Propellant Flow Research Articles

Prediction of cavitating propeller underwater radiated noise using RANS & DES-based hybrid method

ABSTRACT This study focuses on the prediction of the hydrodynamic and hydroacoustic performance of a cavitating marine propeller in open water condition using Reynolds-averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) solvers. The effectiveness of the methods is investigated for the recently introduced benchmark propeller that belongs to the research vessel ‘The Princess Royal’. The main emphasis of the study is to examine the capabilities of the RANS and DES solvers for predicting the hydrodynamic performance of a propeller in the presence of sheet and tip vortex cavitation (TVC). In the numerical simulations of the cavitating propeller flow, the Schnerr-Sauer cavitation model based on a reduced Rayleigh-Plesset equation was used to model the sheet and tip vortex cavitation. An alternative Vorticity-based Adaptive Mesh Refinement (V-AMR) technique was employed for the accurate realisation of the TVC in the propeller’s slipstream. In the hydroacoustic calculations, a porous Ffowcs Williams Hawkings equation (P-FWH) was employed together with the DES solver. The numerical hydrodynamic and hydroacoustic results are compared with those of experimental data for the benchmark propeller available from the University of Genova Cavitation Tunnel. The results show that both the RANS and DES solvers are successful for modelling of the sheet cavitation on the propeller blades. However, the prediction of the TVC extension using the RANS solver is found to be insufficient in comparison to the TVC prediction when using the DES method. This is due to the inherent modelling limitations of the RANS solver. In addition to hydrodynamic performance predictions, the overall noise spectrums were found in an agreement with the experimental data with discrepancies between the low and high-frequency region.

Evaluations of the outcome variability of RANS simulations for marine propellers due to tunable parameters of cavitation models

There are two issues with cavitation modeling that need to be resolved: (1) the lack of sound physical meaning for the Vapor Volume Fraction (VVF) to set a threshold a priori for determining the range of cavitation extension; (2) the outcome variability (uncertainty) on the model's predictability resulting from the uncertainties of the model's tunable parameters, whose exact values are usually hard to obtain. This paper uses as a tool the methodology of the Cavitation Occurrence Probability (COP), which can be regarded as the resolution of the first issue, to resolve the second issue and evaluate the outcome variability due to the tunable parameters of three popular cavitation models, i.e. the Full Cavitation Model (FCM), Zwart-Gerber-Belamri (Z-G-B) and Schnerr-Sauer (S–S) models. RANS simulations were performed for a cavitating propeller flow with these three cavitation models, whose tunable parameters were varied to generate the VVF distributions and thrust data for comparisons with the experimental data. The results show that the FCM model is capable of yielding the most accurate predictions of cavitation at its default setting and thrust at some other setting, while the S–S model is capable of yielding the most precise (certain) predictions of cavitation and thrust.

Fundamental Study on Injector Flow Characteristics of Self-Pressurizing Fluid for Small Rocket Engines

Abstract Nitrous oxide is a suitable propellant for rocket engines and has been widely used in various countries, given its high saturated vapor pressure, which enables self-pressurization. Because nitrous oxide is in a state of vapor–liquid equilibrium in tanks, it is easy to form a gas–liquid two-phase flow by cavitation in feed line. Since accurately estimating the performance of rocket engines requires evaluating the characteristics of propellant flows, tests reported in this paper were conducted using hybrid rocket engines under three conditions: cold flow test, hot firing test at low back pressure, and hot firing test at high back pressure. With consideration to the subcooling degrees, nitrous oxide may be in an unsteady superheated state in the upstream flow of the injector. In a comparison of the pressure ratios between the injector in each test condition, it is observed that a critical two-phase flow was formed in the injector in the cold flow test and in the low backpressure firing test. In the high backpressure hot firing test, the injector flow may be choked, but the large oscillations were observed in chamber pressure and thrust. According to the FFT analysis results, these oscillations were caused by chugging and acoustic oscillation. In light of these experimental results, it is suggested that when the chamber pressure fluctuates due to combustion instability such as chugging and acoustic oscillation, it may affect the injector flow characteristics and the critical two-phase flow.

