall temperature conditions as well as several configurations of cowl and isolator are simulated to validate the computational methodology. The analysis has been carried out at a freestream Mach number of 4.03 and 0° angle-of-attack, corresponding to a unit Reynolds number of about 6.9×107 m−1. The predicted boundary-layer and the wall static pressure distribution using SST k-ω model shows better agreement with the experimental data compared to the BSL model and hence indicates superior capability to capture the onset and the amount of flow separation due to SWBLIs. Moreover, the terminal shock structure at different operating modes as well as the “unstart because of SWBLIs” is predicted quite accurately using the model. The wall temperature condition is found to have a strong effect on the amount of flow separation at the cowl and the subsequent interactions. Further, the results show that the sidewalls have a marginal effect on the centerline wall static pressure, though a three-dimensional flowfield with two stream-wise vortices are observed close to it as a result of the swept SWBLIs of the cowl shock with the sidewall boundary-layer leading to a higher loss in performance.

Numerical investigations on the influence of double ramps in a strut based scramjet combustor

This numerical study addresses the performance of double ramps in a strut injection scramjet combustor. Reynolds Averaged Navier Stokes (RANS) equations with the Shear Stress Transport SST k-[Formula: see text] turbulence model are used for numerical analysis. The dual ramps are located symmetrically at the top and bottom wall of a scramjet combustor downstream of the strut injector. The influence of the location of ramps in the scramjet combustor is analyzed based on the key parameters such as shock waves, static pressures, and temperature distribution across the combustor, which are verified with available DLR scramjet experimental data that show similar acceptable values within the range. Simulation is extended for the investigation of other configurations. The performance of the scramjet configurations has been analyzed using the variables such as shock patterns, Mach number contours, wall static pressures, mass fractions of the reactants and products, combustion efficiency, and stagnation pressure loss of combustor. Numerical shadowgraph indicates that numerous shock reflections occur for the dual ramp cases that decelerate the combustor’s flow downstream. In addition, the recirculation regions are created for the dual ramp cases, which help in anchoring the flame. The static pressure distributions show the variation of peaks due to shock patterns and their interactions. The combustion efficiency increases as the ramps are positioned downstream of the strut injector. The mass fractions of reactants and products indicate complete combustion of the hydrogen issued from the combustor in the vicinity of the cavities. The total pressure loss for the DLR strut model is comparatively lower than dual ramp cases due to the multiple shocks from the ramp decelerating the flow downstream of the combustor.

Ram to scram mode transition in a simulated flight acceleration

Thrust abruption due to mode transition could be catastrophic for hypersonic vehicles. To understand the underlying physics, a direct-connected transient Flight Trajectory Simulator 1 (FTS-1) has been developed at the Institute of Mechanics, Chinese Academy of Sciences. This facility uses advanced high-speed measuring techniques, including thrust and static wall pressure measurement, and Schlieren and hydrocarbon radical chemiluminescence (CH* chemiluminescence) imaging. Kerosene-fueled dual-mode combustor experiments are designed in an acceleration trajectory. The basic operation parameters and the flame and flow dynamics of the acceleration induced mode transition are evaluated. Discussions are given on the triggering mechanisms responsible for the ram to scram mode transition in a simulated flight acceleration.

