Propeller Slipstream Effects Research Articles

Mission-Based Design and Retrofit for Energy/Propulsion Systems of Solar-Powered UAVs: Integrating Propeller Slipstream Effects

Over twenty Solar-Powered Unmanned Aerial Vehicle (SPUAV) designs exist worldwide, yet few have successfully achieved uninterrupted high-altitude flight. This shortfall is attributed to several factors that cause the actual performance of SPUAV to fall short of expectations. Existing studies identify the propeller slipstream as one of these adverse factors, which leads to a decrease in the lift–drag ratio and an increase in energy consumption. However, traditional design methods for SPUAVs tend to ignore the potential adverse effects of slipstream at the top-level design phase. We find that this oversight results in a reduction in the feasible mission region of SPUAVs from 109 days to only 46 days. To address this issue, this paper presents a high-fidelity multidisciplinary design framework for the energy/propulsion systems of SPUAVs that integrates the effects of a propeller slipstream. Specifically, deep neural networks are employed to predict the lift–drag characteristics of SPUAVs under various slipstream conditions, and the energy performance is further analyzed by evaluating the time-varying state parameters throughout a day. Subsequently, the optimal solutions for the energy/propulsion systems specific to certain latitudes and dates are obtained through optimization design. The effectiveness of the proposed design framework was demonstrated on a 30-m wingspan SPUAV. The results indicated that, compared to the traditional design method, the proposed approach led to designs that more effectively accomplished closed-loop flight in designated regions and prevented the reduction of the feasible mission region. Additionally, through the targeted retrofit of the energy/propulsion systems, SPUAVs exhibited enhanced adaptability to the solar radiation characteristics of different mission points, resulting in a further expansion of the feasible mission region. Furthermore, this research also explored the variation trends in optimal solutions across different latitudes and dates and investigated the reasons and physical mechanisms behind these variations.

CFD analysis of wing-propeller interaction on the NASA X-57 Maxwell aircraft wing

Due to global warming concerns, the Aviation industry is trying to reduce its carbon footprint. Electric propulsion (EP) is one way of doing this, where the power is obtained from electrical sources. The concept of distributed electric propulsion (DEP) is in the focus now. NASA’s X-57 Maxwell, a high winged, all-electric experimental aircraft, uses this concept. The present work aims at developing a CFD model (ANSYS Fluent) to evaluate aerodynamic performance of two configurations of NASA’s X-57 aircraft wing; (i) wing and nacelle (clean wing) and (ii) wing, nacelle and one electric propeller under cruise condition; and compare it with the results of wind tunnel experiment performed by NASA/Armstrong X-57 research program. Parameters like lift, drag and pressure coefficients (CL, CD, CP) are compared for both cases. A good match is observed for CL, CD and CP, thus validating the model. The unsteady RANS solver is very efficient in capturing the effects of propeller slipstream on the wing. After validation, this model is further used to simulate aerodynamic performance of a wing with multi-propeller (DEP) configuration.

Flight-Test Determination of Longitudinal Stability Using System Identification

In the present work, system identification methods were applied to the flight data from dynamic maneuvers in order to obtain an aerodynamic model of the longitudinal dynamics of a propeller-driven aircraft, including a model for the elevator hinge moment. As a result, the model allowed numerical computation of elevator deflections and stick forces required to trim the aircraft at different flight conditions, including variations of the center-of-gravity location. From these results, the stick-fixed and stick-free neutral points were computed. When compared to a conventional flight-test technique, the new method provided similar mean values for the neutral point location and reduced the associated uncertainty by about 50%. The data collected for system identification required only a fraction of the flight time used in conventional techniques. Moreover, the aerodynamic modeling revealed nonstandard dependencies, such as the linear influence of the airspeed and thrust coefficients on the aerodynamic coefficients. Therefore, propeller slipstream effects were automatically embedded into the neutral point results obtained.

