Static Pressure Measurements Research Articles

Analysis of the moist air transonic flow in the symmetric and asymmetric nozzle of the low expansion

Condensation has a negative impact on turbomachinery efficiency in many energy processes. This paper compares the expansion of moist air in symmetric and asymmetric nozzles with a low expansion rate. The presented numerical study is supported by analytical and experimental research. The experimental tWesting was carried out using an in-house experimental test rig where two nozzles were examined for moist air with relative humidity of about 25%. The nozzles were tested for a supersonic outlet, as well as for the outlet condition with elevated pressure, which resulted in the occurrence of a normal shock in the test section. The asymmetric nozzle profile is congruent with the symmetric nozzle. However, the nozzle walls are shifted linearly in the flow direction. The Schlieren photography technique and static pressure measurements on the nozzle wall were used for qualitative identification of both condensation and shock waves. The presented numerical modelling was conducted using commercial computational fluid dynamics software extended with an in-house condensation model. The code was validated against in-house experiment as well as against the data available in the literature. The analysis of the flow in the considered two types of nozzles with a very low expansion rate revealed very interesting structures of pressure waves. The impact of the linear shift of the nozzle walls on the condensation process and the interaction of the condensation wave with aerodynamic oblique as well as normal shock waves were investigated.

A comprehensive analysis of the moist air transonic flow in a nozzle with a very low expansion rate

• Experimental study of the moist air transonic flow in a nozzle with a low expansion rate. • Mathematical models of homogeneous condensation. • The study of the effect of air relative humidity on the expansion process. • The study of the interaction between condensation and pressure waves. Inevitable and undesirable as it is, phase transition has a significant impact on the fluid flow efficiency in many energy processes. This paper deals with the impact of water vapour condensation and liquid water evaporation in the moist air expansion in a nozzle with a low expansion rate. The presented comprehensive analysis includes a numerical study supported by analytical and experimental research. The experimental study concerning measurements of atmospheric air transonic flows was carried out using an in-house experimental test rig. A nozzle with a low expansion rate of P ̇ ≈ 1000 s - 1 was investigated experimentally at different inlet air relative humidity values included in the range of 25 to 51 %. The nozzle was measured for supersonic outlet conditions, as well as with elevated back pressure (78 kPa). The technique of Schlieren photography and static pressure measurement on the nozzle wall were used for qualitative identification of both condensation and shock waves. The presented numerical modelling was conducted using commercial computational fluid dynamics software extended with an in-house condensation model. The code was validated against experimental data and data available in the literature. The analysis of the flow in the nozzle with a very low expansion rate revealed very interesting structures of pressure waves. The impact of relative air humidity on the condensation process and the interaction of the condensation wave with aerodynamic oblique as well as normal shock waves were investigated. It is observed that the higher the air relative humidity value, the more difficult it is to identify aerodynamically induced oblique shock waves in the flow. Finally, considering that the efficiency drop induced by the phase change can reach up to 10 %, the impact of condensation on the expansion process efficiency is presented.

Effect of free stream turbulence in critical Reynolds number regime (1.6 × 105−6.1 × 105) on flow around circular cylinder

The flow around a cylinder is a classical aerodynamic problem involving the effect of Reynolds number (Re). Thus far, the impact of turbulence has not been fully clarified despite its important practical value in engineering applications. This study mainly investigates the influence of turbulence in the critical Re regime on the smooth and turbulent flows around a cylinder. The foregoing is accomplished by conducting static pressure measurement model experiments in the Re range of 1.6 × 105–6.1 × 105 and turbulence intensity range (Iu) of 5%–13%. Consequently, a series of useful results for engineering wind resistance design is obtained. The effect of turbulence on each sub-flow regime varies. The structural response to turbulence is more dangerous under conditions such as when the wind pressure coefficients fluctuate strongly and non-Gaussianity is strong. The foregoing effects do not necessarily increase linearly with the turbulence intensity. In addition, the influence of turbulence evidently depends on the Re and corresponding flow regime. Therefore, turbulence must be cautiously managed in scaled model experiments and actual wind resistance design.

Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation

Abstract The first part of the paper presents commissioning of a single-stage high-pressure (HP) turbine employed in a series of extensive experiments to study the aerodynamics and heat transfer on the rotor surface and casing liner. The Oxford Turbine Research Facility (OTRF), a high-speed rotating transient test facility has the capability to take unsteady aerodynamic and heat transfer measurements at engine representative conditions with a variety of inlet temperature profiles including radial distortion and swirl. A temperature profile survey was conducted at the inlet of the HP nozzle guide vane (NGV). Static and total pressure and temperature measurements have been taken at various locations on the rig including NGV surface, inlet and exit, and rotor exit to establish rig operating conditions. Detailed description of mass flow rate measurements along with calculation of heat loss factor in the rig is presented. The second part of the paper presents a parametric study performed to improve heat transfer measurement calculations from high-frequency response thin-film gauges. The effect of parameters like material properties and thickness of substrate on heat flux has been studied. A detailed uncertainty analysis for heat flux is also presented. A thermal model calibrated with analytical solutions has been developed to optimize thin-film gauge configurations and to study side-conduction effects.

