Sonic Jet Research Articles

Forcing Pulsations by Means of a Siren for Gas Turbine Applications

A siren is a robust fast-valve that generates effective flow pulsations and powerful noise levels under well-controlled conditions. It operates under the inlet flow conditions of a gas turbine combustor. Its principle is based on a sonic air jet periodically sheared by a cogged wheel rotating at a given speed. It is used as an alternative to loudspeakers in combustion laboratories when the use of these is made difficult by aggressive flow conditions, such as hot air under pressure, possibly containing impurities. It is also a serious candidate as an effective flow actuator to be deployed on power gas turbine fleets. The authors have gathered more than twenty years of knowledge on siren technology. This pulsator was originally developed for research on thermoacoustics. By scanning through a given frequency range, one detects the acoustic resonance of specific parts of the combustor assembly, or possibly triggers a combustion instability during a sensitivity analysis of a flame to small perturbations. In 2010, Giuliani et al. developed a novel siren model with the capacity to vary the amplitude of pulsation independently from the frequency. In this contribution, the physics, the metrics, and the resulting parameters of the pulsator are discussed. Technical solutions are unveiled about visiting large frequency ranges (currently 6 kHz) and achieving elevated pressure fluctuations (150 dB SPL proven, possibly up to 155 dB SPL) with a compact device. A multimodal excitation is available with this technology, one idea being to dissipate the acoustic energy on nearby peaks. The contribution ends with a summary of the applications performed so far and the perspective of an industrial application.

Study of Correctly Expanded Sonic Jet with Air Tabs

Abstract The present numerical study is to understand the effect of air tabs located at the exit of a convergent nozzle on the spreading and mixing characteristics of correctly expanded sonic primary jet. Air tabs used in this study are two secondary jets issuing from constant diameter tubes located diametrically opposite at the periphery of the primary nozzle exit, normal to the primary jet. Two air tabs of Mach numbers 1.0 to 1.4, in steps of 0.1 are considered in this study. The mixing modification caused by air tabs are analysed by considering the mixing of uncontrolled (free) primary jet as a reference. Substantial enhancement in jet mixing is achieved with Mach 1.4 air tabs, which results in 80 % potential core length reduction. The total pressure profiles taken on the plane (YZ) normal to the primary jet axis, at various locations along the primary jet centreline revealed the modification of the jet cross sectional shape by air tabs. The stream-wise vortices and bifurcation of the primary jet caused by air tabs are found to be the mechanism behind the enhanced jet mixing.

Self-oscillatory flow in the Hartmann resonator – Numerical simulation

Self-oscillatory flow in the Hartmann resonator is numerically calculated within the framework of ideal (inviscid and non-heat-conducting) gasdynamics. The calculations are performed for the case of a sonic jet impinging on a tube varying from that with a sealed inlet (rod) to a fairly deep cavity. The spacing between the tube and the nozzle and the nozzle pressure ratio are also varied in the calculations. On the basis of the calculated results the oscillation process is described in detail and its mechanism is revealed for both shallow and deep tubes. For shallow tubes and a rod it is due to an imbalance in the flow rate and momentum between two regions in the jet that impinges on the obstacle. For deep tubes the oscillations are due to the tube filling and evacuation somewhat reminiscent of the process occurring in a one-quarter-wave resonator. In any case no signature of a feedback loop in the external acoustic field of the jet was detected. The results of the calculations are in good agreement with experimental data. The effects of mounting a lip on the tube (transition from a low- to high-frequency operation mode) and heating in the Hartmann tube are also discussed.

Abrasive and Erosion Wear of Composite NiCrSiB Coatings Inflicted with Subsonic Flammable Structure through a Cold Process

Ni-Cr-B-Si alloys are commonly used in the thermal spraying of steels. Despite their widespread use, their role in protecting metal surfaces from wear is not yet fully clarified. In order to obtain data and understanding of the wear and wear resistance of these coatings, the present work is studied the characteristics of the abrasive and erosive wear of new Ni-Cr-B-Si composite coatings applied by means of a sonic flame jet when heating the substrate to 180 °C (cold process). The powdered compositions used contain particles with an average size of 40 µm and a different percentage of the chemical elements. The abrasion wear is investigated using the thumb-disc pattern for dry surface friction with rigidly attached abrasive particles. Erosion wear is investigated by the interaction of air-jet coatings carrying abrasion particles. All samples in abrasion and erosion are tested under the same contact conditions. The mechanism, speed, and intensity of wear, and wear resistance of coatings at different normal load and slip speeds were obtained.

