Propeller Characteristics Research Articles

Aerodynamic Numerical Simulation Analysis of Water–Air Two-Phase Flow in Trans-Medium Aircraft

A trans-medium aircraft is a new concept aircraft that can both dive in the water and fly in the air. In this paper, a new type of water–air multi-medium span vehicle is designed based on the water entry and exit structure model of a multi-rotor UAV. Based on the designed structural model of the cross-media aircraft, the OpenFOAM open source numerical platform is used to analyze the single-medium aerodynamic characteristics and the multi-medium spanning flow analysis. The rotating flow characteristics of single-medium air rotor and underwater propeller are calculated by sliding mesh. In order to prevent the numerical divergence caused by the deformation of the grid movement, the overset grid method and the multiphase flow technology are used for the numerical simulation of the water entry and exit of the cross-medium aircraft. Through the above analysis, the flow field characteristics of the trans-medium vehicle in different media are verified, and the changes in the body load and attitude at different water entry angles are also obtained during the process of medium crossing.

Experimental research on ultrasonic A-scan testing technology of composite solid propellant

To explore the application and development of ultrasonic non-destructive testing technology in composite solid propellant materials, the theory is combined with the principle and method of ultrasonic non-destructive testing technology and the material characteristics of composite solid propellant; Based on ultrasonic A-scan, the experimental testing of propellant grain with multiphase structure, complex properties and high attenuation was carried out using pulse reflection method and penetration method. For the testing system with probe emission frequency of 1 MHz and gain adjustable range of 60 dB, the thickness of propellant grain is recommended to be 10 ~ 50 mm for the pulse reflection method to effectively observe the first bottom echo and the second bottom echo, and the thickness of propellant grain is recommended to be less than or equal to 100 mm for the penetration method to effectively observe the transmission waveform. The coupling modes of ultrasonic testing technology are further analyzed, and the effect test is carried out. In addition, based on the pulse reflection method of direct contact coupling, the sound velocity of propellant grain is measured with probes with different frequencies. The results show that the higher the probe frequency is, the smaller the sound velocity of propellant grain is.

Особливості розрахунку та моделювання обтікання несучих та тягових гвинтів літальних апаратів в умовах сильно розрідженої атмосфери

This article presents the structure of designing and modeling the flow of rotors and pusher propellers in a highly rarefied atmosphere. The aerodynamic characteristics of an airfoil are key factors in determining design accuracy and performance prediction. The blade elements operate at different Reynolds numbers and angles of attack. The blade profile was selected based on an estimate of the lift-to-drag ratio for expected Reynolds numbers under the design conditions. This paper considers the features of the operation of propellers in a highly rarefied atmosphere. When modeling propellers operate in rarefied atmosphere, it is necessary to pay special attention to the choice of a model for the turbulent viscosity of the medium. The greatest difficulties in the design of stratospheric propellers arise when solving the problems of excessive diameter, weight and shape of the blades. To solve this problem, in this paper, it is proposed to use joined double row blades. This approach made it possible to eliminate the aerodynamic shading of the blades and increase their aerodynamic load. The use of double-row blades will provide the necessary rigidity and strength of the blades and will lead to weight reduction. Additionally, due to the double-row design, it becomes possible to reduce the diametrical dimensions of the propeller. An analytical technique for profiling double-row blades has been developed. The proposed approach is based on the joint application of the one-dimensional propeller theory and numerical gas dynamics methods. The one-dimensional theory is used to obtain the original geometric shape of the propeller for given characteristics, and the methods of numerical gas dynamics, which are based on solving the Reynold averages of the Navier-Stokes equations, are used to solve the problems of spatial modeling of the flow and obtain refined propeller characteristics. Considering the design requirements and operational limitations, it is proposed to use propellers with joined double-row blades in conditions of rarefied atmosphere.