Footwork Pro System Reproducibility of Static and Dynamic Plantar Pressure Indicators

ObjectiveThe purpose of this study was to identify the reproducibility of the Footwork Pro plate in the measurement of static and dynamic plantar pressure in healthy adults. MethodsWe performed a reliability study using a test-retest design. The sample consisted of 49 healthy adults of both sexes, aged 18 to 64. Participants were assessed on the following 2 different occasions: the initial moment and 7 days later. Measurements for the static and dynamic plantar pressure were performed. We used the Student t test for paired data, the concordance correlation coefficient, and bias to estimate reliability. ResultsPlantar pressure values for the static condition (peak plantar pressure, plantar surface contact area, and body mass distribution) and dynamic condition (peak plantar pressure, plantar surface contact area, and contact time) between the first and second measurements did not present statistically significant differences. The concordance correlation coefficients were ≤0.90, and the biases were of low magnitude. ConclusionThe findings showed that the Footwork Pro system offered clinically acceptable reproducibility to identify static and dynamic plantar pressure and thus may be a reliable tool for this purpose.

Reconstruction of flow around a high-rise building from wake measurements using Machine Learning techniques

This paper investigates the unsteady flow around a high-rise building using OpenFoam. A Vortex Method is developed to generate upstream unsteady fluctuations that are validated considering the numerical simulation of a neutral atmospheric boundary layer around a high-rise building. The Vortex Method parameters are tuned to produce an upstream velocity profile whose turbulence characteristics are comparable to experimental data. Comparison between mean and fluctuating velocity profiles of the numerical data measured in the building’s wake with experimental data shows satisfactory results.The resulting database is used to reconstruct the flow from limited velocity measurements inside the wake and static wall pressure measurements on the building surface. Machine learning techniques such as linear regressions (Ridge, Lasso, ElastikNet, MultiTaskLasso regression) and Artificial Neural Network are tested and compared. The flow reconstruction using velocity measurements inside the wake leads to a better result compared to the flow reconstruction from the wall pressure measurements. At the same time, it was noticed that the Artificial Neural Network regression does not lead to more satisfactory results compared to linear regression techniques.

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.

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.

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.

МЕТОДИ ВИМІРЮВАННЯ ТИСКУ ПОРОХОВИХ ГАЗІВ

The article analyzes possible methods for measuring the pressure of powder gases. The phenomenon of a shot is very complex. Many components of the processes themselves are very complex, interconnected one with the other and strongly depend on the scheme of the device and the design of the weapon, the powder charge and the projectile, on the properties of the gunpowder and on the state of the atmosphere in which the projectile moves. In addition, most of the processes of the phenomenon of a shot occur in very short periods of time and are characterized by high values of physical parameters: speed, pressure, temperature. The complexity and intensity of the phenomenon of a shot do not allow us to study it in full. Therefore, in ballistics they confine themselves to studying the basic regularities of the phenomenon of a shot, on which the movement of a projectile depends very much. This study, necessary for artillery practice, is carried out by theoretical and experimental methods. The parameters of the state of powder gases, as well as a number of parameters of most firing processes that are not directly measured, have to be determined indirectly, primarily from the results of measuring the pressure of powder gases. For this, various laws and relations established on the basis of theoretical and experimental research are usually used, which connect the desired quantities with the pressure of powder gases. Static pressure measurement methods are based on the principle of converting pressure values into strain values or other physical quantities associated with it. Dynamic pressure measurement methods are based on the principle of converting pressure values into kinematic elements of motion: acceleration, speed or path as a function of time. Keywords: pressure, static pressure measurement methods, dynamic pressure measurement methods, tensometric method, piezoelectric method, plastic deformation method, spring deformation method.

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.

Simple Pressure Sensor with Highly Customizable Sensitivity Based on Fiber Bragg Grating and Pill-Shaped 3D-Printed Structure

This study presents a simple pill-shaped pressure sensor fabricated by fused deposition modelling (FDM) technology. A fiber Bragg grating (FBG) sensor was embedded inside the structure during the 3D printing process. The dimension of the sensor was simulated by the finite element method to explore the customizability of the pressure sensor. The proposed pill-shaped pressure sensor showed great linearity and achieved high sensitivity with a total Bragg-shifted wavelength of 1.44 nm in the pressure range between 0 and 0.35 MPa, corresponding to a pressure sensitivity of 4.11 nm/MPa. The measured pressure change matched closely with finite element simulation, and the sensitivity could easily increase five times by a thirty percent increase in structure size. The results showed that the pill-shaped pressure sensor had high linearity and great feasibility and could be easily customized to a wide pressure range for static and dynamic pressure measurements in industrial applications.

