Nozzle Wall Research Articles

Efforts to Identify the Most Suitable RANS Turbulence Model for Accurate Conjugate Heat Transfer Prediction in Regenerative Cooled Nozzles

Abstract This study presents a two-part numerical study aimed at improving the prediction and understanding of regenerative cooling in supersonic nozzles. The first objective was to identify the most appropriate Reynolds-averaged Navier–Stokes turbulence model for accurately predicting conjugate heat transfer. Three turbulence models, Shear Stress Transport, Reynolds stress model (RSM)-ω, and RSM-ω with shear flow corrections (SFC), were tested through comparative analysis and simulations to evaluate their accuracy in predicting the heat flux rate and temperature on the nozzle wall. The results indicate that the RSM-ω turbulence model with shear flow corrections provides the best thermal prediction, achieving an improvement of 28% compared to the next-best model. The second part assesses the impact of key parameters on cooling efficiency. High coolant pressure proves advantageous for extremely hot-gas flow due to increased saturation temperature. Interestingly, the height of the cooling slot has less significance, suggesting other factors should be prioritized in film-cooling system design. The study also investigates the effectiveness of hydrogen coolant in reducing wall gas temperatures and preventing excessive heat that could melt the nozzle material. Transient results show that the gas-side wall temperature increases more rapidly than the coolant side during start-up and cooling the walls takes longer than reaching a steady-state for the hot-gas flow. The simulation results align well with experimental data, validating the accuracy and reliability of the numerical approach.

3D concrete printing using computational fluid dynamics: Modeling of material extrusion with slip boundaries

This paper investigates the role of slip boundary conditions in computational fluid dynamics modeling of material extrusion and layer deposition during 3D concrete printing. The mortar flow governed by the Navier-Stokes equations was simulated for two different slip boundary conditions at the extrusion nozzle wall: no-slip and free-slip. The simulations were conducted with two constitutive models: a generalized Newtonian fluid model and an elasto-viscoplastic fluid model. The cross-sectional shapes of up to three printed layers were compared to the experimental results from literature for different geometrical- and speed-ratios. The results reveal that employing free-slip boundary conditions at the extrusion nozzle wall improves layer-mimicking quality for both constitutive models, indicating the presence and importance of a lubricating layer of fine particles at the concrete-solid wall interface. This enhanced performance is primarily due to the observed decrease in extrusion pressure that minimizes layer height- and width-deviations compared to the experimental prints. Furthermore, the free-slip boundary conditions play an important role in predicting the multilayer prints, its deformation and groove shapes.

Condensation shock topologies in carbon dioxide and a non-condensable gas mixture in supersonic nozzles

Condensation shock waves may occur in many flow expansion devices such as turbomachinery, gas ejectors, micro thrust-nozzles, and supersonic gas flow separators. However, their experimental analysis has been barely addressed as condensation shocks comprise complex phenomena such as compressible flow behavior, a shock-like phase transition, and a two-phase flow expansion. This work characterizes experimentally some condensation shock topologies of a mixture of carbon dioxide and dry air at several compositions in a Laval nozzle. Experiments were carried out in a test-rig instrumented with high-response pressure transducers installed along the Laval nozzle wall along with a Schlieren setup equipped with a high-speed video camera imaging the flow behavior within the nozzle. The nozzle wall profile was built by using the method of characteristics developed from a real equation-of-state suited for the testing mixture. Results revealed the influence of the nozzle wall profile on the condensation shock location and topology. Moreover, there types of flow behavior were captured and named as conventional, transition, and Mach wave condensation shocks. The transition from one topology to another occurred due to the interaction between cancelation waves originated from the nozzle wall and the phase-change phenomenon, giving rise to two distinct regions characterized by certain observable droplet population density. The current investigation presents an in-depth phenomenological discussion of the three types of condensation shock topologies as such assessment has not been previously developed.

