John W. Slater

Glenn Research Center, Cleveland, Ohio

Christopher R. Gruber

University of Notre Dame, Notre Dame, Indiana

Planar Inlet Design and Analysis Process

(PINDAP)

NASA/TM—2005-213866

August 2005

AIAA–2005–4203
The NASA STI Program Office . . . in Profile

Since its founding, NASA has been dedicated to

the advancement of aeronautics and space

science. The NASA Scientific and Technical

Information (STI) Program Office plays a key part

in helping NASA maintain this important role.

The NASA STI Program Office is operated by

Langley Research Center, the Lead Center for

NASA’s scientific and technical information. The

NASA STI Program Office provides access to the

NASA STI Database, the largest collection of

aeronautical and space science STI in the world.

The Program Office is also NASA’s institutional

mechanism for disseminating the results of its

research and development activities. These results

are published by NASA in the NASA STI Report

Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of

completed research or a major significant

phase of research that present the results of

NASA programs and include extensive data

or theoretical analysis. Includes compilations

of significant scientific and technical data and

information deemed to be of continuing

reference value. NASA’s counterpart of peerreviewed formal professional papers but

has less stringent limitations on manuscript

length and extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific

and technical findings that are preliminary or

of specialized interest, e.g., quick release

reports, working papers, and bibliographies

that contain minimal annotation. Does not

contain extensive analysis.

• CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored

contractors and grantees.

• CONFERENCE PUBLICATION. Collected

papers from scientific and technical

conferences, symposia, seminars, or other

meetings sponsored or cosponsored by

NASA.

• SPECIAL PUBLICATION. Scientific,

technical, or historical information from

NASA programs, projects, and missions,

often concerned with subjects having

substantial public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific

and technical material pertinent to NASA’s

mission.

Specialized services that complement the STI

Program Office’s diverse offerings include

creating custom thesauri, building customized

databases, organizing and publishing research

results . . . even providing videos.

For more information about the NASA STI

Program Office, see the following:

• Access the NASA STI Program Home Page

at http://www.sti.nasa.gov

• E-mail your question via the Internet to

help@sti.nasa.gov

• Fax your question to the NASA Access

Help Desk at 301–621–0134

• Telephone the NASA Access Help Desk at

301–621–0390

• Write to:

 NASA Access Help Desk

 NASA Center for AeroSpace Information

 7121 Standard Drive

 Hanover, MD 21076
John W. Slater

Glenn Research Center, Cleveland, Ohio

Christopher R. Gruber

University of Notre Dame, Notre Dame, Indiana

Planar Inlet Design and Analysis Process

(PINDAP)

NASA/TM—2005-213866

August 2005

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

41st Joint Propulsion Conference and Exhibit

cosponsored by the AIAA, ASME, SAE, and ASEE

Tucson, Arizona, July 10–13, 2005

AIAA–2005–4203
Acknowledgments

The authors would like to thank the NASA Glenn’s Lewis Educational and Research Collaborative Internship

Program (LERCIP) for support of Christopher R. Gruber.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

Trade names or manufacturers’ names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.

Available electronically at http://gltrs.grc.nasa.gov
I. Introduction 

HE aerodynamic design of inlets for air-breathing propulsion systems across the Mach number range have 

traditionally relied on basic planar flow assumptions and analysis. Planar flow includes both two-dimensional 

and axisymmetric flow. Many of the inlets for subsonic commercial transport aircraft have an axisymmetric shape. 

Many of the inlets for supersonic military and commercial aircraft (production and conceptual) have either an 

axisymmetric or two-dimensional shape. Many of the inlets for vehicles envisioned for hypersonic speeds have 

either an axisymmetric or two-dimensional shape. The use of a planar flow assumption simplifies the geometry and 

flow analysis, which is desired during the preliminary design phase when several configurations may be studied. 

The planar flow analyses may also serve as reference flows for more complex inlet shapes. Thus, planar flow 

analysis remains a part of inlet design. 