RCS Estimation of Drone Motion Using Mesh-Element Rotation in MoM and Micro-Doppler Signatures

For an automatic recognition system, a huge number of micro-Doppler signature images is required to train a classifier. However, in general, measurements are only possible for hovering drones, so the dynamic radar cross section (RCS) of a drone with various motions is estimated through EM simulation and converted into a micro-Doppler signature image. In this work, we use far-field approximation and mesh-element rotation in the method of moments to quickly estimate the dynamic RCS of a drone in various motions. First, 3-D meshes and the impedance matrix of a single propeller are generated only once. Instead of rotating the propeller, the position information of the mesh elements is rotated without recreating 3-D meshes or the impedance matrix. Next, using the mirror-image symmetric characteristics of drone propellers and the far-field approximation, the dynamic RCS of multiple propellers is synthesized from that of a single propeller. Finally, the dynamic RCS was estimated at 3 and 9 GHz and converted to micro-Doppler signatures, spectrogram, and cadence-velocity diagram (CVD). As a result, it was more accurate to estimate the dynamic RCS at 9 GHz, and it was easier to obtain the rotation frequency at 3 GHz in the CVD.

Thermal decomposition and kinetic modeling of HNTO/AN-based composite solid propellant in the presence of GO-based nanocatalyst

The present study has been conducted to investigate the characteristics of composite solid propellant (CSP) based on hydrazinium 3-nitro-1,2,4-triazol-5-one and ammonium nitrate (HNTO/AN) cocrystal as an oxidizer and hydroxyl-terminated polybutadiene (HTPB) as a binder, supplemented with or without nanocatalyst (triaminoguanidine-transition iron, containing graphene oxide). NASA Lewis Code, Chemical Equilibrium with Application (CEA), has been used to select the optimal formulation through the evaluation of the theoretical performance. Compared to the AP/HTPB baseline formulation, the developed one presents promising properties since it may deliver an interesting specific impulse value (231 s−1). On the other hand, based on the DSC data, the kinetic triplet of the studied samples was determined using four model-free integral methods, namely, it-KAS, it-FWO, VYA, and TAS. It was observed that the decomposition peak temperature (Tp) and the activation energy (Ea) decreased obviously after the addition of the nanocatalyst. This study will certainly motivate further researches in the field of energetic cocrystals and graphene-based materials expected to be used in solid rocket propellant formulations.

Modal Analysis of the Wake Instabilities of a Propeller Operating in Coastal Environments

Zhou, J.; Sun, P., and Pan, L., 2022. Modal analysis of the wake instabilities of a propeller operating in coastal environments. Journal of Coastal Research, 38(6), 1163–1171. Coconut Creek (Florida), ISSN 0749-0208. The dynamic characteristics of propeller wakes are a function of hydrodynamics, noise propagation, and structural vibration, among other factors. The evolution of propeller wake flow mechanisms from the near field to the far field has always been a significant topic of turbulence research. Numerical simulations of propeller wakes under different loading conditions were conducted using the improved delayed-detached eddy simulation (IDDES) method. Based on the mode decomposition technique, the results of numerical simulations were used as the input data to perform a reduced-order analysis of propeller wake fields. The results showed that there is a considerable difference between the morphology characteristics of propeller wakes under high and low loading conditions, where the former tends to be unstable earlier in the evolution. According to the mode decomposition results, with decreasing mode frequency, there is strong circumferential diffusion in the tip vortices, which is more pronounced under the high loading condition and at locations further downstream. Circumferential diffusion is a key factor triggering the propeller wake to change from the stable to the unstable state. The present work can provide a significant reference for the design and optimization of next-generation marine propellers operating behind vessels sailing in both coastal and offshore environments.