Experimental and numerical investigation on thermochemical erosion and mechanical erosion of carbon-based nozzles in hybrid rocket motors

In order to enhance energy characteristics of propellants in hybrid rocket motors, aluminum particles are added into the solid fuel. However, these particles may lead to nozzle mechanical erosion, which significantly affects the motor performance. This paper intends to study thermochemical and mechanical erosion mechanism of carbon-based nozzles in hybrid rocket motors with aluminum metallized fuel. A firing test is performed, and 95 % hydrogen peroxide and hydroxyl‑terminated polybutadiene based fuel with aluminum particles are utilized. Experimental results show that many metal particles are ejected from the nozzle, and aluminum oxide deposits heavily on the nozzle inner surface. A method of numerical calculation coupled with two-phase flow, combustion of aluminum metallized fuel, thermochemical ablation reactions, and mechanical erosion is established. The errors of combustion chamber pressure and throat erosion rate between numerical calculation and test results are 0.53 % and 7.76 %, respectively. Simulation results indicate that with the increase of aluminum content, nozzle wall pressure gradually increases, while the mass fraction of H2O, CO2, OH, and O declines. The nozzle wall temperature and thermochemical erosion rate raise first and then reduce as aluminum content increases. The mechanical erosion is mainly distributed in the convergent section, and it raises with the increase of aluminum content. When aluminum content is up to 38 %, the maximum mechanical and thermochemical erosion rates are 0.09185 mm/s and 0.0976 mm/s, respectively. This reveals that effects of mechanical erosion on hybrid rocket nozzles should be carefully considered and evaluated under conditions of high aluminum content.

Multipurpose Additives Toward Improving the Polymer Cold Spray Process

Polymers have proven to be challenging to cold spray, particularly with high efficiency and quality when using inexpensive nitrogen (N2) and air propellants. Helium (He), when used as a process propellant, can improve spray deposit properties but is often undesirable due to its limited availability and high cost. In this study, additives of multiple particle sizes and materials were mixed with polymer powder in an effort to improve the performance of polymer sprays using mainly N2 as a process propellant. The effects of hard-phase additives on deposit microstructure were investigated by precise ion beam polishing of deposit cross sections and subsequent electron microscope imaging. Additional metrics including the density and post-spray composition of deposits were investigated to quantify the peening effect and the amount of embedded additive. Additives, regardless of size, were observed to embed in the spray deposits. Additionally, hard-phase additives demonstrated nozzle cleaning properties that continually remove polymer fouling on the nozzle walls. Inversely, sprays with polymer powder and no additives tended to clog the nozzle throat and diverging section because of continual fouling.

Computational Analysis and Regression Laws for Nozzle Erosion Prediction in Hybrid Rockets

The erosion of the nozzle throat can represent one of the major limitations against the future widespread use of hybrid rocket engines (HREs) in the space industry. In fact, nozzle erosion in HREs can be more severe and harder to predict than in solid rockets due to the higher concentration of oxidizing species in the combustion products and to mixture ratio shifts and/or throttling. Therefore, an accurate understanding of the erosion phenomenon is of fundamental importance for the technological advancement of HREs. This work is focused on the investigation of graphite nozzle erosion in HREs burning high-density polyethylene with two different oxidizers, oxygen and nitrous oxide. First, the results of a computational fluid dynamics parametric analysis are used to derive closed-form regression laws for the rapid estimation of nozzle throat erosion and wall temperature depending on chamber pressure and mixture ratio. Then, a one-dimensional transient heat conduction solver is loosely coupled with the aforementioned regression laws, allowing to reconstruct the transient heating process within the solid. The obtained numerical results are validated against experimental data. Finally, the effect of gas-phase reactions on the heterogeneous reactions occurring at the nozzle surface is highlighted when moving from fuel-rich to oxidizer-rich conditions.