The methods of computational fluid dynamics (CFD) are being used routinely for the aerodynamic analysis of 

inlet flow fields. The work here uses the Wind-US CFD code of the NPARC Alliance1

. Two of the most timeconsuming aspects of CFD analysis are the modeling of the geometry and the generation of the grid. For planar 

flow, the geometry is relatively simple and consists of lines and curves. The grids are also planar. The work here 

uses structured, multi-zone grids. From the simulated flow field, the performance of the inlet can be determined. 

These performance measures include total pressure recovery, distortion, engine flow, bleed flow, and spillage. 

In response to the need to efficiently conduct planar inlet aerodynamic design and analyses, a small-scale project 

has been conducted to develop the Planar INlet Design and Analysis Process (PINDAP). PINDAP mainly collects 

software tools that work together with Wind-US. The next section will discuss all of the elements. A major 

element in PINDAP is a Fortran 90 code named PINDAP that establishes the parametric design of the inlet and 

efficiently models the geometry and generates the grid. The design and analysis process will involve changes in the 

design parameters and grid properties. As these are changed, PINDAP quickly regenerates the geometry and grid 

for further flow analysis. PINDAP also helps set up boundary condition information for the Wind-US CFD code. 

Section 3 will provide an overview of PINDAP. 

Examples of the use of PINDAP for subsonic, supersonic, and hypersonic inlets are provided in Section 4. The 

cases are fairly generic and focus on the process rather than the design results. One aspect of PINDAP is the use of 

methods of statistical design of experiments (DoE) and response surface methods (RSM) to allow the intelligent 

examination of the design factors of the parameterized inlet design to approach an optimum inlet design. This 

aspect is only examined here in the example of the hypersonic inlet design. 

The development of PINDAP is continuing and the last section discusses some future directions for PINDAP. 

PINDAP will eventually be made available to interested US citizens. 

T

Planar Inlet Design and Analysis Process (PINDAP) 

John W. Slater 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Christopher R. Gruber 

University of Notre Dame 

Notre Dame, Indiana 46556 

The Planar Inlet Design and Analysis Process (PINDAP) is a collection of software tools that allow 

the efficient aerodynamic design and analysis of planar (two-dimensional and axisymmetric) 

inlets. The aerodynamic analysis is performed using the Wind-US computational fluid dynamics 

(CFD) program. A major element in PINDAP is a Fortran 90 code named PINDAP that can 

establish the parametric design of the inlet and efficiently model the geometry and generate the 

grid for CFD analysis with design changes to those parameters. The use of PINDAP is 

demonstrated for subsonic, supersonic, and hypersonic inlets. 

NASA/TM—2005-213866 1
II. Software Elements of PINDAP 

The Planar INlet Design and Analysis Process (PINDAP) is a collection of loosely-coupled software elements 

that work together to improve the flow of information during the aerodynamic design of an inlet system. Central to 

PINDAP is a Fortran 90 code named PINDAP. The software elements of PINDAP include: 

1) PINDAP is a Fortran 90 code that encodes the inlet design parameterization and creates the geometry, grid, 

and boundary condition information for the inlet geometry. The inputs to PINDAP are contained within an 

ASCII input file. PINDAP outputs a multi-zone, structured grid file (run.x) in Plot3d format and a boundary 

condition file (gman.com) for use by GMAN.* 

2) *CFCNVT converts the Plot3d file (run.x) to the common grid (run.cgd) file format. 

3) GMAN executes in batch mode to quickly set the boundary conditions within the common grid file (run.cgd) 

using the boundary condition file (gman.com) as input. 

4) Wind-US is the CFD flow solver. Wind-US solves the Reynolds-Averaged Navier-Stokes equations for 

turbulent, compressible flow using a cell-vertex, finite-volume, time-marching approach. Spatial accuracy is 

formally second-order using the Roe flux-difference splitting upwind formulation. Turbulence is modeled 

using the Spalart-Allmaras or SST models. Wind-US is capable of solving for flows of speeds ranging from 

low subsonic to hypersonic. Wind-US is distributed by the NPARC Alliance. 