Controlling the combustion and agglomeration characteristics of a solid composite propellant via a DC electric field

This study explores the use of a DC electric field to control the combustion and agglomeration characteristics of a solid composite propellant as typically deployed for rocket propulsion. Experiments were performed in a custom-built reacting flow facility that supports high-speed photography and the collection of condensed combustion products (CCPs). The propellant burning rate, aluminum agglomeration process, CCP size distribution, and combustion efficiency were systematically examined under a range of electric-field voltages (−5 to 5 kV) in both the forward and backward directions. It was found that as the electric-field voltage increased, both the propellant burning rate and combustion efficiency increased, while the degree of aluminum agglomeration decreased, reducing the particle size of the CCPs. The introduction of an electric field can bring about profound effects via particle charge acceleration, Rayleigh crushing, and ion excitation. For example, aluminum near the burning surface can split into smaller particles, the diffusion flames around droplets can exhibit a higher stand-off ratio, and more hollow agglomerates can form, as evidenced by an inspection of scanning electron microscopy images of the CCPs. The electric field was found to have a more pronounced effect in the forward direction than in the backward direction. A physical mechanism was proposed for how an electric field can alter propellant combustion. Through this, the combustion and agglomeration characteristics of solid composite propellants can be precisely tuned with an electric field without resorting to changes in the propellant formulation. The findings of this study contribute to a better understanding of how an electric field can be used to control propellant combustion and thrust in solid rocket motors.

CFD Analysis on Propeller at Varying Propeller Disc Angle and Advance Ratio

The purpose of this study is to see the feasibility of using Computational Fluid Dynamic (CFD) analysis over wind tunnel testing for propeller performance measurement. Computational Fluid Dynamic (CFD) analysis is conducted on APC 6X4E propeller and 9X6E propeller at propeller disc angle, α of 0°, 30°, 60°, and 90° using commercially available software ANSYS FLUENT at advance ratio ranging from 0 to 0.88 and angular velocity ranging from 1000rpm to 8000rpm. CFD analysis was also performed for different advance ratio at different rotational speed of 4000rpm and 8000rpm. Multiple Reference Frame model is used to simulate the rotating propeller in a flowing airstream by constructing a rotating and static domain around the propeller. The non-zero propeller disc angle is achieved by changing the inlet direction of the static domain. The SST k-ω turbulence model is used, and tetrahedral mesh is constructed. The propeller thrust and torque obtained from the CFD simulation is used to calculate the aerodynamic characteristics of the propellers. The thrust coefficient, torque coefficient and propeller efficiency obtained for both propellers follow the trend of the wind tunnel testing. The results obtained from the CFD simulation matches with the results trend obtained by another researcher performing wind tunnel analysis, where the thrust coefficient decreases with increasing advance ratio at propeller disc angle less than 60° and increases with increasing advance ratio at propeller disc angle more than 70°. The error produce for thrust estimation is lower than 12% for both 6x4E and 9x6E propellers. The error for torque and efficiency estimation is between 15-30% and 12% respectively. In conclusion, CFD simulation can predict the aerodynamic characteristics of Low Reynolds Number propeller at different propeller disc angle.

Initial Temperature Effects on the Combustion Characteristics of Al

AbstractThe combustion of aluminium in propellants plays an important role in the energy release of propellants, and investigations of the combustion mechanism of aluminium can help to further improve the energy release characteristics of propellants. The changes in reaction temperature and product content over time during the reaction of Al(l)/O2 and Al(l)/AP systems at different initial temperatures were calculated using the Closed Homogeneous Batch Reactor in CHEMKIN‐PRO, and a sensitivity analysis was performed for the Al(l)/AP system. The results showed that with increases in the initial temperature, the heat storage time and combustion time of the Al(l)/O2 system were shortened and the equilibrium temperature increased, which was also true for the Al(l)/AP system. Moreover, the increase of initial temperature was favourable to the decomposition of O2 and the formation of AlO in Al(l)/O2 system but had little effect on the Al/AP system. The main reaction path of the Al(l)/AP system changed with increases of initial temperature, although , , , and are common elementary reactions with high temperature sensitivity and thus play a decisive role in the change of H2, AlCl, AlO and O contents as well as the changes of the reaction temperature of the system. In this paper, the combustion characteristics of an Al/AP system were investigated in depth, and the results can provide a theoretical basis for revealing the combustion mechanism and improving the energy release characteristics of aluminium‐based AP‐containing solid propellants.