Effects of propeller flow on the longitudinal and lateral dynamics and model couplings of a fixed-wing micro air vehicle

This paper analyzes the effects of propeller flow on the linear coupled longitudinal and lateral dynamics of a 150 mm wingspan fixed wing micro air vehicle (MAV). The effects propeller flow on the lift, drag, pitching moment and side force is obtained through wind tunnel tests. The aerodynamic forces and moments are modeled as a function of angle of attack, sideslip angle, control surface deflection and propeller rotation per minute. The nonlinear six degrees of freedom model is linearized about straight and constant altitude flight conditions for different trim airspeed to obtain linear coupled longitudinal and lateral state space model. The eigenvalues and eigenvectors of linear coupled longitudinal and lateral state space model are compared with and without propeller flow effects. The variation in the natural frequencies and damping ratios of short period mode, phugoid mode and Dutch roll mode are analyzed for various trim airspeed. An increase in the natural frequency is observed for phugoid mode and Dutch roll mode with propeller effects. The stability of the spiral mode is enhanced by the propeller flow and also the response of the roll subsidence mode is faster with propeller effects. Detailed analysis of eigenvalues and eigenvectors shows the importance of incorporating propeller flow in analyzing the dynamics of the MAV.

The wake structure of a propeller operating upstream of a hydrofoil

Abstract

Continuous ultrasonic flow measurement for aerospace small pipelines

Aerospace explorations stimulate extensive research on innovative propellant flow measurement technologies in microgravity conditions. Ultrasonic-based measurements have advantages of non-invasive and non-moving-component constructions as well as fast responses to bi-directional flow detection, its applications in aerospace explorations have already been reported. To avoid the shortages of pulse ultrasonic measurement configurations, flow measurement of continuous ultrasonic wave propagation is presented to match the requirements of large measurement range and high precision. Fabrication process and laboratory validations using water flow are presented. Ground experiments show that the linearity of the proposed ultrasonic flow meter is obtained in the measurement range [0, 80 ml/s] which is typical requirement in aerospace applications. Meanwhile, the fitted linear feature from the experimental data matches well the theoretical prediction except the flow prediction of stationary fluid. Under specific configurations, the absolute measurement error is significantly affected by the corresponding Reynolds number. Furthermore, the absolute measurement error is smaller when excitation signals with higher frequency are used if the phase tracking performance for different frequencies is identical.

The Two-Point Boundary-Value Problem for Rocket Trajectories

The two dimensional gravity turn problem is addressed allowing for the effects of variable rocket mass due to propellant consumption, thrust and thrust vector angle, lift and drag forces at an angle-of-attack and atmospheric mass density varying with altitude; Coriolis and centrifugal forces are neglected. Three distinct analytical solutions are obtained for constant: propellant flow rate, thrust, thrust vector angle, angle-of-attack and acceleration of gravity; the lift and drag are assumed to be proportional to the square of velocity, and the mass density is assumed to decrease exponentially with altitude. The method III uses power series of time for the horizontal (downrange) and vertical (altitude) coordinates; the method II replaces the altitude as variable by the atmospheric mass density and method I by its inverse. Thus the three solutions have distinct properties, e.g., I and III converge best close to lift-off and II close to burn-out. The three solutions: I, II, III, can be applied in isolation (or matched in combination) to the single-point boundary-value problem (SPBVP) of finding the trajectory with given initial conditions at launch. They can also be used as pairs in six distinct ways (I + II, I + III, II + III or reverse orders) to solve the two-point boundary-value problem (TPBVP), viz.: from given conditions at launch achieve one (not more) specified condition at burn-out, e.g., ã desired horizontal velocity for payload release. Each of the six distinct combinations of methods of addressing the TPBVP shares three features: (i) it can determine if there is a solution, viz. if the rocket has enough performance to reach the desired burn-out condition; (ii) if the desired burn-out condition is achievable it can calculate the complete trajectory from launch to burn-out; (iii) it can determine the range of achievable burn-out conditions, e.g., the minimum and maximum possible horizontal velocity at burn-out for given initial conditions at launch.