A passive loss reduction method of square-to-square sudden expansions

Mechanical ventilation in edifices is a key contributor to the significant energy consumption of the building industry. Therefore, rational energy management in ventilation systems plays a major role in promoting the energy efficiency of buildings. The present investigation aims at the moderation of fluid mechanical losses – thus the overall energy expenditure of ventilation ducts – of a symmetric square-to-square sudden expansion, frequently found in ventilation systems. A simple passive flow control method with moderate manufacturing costs was proposed, and its efficiency was examined experimentally. The loss reducing appendages were short rectangular sheets of adjustable angle, so-called miniflaps, placed at the step edge of the sudden expansion. Flow characteristics were examined for a fully developed turbulent flow at the inlet of the sudden expansion, for an area ratio of 2.78 and a miniflap length of 0.4 step heights. The investigated Reynolds number range was Re = (0.37–1.82)·105, being representative of ventilation systems. Fluid mechanical losses were determined from wall static pressure measurements. Velocity and turbulence intensity fields were mapped with the help of a laser Doppler anemometer. The miniflaps successfully reduced the loss coefficient of the sudden expansion through quick uniformization of the velocity profile. The loss coefficient was reduced by an absolute value of 0.07–0.11, i.e. a relative value of 14%–25%, for an optimum miniflap angle of α = 12° ± 1°. Reattachment length was also reduced from 11 to 7 step heights in the wall-normal and from 14 to 13 step heights in the diagonal plane. The loss reducing capacity together with the compactness of the miniflaps and the overall reduction of the affected zone downstream of the element presents a competitive advantage of the miniflaps in the building industry, which is often characterized by limited space allowance.

Adverse-pressure-gradient turbulent boundary layer on convex wall

Direct numerical simulations (DNSs) of an incompressible turbulent boundary layer on an airfoil (suction side) and that on a flat plate are compared to characterize the non-equilibrium turbulence and the effect of wall curvature on the flow. The two simulations effectively impose matching streamwise distributions of adverse pressure gradient (APG) quantified by the acceleration parameter (K). For the airfoil flow, an existing compressible DNS carried out by Wu et al. [“Effects of pressure gradient on the evolution of velocity-gradient tensor invariant dynamics on a controlled-diffusion aerofoil at Rec = 150,000,” J. Fluid Mech. 868, 584–610 (2019)] of the flow around a controlled-diffusion airfoil is used. For the flat-plate flow, a separate simulation is carried out with the aim to reproduce the flow in the region of the airfoil boundary layer with zero to adverse pressure gradients. Comparison between the two cases extracts the effect of a mild convex wall curvature on velocity and wall-pressure statistics in the presence of APG. In the majority part of the boundary layer development, curvature effect on the flow is masked by that of the APG, except for the region with weak pressure gradients or a thick boundary layer where the effect of wall curvature appears to interact with that of APG. High-frequency wall-pressure fluctuations are also augmented by the wall curvature. Overall, the boundary layers are qualitatively similar with and without the wall curvature. This indicates that a flat-plate boundary layer DNS may serve as a low-cost surrogate of a boundary layer over the airfoil or other objects with mild curvatures to capture important flow features to aid modeling efforts.

Exploration of an unconventional validation tool to investigate aero engine transonic fan flutter signature

Abstract Flutter, an aeroelastic blade vibration phenomena, experienced by the fan of an developmental aero gas turbine engine, result in blade failure. Hence, suitable flutter detection instrumentation is required during engine testing. Flutter signature capture from revolving blades is a challenging task that necessitates either a complicated strain gauge-based rotating instrumentation or a noncontact tip timing system. Authors investigated a unique way for identifying, measuring, and validating flutter signature by assessing wall static pressure pulsations produced during blade tip transit across a casing mounted high bandwidth sensor during this research. The authors devised a mathematical model to explain signal spectrum components that feature both amplitude and angle modulation properties at the same time. The theory was tested using first-stage fan rotor blades that were fluttering in the first flexural mode (1F) and forming the second nodal diameter (2ND). The approach’s estimated blade deflection was compared to measurements taken using a traditional tip timing method up to 7 mm and determined to be within 1% inaccuracy. This research provides a low-cost, easy alternative technique for measuring flutter during engine development testing.

Research on quality control of precision machining straight internal gear by abrasive flow based on large eddy simulation

Traditional finishing technology is difficult to realize the precision machining of complex geometric parts. Abrasive flow machining technology solves this problem well. Taking the spur internal gear as the research object, the wall shear force, static pressure, dynamic pressure, and abrasive velocity vector of the internal channel of the straight internal gear under different inlet velocity, abrasive concentration, and abrasive particle size are analyzed by using the large eddy simulation method, and the action law of different parameters on the machining of straight internal gear by solid–liquid two-phase abrasive flow is discussed. At the same time, the orthogonal test was carried out. The results show that the solid–liquid two-phase abrasive flow machining technology can effectively remove the burrs, pits, and bulges on the tooth surface of spur internal gear, reduce the tooth surface roughness, and improve the surface quality. The optimal combination of processing parameters and the primary and secondary order of various factors affecting processing are obtained by range analysis and analysis of variance. The regression equation is constructed by regression analysis to verify the effectiveness and accuracy of the model, which provides theoretical support and data reference for actual processing and production.