Long‐Term and Short‐Term Creep Characteristic Analysis for HTPB Propellant

AbstractA solid rocket motor is in storage for most of its life cycle, and propellant creep occurs subjected to gravity load. To analyse the creep characteristics of HTPB propellant during long‐term storage, MSC Marc is used to calculate the maximum von Mises stress of the motor under horizontal and vertical storage conditions. Based on the numerical results, the short‐term reciprocating creep test and long‐term creep test are designed and carried out. The results illustrate that the process of propellant creep from deformation to final failure can be divided into four stages: instantaneous deformation stage, attenuation creep stage, steady‐state creep stage and accelerated creep failure stage. When the creep stress level is less than 0.1 MPa, the creep characteristics tend to be stable. When the creep strain exceeds a certain critical value, the propellant will enter the steady‐state creep stage. The damage caused by creep rises with the increase of creep time and stress. When the maximum creep strain is less than 10 %, the creep damage can be fully recovered. The splicing curve of short‐term creep test data is in good agreement with that of long‐term creep test data. A mechanical long‐term creep test method is provided, and the parameters of the modified Burgers model are fitted. The text methods and conclusions can provide a reference for the evaluation of structural integrity and storage life of solid motor.

1,2-Bis(nitroazol-1-yl)diazenes: improved methods of synthesis, determination of the enthalpies of formation, and calculations of main energy characteristics of solid composite propellants based on these compounds

1,2-Bis(nitroazol-1-yl)diazenes: improved methods of synthesis, determination of the enthalpies of formation, and calculations of main energy characteristics of solid composite propellants based on these compounds

Sharp Profile for Icebreaking Propellers to Improve Their Ice and Hydrodynamic Characteristics

Stern-first operation under severe ice conditions (ridges) is one of the most effective modes to increase the operating efficiency of icebreakers and ice ships. However, when a ship overcomes the ridge astern, the propellers continuously interact with ice blocks, and ice moment affects the propeller and the main engine. This leads to propeller speed drop and propeller thrust reduction. Propeller stop is also possible. This is the reason why the propeller ice moment needs to be decreased. Blade profiles with a sharp leading edge are used for this purpose because their thickness is significantly less than that of a traditional icebreaking profile. The application of sharp profiling makes it possible to significantly reduce the ice moment (ice loads) on the propeller, reduce the drop in its speed, and increase the hydrodynamic thrust. The main task when installing blades with sharp profiles is to ensure the strength of their leading edges exposed to ice pressure. In this article, the authors tackle upon some methods of assigning integral and local ice loads on propellers. Solutions for ensuring the local strength of the blade edges were developed and presented. The influence of sharp profiling on the hydrodynamic and cavitation characteristics of ice propellers was considered. The article presents examples of calculating the hydrodynamic propeller thrust and moment, as well as ice loads on a propeller with a sharp and traditional profile, when an ice ship moves through a ridged ice isthmus with its stern first.

The influence of aluminum nanoparticles on the laser ablation characteristics of hydroxylamine nitrate-based liquid propellants

Hydroxylamine nitrate is a nontoxic green energetic propellant that has a high energy density and wide application prospects in the field of aerospace propulsion. Here, the laser ablation and propulsion properties of hydroxylamine nitrate-based propellants doped with aluminum nanoparticles were studied. The results showed a significant improvement in the laser absorption properties of hydroxylamine nitrate doped with aluminum nanoparticles. The maximum absorption rate increased by more than 80%, while the absorption depth decreased considerably with a minimum of 277 μm. The sputtering behavior also weakened during laser ablation, and the impulse of hydroxylamine nitrate could be enhanced by doping aluminum nanoparticles. With the 0.7wt% mass fraction of aluminum nanoparticles, a maximum impulse bit of 57.55 μN·s at 90 mJ laser energy. This is led to a maximum energy conversion efficiency of 218.1% and an enhancement of the kinetic energy of the hydroxylamine nitrate-based propellant of 56% with laser energy of 25 mJ. Compared with ordinary liquid propellants, doped samples have better propulsion performance.