5) *CFPOST performs some simple visualization of the flow field and extracts flow field information such as 

mass flows, total pressure recoveries, distortion, and other derived flow field information. 

6) Design-Expert is a statistical design of experiments (DoE) software package that performs statistical 

analysis of the DoE design and can apply response surface methods (RSM) to examine design factors.2

*The CFCNVT, GMAN, and CFPOST elements are utilities that are distributed with the Wind-US CFD code. 

III. PINDAP 

The operations of the PINDAP code include 1) form the geometry model of the inlet, 2) establish the grid 

topology, 3) generate the structured, multi-zone grid, and 4) output files for use with the Wind-US CFD code. The 

input to PINDAP is an ASCII text file. 

A. PINDAP Geometry Model 

The PINDAP geometry model was established to provide a simple description of the geometry of planar inlets 

while allowing a wide variety of inlet shapes. The geometry model assumes that the inlet consists of combinations 

of a body and a cowl. The shape of the body and cowl can vary based on the design conditions, such as Mach 

number. Both the body and cowl can have an interior and exterior component. In addition to the inlet surfaces, the 

geometry model describes the boundaries of the enclosed flow domain upon which the flow equations are solved. 

For a planar analysis, the flow domain is a planar area. The flow domain is divided into zones. A structured grid is 

then generated within each zone. The PINDAP geometry model consists of the following five components: 

1) Body (BOD). This component models the geometry such as the spinner of a subsonic inlet, the centerbody 

of a supersonic inlet, and the body of a 2D hypersonic inlet / vehicle. The start of the body component is 

referred to as the nose. 

2) Body Exterior (BEX). This component models the geometry of the body that is external to the inlet flow. 

One example is the external (top) surface of a 2D hypersonic body. This external component is needed for 

simulations at non-zero angle-of-attack. The body external component also starts at the nose. If the end of 

the body exterior connects with the end of the body component, the point is referred to as the tail. 

3) Cowl Interior (CIN). This component models the geometry of the interior of a cowl. The cowl interior is 

wetted by flow entering the inlet. The start of the cowl interior is the cowl lip. 

4) Cowl Exterior (CEX). This component models the geometry of the exterior of a cowl. The cowl exterior 

also starts at the cowl lip. If the end of the cowl exterior connects with end of the cowl interior, the 

connecting point is referred to as the trailing edge. 

5) Domain (DOM). This component models the geometry that defines the boundaries of the flow domain and 

the boundaries of the grid zones. The flow domain must be an enclosed area for planar domains. 

Modeling the geometry in terms of components allows a logical grouping of the geometry that can be used to 

simplify other tasks of PINDAP. An inlet geometry model can have each of these components in a variety of 

NASA/TM—2005-213866 2
combinations. An inlet is not required to have all of these components. It is possible to generate a geometry and 

grid with only one of these components. The examples of Fig. 1 illustrate a small variety of inlet geometries that 

can be created with this geometry model. 

Each component consists of one or more of entities. Each entity has its unique mathematical description and can

be mathematically described as a line, conic, non-uniform rational B-spline (NURBS), or cubic spline. Each entity 

has a set of control points. The control points are defined with respect to the Cartesian (x,y) frame for twodimensional shapes and the cylindrical (x,r) frame for axisymmetric shapes. A line entity is described by two 

control points which are the endpoints of the line. Various options exist for determining the two endpoints that 

include specifying the length or angle of the line. A conic entity is a section of a circle or ellipse. A NURBS curve 

entity is defined by its control points. The NURBS curve does not interpolate through the control points, but rather 

the control points control the local curvature of the NURBS curve. The slopes of the ends of the NURBS curve are 

tangent to the respective lines connecting the two control points at the respective ends of the NURBS curve. A 

cubic-spline curve entity is defined by a set of control points through which the curve interpolates. Each entity has a 

parameter associated with the distance along the entity. The parameter is directed from the first control point to the 

last control point along the entity. At any point along the entity a tangent vector is defined as being in the direction 

of the parameter. The normal to the entity is the cross product of the unit vector normal to the plane to the tangent 

vector. The entities of a component are not required to be contiguously connected. 

