# AEROM: NASA’s Unsteady Aerodynamic and Aeroelastic Reduced-Order Modeling Software

## Abstract

**:**

## 1. Introduction

^{TM}environment for rapid calculation of aeroelastic responses, including the prediction of flutter. A comparison of the aeroelastic responses computed using the aeroelastic simulation ROM with the aeroelastic responses computed using the CFL3Dv6 code showed excellent correlation.

## 2. Computational Methods

#### 2.1. FUN3D Code

#### 2.2. System Identification Method

#### 2.3. Simultaneous Excitation Input Functions

## 3. ROM Development Processes

#### 3.1. Improved ROM Development Process

- Create as many orthogonal functions as the number of structural modes of interest;
- Starting from the restart of a steady rigid CFD solution, execute a single CFD solution using the orthogonal excitation inputs simultaneously, resulting in GAF responses due to these inputs;
- Identify the individual impulse responses from the responses computed in Step 2 using the PULSE algorithm;
- Using the ERA, convert the impulse responses from Step 3 into an unsteady aerodynamic state-space model;
- Using full-solution CFD results, compare with solutions generated using the model generated in Step 4;

#### 3.2. Error Minimization

## 4. Sample Results

#### 4.1. Low-Boom N+2 Configuration

#### 4.2. KTH Generic Fighter

^{2}(or 169 psf) via a coalescence of modes 5 and 6. Using the ROM, any dynamic pressure can be quickly evaluated to determine the aeroelastic response, consistent with the root locus plots. At this dynamic pressure, the ROM-based flutter prediction is above the experimental flutter dynamic pressure at M = 0.9. Typically, a conservative flutter result occurs when the analysis predicts a flutter condition below the experimental flutter result. This result, therefore, implies a non-conservative result, indicative of potentially significantly non-linear phenomena. All results presented are for zero structural damping. Using the ROM, the effect of structural damping can be quickly evaluated as well but is not pursued in the present discussion.

#### 4.3. AGARD 445.6 Wing

#### 4.3.1. Inviscid Results

#### 4.3.2. Viscous Results

## 5. Conclusions

## Conflicts of Interest

## References

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**Figure 2.**Improved process for generation of an unsteady aerodynamic reduced-order modeling (ROM) (Steps 1–4).

**Figure 4.**Process for generation of an aeroelastic simulation ROM consisting of an unsteady aerodynamic ROM and a structural dynamic state-space ROM.

**Figure 5.**Error defined as difference between the FUN3D solution and the unsteady aerodynamic ROM solution due to input of orthogonal functions.

**Figure 7.**Comparison of full FUN3D aeroelastic response and ROM aeroelastic response for the first mode of the N+2 configuration at M = 1.7 and a dynamic pressure of 2.149 psi.

**Figure 8.**Comparison of full FUN3D aeroelastic response and ROM aeroelastic response for the second mode of the N+2 configuration at M = 1.7 and a dynamic pressure of 2.149 psi.

**Figure 9.**Aeroelastic root locus plot for the low-boom N+2 configuration at M = 1.7 with each colored marker indicating an increment of 2 psi in dynamic pressure for a given mode.

**Figure 11.**The generic fighter aeroelastic wind-tunnel model installed in the Transonic Dynamics Tunnel (TDT).

**Figure 12.**Pressure distributions at M = 0.7, AoA = 0 degrees on the KTH wind-tunnel model, as simulated inside the TDT using FUN3D code.

**Figure 13.**Root locus plot generated from ROM model indicating an aeroelastic instability at M = 0.90 in air test medium for the third configuration with each colored marker indicating an increment of 450 N/m

^{2}in dynamic pressure for a given mode.

**Figure 14.**Aeroelastic response in mode 3 for the FUN3D (blue) and ROM (orange) solutions for the configuration including the Transonic Dynamics Tunnel (TDT).

**Figure 15.**Aeroelastic response in mode 4 for the FUN3D (blue) and ROM (orange) solutions for the configuration including the TDT.

**Figure 19.**FUN3D full solution generalized coordinates at M = 1.141, Q = 30 psf, inviscid solution. Mode 1 = blue, Mode 2 = green, Mode 3 = red, Mode 4 = cyan.

**Figure 20.**FUN3D full solution third generalized coordinate at M = 1.141, Q = 30 psf, inviscid solution.

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**MDPI and ACS Style**

Silva, W.A.
AEROM: NASA’s Unsteady Aerodynamic and Aeroelastic Reduced-Order Modeling Software. *Aerospace* **2018**, *5*, 41.
https://doi.org/10.3390/aerospace5020041

**AMA Style**

Silva WA.
AEROM: NASA’s Unsteady Aerodynamic and Aeroelastic Reduced-Order Modeling Software. *Aerospace*. 2018; 5(2):41.
https://doi.org/10.3390/aerospace5020041

**Chicago/Turabian Style**

Silva, Walter A.
2018. "AEROM: NASA’s Unsteady Aerodynamic and Aeroelastic Reduced-Order Modeling Software" *Aerospace* 5, no. 2: 41.
https://doi.org/10.3390/aerospace5020041