RESEARCH OF SUPERSONIC FLOW IN SHORTENED NOZZLES OF ROCKET ENGINES WITH A BELL-SHAPED TIP

The flow in a shortened nozzle with a bell-shaped tip is considered. A comparison of the wave structures of the supersonic gas flow in shortened nozzles with short and long tips formed by compression and stretching of the original bell-shaped nozzle for connection, respectively, with the long and short conical part of the base nozzle at the same nozzle length was carried out. Under operation conditions at sea level and low pressure at the nozzle inlet (P0<50·105 Ра), a large-scale vortex structure, starting from the corner point of the nozzle inlet, is observed in both nozzles. In addition, in the long tip, a small-scale vortex is observed on the wall near its cut. A barrel-shaped wave structure of hanging jumps with a closing Mach disc is formed in the flow in both nozzles, inside which a "saddle-shaped" wave structure of low intensity is noticed. In the separation flow in the tip (when Р0<50·105 Ра and Рн = 1·105 Ра), the pressure on the wall in the separation zone is slightly lower (by ≈ 5-10%) than the external pressure Рн. When the engine is operating in the upper layers of the atmosphere, the static pressure on the section of both tips is proportional to the pressure at the entrance of the nozzle. In the cross-section, starting from the axis of the nozzle to ~0.89 R/Ra (the ratio of the current value of the radius R to the radius of the nozzle wall at the outlet Ra), the pressure decreases to a value proportional to the pressure at the nozzle inlet. Then, it increases linearly to the value of the pressure on the tip wall, which is proportional to the pressure at the nozzle inlet. This is due to the wave structure of the flow inside the nozzle. It was established that with a decrease in the length of the nozzle conical part, the impulse coefficient of the nozzle decreases significantly for operating at sea level and slightly decreases for operating in the upper layers of the atmosphere. The results of calculations correlate satisfactorily with the experimental study results of the flows in shortened nozzles with a bell-shaped tip

Experimental investigation about the aerodynamic noise caused by hypersonic turbulence

In this study, experimental investigations pertaining to aerodynamic noise are conducted in a hypersonic quiet wind tunnel, which possesses the unique capability of operating in both quiet and conventional modes, achieved by controlling the bleed slot to regulate the boundary layer flow. The measurement of aerodynamic noise and analysis of coherent structures of hypersonic turbulence are accomplished employing pressure probes and the nano-tracer-based planar laser scattering technique. The characterization of aerodynamic noise within the freestream unveils that noise generated by turbulent structures on the nozzle wall is the primary factor affecting the turbulence intensity of the freestream flow. Regarding the acoustic radiation noise generated by the turbulence on the nozzle wall, a peak frequency ranging from 54 to 57 kHz is observed in its spectrum within a unit Reynolds number range of 0.3×107–1.1×107 m−1. Under different operation modes, the freestream pitot-pressure data feature the similar spectral slope of f−2.2 and f−12 before and after the aforementioned peak. Through wavelet analysis, scales of the coherent structure in the turbulent boundary layer are examined, revealing that the maximum energy streamwise scale of the coherent structure is approximately 2.47 mm under the unit Reynolds number of 0.7×107 m−1. The product of this scale with the characteristic frequency of 56 kHz obtained from fluctuating pressure measurements is close to the local sound speed of about 140 m/s.

Численное исследование полидисперсных двухфазных течений в осесимметричном сопле Лаваля с учетом силы Магнуса, действующей на вращающиеся капли