On the instability mechanisms of ship propeller wakes

This paper evaluates the propeller wake characteristics of the benchmark ship propeller INSEAN E779A using large eddy simulations and identifies instability mechanisms that lead to wake breakdown. The effects of propeller blade loading on wake stability are considered by conducting simulations at different advance coefficients (J = 0.85, J = 0.65 and J = 0.45). The hydrodynamic results capture the propeller wake vortical structures and flow features from the onset and evolution of the instability to the far wake. The simulation results are verified and validated against experimental measurements from the literature. A new instability mechanism concerning mutual interaction among adjacent helical vortex sheets in the transition region is identified. Further, the formation of short wave instabilities in the vortex filaments is found to be initiated by the same mutual interactions among sheets. Lastly, it is shown that interaction of sheets with the preceding tip vortex induces the onset of tip vortical filaments breakup, mutual-interaction and long wave instability.

Analysis of the blade boundary-layer flow of a marine propeller using a RANS solver

In this paper a comparison between RANS simulations carried out with the k−ω SST turbulence model and γ−R̃eθt transition model, and experimental measurements for marine propeller P4119 is made. The experiments were conducted at the David Taylor Model Basin and comprehended three-dimensional velocity components measurements of the blade boundary-layer using a LDV system in uniform conditions. The present work includes an estimation of the numerical errors that occur in the simulations, analysis of the propeller blade flow, chordwise and radial components of the boundary-layer velocity profiles and boundary-layer characteristics. From this comparison and depending on the selected inlet turbulence quantities, we conclude that the transition model is able to predict the extent of laminar and turbulent regions observed in the experiments. Moreover, the predicted velocity profiles show good agreement with the experimental measurements and verified the location of transition.

Optimum characteristic length of gas generator for liquid propellant rocket engine

Gas generator is an essential part of gas generator cycle Liquid Propellant Rocket Engine (LPRE). While designing the Gas Generator (GG), the selection of an unoptimized characteristic length result in an increase in mass flow rate of propellants required to drive turbine. As the exhaust of the gas generator is of little importance in the thrust of the engine, therefore, the specific impulse of the engine decreases with increase in the propellant flow rate to the gas generator. In literature, it is witnessed that researchers have conducted investigation of gas generator performance in terms of variation in mixing ratio or some models have been used to predict the characteristic length; however, it lacks the experimental investigation of gas generator performance in terms of characteristic length. In this paper, an experimental investigation of the gas generator of LPRE is conducted to determine the optimum characteristic length of the gas generator with liquid oxygen and kerosene. Hot tests are conducted with two different types of injectors, namely pressure swirl injector and impinging injectors in a modular water cooled gas generator. The gas generator is tested using six different characteristic lengths (i.e., from 1.75 m up to 9.67 m) for pressure swirl injector and with three different characteristic lengths (i.e., from 1.75 m up to 7.15 m) for impinging injector. The experimental results of hot tests show that the highest characteristic velocity of gas generator is achieved at a characteristic length of 4.27 m. It is demonstrated that a higher characteristic velocity of gas generator is achieved using impinging injector as compared to liquid-liquid pressure swirl coaxial injector at mixing ratio of 0.28 at optimum characteristic length. The effects of increase in mixing ratio with decrease in total mass flow rate on the chamber pressure are also discussed.

Effect of pre-swirl stator on wake flow of an ducted propeller

Numerical simulations of wake flow field of ducted propellers with and without pre-swirl stator are carried out by means of k-ω model. Then the velocities and the pressure fluctuations of the wake flow at different positions from the propeller are analyzed. The result shows that both the near-propeller blade velocity and the overall averaged velocity are obviously increased by the pre-swirl stator. Moreover, the pre-swirl stator can improve the surface pressure distribution near the blade but at the same time can enhance the pressure pulsation in the wake flow, especially at the downstream region.