Study of underexpanded sonic jets from square convergent micro nozzles

Numerical simulations using the RANS with the SSTk-ω turbulence model are performed to understand the flow feature of an underexpanded sonic jet from a convergent nozzle with a square cross-section of 1 mm × 1 mm at the nozzle exit. The nozzle pressure ratio, which is the ratio of the plenum pressure upstream of the nozzle to back pressure, is held constant at 4.0 and the Reynolds number based upon the flow properties and the height at the nozzle exit is 5.94 × 104. The near-field shock structure in shock-containing square jets is demonstrated with the three-dimensional representations of the magnitudes of the density and pressure gradient vectors.

Effect of location of a transverse sonic jet on shock augmented mixing in a SCRAMJET engine

Transverse sonic injection into supersonic cross flow is a well-established technique to inject fuel into a SCRAMJET combustor. A SCRAMJET combustor with a backward facing step acting as a flame-holder has been used for this study. The jet is placed at various locations downstream of the step, where each location represents a distinct flow region. Three-dimensional simulations have been performed using Menter's SST model in our in-house parallel 3-D RANS unstructured grid CFD solver. In such a SCRAMJET configuration, mixing between air and fuel is augmented by shocks generated by the under-expanded jet injected into the supersonic cross flow, hence the jet location is expected to be critical. The performance and mixing of the combustor has been quantified for each of the distinct configurations. The length of the combustor required for complete mixing has also been estimated for the different cases. It is observed that the mixing and performance are strongly affected by the location of the jet in the combustor flow-field. From the results presented in this paper, the optimal location for the jet is somewhat before the end of the recirculation region behind the backward facing step.

Self-similarity of surface heat transfer fields on a pre-heated rectangular plate in an obliquely impinging sonic jet

This paper presents an experimental study of the time-dependent surface temperature, heat flux and Nusselt number fields on a pre-heated, rectangular aluminum plate due to an obliquely impinging sonic jet at different total pressures. Surface temperatures are measured by detecting the luminescent emission from temperature sensitive paint. An analytical inverse solution of the one-dimensional time-dependent heat conduction equation is used to determine the heat flux from the temperature measurements. When normalized, the ensemble-averaged heat transfer fields (surface temperature, heat flux and Nusselt number) exhibit self-similarity (time-invariance) for different test conditions and therefore are found to exhibit a somewhat universal nature. A theoretical description of the self-similar behavior is presented for scaling experimental heat transfer data. Furthermore, the skin friction fields extracted from surface temperature and heat flux fields reveal generic topological structures of the flows.

Numerical study of flow structures and mixing characteristics of a sonic jet in supersonic crossflow

This study numerically investigated the influence of flow structures on the mixing characteristics of a sonic transverse gaseous ethylene jet in a supersonic crossflow with a Mach number of 2.95. RANS (Reynolds Average Navier-Stokes) simulations were employed to reveal the transport mechanism of jet fluid. The influencing factors, the jet-to-crossflow momentum flux ratio (J) and the nondimensional thickness of the turbulent boundary layer in the mixing characteristics of the sonic transverse gaseous jet are investigated. In the near-wall field, there is a V-shaped region in the front of the separation bubble that contains more jet gas under a lower momentum flux ratio (J) condition, which is caused by the collision of different inflow streamlines. As the turbulent boundary layer grows, there is more space for the jet gas to expand so that the penetration of the jet is much higher.

Detailed Comparative Analysis of Interaction of a Supersonic Flow with a Transverse Gas Jet at High Pressure Ratios

The interaction of a 3D supersonic turbulent gas flow with a transverse sonic jet injected from the wall has been studied in detail both numerically and experimentally. However, the main drawback of such studies is the lack of detailed description of formation and propagation of vortex structures for moderate and large parameters n (ratio of pressure in the jet to pressure in the flow). Analysis performed in this study is aimed at revelation and detailed explanation of mechanisms of formation of vortices behind the injected sonic jet in a supersonic oncoming flow depending on n for improving the effectiveness of mixing of the jet with the flow. As initial equations, we have used 3D Favre-averaged Navier–Stokes equations closed by the k–ω model of turbulence; these equations are solved using the algorithm based on the essentially nonoscillatory scheme of the third approximation order. We have demonstrated the presence of the following vortex structures known from a number of theoretical publications: two oppositely rotating vortices in front of the jet, a horseshoe vortex; and two pairs formed in the mixing zone between the jet and the flow (one in the wake behind the jet and the other on the lateral line of the jet). We have determined the pressure ratios for which extra pairs of vortices appear (one pair emerges at the Mach disk edge as a result of interaction of a retarded flow of the jet behind the Mach disk with a high-velocity ascending flow behind the barrel and the other pair is formed due to the interaction of the ascending jet flow with the incoming main gas flow). As a result of comparative analysis, the pressure ratios for which a clear pattern of additional horn vortices is observed near the wall in the region behind the jet, have been determined. The dependence of the slope of the bow shock on the pressure ratio has been plotted. It is found that the pressure distribution at the wall in front of the jet in the symmetry plane is in satisfactory agreement with experimental data.