Investigation of propeller slipstream effects on lateral and directional static stability of transport aircraft

ABSTRACT The aerodynamic characteristics of turboprop aircraft are greatly affected by the running propellers. In this paper, propeller slipstream effects on the static lateral-directional stability characteristics of a typical twin-engine turboprop aircraft with clockwise rotating propellers were investigated through unsteady computational fluid dynamics (CFD) simulations and wind tunnel experiments. The propeller slipstream led to a significant decrease in the lateral static stability contribution of the wing-body-nacelle (WBN), and the most affected wing sections were located near the left boundary of the port propeller slipstream region. Moreover, the influence of the propeller slipstream on the lateral static stability contribution of the vertical tail plane (VTP) significantly altered the rolling moment curve slope of the entire airframe. Due to the effects of the propeller slipstream on the local dynamic pressure and therefore the effectiveness of the VTP, the aircraft showed significantly different directional static stability behaviors between the positive and negative sideslip conditions. Furthermore, it was found that the configurations with clockwise rotating propellers readily experience dramatic losses in directional static stability at large negative sideslip angles.

Research on the Key Technology of Propulsion Drag System Division and Performance Analysis of Turboprop-powered Aircraft

The remarkable characteristic of turboprop-powered aircraft is that its power system has great influence on the aerodynamic characteristics of the aircraft. Due to the action of turboprop slipstream, the airflow velocity after the propeller is obviously increased compared with the velocity of free flow. The turbulence caused by turboprop slipstream affects the aerodynamics of the aircraft, which in turn affects the performance of turboprop blades. In this paper, the layout characteristic and development trend of turboprop powered aircraft are briefly analysed. According to the characteristics of turboprop aircraft, a thrust/drag system division principle and interference characteristics treatment method for turboprop powered aircraft are introduced. Finally the influence of slipstream on a typical turboprop powered aircraft is analysed, It is very necessary to study the influence of propeller slipstream on aircraft aerodynamic performance in the early stage of developmental the effect of propeller slipstream on the aerodynamic characteristics of the whole aircraft is the strongest in take-off state, the influence of climbing state is weakened the influence of cruise state is the lease and the effect of slipstream effect increases with the increase of thrust.

Design and Analysis of Twin-Vertical-Tailed Fixed-Wing Unmanned Aerial Vehicle

Unmanned Aerial Vehicles possess characteristics that make them suitable for use in multiple areas. This project proposes the design of a small fixed-wing UAV that can be used to carry a payload of around 1 kg. The design is developed performing aerodynamic, structural, and stability analysis using analytical methods as well as commercial code. It is then fabricated into a physical model. Take-off is achieved by launching with the hand or a launcher. Low stall speed allows the UAV to land softly during landing. Twin vertical stabilizers are used, one at each end of the horizontal stabilizer, to reduce the effect of propeller slipstream. Pusher configuration is chosen to allow unobstructed view when imaging devices are attached to the nose of the UAV.

Effects of propeller slipstream on diamond joined-wing configuration solar-powered UAV

Effects of propeller slipstream on diamond joined-wing configuration solar-powered UAV

Numerical Simulations Study on the Effect of Propeller Slipstream on Inlet Flow Field for a Turboprop Aircraft

Numerical Simulations Study on the Effect of Propeller Slipstream on Inlet Flow Field for a Turboprop Aircraft

Experimental and numerical study of wing boundary layer behavior in propeller flowfield

In this research, the effects of propeller slipstream on wing boundary layer and transition front were studied through wind tunnel tests and numerical analysis. In this respect, the flow around a NACA 6-series airfoil section was simulated in a computational fluid dynamics solver without and with propeller flowfield. The numerical study, presented in this paper, was concerned with the effect of propeller slipstream on both wing aerodynamics and boundary layer treatment. For experimental tests, oil flow visualization technique was used to determine laminar to turbulent transition location, laminar separation bubble with turbulent reattachment and turbulent separation line over the wing surfaces. Existence of propeller slipstream changed pressure and skin friction distribution over the wing surfaces, in both chordwise and spanwise directions and it hence affected on the wing loading distribution. Also upstream propeller affected on boundary layer characteristics including laminar/turbulent transition onset and separation over the wing. The results showed that the transition location moved toward the leading edge, and the separation bubble was washed out due to propeller slipstream.

Effects of Propeller Slipstream of Distributed Electric Propulsion on the Wing-Flap System

The studies are aimed at investigating the mechanism to ensure the high lift by installing propellers in front of the wing and using interference effects. The model of the wing section of a regional STOL aircraft with DEPSis considered. The wing section is equipped with a trailing edge device (Fowler flap) and DEPS consisting of motors with propellers. Parametric and experimental studies of the interaction between DEPS propellers and the regional STOL aircraft wing-flap system were carried out. The development and verification of aerodynamic calculation method for the wing section at low Reynolds numbers were performed. The comparison with the wind tunnel test data obtained at TSAGI was made. It was found that: - for fixed power of propellers there is an optimal propeller diameter ensuring maximum increase in the wing section lift; - at low thrust the total lift weakly depends on DEPS inclination angle.