Each entity can also be divided into segments. The points at which an entity is broken into segments are called 

breakpoints. The locations of the breakpoints are defined by the normalized distance along the entity. Dividing the 

entity into segments makes it easier to construct the flow domain and divide the flow domain into zones for grid 

generation. The segments also allow greater flexibility in the generation of the grid along the entities. 

BOD

CIN

CEX

nose

leading 

edge 

CIN

CEX

leading 

edge 

trailing 

edge 

BOD

CEX

CIN

Subsonic Pitot Inlet 

(axisymmetric) 

Airfoil (2D) or Cowl (axisymmetric) 

Supersonic Inlet 

(2D or axisymmetric) 

Hypersonic Vehicle (2D) 

CEX

BEX

BOD

CIN

nose

cowl lip

trailing 

edge

tail

CEX

BEX

BOD

CIN

nose

cowl lip

trailing 

edge

tail

Figure 1. Examples of subsonic, supersonic, and hypersonic inlet geometries that can 

be modeled with PINDAP. 

NASA/TM—2005-213866 3
B. PINDAP Grid Zone Topology and Grid Generation 

The CFD analysis requires that a multi-zone, structured grid be generated about the inlet shape and within the 

flow domain. The flow domain is first divided into abutting zones. Each zone is a topological quadrilateral with 

four edges. The shape of each edge is defined by specifying the segments of the entities that comprise the edge. A 

structured grid zone has i and j coordinates associated with the edges. The direction of the grid coordinate must be 

specified with respect to the direction of the entity. Generating the grid for the zone involves generating the grid 

along each segment of each entity. The basic grid generation method for generating a grid on a segment is the 

hyperbolic tangent method in which one specifies the grid spacing at the ends of the entity segment and the number 

of grid points for the segment. PINDAP has the ability to determine the appropriate number of grid points along a 

segment based on the grid spacing and other grid quality parameters. A structured grid for a zone requires that 

opposite edges of the zone have the same number of grid points, and so, the procedure for specifying the number of 

grid points for each entity segment must provide this match. Once the grid points are distributed on the edges of the

zone, the zonal grid is computed using a basic trans-finite interpolation method. PINDAP outputs the grid (run.x) 

in multi-zone, whole, unformatted Plot3d file format. The Plot3d grid file is converted to a common grid format 

(run.cgd) using the CFCNVT utility. 

C. Boundary Conditions 

The common grid file (run.cgd) for input to the Wind-US code requires that boundary condition information be 

specified. The PINDAP code creates a file named gman.com that is used as the input for the GMAN utility. 

GMAN reads the common grid file (run.cgd) to get the grid coordinates and reads the gman.com file for 

information on how to set the boundary conditions. 

D. Direct Specification of the Geometry and Grid and the Concept of the Design Module 

The basic method of input of information into PINDAP is the direct specification of the geometry and grid in the 

ASCII input data file. For each entity, all of the information is specified in the input data file, such as, the geometry 

coordinates, number of segments, segment end-point grid spacing, number of grid points of each segment, and more. 

The direct specification mode is flexible, but can be tedious to enter the complete information for every entity and 

segment for even simple shapes. Further, information is often duplicated within the input file. Thus PINDAP allows 

one to code a design module, which is a Fortran 90 subroutine, to allow the input of a minimum set of information to 

describe the inlet shape and generate the grid. As an example, a design module was written to generate a grid 

about a NACA 4-digit airfoil such that a user is only required to input the three digits describing the airfoil,

distances defining the extent of the flow domain, and select grid spacings, such as those at the leading and trailing 

edges and the grid spacing at the airfoil surface. The design module then computes the remaining information to 

generate the geometry and generate the grid. The design module can encode assumptions about the geometry, 

topology, and grid so that a designer does not have to get bogged down with the details, and so, can focus on the 

design of the inlet. The design module can be designed to be applicable for a certain class of inlets, such as 

supersonic, axisymmetric, mixed-compression inlets. 