Visualization study on direct contact condensation characteristics of sonic steam jet in subcooled water flow in a restricted channel

Steam jet in subcooled water is a typical mode of direct contact condensation (DCC) where condensation occurs on the interface between steam and water. A visualization study of sonic steam jet condensation in subcooled water flow in a restricted channel has been performed for a convergent nozzle over a wide range of operating conditions. The DCC characteristics, including steam plume shapes, penetration length and average heat transfer coefficient, were discussed in detail. Method of digital image processing using MATLAB software was employed to evaluate steam plume shapes, penetration length, interface area and contours of gas volume fraction. Using a high-speed camera, five different steam plume shapes were typically observed, i.e. hemispherical, conical, contraction–expansion-contraction, ellipsoidal and divergent shapes, which are described in a three-dimensional map of plume shapes depending on steam mass flux, subcooled water temperature and Reynolds number of water flow. The measured data of dimensionless penetration length and average heat transfer coefficient are found to be in the range of 0.8–4.5 and 1.6–5.5 MW/(m2·K), respectively. By means of fitting 140 groups of measured data, the empirical correlations for dimensionless penetration length and average heat transfer coefficient as a function of dimensionless steam mass flux, condensation driving potential and Reynolds number of water flow were proposed. Both of the measured data and predictions show a good agreement with each other, which are suggested to predict the condensation characteristics of sonic steam jet in water flow in a restricted channel.

Evaluation of Quasi-One-Dimensional Unstructured Method for Jet Noise Prediction

The paper presents a lower-cost higher-accuracy algorithm for numerical simulation of jet aerodynamics and acoustics on unstructured meshes. To provide a higher-accuracy prediction of unsteady jet flow, the scale-resolving delayed detached-eddy simulation approach is implemented on unstructured meshes using the edge-based reconstruction schemes. The jet far-field noise is calculated with the help of the Ffowcs-Williams and Hawkings method. The efficiency of the resulting “unstructured” algorithm is demonstrated on two popular cases: a subsonic unheated jet of Mach number 0.9, and a sonic underexpanded hot jet.

Experimental investigations on the interfacial characteristics of steam-air mixture sonic jets in subcooled water

Interfacial characteristics of steam-air mixture sonic jets are recorded and processed using image processing technique. Interfacial shape, radius, fluctuation height, fluctuation velocity and fluctuation acceleration are analyzed. Four typical interfacial shapes including expansion-contraction, double expansion-contraction, expansion-contraction-divergence and expansion-divergence are observed and a three-dimensional interfacial shape map is developed. Gas dynamic effect is notable in the axial region of the near field. The interfacial radius increases linearly with the axial distance in the far field. The spreading rate increases with the rise of air mass fraction and its value is in the range of 0.12–0.27. The interfacial fluctuation height is proportional to the axial distance both in the near field and far field. The spreading coefficient is in the range of 0.03 ± 0.008. In general, both interfacial fluctuation velocity and acceleration increase with the axial distance. The growth rate decreases rapidly in the near field and then increases slightly again in the far field. The maximum velocity and acceleration of interface fluctuation are estimated to be around 6 m/s and 20,000 m/s2, respectively.

Effect of Area Ratio on Base Pressure and Control Effectiveness

Reducing the base drag and increasing the base pressure from aerodynamic devices involving suddenly expanded flows is of vital importance due to the higher rate of drag associated with them. The experimental effort put into understanding the variation in base pressure using active control of suddenly expanded flows employing microjets is reported in this article. The effect of tiny jets and nozzle pressure ratio (NPR), and length to diameter (L/D) ratio on the percentage change in base pressure is investigated at supersonic Mach numbers at 1.7, 2.3, and 2.7, for area ratios of 2.56, 5.06, and 7.56. Apart from NPR, the L/D ratio has an influential role in percentage change in base pressure at different Mach numbers. An improvement of up to 360 % in base pressure is obtained with the use of sonic micro jets at a particular Mach number and L/D ratio.