Transitional flight equilibrium and performance study for the X-NMRL tail-sitter VTOL MAV

An investigation on transitional flight equilibrium, performance analysis and parameter impacts is conducted in a conversion corridor, based on the proposed X-NMRL tail-sitter Vertical Takeoff and Landing Micro Air Vehicles (VTOL MAVs). Dependent on a propulsion model, aerodynamic model and physical control model, a nonlinear mathematical transitional model of the vehicle dynamics was constructed with consideration of the velocity, angle of attack, thrust, control surface deflection and pitching angle. The momentum theory and estimation method are applied to simulated propeller slipstream effects on aerodynamics, and an aerodynamic model for all regions of angles of attack and velocities is built. The nonlinear indefinite high-order dynamic model is solved by the improved Newton iteration algorithm. The corridor of the pitching angle or flight-path angle to the velocity reveals that the boundaries are mainly governed by the stalling performance, full throttle thrust and zero thrust, respectively. The performance corridor indicates different performance parameter variations under different conditions of steady climbing, cruising and descending states. Additionally, the performance for a steady transitional strategy can be illustrated to some extent. In terms of the parameter impacts, the increasing max propulsive power, supplied voltage, and decreasing total weight can widen the transitional corridor effectively, and the changes in the aerodynamics will only move the boundaries toward the same direction. These results will benefit transitional vehicle designs and control designs.

Experimental investigation of propeller slipstream effects on the wing aerodynamics and boundary layer treatment at low Reynolds number

In this research, an experimental investigation was conducted to predict the Laminar-turbulent transition over the wing surface. Furthermore, the effects of a tractor propeller slipstream on both wing aerodynamics and transition front were studied. For tests, a rectangular wing was used with a NACA 6-series airfoil section and with a total of 22 pressure orifices. Unsteady pressure measurements were performed over the upper and lower surfaces of the wing in different spanwise locations at different incidence angles. Existence of propeller slipstream changed pressure distribution over the wing surfaces, in both chordwise and spanwise directions and hence affected the wing loading distribution. Statistical analysis of pressure signals was used to predict the boundary layer transition over the wing by computing the root mean square and skewness of the pressure data. The results showed that the transition location moves toward the leading edge due to propeller slipstream. Increase in propeller rotational speed causes that the turbulent flow covers whole portion of the wing surface.

Investigation on Propeller Slipstream by Using an Unstructured Rans Solver Based on Overlapping Grids

AbstractBased on unstructured hybrid grid and dynamic overlapping grid technique, numerical simulations of Unsteady Reynolds Averaged Navier-Stokes equations were performed and investigation on isolated propeller aerodynamic characteristics and effects of propeller slipstream on turboprops were undertaken. The computational grid consisted of rotational subzone of propeller and stationary major-zone of aircraft, and walls criterion was used in the automatic hole-cutting procedure. Distance weight interpolation and tri-linear interpolation were developed to transfer information between the rotational and stationary subzones. The boundaries of overlapping grids were optimized for fixed axis rotation. The governing equations were solved by dual-time method and Lower Upper-Symmetric Gauss-Seidel method. The method and grid technique were verified by isolated propeller configuration and the computational results were in well agreement with the experimental data. The grid independence was studied to establish the numerical results. Finally, the flow around a turboprop case was simulated and the influence of propeller slipstream was presented by analyzing the surface pressure contours, profile pressure distribution, vorticity contours and profile streamline. It's indicated that the slipstream accelerates and rotates the free stream flow, changing the local angle of attack, enhancing the downwash effects, affecting the pressure distribution on wing and horizontal tail, as well as increasing the drag coefficient, pitching moment coefficient and the slope of lift coefficient.