The Performance of Single and Double Intake Designs of Propeller Flow Cooling System (PFCS)

In order to save spaces inside a small-sized fishing boat, the high-pressure flow behind propeller is utilized instead of a special cooling pump to cool the main engine. From the previous study, the system is referred to as the Propeller Flow Cooling System (PFCS). As a continuation of the previous study, the present study conducted more experiments in order to compare the performance of a single and a double intake designs of the PVCS with the same cross-sectional area. The designs with circular and elliptical intakes shapes were measured. The experiments were also conducted at the Circulating Water Channel (CWC) facility. The main parameter which was compared in the experiment and analysis was the flow capacity produced by both designs for various propeller revolution (RPM). The experimental results showed that single intake design has a higher flow capacity than the double intake one which was caused by higher flow losses inside the pipe of single intake design mainly due to higher surface friction as well as an additional elbow joint needed in double intake design. This tendency occurred for both circular and elliptical shapes cases.

Interactions between turbulent flow and diffusion flame of composite propellant in a solid rocket motor with sidewall mass injection

The numerical procedure for a diffusion flame based on Ammonium Perchlorate/Hydroxyl-Terminated Polybutadiene (AP/HTPB) composite propellant in a solid rocket motor (SRM) is presented. This article accounts for the turbulence effects in a combustion chamber with sidewall mass injection and the propellant diffusion flames at various axial locations are studied. The mutual coupling between the vortical and entropy modes is discussed comprehensively, with the inclusion of the influence of the chamber pressure. The effects of the AP particle size and the combustion environment are also analyzed. The flow evolution in the SRM is clearly observed in the results: laminar, transitional, and turbulent. Compared with the laminar area, the flames fluctuate drastically in the turbulent flow, and the chemical kinetics processes are altered greatly. The diffusion and mixing processes of the reactants are enhanced due to the contribution of the turbulence, and the heat release of the flames is elevated. The high chamber pressure and smaller AP size could lead to more intensive fluctuations of the flame heat release. This may drive thermoacoustic instability in the SRM.

Development of the MiXI Thruster with the ARCH Discharge

The Miniature Xenon Ion (MiXI) thruster with the Axial Ring-Cusp Hybrid ‘MiXI(ARCH)’ discharge was developed and operated with beam extraction at 1 kV. The thruster achieved 59% cathode-free total discharge efficiency at 23.7 mA xenon beam current with filament cathodes and low temperature operation, corresponding to a discharge loss of 226 W/A and propellant utilization of 72%. Thruster efficiency was observed to increase with increasing flow rate and decrease with increasing temperature up to thermal steady state. At thermal steady state, the thruster anode reached ∼320 °C due to the thermal isolation of the thruster head. Reducing the discharge chamber aspect ratio from 0.5 to 0.4 increased thermal steady state efficiency from 46% to 57% but required slow ramping of beam voltage and was limited to stable operation to above 0.5 sccm discharge propellant flow. In contrast to the 3-ring cusp configuration, MiXI(3-Ring), the performance is generally higher but is not able to achieve lower thrust levels and requires more complex start-up for stable operation. An analytical single-cell model was developed and applied to investigate internal processes of the MiXI(ARCH) discharge. The model emulated the effect of increasing flow on performance, indicating that the dominant loss mechanism is plasma electron current to the anode, in contrast to the 3-Ring geometry, which is dominated by primary electron losses. This model also matched trends reported in previous works of strongly increasing electron temperature and primary density with propellant utilization. Through this effort, the MiXI thruster’s highest achievable total efficiency has been increased, and several mechanisms for further improved efficiency have been identified.