The available papers on two-phase flows in de Laval nozzles are focused on the effect of various initial conditions, models of coagulation, fragmentation, and rotation of droplets on their local and integral characteristics. Some papers note that due to the difference in the velocities of the gas and droplets along the nozzle axis, the Magnus force acts on the rotating droplets perpendicular to the specified difference and deflects the trajectories of the droplets toward the nozzle wall. In an earlier paper, the authors proposed a mathematical model of a two-phase flow in an axisymmetric de Laval nozzle that accounts for the Magnus force on the basis of the kinetic equation. The present article is devoted to a numerical study of a polydisperse two-phase flow in a de Laval nozzle with account for the coagulation, fragmentation, and rotation of droplets and the Magnus force. This study is based on the “monodisperse” model of fragments developed by I.M. Vasenin and A.A. Shreiber, the method of labeled drops (the Lagrange method), and the finite-difference schemes of second order accuracy. The calculations are carried out for a test nozzle configuration with condensate formation on the nozzle wall both with and without the Magnus force accounted. The calculated results show that the Magnus force has different impacts on the trajectories of droplets of various sizes. It should be noted that the limiting trajectories of the droplets approach the nozzle wall due to the Magnus force, resulting in the earlier dropout on the wall. Therefore, when designing the divergent section of the nozzle, it is necessary to consider the revealed approach of the location of the dropout, which is associated with the Magnus force, to the nozzle throat.

Minimally-intrusive, dual-band, fiber-optic sensing system for high-enthalpy exhaust plumes

<abstract> <p>The propulsion research lab at Utah State University has developed a minimally-intrusive optical sensing system for high-temperature/high-velocity gas-generator exhaust plumes. For this application glass fiber-optic cables, acting as radiation conduits, are inserted through the combustion chamber or nozzle wall and look directly into the flow core. The cable transmits data from the flame zone to externally-mounted spectrometers. In order to capture the full-optical spectrum, a blended dual-spectrum system was employed, with one spectrometer system tuned for best-response across the visible-light and near-infrared spectrum, and one spectrometer tuned for best-response in the near- and mid-infrared spectrum. The dual-band sensors are radiometrically-calibrated and the sensed-spectra are spliced together using an optimal Wiener filtering algorithm to perform the deconvolution. The merged spectrum is subsequently curve-fit to Planck's black-body radiation law, and flame temperature is calculated from associated curve maxima (Wien's law). The presented fiber-optic sensing systems performs a function that is analogous to Raman spectroscopy. The system non-contact, high-temperature measurement, and does not interfere with the heat transfer processes. In this report data collected from a lab-scale (200 N) hybrid rocket system are analyzed using the described method. Optically-sensed flame-temperatures are correlated to analytical predictions, and shown to generally agree within a few degrees. Additionally, local maxima in the optical spectra are shown to correspond to emission frequencies of atomic and molecular oxygen, water vapor, and molecular nitrogen; all species known to exist in the hybrid combustion plume. Presented data demonstrate that selected fiber-optics can survive temperature greater than 3000 ℃, for durations of up to 25 seconds.</p> </abstract>

Propulsive characteristics of single-pulsed jets with tube and orifice openings

The effects of the nozzle exit geometry on the unsteady propulsive characteristics of single-pulsed jets are studied numerically. For both tube and orifice nozzles, the jet exit configuration is parameterized by the diameter ratio RD, which is defined as the ratio of the nozzle entrance D0 to the jet exit diameters D. It is found that the diameter ratio has significant influence on the propulsive characteristics of the single-pulsed jet during its entire ejection phase. The total impulse production is augmented considerably as the diameter ratio increases until a critical value of RD_cir≈2.0 is approached. The larger impulse production by the orifice nozzles over the tube nozzle stems from the persistent over-pressure contribution at the jet exit due largely to the fact that the flow contraction near the jet exit of the orifice nozzle results in the intensification of the radial velocity gradients and higher local pressure. By using the existing prediction of the contraction coefficient Cc to account for the flow contraction, a theoretical model has been developed with the quasi-one-dimensional flow approximation to predict the pressure thrust at the jet exit during the steady discharging stage, showing good agreement with the present numerical results. Moreover, the pressure force acting on the vertical wall of the orifice nozzle, which is proportional to the wall area, is found to be primarily responsible for the larger transient variations in the jet impulse during the onset and end of the jet ejection phase as the diameter ratio increases.