E. Isolator and Nozzle Zone 

The CFD analysis of inlet flows requires a boundary condition to be specified at the engine-face outflow 

boundary. One successful approach has been to attach at the engine-face a grid zone which contains an isolator and 

nozzle. The isolator is a straight duct that gives the flow time to mix out prior to reaching the nozzle. The nozzle 

is constricted such that its throat is choked. The boundary conditions at the outflow of the nozzle are simple 

extrapolation boundary conditions. The back-pressure at the engine-face is set by the height of the throat. This 

approach has been found to be fairly non-reflective, which improves iterative convergence of the simulation. 

F. Three-Dimensional Grids 

PINDAP has the capability of generating a three-dimensional grid obtained by extruding the planar grid in the zcoordinate or circumferential direction. The three-dimensional grid can then be used for simulations at non-zero 

angles-of-attack or angles-of-sideslip. 

NASA/TM—2005-213866 4
IV. Examples 

Several examples illustrate the use of PINDAP across the Mach number range. 

A. Subsonic Pitot Inlet 

A common inlet for subsonic transport aircraft with high-bypass turbo-fan engines is a pod-mounted, pitot inlet. 

The cowl is typically axisymmetric. The engine has a spinner to provide for smooth flow about the hub of the fan. 

Figure 2 shows a generic planar geometry for a subsonic pitot inlet. The blunt-nosed spinner is the body component 

of the geometry model and contains a single entity of a NURBS curve. The cowl consists of a cowl interior 

component and a cowl exterior component. The cowl has a blunt cowl lip. The cowl interior consists of two entities 

of NURBS curves. The cowl exterior consists of two entities – the first a NURBS curve and the second a line. The 

flow domain boundaries consist of lines and NURBS curves to divide the flow domain into 13 zones. The use of 

NURBS curves for zonal boundaries allows the generation of orthogonal grids within the zones. Note that some of 

the zonal boundary curves connect at breakpoints in the body and cowl entities. The distribution of the grid is 

guided by the normal grid spacing at the surfaces to resolve boundary layers on the cowl and spinner and the desired 

axial and radial grid resolution in the core flow. PINDAP generates the grid and boundary condition file for the 

Wind-US simulations. Figure 2 shows the grid and Mach number contours for a representative simulation. Once 

the inputs are established, PINDAP can be used to generate new grids quickly if modifications are made to the cowl 

shape or if the grid properties are modified to provide increased resolution. PINDAP can also extrude the grid 

circumferentially over a 180-degree or 360-degree section for flow simulations at angle-of-attack and / or angle-ofsideslip. 

Figure 2. Planar geometry model, grid, and Mach number contours for the subsonic pitot inlet. 

NASA/TM—2005-213866 5
American Institute of Aeronautics and Astronautics 

6

B. Supersonic, Mixed-Compression NASA-Ames Inlet 

PINDAP was used to model the geometry and generate the grid for a CFD validation study involving a NASAAmes, supersonic, mixed-compression inlet.3

 The inlet was axisymmetric with a centerbody and cowl. Figure 3 

shows the planar geometry. The centerbody had a conical nose, which was modeled as a line entity. The rest of the 

centerbody was modeled with a cubic spline to interpolate the (x,r) geometry coordinates published in the test report. 