Flowfield structures of pylon-aided fuel injection into a supersonic crossflow

Flowfield structures of pylon-aided fuel injection of a sonic jet into a supersonic crossflow with Ma = 2.95 have been investigated by Nanoparticle-based Planar Laser Scattering (NPLS) technique and oil flow technique, separately. Two experimental cases have been done for jet-to-crossflow momentum flux ratios (J) of 7.7 and 20.6, respectively, and the results are compared with those obtained by normal injection of a single jet from a flat plate without a pylon. Experimental results indicate that the flow structures of pylon-aided injection cases are very similar to those found in the normal injection cases in the downstream region of the jet. Upstream of the jet orifice, the detached shock generated at the leading edge of the pylon is identified by inserting with the separation shock. For lower injection pressure case there is always larger influences of the pylon in the flow structures in terms of jet plums' position and the shock intensity. Besides, the mechanism of mixing enhancement resulting from the pylon is also elaborated in the present work.

Effective momentum induced by steam condensation in the oscillatory bubble regime

The spargers used in Boiling Water Reactors (BWR) discharge steam from the primary coolant system into a pool of water. Direct steam condensation in subcooled water creates sources of heat and momentum determined by the condensation regimes, called “effective sources” in this work. Competition between the effective sources can result in thermally stratification or mixing of the pool. Thermal stratification is a safety concern in BWRs since it reduces the steam condensation and pressure suppression capacity of the pool. In this work, we present semi-empirical correlations to predict the effective momentum induced by steam condensation in the oscillatory bubble regime, relevant for the operation of spargers in BWRs. A Separate Effect Facility (SEF) was designed and built at LUT, Finland, in order to provide the necessary data. An empirical correlation for the effective momentum as a function of the Jakob number is proposed. The Kelvin Impulse theory was also applied to estimate the effective momentum based on information about the bubble dynamics. To do this, new correlations for the bubble collapse frequencies, maximum bubble radius, velocities, pressure gradient and heat transfer coefficient are proposed and compared to available data from the literature. The effective momentum induced by sonic steam jets appears to be constant in a wide range of studied Jakob number. However, further experimental data is necessary at larger Jakob numbers and steam mass fluxes.

Role of aerodome in pulsation/oscillation control and aeroheating reduction

There exist two distinct modes of flow instability, namely pulsation and oscillation, related to the flat-ended cylinder with pointed spike in high-speed flights. A new method is proposed in this article to weaken the pressure fluctuations and aeroheating acting on the cylinder, through mounting an aerodome on the spike tip, which creates a cavity-like flow in front of the afterbody. Turbulent, axisymmetric flow at a freestream Mach number of Ma∞ = 6.0 and a Reynolds number (based on the cylinder diameter D) of ReD = 0.13 × 106 is simulated using a temporally and spatially second-order-accurate finite volume method. Numerical results are verified by comparison with the experimental data available in the open literature. It is shown that flow pulsation under the spike length of L/D = 1.0 can be totally controlled as the aerodome diameter increases to DA/D = 23.0%, whereas flow oscillation under the spike length of L/D = 2.0 is suppressed as the aerodome diameter reaches DA/D = 10.0%. Besides, the combination of the double-aerodome and sonic jet is proved the most effective way to provide thermal protection for the afterbody, which smooths down the heat flux peak in the vicinity of the reattachment.

Modeling of a reaction control jet interacting with high-speed cross-flow in slip flow regime

Numerical investigation of a sonic reaction control jet interacting with the high-speed cross-flow has been carried out over a generic missile body. Simulations are performed in the early-hypersonic slip flow regime for air, CO2, and helium jet gases. An open source computational fluid dynamics tool, OpenFOAM is used to model the steady state, three-dimensional compressible Navier–Stokes equations with k-ω shear stress transport turbulence model. The conventional computational fluid dynamics solver is extended with additional features, such as transport of species, nonequilibrium boundary conditions for velocity slip and temperature jump, and a heat load calculation utility based on the sliding friction effect. The extended solver is validated with the direct simulation Monte Carlo results for the case of a sonic argon jet injected into hypersonic nitrogen cross-flow. The extended solver is able to accurately capture all the qualitative flow features like separation shock, bow shock, and barrel shock, and it also improves heat load predictions in the slip flow regime. The main objective of the present work is to study the effect of rarefaction and change in jet gas species on the complex flow topology, heat load distribution, and spread of jet gas on the missile body. Heat load predictions are found to be strongly dependent on the slip velocity of molecules in addition to the temperature gradient near the wall. The strength of a bow shock and a barrel shock is higher for helium jet, compared to air and CO2 jets, which spread more along the missile body, and weaker shocks and reduced heat load is generated. The current work is significant from the perspective of the thermal design of spacecraft surfaces and positioning of the optical sensors.