ОСОБЛИВОСТІ КОНСТРУКТИВНИХ СХЕМ ДВИГУНІВ З ІМПУЛЬСНИМИ ДЕТОНАЦІЙНИМИ КАМЕРАМИ

The pressure of the products of chemical reactions in the chamber of a rocket engine increases significantly if the rocket fuel components burn in the detonation mode. In this case, it can get to a simpler and more reliable expulsion propellant feed system instead of a turbopump feed system. The value of heat release power (MW / liter) of detonation engines is several orders of magnitude larger than that of aircraft and rocket engines operating in the Brighton cycle. The high rate of energy released in the detonation mode can significantly reduce the mass, the inertia, and overall dimensions of the propulsion system. Due to these features, detonation chambers are advisable to be used as part of ejector pulsed detonation engines, together with a turbine – in electric power generators of spacecraft, in a hybrid design – together with turbofan or turboprop engines, etc. In the article are considered various design schemes of pulse detonation engines (PDE): single-chamber and multi-chamber pulsed detonation engines; an ejector PDE system; a hybrid PDE and an integrated detonation-turbine unit with a detonation chamber in the form of a spiral and with a multi-chamber detonation device. The possibility of pulsation frequency increase is realized in the multi-chamber pulsed detonation engine, and the possibility of thrust size increase is realized in PDE with ejector. Replacing traditional chambers with detonation chambers in the construction of gas turbine jet engine will allow providing a decrease in propellant flow rate value from 8 % to 10 % on some estimations. In the hybrid detonation propulsion plant advantages inherent to the detonation cycle combine with positive features of a turbo-compressor jet engine. A combination of PDE and turbine allows creating the cogeneration propulsion system in that a turbine is used for the production of electric power, and detonation chamber – for the creation of thrust impulse. Practical realization of hybrid pulse detonation turbo-engine and the integrated detonation-turbine device is possible if two key complex problems will be solved. These problems are the detonation waves weakening on input in a turbine and the bearing and shaft necessary work resource increasing into a detonation pulsating stream

Experimental Study on the Effects of Discharge Chamber Length on 5 cm Radio-Frequency Ion Thruster

For keeping microgravity level of microgravity and space science satellites, a kind of electric thruster, the radio-frequency ion thruster (RIT) has been designed and applied. The RIT produces thrust through ionizing neutral particles in the discharge chamber and extracting ions by the ion optics system. The length of discharge chamber affects the ionization of neutral particles as well as the performance of RIT. In this paper, an experimental study has been carried out for analyzing the influence of discharge chamber length. In the experiment, the RIT-5 with various discharge chamber lengths, 27.6 mm, 30.0 mm, 31.9 mm, 35.5 mm, 40.0 mm, has different performances under the same condition. With the same radio frequency power and propellant flow rate, the RIT-5 has the optimal performance in beam current and efficiency when the discharge chamber length is 30.0 mm or 31.9 mm.

Numerical investigation on hydrodynamic characteristics of two-phase flow with liquid hydrogen through cryogenic feed lines at terrestrial and microgravity

Two-phase flow of cryogenic propellants in feed lines during the chill-down operation for space application system is inevitable. Such cooling process exhibits dynamic response, which are difficult to control due to flow instabilities and differential cooling rates. Moreover, the dynamics of two-phase phenomena in microgravity differ from that operated at terrestrial gravity. Hence, in the present work, transient modelling for two-phase flow of liquid hydrogen (LH2) is presented. A 3-dimensional computational model of a cryogenic feed line have been developed and meshed using commercial software ICEM CFD and exported to the solver ANSYS-FLUENT. Volume of Fluid (VOF) method based on Eulerian flow scheme is implemented in order to capture the two-phase flow of LH2 and for reliable prediction of hydrodynamic characteristics at various gravity conditions. Void fractions at different locations of the vertical pipe are obtained and Probability Density Functions (PDFs) are generated in order to predict the morphology of the flow regime. Moreover, velocity profiles along with phase distribution are presented to analyze the interfacial behaviour and reveal the structure of two-phase flow. Annular dominant slug flow is obtained in the present work, whereas bubbly dominant slug flow was obtained in the reference work for conventional fluids (air-silicone mixture). Moreover, PDF signatures reveal that the probability of occurrence of annular characteristic is ~1.3 and 3.5 times to that of bubbly feature at terrestrial and microgravity conditions respectively. Hence, the present methodology is useful in the prediction of flow structure and phase distribution at terrestrial and microgravity conditions.