Effect of porous blocks on flow development through a serpentine cooling passage under stationary and rotating conditions

This study investigates how the inclusion of porous block influences the flow development in a serpentine passage, which consists of two straight square-sectioned ducts connected with a square-ended bend. Aluminium porous foam blocks have been attached to two opposite walls of the straight sections normal to the bend in a staggered manner, used as turbulence promoters. The investigation considers flows in the passage in stationary conditions, and in orthogonal rotation. Particle image velocimetry (PIV) is used to map out the flow development. The wall static pressure distribution along two sides of the passage (the leading and trailing under rotating conditions) is also provided. Tests are carried out at Reynolds numbers of 16,000, 26,000 and 36,000 and rotation numbers of 0.32 and 0.64. Preliminary tests, in a smooth (without porous blocks) passage of identical geometry, establish the reference conditions and enable the identification and quantification of the effects of the porous blocks on the flow development. PIV results show the meandering manner of the flow both upstream and downstream of the bend region, due to the presence of the porous blocks. Within the bend, in contrast to the case with a smooth upstream section, a single vortex dominates the flow. While rotation does not change the overall flow character, it does force more fluid through the blocks along the trailing (pressure) side of the duct. For both stationary and rotating conditions, the upstream section is long enough for the flow to become periodic over successive rib intervals, which produces very attractive data for CFD validation. These data include mean flow as well as second-moment profiles. The pressure coefficient is found to decrease linearly along the channel, due to the high blockage by the porous blocks. Rotation does not change the shape of the pressure coefficient profile but causes a greater reduction along the passage.

Separation of conduction and convection heat transfer effects for a metal foamed flat plate impinged by a circular jet

The present study is concerned with an experimental investigation of the local heat transfer coefficient for an air jet impinging on a flat plate with porous foam (aluminum and resin foam) using a thin metal foil technique. The experiments are performed for the Reynolds number (based on a nozzle diameter) ranging from 10,000 to 25,000 and nozzle to plate spacing varying from 2 to 10 times the inner diameter of a nozzle. The thickness, porosity, and pore density used are 8 mm, 92%, and 20 pores per inch. The static wall pressure distribution for the smooth flat plate and a foamed flat plate is measured. An infrared thermal imaging technique is used for temperature distribution measurement. The wall static pressure distribution shows that the presence of the porous foam offers extra additional hydraulic resistance to an incoming jet. Metal foamed flat plate experiences an increase in heat transfer because of conduction caused by the metal foam and decrease in heat transfer because of additional hydraulic resistance. However, the resin foamed flat plate experiences only decreases heat transfer caused by the additional hydraulic resistance. Hence, the conduction effect experienced by the metal foamed flat plate can be separated. Region-wise correlations for Nusselt number based on the Reynolds number (Re), a non-dimensional radial distance (r/d)and nozzle to plate spacing (z/d) are proposed.

Influence of wall mounted ramps on DLR strut scramjet combustor under non-reacting flow field

The scramjet technology is considered to be the advanced engine for high-speed transportations. The present numerical examination addresses the influence of double ramp's implications in the scramjet engine combustor walls accompanied by strut injection technique under non-reacting flow conditions. The numerical analyses are performed using simulation software, ANSYS Fluent 18.0. Computational problems have been modeled using Reynolds averaged Navier-Stokes (RANS) equations. The inlet flow condition of the model is Mach (Ma) 2 and sonic speed hydrogen fuel from the strut is driven along the flow direction. The characteristics of flow for the two-dimensional (2D) combustor models are studied using shadowgraph images and Mach number contours. Numerical solutions are analogized with the published experimental outcome for validation. The wall static pressure values are higher at the vicinity of the strut ramps regions due to the additional shock interactions generated from the ramps compared to the DLR scramjet model. The subsonic zones are created due to additional shock waves and enhance air–fuel mixing for ramp-mounted combustors. The total pressure loss across the combustor increases as the ramps are positioned downstream of the strut.