Similarly a cubic-spline entity was used to model the cowl interior to interpolate the published coordinates. The 

cowl lip was modeled as being sharp. The first entity of the cowl exterior was a line. The second entity was a 

NURBS curve to provide a smooth shape to the third entity, which was a constant-radius line. The cowl exterior 

geometry was not provided in the test report, and so, was approximated, which is acceptable since at supercritical, 

supersonic flow conditions, the cowl exterior should not affect the flow through the inlet. Figure 3 shows the grid 

and Mach contours for one of the simulations. A useful feature in PINDAP is the ability to translate or rotate 

geometric entities. For the NASA-Ames inlet, the cowl translated to alter the internal area distribution of the inlet 

for start-up and for off-design conditions. Thus, once the inlet is modeled within PINDAP, one can quickly 

regenerate the grid when the cowl needs to be translated for another configuration. This example also shows the use 

of the isolator and nozzle. The isolator allows the separated flow from the subsonic diffuser to settle before 

reaching the nozzle. The nozzle radius can be varied to vary the back-pressure of the inlet. For a mixedcompression inlet, the back-pressure adjusts the location of the terminal shock. 

Figure 3. Planar geometry model, grid, and Mach number contours for the 

NASA-Ames mixed-compression inlet. 

NASA/TM—2005-213866 6
C. Supersonic Business Jet Inlet 

PINDAP was used for a preliminary study for the design and analysis of an inlet for a supersonic business jet.4

The business jet was designed to carry six passengers with a range of 4000 nautical miles at a cruise speed of Mach 

2.0 at an altitude of 50,000 feet. For this design study, it was assumed that the turbo-fan engine had a fan diameter 

of 60 inches and with a fan face Mach number of 0.6 at cruise. Further, it was assumed that the inlet used up to 3% 

bleed with 2% spillage. A two-dimensional, external-compression inlet was modeled. The geometry model 

consisted of a body, cowl interior, and cowl exterior components. Figure 4 shows the geometry model of the inlet. 

The body consisted of three entities. The first entity was a line representing the nose of the compression ramp 

defined by the nose angle. The second entity was a compression ramp defined by five control points that were 

interpolated using a cubic spline. The method of characteristics was used to determine the placement of the control 

points such that the Mach lines of the compression surface intersected at the focal point. The third entity was a 

NURBS curve defining the body surface of the internal duct leading to the fan. At the junction of the compression 

ramp and the internal body surface a “break” existed that resulted in a discontinuity of the slope of the body surface. 

The NURBS curve was defined by eight control points. The first three were collinear and defined the angle and 

strength of the start of the curve. The last three control points were also collinear and defined the angle and strength 

of the end of the curve. Two control points on the interior of the curve allowed local shaping of the middle of the 

curve. 

The cowl interior consisted of two entities. The first entity started at a sharp cowl lip and was a line entity whose 

angle was a design factor. The second entity of the cowl interior defined the rest of the interior cowl surface of the 

inlet. The second entity was a NURBS curve consisting of eight control points in the same fashion as the body 

curve. The cowl interior curve ended at the fan face. 

The cowl exterior contained three entities. The first entity was a line that started at the cowl lip with an angle. 

The second entity was a NURBS curve with four control points that matched the angles of the first and third entities. 

The third entity was a straight line that was flat. 

The flow domain boundaries consisted of an inflow boundary, farfield boundary, and outflow boundary for the 

exterior boundaries. The interior outflow boundary consisted of a straight line at the fan face connecting the body 

and cowl interior. The fan face was defined by the position of the axis of the fan at the fan face and the height of the 

fan. The fan face could also be at an angle. The interior boundaries extended downstream with the addition of an 

isolator and outflow nozzle. 

The main design factors for the inlet design included the factors for the shaping of the NURBS curves for the 

body and cowl interior, placement of the cowl lip, slope of the interior of the cowl lip, placement of the fan relative 

to the cowl lip. A design module was created for PINDAP that allowed the input of these design factors along with 

other geometric factors that define the geometry and domain. 

The design module also establishes the grid topology as a 2-zone grid. Zone 1 starts just ahead of the leading 

edge of the body nose and extends through the inlet to the fan face. Zone 2 encompasses the exterior of the inlet. 

The design module also reads in the grid quality information. Figure 5 shows an example of the grid for the inlet. 