Numerical investigation on the effect of shaft inclination angle on hydrodynamic characteristics of a surface-piercing propeller

The global demand for fast sea transportation has led to an ongoing development of high-speed vessels and surface-piercing propeller, as a high performance propulsor, has played an important role in this development. However, the complexity of the two-phase flow field around the propeller has made its numerical analysis enough challenging. The performance of surface-piercing propeller depends on propeller geometric parameters and flow conditions at propeller disk. Among these parameters, shaft inclination angle is a key parameter which significantly affects the flow conditions at propeller disk. In this paper, RANS computations were applied to investigate the unsteady flow around an optimized surface-pricing propeller in various shaft inclination angles. Likewise, the homogeneous Eulerian multiphase model was employed along with Volume of Fluid model to solve the two-phase flow field equations. Rotational motion of the propeller was simulated by CFX sliding mesh technique. The effect of shaft inclination angle on the hydrodynamic coefficients of the propeller and the behavior of the fluid flow around the propeller key blade are among the principal objectives clarified in this study. As the results indicated, the propeller thrust and torque coefficients were gone up with an increase in the shaft inclination angle. Moreover, as the shaft inclination angle increases, the maximum thrust and torque coefficients of the key blade take place at the lower rotation angles. Additionally, it was revealed that the effect of shaft inclination angle on the torque coefficient of the key blade depends on the angular position of the key blade. Furthermore, the flow patterns around the propeller were predicted in different shaft inclination angles. In order to verify the accuracy of the numerical method used in this paper, numerical simulations were run on SPP-841B propeller with available experimental data. The comparison between the simulated and measured SPP-841B open characteristics as well as the ventilation pattern of the key blade indicates a reasonable agreement with the experimental data.

Numerical Simulation of Hydrodynamic Characteristics of Underwater Hull Cleaning Robot Using CFD Techniques

In this article, an underwater hull cleaning robot model based on propeller thrust adsorption is established for near-wall conditions. By using a computational fluid dynamics method, which is proven feasible by comparing a calm water resistance simulation with its experimental data, the influence of floating body shape and wall distance on its hydrodynamic characteristics is studied. Then, the body force propeller model is used to analyze the interaction between the propeller flow field and the flow field around the underwater cleaning robot. Compared with the cuboid floating body, the results show that the streamlined appearance can greatly reduce front high-pressure area, the pressure drag between the front and rear ends, and the viscous resistance. Its drag coefficient is reduced by 11.5%. The presence of the hull will increase the pressure drag and viscous resistance of the underwater hull cleaning robot, which is similar to the "shallow water blockage effect" of a ship. For this model, the decrease in the wall distance results in a progressive increase in resistance and drag coefficient. As the wall distance is .15 m, the drag coefficient of the underwater hull cleaning robot increases by 4.55%, compared with the limitless water field. For the body force propeller model, the study indicates that when the flow velocity is constant, both the resistance in the forward direction and the adsorption force of the underwater hull cleaning robot increase with the increase in rotation speed of the propeller. The thrust propeller generates a higher increase in resistance and a lower increase in adsorption force compared with the adsorption of the propeller. When the rotation speed is constant, the resistance of the underwater hull cleaning robot increases, with the increase in the flow velocity, and the adsorption force of the underwater hull cleaning robot first decreases and then increases. Therefore, it must be fully considered that the significant influence of the hull and the propeller on the underwater hull cleaning robot can provide theoretical guidance for future related design and research.

Characterization of a Capillary Flow Controller for Electric Propulsion

A low-cost and reliable propellant flow controller is necessary to offer competitive electric propulsion systems. This paper first reviews xenon flow control methods for Hall thrusters and ion engines. Through a trade study, a simple and low-cost xenon flow controller applying a heated capillary is proposed. The test article is fabricated based on a developed theory and tested with xenon. The estimation based on laminar flow shows slightly different characteristics from those of the experiment, although the Reynolds number indicates a laminar condition. The turbulent flow assumption is in good agreement with the experiment at a high mass flow rate while the flow characteristics are between laminar and turbulent at a low mass flow rate. That implies that the surface roughness and tube curvature induce the laminar–turbulent transition even in the low mass flow rate case. To obtain a wider flow rate range, maintaining laminar flow in the capillary is desirable because of the high sensitivity of the friction coefficient with temperature in the laminar flow. Component improvements achievable through miniaturization and reduction of the inner wall surface roughness and capillary curvature are considered to be necessary to prevent the turbulent transition.