Combustion and agglomeration characteristics of aluminized propellants containing Al/CuO/PVDF metastable intermolecular composites: A highly adjustable functional catalyst

In this experimental study, we explore how the combustion and agglomeration characteristics of solid propellants can be modified by replacing aluminum with ternary Al/CuO/PVDF(Polyvinylidene Fluoride) metastable intermolecular composites (MICs). Using thermogravimetric−differential scanning calorimetry, a laser ignition setup, and a high-pressure propellant combustion system, we examine the thermal reactivity, ignition behavior, burning rate, agglomeration, and condensed combustion products of various MICs-inclusion propellants. We find that the use of ternary Al/CuO/PVDF MICs can decrease the onset temperature and increase the oxidation efficiency of Al, as compared with common binary MICs. The ratio of CuO/PVDF is found to have a strong effect on the combustion intensity of the metallic powders, but only a weak effect on their ignition delay. Higher proportion of PVDF is found to have a negative effect on the combustion rate. Specifically, the combustion intensity is found to decrease first and then increase as the PVDF content increases. The exothermic Al/CuO reaction is found to alter the heat transfer of the condensed layer on the propellant surface, while PVDF plays a critical role in the thermal feedback of the gaseous reaction. When combined, these two factors lead to a ± 30% variation in the propellant burning rate. Furthermore, ternary MICs are found to reduce agglomeration during propellant combustion. The two optimal formulations are 2.5 wt.% CuO/2.5 wt.% PVDF and 3.5 wt.% CuO/1.5 wt.% PVDF. The use of these formulations is found to decrease the mean particle size of the condensed combustion products to only 11 μm, as compared with 76 μm for the original Al-inclusion propellant. High-speed microscope images reveal the existence of crack phenomena in the pockets surrounding the AP particles on the burning surface due to the Al/CuO reaction, as well as the floccule breakup mechanism of Al aggregates in the presence of PVDF, both of which reduce agglomeration. Overall, this study shows that replacing Al with ternary Al/CuO/PVDF MICs has significant effects on the agglomeration, combustion and ignition features of aluminized propellants. The findings of this study can be used to aid the development of highly adjustable functional catalysts for solid propellants.

Experimental Research on Microwave Ignition and Combustion Characteristics of ADN-Based Liquid Propellant.

Microwave ignition has attracted much attention due to its advantages of reliable ignition, large ignition area and cold-start capability. In this paper, the experimental method is used to explore the ignition ability of the microwave device to ADN-based liquid propellant. Additionally, we discuss the influence of the inlet power and rate of propellant injected into the ignition system on the height of the combustion jet and the combustion temperature. In the experiment, a microwave-assisted ignition system was established based on a special microwave resonant cavity. The liquid propellant and working gas were sprayed into the resonator cavity through the hollow straight tube beneath the resonant cavity. The test results show that the device can ignite the propellant under the condition of 800 W input power, which proves the feasibility of the microwave ignition device for ADN-based liquid propellant. Microwave power has some influence on the flame spray height at the initial stage of combustion. The spray height at 2000 W is increased by 55.7% in comparison to 1000 W. In the stable combustion stage, the input power has a very significant increase in the average temperature of the flame, which is increased by 25%. The combustion is relatively better when the propellant flow rate is 30 mL/min, and the height of the flame spray increases by 25.2%. The increase in throughput did not have a significant impact on the flame temperature.

CFD and system-based investigation on the turning maneuver of a twin-screw ship considering hull-engine-propeller interaction

Ship maneuver is a dynamic process accompanied by strong interaction among hull, engine, and propeller, and the interaction phenomenon is more complicated for twin-screw ships. In this paper, numerical investigation on the turning maneuver of a twin-screw ship considering hull-engine-propeller interaction is carried out by using CFD and system-based methods. Taking the twin-screw ship ONRT model as the study object, a series of captive model tests are simulated by using RANS method. Based on the computed global loads on the propellers and the corresponding flow field details, the hydrodynamic characteristics of the propellers operating under the maneuvering conditions are analyzed. The effective wake fraction is computed and the mathematical model of propeller performance under the maneuvering conditions is obtained through data fitting. Based on the established mathematical model, the turning circle maneuver considering hull-engine-propeller interaction is simulated. Three control strategies of main engine, i.e., constant RPM, constant torque, and constant power, are considered. The effects of the control strategies on the turning motion and the propulsive loads during turning motion are explored. This study is useful to provide a deeper insight into the ship maneuvering behaviors and the propeller characteristics during maneuvering motion under the influence of hull-engine-propeller interaction.