비행시험과 전산해석을 통한 소형무인기 항력 예측

This paper presents the procedure of drag prediction for EAV-1, based on a numerical analysis correlated to an in-flight test. EAV-1, developed by Korea Aerospace Research Institute, is a small-sized UAV to test a hydrogen-fuel cell power system. The long-endurance test flight of 4.5 hours provides numerous in-flight data. The thrust and drag of EAV-1 during the flight test are estimated based on the wind-tunnel test results for EAV-1`s propeller performance. In addition, the CFD analysis using a commercial Navier-Stokes code is carried out for the full-scale EAV-1. The computational result suggests that the initial CFD analysis substantially under-predicts the in-flight drag in that the discrepancy is up to 27.6%. Therefore, additional investigation for more accurate drag prediction is performed; the effect of propeller slipstream is included in the CFD analysis through fan disk modelling. Also, the additional drag from airplane trim and load factor that actually exists during the flight test in a circular path is considered. These supplemental analyses for drag prediction turn out to be effective since the drag discrepancy reduces to 2.3%.

Aerodynamic Effects of Propeller Slipstream on a Wing with Circulation Control

The German Bürgernahes Flugzeug (Citizen-Oriented Airplane) research program advances technologies for high-lift systems using circulation control Coandă-type flaps. The interaction of these high-lift systems with a propeller engine is the subject of the present work. A large and complex wind-tunnel model equipped with an active high-lift system and a powered propeller was designed, manufactured and instrumented. The wind-tunnel data show the potentials of the active high-lift system in three-dimensional wing applications. The results characterize and quantify the interactions between a propeller and a high-lift wing by using systematic variations of blowing momentum and propeller thrust. The results represent a unique database for future efforts to improve the efficiency of active lift and for validation of numerical simulation methods.

Propeller-induced effects on the aerodynamics of a small unmanned aerial vehicle

The present paper has discussed investigations about the propeller slipstream effects on the aerodynamics of a generic unmanned air vehicle platform in the wind tunnel for a broad advance ratio range. The propeller-induced effects for small unmanned air vehicles are more significantly pronounced than general aviation aircraft, because of their high propeller-diameter-to-wing-span-ratio. The stall angle of attack of the small unmanned air vehicle is generally delayed under slipstream effects. The study evaluated the shift in stall angle of attack as a function of propeller-diameter-to-wing-span and advance ratios of the propeller. The aerodynamics of the unmanned air vehicle platform is estimated through wind-tunnel experiments. The study reported in this paper is part of an effort to develop the framework for the analysis of propeller-wing interaction for small/micro unmanned air vehicles at an early design stage. Specifically, the slipstream effects on the aerodynamics of a generic small unmanned air vehicle are studied in the wind tunnel for the shift in the aircraft stall angle of attack. The lift-curve slope of the aircraft is independent from the variation of advance ratio. The stall characteristics show strong dependence on the advance ratio. Therefore, the relationship is modeled accurately using inverse-quadratic relationship. This empirical trend of the stall behavior with advance ratio can be useful in the analysis and simulation of the resulting flight and estimation of performance envelopes.

Effect of Propeller Slipstream on Heat-Exchanger Installations at Low Reynolds Number

An experimental program whose objective was an improved understanding of the effects of intermittent turbulence shed by a propeller on the aerodynamics of heat-exchanger installations at low Reynolds numbers is reported. The primary application is unmanned high-altitude atmospheric science aircraft, forming part of Old Dominion University's effort to develop technology applicable to ERAST (Environmental Research Aircraft and Sensor Technology) class aircraft. Wind-tunnel results indicate that the propeller wake affects, but does not eliminate, laminar separation bubbles on a representative wing. Rather, the bubbles reform between wake passages, limiting the drag penalty caused by increased skin friction. Further, there appears to be a possibility of an enhancement in performance of suitably designed ducted heat-exchanger installations

Development of a Low-Cost and Versatile Flight Test Platform

This paper describes the creation of an independent e ight test facility in Portugal, based on international and national cooperation; the e ying element is the basic aircraft for e ight research (BAFR), a CASA 212 Aviocar twin-turboprop light transport, e tted with a e ight test instrumentation (FTI) system, from which smaller dedicated FTIs were developed for several other aircraft. A part of one of the research projects carried out with BAFR, viz., a linear longitudinal stability model, including propeller slipstream effects is described. The model is reduced from 3 3 5 form to a 4 3 4 autonomous system of differential equations, from which the frequency and damping of the phugoid and short period modes are determined. The model parameters were identie ed from e ight tests of selected maneuvers and the reconstruction of e ight data using the model served to validate the latter.

Effects of Propeller Slipstream and Tail Position on the Vibration Characteristics of the Lockheed Lodestar

Effects of Propeller Slipstream and Tail Position on the Vibration Characteristics of the Lockheed Lodestar