Experimental study on boundary layer of internal flow visible supersonic nozzle

The high-frequency pulsation noise generated by the turbulent boundary layer on the wall of a Laval nozzle can significantly affect the quality of the flow field at the nozzle outlet. In this study, a supersonic wind tunnel with visible internal flow is designed and fabricated to observe the development and evolution of the boundary layer on the contraction and expansion surfaces of a Laval nozzle, as well as to study the flow field inside the supersonic nozzle. The subsonic, transonic and supersonic profiles of the nozzle are designed by bicubic curve, Hall method and classical characteristic line method respectively. The results of numerical calculation and total pressure measurement show that the flow field at the nozzle outlet of the wind tunnel is uniform and stable, and the deviation of Mach-number-root mean square is better than the qualified level of China's national military standard. Nanoparticle-tracer based planar laser scattering (NPLS) technology is used to carry out the flow display test of the internal flow visual supersonic nozzle, and the fine structure image of the whole flow field in the nozzle is obtained. The image clearly shows the development and evolution of the boundary layer in the nozzle. The interface between boundary layer and main stream and the wall curve of nozzle transition region are extracted by image processing technology. The fractal dimension of the extracted boundary layer contour is calculated, thereby establishing the corresponding relationship between the fractal dimension and the boundary layer state, and determining the transition position of the boundary layer. The results show that the transition position of the nozzle profile is closer to downstream than that of the nozzle straight wall. The fractal dimension can qualitatively judge the flow state of the boundary layer; however, it is necessary to distinguish between laminar boundary layers and hairpin vortices in the initial transition stage by considering the thickness of boundary layer.

Computational modeling of heat transfer and flow separation in supersonic cooled nozzles: Parametric study

Flow separation is necessary for the construction of a rocket engine nozzle. Regenerative cooling is one of the most significant criteria for the safety of wall nozzles because of the high temperature and pressure in the thrust chamber. A review of a comprehensive numerical investigation of the boundary layer separation and heat transfer in a 30??15? cooled nozzle is presented. The accuracy of the SST-V turbulence model in this study was numerically investigated. For this purpose and for a wide range of chamber conditions, the effects of various parameters, such as wall temperature, turbulent Prandtl number, and constant specific heat ratio vary from 1.31 to 1.4 for constant fluid properties for N2O, CH4, Cl2, and air, respectively. The variable specific heat ratio ranged from 1.39 to 1.66 for variable fluid properties for air, CH4, O2 and Helium, respectively, and we investigated how various parameters impact the position of flow separation and local wall heat transfer.

Numerical analysis of the effects of the nozzle shape and outlet area of a waterjet propulsion system on its efficiency

The waterjet propulsion system is a marine propulsion device prevalently used on contemporary high-speed vessels. The performance of a waterjet propulsion system is considerably affected by the nozzle. In this study, the influences of the shape and the outlet area of a waterjet propulsion system on the efficiency of the propulsion system is investigated using the computational fluid dynamics method. A total of 10 different nozzle designs, including cylindrical and conical nozzles with 5 different outlet areas, are analyzed in terms of nozzle efficiency and overall efficiency, and the possible reasons and explanations behind the variations of the nozzle efficiency and the overall efficiency are proposed in this study. The simulated results indicate that the conical nozzles consistently have higher nozzle efficiency than the cylindrical nozzles, and the maximum nozzle efficiency occurs in the conical nozzle with an outlet area of 60% of the inlet duct area. The abrupt change in the flow direction at the transition between the guide vane section and the nozzle, as well as the skin friction on the nozzle wall, are predominant factors affecting the nozzle efficiency. The waterjet propulsion units equipped with conical nozzles generally have higher overall efficiency than their counterparts equipped with cylindrical nozzles, while the maximum overall efficiency occurs in both the cylindrical nozzle with an outlet area of 50% of the inlet duct area and the conical nozzle with an outlet area of 60% of the inlet duct area. The loss of mechanical energy due to viscosity and turbulence in a propulsion unit is the major source of energy loss, while the kinetic energy carried by the exit flow is also a considerable factor affecting the overall efficiencies of the propulsion units equipped with conical nozzles with relatively large outlet areas.