Investigation into the Hydrodynamic Noise Characteristics of Electric Ducted Propeller

Ducted propeller is a kind of special propeller widely used in unmanned underwater vehicles, its flow characteristics and hydrodynamic noise are very important for marine environmental protection and equipment concealment. The hybrid techniques based on the acoustic analogy theory are adopted in the present study to calculate the unsteady flow field and sound field characteristics of a ducted propeller. The full scale flow filed and hydro-acoustic sources of the propulsion system are simulated by Detached-Eddy computational fluid dynamics (CFD) method. Hydrodynamic noise are calculated by FWH equation based on the CFD results. The frequency domain and directivity of sound pressure level at different sound field monitoring points are analyzed at four navigational speeds. The results show that the navigational speed that is in the inflow condition of the ducted propeller play important roles in the flow structure and underwater radiated noise. Under the fixed impeller rotational speed, the propulsion efficiency of ducted propeller increases first and then decreases with the raise of navigational speed. The maximum errors of thrust and power between simulation and experiment values are 0.5% and 0.1% respectively, which means that the adopted DES numerical simulation method has high credibility in calculating the acoustic source. At impeller rotational speed of 2000 r/min, the best state of flow field distribution is at the navigational speed of 1.54 m/s, which is corresponding to the highest propulsion efficiency condition. The propeller noise presents dipole characteristic in all working conditions, and at the obvious blade passing frequency, multiple characteristics are presented; most of the noise contribution is also concentrated below four times of the blade passing frequency. The total sound pressure level of the hydrodynamic noise is the smallest at the optimal efficiency condition (the navigational speed is 1.54 m/s). At high navigational speed, the low frequency characteristics below blade passing frequency increase and the amplitude becomes larger. This indicates that the component of turbulent noise becomes more important with the increase of navigational speed. The research focuses on analyzing the relationship between the energy loss of the ducted propeller wake field and the noise level, and it is found that the vortex at the tail makes a certain contribution to the noise. The research conclusions could provide some reference for the acoustic performance evaluation and noise reduction optimization of ducted propeller design as well as the improvement of UUV stealth performance.

Effect of spherical Al-Mg-Zr on the combustion characteristics of composite propellants

In this work, spherical Al-Mg-Zr alloy with intensive heat release were characterized and compared to neat Al powders. The morphology, element distribution and thermal performance were characterized by TEM, SEM, Mapping and TG-DSC. The laser-induced ignition and combustion characteristics of Al-Mg-Zr alloy powders were performed by microscopic high-speed video-recording. The effect of Al-Mg-Zr on the combustion process of HTPB-based solid propellants were carried out as well. It was observed that, the energy release process of Al-Mg-Zr is accompanied by the phenomena of gas emission and microexplosion, which is useful for improving the combustion efficiency of the alloy and reducing the combustion product particles of solid propellants. The findings in this work validate the potential of Al-Mg-Zr as an additional fuel for high aluminum content solid propellants.

A study on the wake characteristics of rim-driven propeller for underwater robot using the PIV

A study on the wake characteristics of rim-driven propeller for underwater robot using the PIV

Experiment research of Al particle’s ignition and combustion characteristics of NEPE propellant

Based on optical photography analysis method, agglomeration process of Al particles at aluminized NEPE propellant’s surface, dynamic combustion process after leaving burning surface and the collision under different pressure of N2, were photographed by highspeed camera. MATLAB was used to deal with the images to analyze the size of agglomerated particles. Experiment research results showed that higher pressure was helpful for improving ignition performance and increasing combustion efficiency of the aluminized NEPE propellant. For the agglomeration products, dimension was reduced, size distribution became more uniform, and amount of the mass increased with higher pressure environment.