Drag Prediction / Reduction
Understanding the drag characteristics of an aircraft is essential for performance prediction. Speed, range, and fuel efficiency are all directly influenced by drag and are of greatest concern to potential customers. In addition to cruise performance, it is important to understand the drag characteristics in other phases of flight.
Drag analysis fall into two categories: total aircraft drag estimation and incremental drag studies. CFD by itself is an excellent tool to investigate the incremental effect of a proposed modification or excresence. In order to determine the total aircraft drag it is important to consider the effects of surface imperfections on the airframe, additional drag associated with the induction system, or an increase in drag due to accelerated air via a propulsion system. These factors can be accounted for by increasing the simulation complexity but are often considered using empirical flight test or wind tunnel data.
Optimum Aero uses a number of tools to analyze aircraft drag and find ways to reduce it, one method that isn’t commonly considered is a contour plot of pressure drag. This is a derived parameter which captures the effect of surface pressure as well as the orientation of the surface relative to the freestream flow. Often used for fairing optimization to give the designer an idea of what features can be modified or faired to reduce an unwanted area of increased drag. This type of analysis is shown below as the effect of aft fillets are investigated on the wing-fuselage fairing design.
Pressure Drag Contours for Wing-Fuselage Fairing Optimization
High Lift Prediction and Optimization
Maximum lift capability is required to estimate the aircraft stall speed, a critical value in the regulatory process.
CFD has shown to be an accurate tool to estimate the lift capabilities of various aircraft configurations. See the lift curves for three different flap settings and corresponding wind tunnel data in the image below. The potential for cost savings is great by providing an accurate means of conceptual design validation before spending larger sums of money on wind tunnel models or proof of concept aircraft.
CFD is used for high lift optimization by determining required wing sizing, flap to aileron area distribution, and flap and/or slat gap and overlap studies.
CFD and Wind Tunnel Data Comparison
Systems Integration
Optimum Aero has experience with a number of systems integration solutions. This includes:
- Static Port Position Error Analysis
- Can help to choose an optimal location or estimate the static position error given a known location of interest
- Inlet Design
- Environmental Control System (ECS)
- Engine Air Intake and Ram Recovery Prediction
- Submerged Inlet (NACA Style) Design and Drag Estimation — see image below
Submerged Inlet Simulation
- Ice Shape Analysis
- NASA LEWICE & CFD Analysis — see image below
2D CFD Airfoil Mesh with LEWICE shape
Propulsion Integration
Optimum Aero has a unique skill set regarding propeller and rotor propulsion systems. Both actuator disk and actuator blade simulations have been developed, in some cases we have been able to validate the models with powered wind tunnel data and finally compare with real world flight test data. It is important to be aware of the influence of a high powered propeller system and the impact it will have on aircraft stability, drag, and control surface effectiveness.
See the image below which shares non-proprietary work comparing actuator disk CFD and wind tunnel data of an axi-symmetric nacelle with a powered propeller. CFD nacelle surface pressure distribution and slipstream swirl angle show excellent agreement with experimental data. This methodology has been readily utilized on more complex geometries.
Actuator Disk Validation Simulation
Experimental Data Reference:
Samuelsson, I., “Low Speed Propeller Slipstream Aerodynamic Effects,” AGARD AR-303, pp. E6-1, E6-21.
Load Generation
Macro level aircraft loads as well as loads on individual components must be provided to stress engineers during the detail design phase of a program. Vortex lattice methods (VLM) are often used for macro level load generation on the lifting surfaces but CFD is often employed for a number of other load generation tasks. This include developing loads for flaps, fuselage, and smaller components.
Optimum Aerodynamics is able to develop air loads using CFD and then transfer these loads onto the Finite Element Method (FEM) mesh. This technique is advantageous because it provides the stress analyst with an accurate load distribution without requiring conservative approximations; additionally, it saves time by eliminating the stress engineer’s job of populating the FEM mesh.
CFD mesh (top) and FEM mesh (bottom)