Details

ESDU 75031 gives an empirical method for the prediction of the drag increment due to a variety of two-dimensional excrescences, each mounted normal to the flow direction on a flat plate, and immersed in a turbulent boundary layer for Mach numbers up to 3. The excrescence types are

• a forward-facing step, ramp (chamfered step), or a radiused step,
• a rearward-facing step, ramp (chamfered step), or a radiused step,
• a square section ridge or a rectangular section ridge (of height/length ratio 2), with or without radii to the top corners.

In this program the method of ESDU 73031 has tentatively been extended to cover situations in which steps and ridges are inclined to the flow at other than 90 degrees, along the lines suggested in ESDU 93032.

ESDU 73017 and ESDU 77021 provide atmospheric data, if required. These Items are complemented by the ISA Toolbox App.

ESDU 68020 provides data for a turbulent boundary layer on a flat plate, if required. Estimates for local and mean skin friction coefficients may be obtained from the CFM Toolbox App.

Details

Details

This App uses the semi-empirical method of Spalding and Chi to obtain the local and mean skin friction coefficients for a turbulent boundary layer on a smooth flat plate with zero pressure gradient and zero heat transfer.

The data are applicable to flows with Reynolds numbers based on streamwise distance over the range 100 thousand to 1000 million and for Mach numbers up to 5.

The equations used are taken from Appendix A of ESDU 78019, which itself is based on the method described in ESDU 68020. Both of these Items are to be found in the Aerodynamics Series.

Details

The ASTEROID program brings together the various ESDU methods for the calculation of excrescence drag due to steps, ridges, grooves and cavities on the external surfaces of aircraft. The app provides a simple interface that enables users to define the excrescences and then calculate the drag increments within a few minutes.

ASTEROID integrates the programs associated with ESDU 75031, ESDU 74036 and ESDU 75028 within the context of a specified and predetermined aircraft flow field. Multiple excrescence geometries can be specified on selected aircraft major components (i.e. a wing upper or lower surface, fuselage, nacelle, horizontal tail or fin). The app first asks the user to select an aircraft type (e.g. single-aisle transonic airliner, low-speed commuter airliner, etc) from a list and to choose an appropriate cruise Mach number for consideration. The app then allocates the appropriate pre-generated local flow field so that typical flow conditions (including flow direction) at each excrescence can be determined. The flow data for the single-aisle and low-speed commuter aircraft are presented for the whole airframe, together with a range of wings representative of short-, medium- and long- range jet transports, and a blended-wing body design.

Excrescence geometries are then specified either as circular cavities or as multi-node excrescences, which can be closed (e.g. to model a repair plate or cover) or open (e.g. to model a control surface gap). The edges of the excrescence can be characterised as steps (with or without edge treatments), rectangular or square ridges, grooves or gaps (with or without sealing).

When the excrescences have been defined, the app automatically selects the method from the appropriate Data Item and calculates the drag coefficients based on both the excrescence and aircraft reference areas. The aircraft drag coefficient penalty summed for all excrescences is also calculated.

Details

ASTEROID fp (flat plate) is a version of the ASTEROID drag prediction tool that uses the graphical and calculation modules (and data management capabilities) offered by the original program, but the user is freed from having to select one of the flow-fields for specific aircraft or generic wings in the current database. Instead, all flow conditions are specified by the user, thereby extending ASTEROID's applicability, not only to aircraft whose airframes or components are not presently represented within the flow-field library, but also missiles, rockets, drones and non-aeronautical applications such as rail and road transports and wind engineering.

The designation 'fp' relates to the 'flat plate' condition, which is that addressed in all the excrescence drag calculation methods in the Aerodynamics Series' Data Items relating to specific excrescence types. Most of the wind-tunnel data were indeed for excrescence models mounted on flat plates but, in the wider context of applying such data to drag prediction, this should be interpreted as the drag in the absence of a pressure gradient. Therefore, no allowance is made in ASTEROID fp for any drag magnification that may be present, so that, in effect, the drag magnification factor is set to unity. The subject of excrescence drag magnification is discussed in detail in ESDU 90029.

Note that the use of ASTEROID fp is, in most respects, identical to ASTEROID, so the help files and instructional videos are applicable; the exception, of course, being references to the flow-field data library.