Lean flameout characteristics and unsteady dynamics of swirling non-premixed flame with and without outer flame

The planar laser induced hydroxyl fluorescence (OH-PLIF) technique was used to study three kinds of swirling flame, namely flames I, II, and III, by changing swirl conditions. According to the PLIF results, double structure exists in flames I and II. The inner flame burns in the inner shear layer and is anchored by vortex breakdown, which is similar to the M- or V-shaped flame. The unique outer flame is attached to the inner wall of the air annular nozzle and burns in the outer shear layer. The lean blowout (LBO) equivalent ratio of swirling flame with outer flame is lower than that without outer flame. It is interesting to compare the LBO mechanisms among the three types and the traditional swirling flame, and investigate their unsteady characteristics. Firstly, the flameout process of flames I and II starts from the local extinguishing at the root of the outer flame. However, the LBO process of flame III is consistent with that of traditional swirling flame, that is, it starts with repeated extinguishing and reigniting at the root of the inner recirculation zone (IRZ). Secondly, the unsteady characteristics of the three flames are analyzed by spectral proper orthogonal decomposition. It is found that flame oscillations, asymmetric disturbances, and longitudinal disturbances of different frequencies exist in different combinations under near-LBO conditions. In particular, asymmetric and P-wave disturbances mainly exist in the inner shear layer and jet breaking down, which further indicates the stability and anti-LBO potential of the outer flame.

Investigation of nozzle geometry and wall roughness effects on diesel injector flow

The flow and design of fuel injector nozzles have a considerable influence on the spray and combustion characteristics of a diesel engine. In-cylinder combustion, atomization, and primary breakdown are all highly influenced by the cavitation and turbulence in the fuel injector nozzle. In this paper, the effect of the nozzle geometry parameters, wall roughness parameters, and pressure difference on the swirl number, mass flow rate, turbulent kinetic energy, and vapor volume fraction is explored. U-type nozzle hole geometry, a well-known benchmark for the injector nozzle flow, is used to evaluate mesh independence and model validation. Large-eddy simulations are performed to provide a precise presentation of the flow structures and turbulent eddies inside the nozzle. Multiphase flow is studied using the mixture model, whereas cavitation is studied using the Schnerr–Sauer model based on the Rayleigh–Plesset equation. We find that the wall roughness parameters have an exciting impact on the discharge coefficient, swirl number, and vapor volume fraction. Due to the non-monotonic dependence of nozzle flow characteristics on the pressure difference and the wall roughness parameters, we can always find such values of these input parameters that render optimal nozzle flow characteristics. In this way, these parameters provide good control of spray formation and consequently on the quality and rate of combustion in the diesel engine.

Numerical research on kerosene/hydrogen/air rotating detonation engines with discrete injection strategies

The two-dimensional simulation of two-phase rotating detonation engines commonly adopts the nozzle–wall configuration, which is inconsistent with the real configurations in experiments. In the annular slot–nozzle structure, the oxidant is completely injected into the annular gap, whereas the fuel is partially injected into the nozzle hole, which is closer to the real operation condition. In this study, a gas–liquid two-dimensional numerical investigation was conducted to explore a more accurate operating condition with a discrete injection configuration. The effects of the kerosene/hydrogen injection area ratio and hydrogen equivalence ratio on the propagation mode and operating performance were investigated. The simulation results show that the kerosene droplet/hydrogen/air gas–liquid two-phase rotating detonation wave exhibits different propagation modes depending on the hydrogen equivalence ratio. When the hydrogen equivalence ratio (φH2) is 0, the detonation wave cannot be successfully initiated. When φH2 is increased to 0.2 and 0.5, a single-wave propagation mode is generated. When φH2 is 1, a double-wave propagation mode is produced initially in the combustion chamber and is subsequently converted into the deflagration mode. The flow field structure, velocity performance, and propulsive performance in the detonation combustion chamber are analyzed. It was found that an appropriate amount of hydrogen addition to the liquid kerosene detonation can aid in stabilizing the propagation of the detonation wave and improving the performance of the detonation engine.

