scholarly journals Propeller Efficiency - Simple Methods

2021 ◽  
Author(s):  
Dieter Scholz
Keyword(s):  
Angular Momentum ◽  
Characteristic Parameter ◽  
Flight Speed ◽  
Engine Torque ◽  
Turboprop Engine ◽  
Disc Area ◽  
Blade Tip ◽  
Exit Speed ◽  
Propeller Blades ◽  
Drag Ratio

In order to produce thrust, the air needs to be accelerated by the propulsor (the propeller or the jet engine). The more the air gets accelerated from flight speed v = v_1 to exit speed v_4 (i.e. the higher v_4/v_1), the lower the efficiency. However, without accelerating the air, no power or thrust is produced. The efficiency depends on the non-dimensional thrust, called thrust loading, c_S, which is a function of aircraft speed. Disc loading k_P is calculated from power, P air density, rho and propeller disc area, A_S. k_P is independent of speed and as such a good characteristic parameter of a propeller. Together, this makes the propulsive efficiency a function of disc loading, k_P and flight speed, v. Further losses come from angular momentum. The efficiency calculated considering angular momentum in addition dependents on the ratio of forward speed, v and tip speed u (v/u). A constant speed propeller can run at a favorable speed for the piston or turboprop engine at a limited Mach number of the blade tips. At higher speeds, v and also v/u increases and hence required engine torque. This increases the angular momentum and reduces the efficiency. At low speeds, the ratio v_4/v_1 gets unfavorably high and the efficiency is low. At zero speed v_4/v_1 goes to infinity and the efficiency to zero. For an example calculation, optimum efficiencies were obtained at v/u between 3 and 5 depending on disc loading. Not considered is the limited lift-to-drag ratio (L/D) of the propeller blades and losses at blade tip (which could be accounted for by a performance factor between 0.85 and 0.9).

Development of a Simplified Procedure for the Determination of the Ultimate Load and Associated Spindle Torque of Propeller Blades

2016 ◽  
Vol 60 (03) ◽  
pp. 171-185
Author(s):  
Claas Fischer ◽  
Wolfgang Fricke ◽  
Andreas Junglewitz
Keyword(s):  
Stress Distribution ◽  
Numerical Simulations ◽  
Ultimate Strength ◽  
Ultimate Load ◽  
Plastic Material ◽  
Plastic Behavior ◽  
Simplified Approach ◽  
Elastic Plastic ◽  
Blade Tip ◽  
Propeller Blades

Blade deflection observed in experiments regarding the ultimate strength of controllable pitch propeller blades does not agree with the one that is assumed in the load case for the blade failure load currently defined in the Polar Class Rules. The reason is that a failure of the blade tip due to large plastic deformation is not taken into account, but can occur in reality if the load is applied relatively close to the trailing edge of skewed propellers. The plastic blade deformation can be computed by numerical simulations using an elastic-plastic material curve. These simulations, however, are time consuming and, hence, unpractical in the daily design process of propeller blades. Therefore, a simplified approach to determine the ultimate load and the associated spindle torque of the blade is presented. It requires elastic finite element (FE) analyses with varying point of load application, geometrical data, and a simplified material curve. The critical blade section is determined from highly stressed locations found in the elastic FE analysis. Afterward, the ultimate bending moment which the section can carry is determined by assuming a linear strain distribution over the thickness and a definite limit strain on the pressure surface. This allows the stress distribution to be transferred directly from the material curve. The ultimate load is determined by integrating the stress distribution over the section thickness and along the chord length, the latter in a simplified way. The approach is supported by various numerical simulations showing the fundamental elastic-plastic behavior of propeller blades and their response due to superimposed bending and torsional loads. In conclusion, the ultimate strength is mainly controlled by bending loads and the approach considers a failure of the blade tip, leading to more realistic spindle torques compared to the approach in the Polar Class Rules.

scholarly journals ВПЛИВ ЗАЗОРУ МІЖ РЯДАМИ СПІВВІСНОГО ПОВІТРЯНОГО ГВИНТА НА ТЯГУ

2020 ◽  
pp. 19-23
Author(s):  
Вячеслав Юрьевич Усенко ◽  
Екатерина Викторовна Дорошенко ◽  
Михаил Владимирович Хижняк
Keyword(s):  
Guide Vane ◽  
Turbulent Viscosity ◽  
External Environment ◽  
Calculation Model ◽  
Hydraulic Loss ◽  
Flow Modeling ◽  
Turboprop Engine ◽  
Air Intake ◽  
Axial Clearance ◽  
Propeller Blades

The thrust of a turboprop engine depends on many factors, one of which is hydraulic loss when flowing around the propeller blades. When using coaxial propellers, this factor plays an even greater role, since in this case the losses associated with the swirl sheet behind the first propeller were added. The aim of the work is to assess the influence of the axial clearance between the rows of the coaxial propeller on the thrust. The object of the study is a coaxial propeller. The axial clearance between the rows of the propeller ranged from 650 mm to 950 mm. Geometrically, the calculation model was a cylinder with a radius of 75 m and a height of 150 m. A coaxial propeller was located in the center of the cylinder. The investigated computational model is divided into four subregions: the external environment, the input guide vane, the first row of the propeller, the second row of the propeller. Separation of the calculation model into those listed below for the region allows us to evaluate the effect of the engine air intake on the propeller parameters and to ensure the correct modeling of flow around two rows of the propeller. In the first step of the study, a comparison was made of the results of numerical simulation with the results of an approved mathematical model for a version of a propeller with an axial clearance of 650 mm. The calculations were carried out with three models of turbulent viscosity: k-ω, SST, SST Gamma Theta Transitional. Based on the comparison, the SST turbulent viscosity model was selected for further research. The second research step included flow modeling for a modified coaxial propeller with an axial clearance between the propeller rows of 950 mm. According to the results of the study, it was found that the magnitude of the axial clearance between the rows of coaxial propeller affects the thrust. It is shown that when the clearance between the rows of the propeller increases from 650 mm to 950 mm, the thrust of the propeller increases by 17 %. This can be explained by a decrease in the level of unevenness and hydraulic losses behind the second row of the propeller. In the future, the obtained results of a numerical experiment require agreement with a field experiment.