Auto-Processing Of Filtered Rayleigh Scattering Images Including Mie And Background Scattering Contributions

Filtered Rayleigh scattering (FRS) is a non-intrusive, optical-based technique that allows for simultaneous, time-averaged, measurements of three-component velocity, static temperature, and static pressure. The method of post-processing the raw images to get these variables is a non-trivial task. The post-processing scheme starts with building a model to generate simulated spectra given known velocity, temperature, and pressure values which can be iterated upon. The model also includes Mie scattering and background scattering contributions that must be taken into account. This iteration scheme allows for the simulated spectra to be matched to the experimental spectra to back out the desired flow variables. This iteration process can be lengthy and so it is important to make spectrum generation/iteration as fast as possible. This is done through the use of support vector spectrum approximation (SVSA), which is a machine learning algorithm, as well as a multivariable minimum error solver based on the least-squares fit between the simulated data and the experimental data. To prove the methodology, simulated results were first compared at different signal-to-noise ratios to determine the expected uncertainty at each SNR level. It was shown that to achieve an error of less than 1\% in all variables (velocity, static temperature, Mie intensity ratio, and background intensity ratio), the SNR must be near 40dB. This kind of SNR level is generally not expected in an experiment. Therefore, a representative experiment was conducted which included Mie and background scattering contributions. It was shown that manually processed data was capable of achieving velocity results that were within 2\% of the probe data. No other variables were achieved. The auto-processing scheme was able to achieve an error of approximately 2.5\% in velocity when compared to probe data. It was also capable of providing static temperature, Mie intensity ratio, and background intensity ratio values. The manual iteration results took several days to achieve while the auto-processing took about an hour. It is clear that this methodology is capable of automatically processing images from experiments with Mie and background scattering contributions while saving time.

Aerodynamic mechanism of triggering and suppression of vortex-induced vibrations for a triple-box girder

With the objective of exploring the aerodynamic mechanism of triggering and suppression of vortex-induced vibration (VIV) for a triple-box girder, wind tunnel tests involving both static and dynamic pressure measurements, as well as CFD simulation for flow visualization were carried out on a bare girder. Both vortex-induced vibrations and surface pressures were obtained from static and dynamic sectional model tests for three typical wind incidence angles, namely α = 0°, +3°, and −3°. Results indicated that vortices shed regularly from the downwind sides of both windward box and middle box, then impinged on the upwind sides of middle box and leeward box respectively, resulting in prominent fluctuating pressures here, which was likely to render the triple-box girder more susceptible to VIV. Specifically, fluctuating lift of middle box was the main trigger of VIV at wind incidence angle α = +3°, while that of leeward box was the main trigger at α = 0° and −3°. The regular vortex shedding and impinging process could be effectively suppressed by the grid plates over girder slots, which was favorable to VIV mitigation. When VIV occurred, self-excited force became the main component of the fluctuating force, and it could be the major driver of the large-amplitude oscillation.

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.

Combustion Instability due to Combustion Mode Transition in a Cavity-Stabilized Scramjet

This study experimentally investigates flame dynamics during a combustion-driven mode transition in a cavity-stabilized scramjet model with an inlet Mach number of 2.2 using a split fuel injection scheme. Fueling into the cavity was gradually increased while keeping a constant global equivalence ratio of 0.3. A cavity-fueling percentage below 15% resulted in low-intensity combustion that corresponded to operation in scram mode. Redirecting 29% of the fuel from the upstream injection port to the cavity yielded flame spreading into the main flowpath, inducing intense combustion. A sharp pressure rise and an intense combustion region in the diverging section suggest dual-mode combustion, with thermal choking and a pseudoshock formation downstream of the cavity. An intermediate cavity-fueling fraction of 21% led to a low-frequency instability () with intermittent transitions between the combustion modes, indicating operation at the thermal choking limit. Spectral and modal analyses of chemiluminescence images and static-pressure measurement indicate peak response at 10–20 Hz and , originating from oscillations in the air heater and a fuel jet instability, respectively. Thermally chocked conditions significantly amplify oscillations at these frequencies. At the thermal choking limit, there was high-amplitude response at , preventing stable dual-mode operation.