The grid is clustered along the inlet surfaces. The grid also contains zones for an isolator and outflow nozzle 

attached to the fan face to apply outflow boundary conditions. 

The sizing of the inlet provided the location of the focal point. The inlet was sized for cruise conditions. With 

the diameter of the fan and the average Mach number at the fan face provided, the corrected weight flow through the 

fan was computed. With an estimate of the total pressure loss and assuming constant total temperature through the 

inlet, the actual weight flow through the fan face at the design condition was computed. With an assumption of the

allowable bleed and spillage, the design capture weight flow was computed. With a supersonic inlet, the captured 

Figure 4. Geometry model for the 2D SBJ inlet. 

NASA/TM—2005-213866 7
weight flow was the amount of flow through the area enclosed by the focal point. The cowl lip was then placed to 

capture the sum of the assumed fan-face and bleed flow. Actual conditions caused the amounts of weight flows to 

vary, but PINDAP allowed the cowl lip position and bleed region design factors to be varied to adjust these values 

to desired levels. Figure 5 shows the Mach number contours for one of the simulations. 

D. Hypersonic Inlet 

The PINDAP design process was exercised during the design of a generic, two-dimensional hypersonic inlet for 

Mach 5 flow. The design point was an altitude of 65000 feet and angle-of-attack of 0 degrees. Figure 6 shows the 

design factors for this study. The design requirements included a specified engine weight flow with an average 

Mach number into the isolator of approximately Mach 2.5. For this study, the geometry was parameterized with 

respect to a number of design factors. A Microsoft Excel spreadsheet was created to generate the geometry 

coordinates for the inlet based on the set of design factors and some calculations based on oblique shock theory and 

the engine weight flow requirement. Figure 6 shows a diagram of the design factors and the entities modeled for the 

body and cowl. The body component consisted of four entities. The first two were the ramps modeled as line 

entities. Within the diffuser, the body was modeled with NURBS curve entities. The position of the shoulder (xs

, 

ys) was a variable design factor. A body exterior component was specified with a single line entity. The cowl lip 

was modeled as being a sharp point located at (xcowl, ycowl) whose position was determined by requirements that the 

oblique shocks from the ramps intersect near the cowl lip with a specified spillage and inlet capture flow. The cowl 

interior component consisted of two entities. The first was a line that established the interior angle of the cowl. This 

angle set up the oblique cowl shock. The remainder of the cowl interior was modeled with a NURBS curve entity. 

The engine-face height (hf) was mostly determined by the requirement of approximately Mach 2.5 at the entry to the 

isolator. The coordinate (xcf, ycf) set the position of the engine face. The cowl exterior was modeled with two line 

entities. The geometry coordinates produced from the spreadsheet for a specific design were then input into 

PINDAP to generate the grid. Figure 7 shows an example grid. CFD simulations were then performed. Figure 7 

shows the sample Mach number contours. Based on preliminary CFD simulations, two of the design factors were 

selected to vary for the DoE study – the axial position of the shoulder (xs) and the vertical position of the bottom of 

the engine face (ycf). A statistical design was established to generate a quadratic response surface of the total 

pressure recovery with respect to the two design factors. This required a full-factorial design requiring 9 CFD 

simulations (2 factors with 3 levels each). Figure 8 shows a typical response surface generated during the process. 

The optimum set of design factors was obtained from examining the response surfaces during the design process. 

Figure 5. Grid and Mach number contours for a 2D SBJ inlet. 

NASA/TM—2005-213866 8
American Institute of Aeronautics and Astronautics 

9

The PINDAP code was useful since each set of design factors requires a slightly different geometry and the grid 

generated for that geometry. With simple changes to the input file, the grids were quickly generated. 

 

Figure 6. Design factors and geometry entities for the hypersonic inlet. 

Figure 7. Planar geometry model, grid, and Mach number 

contours for the hypersonic inlet. 