scholarly journals Investigation on the Performance of a Ducted Propeller in Oblique Flow

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Qin Zhang ◽  
Rajeev K. Jaiman ◽  
Peifeng Ma ◽  
Jing Liu
Keyword(s):  
Open Water ◽  
Flow Dynamics ◽  
Navier Stokes ◽  
System A ◽  
Oblique Flow ◽  
Ducted Propeller ◽  
Blade Tip ◽  
Propeller Blades ◽  
Les Model ◽  
Thrust And Torque

In this study, the ducted propeller has been numerically investigated under oblique flow, which is crucial and challenging for the design and safe operation of the thruster driven vessel and dynamic positioning (DP) system. A Reynolds-averaged Navier–Stokes (RANS) model has been first evaluated in the quasi-steady investigation on a single ducted propeller operating in open water condition, and then a hybrid RANS/LES model is adapted for the transient sliding mesh computations. A representative test geometry considered here is a marine model thruster, which is discretized with structured hexahedral cells, and the gap between the blade tip and nozzle is carefully meshed to capture the flow dynamics. The computational results are assessed by a systematic grid convergence study and compared with the available experimental data. As a part of the novel contribution, multiple incidence angles from 15 deg to 60 deg have been analyzed with different advance coefficients. The main emphasis has been placed on the hydrodynamic loads that act on the propeller blades and nozzle as well as their variation with different configurations. The results reveal that while the nozzle absorbs much effort from the oblique flow, the imbalance between blades at different positions is still noticeable. Such unbalance flow dynamics on the blades, and the nozzle has a direct implication on the variation of thrust and torque of a marine thruster.

Performance and Loads of a Reduced-Scale Coaxial Counterrotating Rotor

2019 ◽  
Vol 64 (4) ◽  
pp. 1-15
Author(s):  
Christopher Cameron ◽  
Jayant Sirohi ◽  
Joseph Schmaus ◽  
Inderjit Chopra
Keyword(s):  
Rotor System ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Forward Flight ◽  
Blade Tip ◽  
Advance Ratio ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Reduced Scale ◽  
Blade Tip Clearance

The results of hover and wind tunnel tests of a reduced-scale, closely spaced, rigid, coaxial counterrotating rotor system are presented, along with results from a comprehensive analysis. The system features two-bladed upper and lower rotors, 2.03 m in diameter, with uniform section, untwisted rotor blades. Measurements include upper and lower rotor steady and vibratory hub loads, as well as control angles and control loads. Blade tip clearance was measured using an optical sensor. The rotor system was tested in hover and at advance ratios between 0.21 and 0.53, at collective pitches ranging from 2° to 10° achieving blade loadings in excess of 0.10. At each forward flight operating condition, sweeps of lift offset up to 20% were performed, while selected test conditions were repeated at different rotor speeds and interrotor index angles. Hover tests showed that aerodynamic interaction between upper and lower rotors decreased individual rotor performance compared to isolated rotors and induced a four-per-revolution vibratory load corresponding to the blade passage frequency. In forward flight, the rotor effective lift-to-drag ratio was found to increase with increasing advance ratio and lift offset, resulting in a 30% improvement at 20% lift offset and 0.5 advance ratio. The lower coaxial rotor was found to operate at higher lift-to-drag ratio than the upper rotor, in contrast to the behavior in hover. Lift offset resulted in a decrease in blade tip clearance with a corresponding increase in rotor side force. Vibratory loads increased with advance ratio, with the largest loads in the two- and four-per-revolution harmonics. Lift offset, in conjunction with interrotor index angle, is shown to modify vibratory forces and moments transmitted to the fixed frame, increasing some force components while decreasing others.

scholarly journals Aerodynamic Characteristic Optimization on The Design of Anti - Ship Missile for Indonesian Fast - Attack Boat

2019 ◽  
Vol 17 (2) ◽  
pp. 91
Author(s):  
Fuji Dwiastuty
Keyword(s):  
Cross Sections ◽  
Aerodynamic Characteristics ◽  
Flight Speed ◽  
Cruise Missile ◽  
Surface Ship ◽  
Nose Cone ◽  
Body Cross Section ◽  
Drag Ratio ◽  
Cruise Flight ◽  
Lift To Drag Ratio

Missile is one of Indonesia 7 self – reliant main weapon system programs. Therefore research on the anti – surface ship missile system concept had been carried out at the Faculty of Defense Technology, Defense University. This research aims to abtain optimal design of anti – ship missile concept from previous research, i.e. 2 stages cruise missile with diameter of 0.36 m, total length of 5.19 m, cruise flight altitude of 17 m, and cruise flight speed of 0.88 Mach. The optimation is done on the missile’s aerodynamics characteristics to maximize its lift to drag ratio, which is one of the factor that determine the missile’s performance. Variables of nose cone shapes, number of wings, and body cross sections were chosen for evaluation of lift to drag ratio. The research found that nose cone shape did not affect the aerodynamic characteristics since the flight speed is subsonic. From the rest of the variables, it is found that the best configuration is missile with 2 wings with root length of 1.18 m, height of 0.79 m, and tip length of 0.71 m, elliptical body cross section,  and the missile is to be flown at 6o angle of attack.

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