Characterization of reflected shock tunnel air conditions using a simple method

A new method to characterize air test conditions in hypersonic impulse facilities is introduced. It is a hybrid experimental–computational rebuilding method that uses the Fay–Riddell correlation with corrections based on thermochemical nonequilibrium computational fluid dynamic results. Its benefits include simplicity and time-resolution, and using this method, a unique characterization can be made for each individual experimental run. Simplicity is achieved by avoiding the use of any optical techniques and overly expensive numerical computations while still maintaining accuracy. Without making any assumptions to relate the reservoir conditions to the nozzle exit conditions, the work done characterizing four test conditions in a reflected shock tunnel is presented. In this type of facility, shock compression is used to produce an appropriate reservoir, which is then expanded through a nozzle to produce hypersonic flow. Particular focus is given to the nozzle exit total enthalpy where a comparison is made with the reservoir enthalpy obtained using the measured shock speed and pressure in the shock tube. Good agreement is observed in all cases providing validation of the new approach. Additionally, static pressure measurements showed clearly that conditions III and IV have a thermochemical state which likely froze shortly after the nozzle throat. Also, the nozzle flow is shown to be almost isentropic. Due to the simplicity of the current method, it can be easily implemented in existing facilities to provide an additional independent estimate alongside existing results.

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.

Experimental approach of surface pressure measurements on additive manufactured nozzle guide vane in a turbocharger turbine

Obtaining the surface pressure measurement of the pneumatic blades in turbomachinery is beneficial in understanding the flow mechanism around the blades and designing of the blades to improve the turbomachinery performance. However, it is difficult for the turbocharger turbine due to the space limitation, high rotational speed, and small geometric size. The present study investigates a novel measuring approach of the surface pressure of the guide vane in a turbocharger turbine based on the additive manufacturing techniques, which is not reported in the previous literature. The static pressure on the pressure side and suction side of the guide vanes in the variable nozzle turbine was investigated using both the experimental and numerical methods. The results show that the majority of the measuring results generally agree with the numerical prediction at different operating points with the relative difference below 5%. Besides, the trends of the static pressure as the rotational speed and mass flow rate between the pressure side and suction side were also captured in the experimental methodology. The highest deviations between experimental and calculated models were found in the first and fifth pressure taps on the guide vanes with an averaged absolute relative difference of up to 11.61% and 16.1% for 20% opening and 60% opening, respectively. The ratio of the kinetic pressure to total pressure and the flow field in the guide vane passage were analyzed to estimate the influence on the static pressure measurement. Nevertheless, the preliminary comparison results still encourage and extend the bounds of the possibility in the use of additive manufacturing techniques for miniature pneumatic blade surface pressure measurement.

Hydrodynamic and acoustic pressure fluctuations in water pipes due to an orifice: Comparison of measurements with Large Eddy Simulations

The present article investigates the turbulent wall pressure fluctuations due to flow through single-hole sharp-square-edged orifices (opening area ratios of 11%, 20% and 31%) in a water-filled pipe by means of measurements and incompressible Large Eddy Simulations (LES) for opening area ratios of 20% and 31%. The orifice plate thickness was half the orifice diameter. The static pressure measurements and simulations show that the vena-contracta factors of the orifices are dependent on Reynolds numbers, which is due to the finite thickness of the orifices. These LES simulations provide a good prediction of the near-field hydrodynamic wall pressure fluctuations, which dominate up to the first three pipe diameters downstream of the orifice. Upstream and far downstream wall pressure fluctuations are dominated by acoustic pressure fluctuations. The source of the radiated sound field was estimated from the surface integral of the fluctuations across the orifice in the LES. The sound field was calculated by implementing the sound source in a one dimensional acoustic model of the test section. The power spectrum density (PSD) of the wall pressure fluctuations for pipe Reynolds numbers varying from 4000 to 10000 collapsed when presented in dimensionless form, which uses the dynamic pressure in the orifice as reference pressure and the ratio of cross-sectional averaged orifice velocity and orifice diameter as characteristic frequency. In the inertial range of the turbulence a global decay of the pressure PSD and of the sound source show a power of the Strouhal number between −113 and −2.8. For higher frequencies the pressure fluctuations were dominated by acoustic resonances. For wider orifices the magnitude of these acoustic pressure fluctuations is predicted within a factor two by the acoustic model. For the narrowest orifice (opening ratio of 11%) the measured PSD of pressure fluctuations displays sharp peaks due to self-sustained oscillations (whistling). A simple power law of the sound source is not accurate due to the unstable hydrodynamic modes related to orifice thickness. However, using the simple model for the sound source the acoustic model predicts the acoustic pressure fluctuations reasonably well for all orifices. At low frequency one observes a peak in the PSD hydrodynamic wall-pressure fluctuations at one pipe diameter downstream of the orifice. It is probably due to an acoustically silent “edge-tone-like” sinusoidal self-sustained motion of the jet.