Turbulence decay in a supersonic boundary layer subjected to a transverse sonic jet

The turbulence state in a supersonic boundary layer subjected to a transverse sonic jet is studied by conducting direct numerical simulations. Turbulence statistics for two jet-to-cross-flow momentum flux ratios $(J)$ of 2.3 and 5.5 based on the previous simulation (Sun & Hu, J. Fluid Mech., vol. 850, 2018, pp. 551–583) are given and compared with a flat-plate boundary layer without a jet $(J=0.0)$. The instantaneous and time-averaged flow features around the transverse jet in the supersonic boundary layer are analysed. It is found that, in the near-wall region, turbulence is suppressed significantly with increasing $J$ in the lateral boundary layer around the jet and the turbulence decay is retained in the downstream recovery region. The local boundary-layer thickness decreases noticeably in the lateral downstream of the jet. Analysis of the cross-flow streamlines reveals a double-expansion character in the vicinity of the jet, which involves the reattachment expansion related to the flow over the jet windward separation bubble and the jet lateral expansion related to the flow around the jet barrel shock. The double expansion leads to the turbulence decay in the jet lateral boundary layer and causes a slow recovery of the outer layer in the far-field boundary layer. A preliminary experiment based on the nanoparticle laser scattering technique is conducted and confirms the existence of the turbulence decay phenomenon.

Experimental study on the condensation of sonic steam in the underwater environment

Abstract Steam jet condensation is of great importance to pressure suppression containment and automatic depressurization system in nuclear power plant. In this paper, the condensation processes of sonic steam jet in a quiescent subcooled pool are recorded and analyzed, more precise understanding are got in direct contact condensation. Experiments are conducted at atmospheric pressure, and the steam is injected into the subcooled water pool through a vertical nozzle with the inner diameter of 10 mm, water temperature in the range of 25–60 °C and mass velocity in the range of 320–1080 kg/m2s. Richardson number is calculated based on the conservation of momentum for single water jet and its values are in the range of 0.16–2.67. There is no thermal stratification observed in the water pool. Four condensation regimes are observed, including condensation oscillation, contraction, expansion-contraction and double expansion-contraction shapes. A condensation regime map is present based on steam mass velocity and water temperature. The dimensionless steam plume length increase with the increase of steam mass velocity and water temperature, and its values are in the range of 1.4–9.0. Condensation heat transfer coefficient decreases with the increase of steam mass velocity and water temperature, and its values are in the range of 1.44–3.65 MW/m2°C. New more accurate semi-empirical correlations for prediction of the dimensionless steam plume length and condensation heat transfer coefficient are proposed respectively. The discrepancy of predicted plume length is within ± 10% for present experimental results and ± 25% for previous researchers. The discrepancy of predicted condensation heat transfer coefficient is with ± 12%.

Oxygen lancing methods for industrial processes

Oxygen is often used in industrial combustion processes to improve emissions, reduce fuel cost and/or increase production. As opposed to simply enriching combustion air with oxygen, oxygen lancing is utilized when targeting the oxygen to a specific part of the combustion process is beneficial.This work compares 2 methods of lancing oxygen into a process, the first comprising a sonic velocity jet of ambient temperature (“cold”) oxygen and the second an oxygen jet heated to temperatures exceeding 1500 °C (“hot oxygen”). The hot oxygen jet is accelerated to a velocity 2–4 times higher than is possible with comparable cold oxygen jets. Simple jet theory is used in conjunction with detailed kinetic simulations to investigate differences in lance reactivity and effectiveness. A range of conditions is investigated, including oxygen preheat temperature, ambient gas conditions and turndown capability. In all cases, hot oxygen lancing provides better mixing capability than cold oxygen lances. In addition, the increased reactivity of hot oxygen proves more effective than cold oxygen when reacting with ambient gases.A real world comparison of cold and hot oxygen lancing into a cement kiln for CO emission reduction is also presented. In practice, a non-optimized hot oxygen lance reduces CO emissions from the flue gas by more than 25% over a fully optimized cold oxygen lance.