Characterization and Development of Universal Ventricular Assist Device: Computational Fluid Dynamics Analysis of Advanced Design.

We are developing a universal, advanced ventricular assist device (AVAD) with automatic pressure regulation suitable for both left and right ventricular support. The primary goal of this computational fluid dynamics (CFD) study was to analyze the biventricular performance of the AVAD across its wide range of operating conditions. An AVAD CFD model was created and validated using in vitro hydraulic performance measurements taken over conditions spanning both left ventricular assist device (LVAD) and right ventricular assist device (RVAD) operation. Static pressure taps, placed throughout the pump, were used to validate the CFD results. The CFD model was then used to assess the change in hydraulic performance with varying rotor axial positions and identify potential design improvements. The hydraulic performance was simulated and measured at rotor speeds from 2,300 to 3,600 revolutions/min and flow rates from 2.0 to 8.0 L/min. The CFD-predicted hydraulic pressure rise agreed well with the in vitro measured data, within 6.5% at 2300 rpm and within 3.5% for the higher rotor speeds. The CFD successfully predicted wall static pressures, matching experimental values within 7%. High degree of similarity and circumferential uniformity in the pump's flow fields were observed over the pump operation as an LVAD and an RVAD. A secondary impeller axial clearance reduction resulted in a 10% decrease in peak flow residence time and lower static pressures on the secondary impeller. These lower static pressures suggest a reduction in the upwards rotor forces from the secondary impeller and a desired increase in the pressure sensitivity of the pump. The CFD analyses supported the feasibility of the proposed AVAD's use as an LVAD or an RVAD, over a wide range of operating conditions. The CFD results demonstrated the operability of the pump in providing the desired circumferential flow similarity over the intended range of flow/speed conditions and the intended functionality of the AVAD's automated pressure regulation.

Computational fluid dynamic modelling of supersonic ejectors: comparison between 2D and 3D modelling

It is known that the global performances of ejector-based systems (viz., at the “global-scale”) depend on the local flow properties within the ejector (viz., at the “local-scale”). For this reason, reliable computational fluid-dynamics (CFD) approaches, to obtain a precise and an a-priori knowledge of the local flow phenomena, are of fundamental importance to support the deployment of innovative ejector-based systems. This communication contributes to the existing discussion by presenting a numerical study of the turbulent compressible flow in a supersonic ejector. In particular, this communication focuses on a precise knowledge gap: the comparison between 2D and 3D modelling approaches as well as density-based and pressure-based solvers. The different approaches have been compared and validated against literature data consisting in entrainment ratio and wall static pressure measurements. In conclusion, this paper is intended to provide guidelines for researchers dealing with the numerical simulation of ejectors.

Unsteady flow phenomena in turbine shroud cavities

This paper presents those flow parameters at which coherent structures appear in the blade tip cavities of shrouded turbine blades. To the authors’ knowledge, this is reported for the first time in the open literature. The unsteady flow in a shroud cavity is analysed based on experimental data recorded in a labyrinth seal test rig. The unsteady static wall pressure in the shroud cavity inlet and outlet is measured using time-resolving pressure sensors. Sensors are located at staggered circumferential positions to allow cross-correlation between signals. The unsteady pressure signals are reduced using Fourier analysis and cross-correlation in combination with digital filters. Based on the data, a theory is formulated explaining the phenomena reflected in the measurements. The results suggest that pressure fluctuations with distinct numbers of nodes are rotating in the shroud cavity outlet. Moreover, modes with different node numbers appear to be superimposed, rotating at a common speed in circumferential direction. The pressure fluctuations are not found at all operating points. Further analysis indicates that the pressure fluctuations are present at operating points matching distinct parameters correlating with the cavity flow coefficient. Unsteady RANS simulations predict similar flow structures for the design operating point of the test rig.