NASA/TM—2005-213866 9
V. Summary and Conclusion 

PINDAP provides a framework for efficient design-based CFD analysis of planar inlet systems. By 

automatically generating the geometry, grid topology, and grid, it removes some of the most tedious and demanding 

aspects of the use of CFD for inlet design. This will allow designers and engineers possessing only fundamental 

knowledge of CFD to use a CFD tool for their aerodynamic analysis of inlet systems. 

VI. Future Work 

The development of the PINDAP code is ongoing. Further work is proceeding to improve the geometry 

modeling and grid generation capabilities and develop design modules for certain classes of inlets. PINDAP will 

be developed to generate geometry and grids for three-dimensional inlets with flow control devices such as vanes 

and jets. PINDAP will also be able to generate grids for a turbo-fan simulation module. 

References 1

NPARC Alliance, “The Wind-US Code”, www.grc.nasa.gov/www/Wind-US docs [cited 3 November 2004]. 2

State-Ease, Inc. www.stat-ease.com. [cited 3 November 2004]. 3

Sorensen, Norman E.; and Smeltzer, Donald B.: Investigation of a Large-Scale Mixed Compression Axisymmetric Inlet 

System Capable of High Performance at Mach Number 0.6 to 3.0. NASA TM X-1507, 1968. 4

Bruckner, R.J., “Conceptual Design of a Supersonic Business Jet Propulsion System,” AIAA Paper 2002-3919, July 2002. 

0.720718 

0.735184 

0.749649 

0.764115 

0.77858 Recovery 

-6.24 

-6.19 

-6.14 

-6.09 

-6.04 30.50

 30.75

 31.00

 31.25

 31.50

 A : ycf B : xs 

Figure 8. Response surface for total pressure 

recovery for the hypersonic inlet design. 

NASA/TM—2005-213866 10
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

REPORT DOCUMENTATION PAGE

2. REPORT DATE

19. SECURITY CLASSIFICATION

 OF ABSTRACT

18. SECURITY CLASSIFICATION

 OF THIS PAGE

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

Form Approved

OMB No. 0704-0188

12b. DISTRIBUTION CODE

8. PERFORMING ORGANIZATION

 REPORT NUMBER

5. FUNDING NUMBERS

3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE

6. AUTHOR(S)

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

13. ABSTRACT (Maximum 200 words)

14. SUBJECT TERMS

17. SECURITY CLASSIFICATION

 OF REPORT

16. PRICE CODE

15. NUMBER OF PAGES

20. LIMITATION OF ABSTRACT

Unclassified Unclassified

Technical Memorandum

Unclassified

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135–3191

1. AGENCY USE ONLY (Leave blank)

10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546–0001

Available electronically at http://gltrs.grc.nasa.gov

August 2005

NASA TM—2005–213866

AIAA–2005–4203

E–15236

WBS–22–714–09–25

16

Planar Inlet Design and Analysis Process (PINDAP)

John W. Slater and Christopher R. Gruber

Inlet flow; Computational fluid dynamics; Design

Unclassified -Unlimited

Subject Category: 07

Prepared for the 41st Joint Propulsion Conference and Exhibit cosponsored by the AIAA, ASME, SAE, and ASEE,

Tucson, Arizona, July 10–13, 2005. John W. Slater, NASA Glenn Research Center; and Christopher R. Gruber, University

of Notre Dame, Notre Dame, Indiana 46556. Responsible person, John W. Slater, organization code RTL, 216–433–8513.

The Planar Inlet Design and Analysis Process (PINDAP) is a collection of software tools that allow the efficient

aerodynamic design and analysis of planar (two-dimensional and axisymmetric) inlets. The aerodynamic analysis is

performed using the Wind-US computational fluid dynamics (CFD) program. A major element in PINDAP is a Fortran 90

code named PINDAP that can establish the parametric design of the inlet and efficiently model the geometry and generate

the grid for CFD analysis with design changes to those parameters. The use of PINDAP is demonstrated for subsonic,

supersonic, and hypersonic inlets.