Ignition delay and low-frequency coupling in hybrid rocket combustion

Hybrid rocket engines (HREs) require a post chamber to allow additional enthalpy production of unburned mixture, which may be expelled without participating in combustion. Many studies have confirmed that the post chamber is responsible for generating low-frequency instability (LFI). This study performed various tests with increasing post-chamber lengths. The test results show that post-chamber length is an important factor that determines the occurrence of the LFI. While the LFI persists, there is an observed positive coupling between pressure oscillations (p′) and heat release oscillations (q′), which share the same high-frequency band (400–500 Hz). But a phase difference changes periodically over time, it forms pressure beats of approximately 15–20 Hz. Video images (with LFI) show that combustion flows bounce back upstream after impinging on the nozzle wall. The bounced-back flow then collides with the incoming flow and forms a counter flow in the post chamber. In addition, re-ignitions with delays are observed in the counter-flow region, which is discontinuous and periodic. This study revealed that the periodic positive coupling of p′ and q′ is one of the manifestations of thermoacoustic instability. A modified kick oscillator model is used to account for the ignition delay and successfully predicted the pressure beats.

Optimization Design And Experimental Study of Self-oscillating Cavitating Jet Descaling Nozzle Based On Cleaning Operation

The scale of tubing in polymer flooding and ASP flooding Wells is serious in Daqing oilfield. In order to improve the cleaning effect of tubing, the self-vibrating cavitation jet nozzle was developed and the cavitation jet technology was used to remove scale. In the design of nozzle structure, it is necessary to derive the basic relation that the structure of the oscillating cavity should satisfy when strong resonance is generated, and calculate the key length dimension L1 of the oscillating cavity. The numerical simulation method the different diffusion Angle α and diffusion length L3 nozzle wall under the condition of gas generation rate and axial velocity distribution, determine the optimum size of diffuser. The scale-removing performance test of cavitation jet verifies the performance of self-vibration cavitation nozzle and determines the optimal target distance and injection Angle. According to the reasonable dimension relation of the oscillating cavity when resonance occurs, the length L1 of the oscillating cavity when strong resonance occurs is calculated as 10.4mm. Use Fluent fluid calculation software painted wall gas generating rate, the relationship between the axial velocity curve, determine the diffusion Angle α to 30°, spread long L3 is 2.5 mm, jet cavitation effect is best. The descaling performance test shows that under the inlet pressure of 20MPa, the target distance of 15mm and the injection Angle of 60°, the effective cleaning area is the largest within 1s. The designed nozzle has a reasonable structure and efficient descaling performance.

Numerical investigation of the non-equilibrium condensation inside a fuel cell turbine with variable geometry

A turbine with variable geometry can fully recover energy from the fuel cell exhaust gas and effectively reduce parasitic power consumption of the compressor. In this study, an electric turbocharger is developed for a 100 kW fuel cell system. To investigate condensation occurring inside the turbine, a wet air condensation model based on a classical nucleation theory and the Hertz-Knudsen droplet model is proposed. Validation of the model is made by testing aerodynamic performances of the turbine. In order to do this, an air humidification bench is built and exhaust gas from the fuel cell cathode outlet is replaced by humidified high-pressure air. Numerical simulation and experiment results are in good agreement. Influences of nozzle vane angle and wall temperature of the turbine on its aerodynamic performances are examined. Results show that when the nozzle opening turns small, flow capacity of the turbine decreases, pressure at the nozzle outlet declines, and condensation is more likely to occur in the rotor area. As the wall temperature drops, area in which water vapor condenses rapidly moves forward from the rotor to the nozzle. Liquid water mass fraction at different locations increases approximately 5 % as the wall temperature decreases from 310 K to 290 K.