---
# System prepended metadata

title: cfd
tags: [AIAA DBF]

---

# CFD紀錄
- [name=卓廷典]

[TOC]

## 目的
- [x] 1. 展示巡航攻角下飛機整體附近流場(Stream line)
- [x] 2. 各部件不同攻角升阻力係數，==計算升阻力與升阻力曲線==，分析機身對整體氣動力造成的影響
- [x] 3. 找出==失速攻角與最大升力係數==
- [x] 4. 找到==NP點==，驗證重心是否正確
- [x] 5. 跑整體在不同側滑角下的力矩，計算橫向穩定 ==Cn$_\beta$ 、 Cl$_\beta$== 數值
- [ ] 6. 進行流場分析，比較高攻角下==翼尖與翼根失速情況==
- [x] 7. 找到==CP點==

## 基本參數
### 基本reference vaule
* c = 0.277 m
* S = 0.422 m
* v = 19 m/s

### enclosure
* 離地 10000 mm
* 左右邊界距離翼尖 5000 mm
* 離天花板 5000 mm
* 離inlet 1000 mm
* 離outlet 10000 mm

### 網格設定:
* hex(四邊形)去長，但系統自動判斷在邊角處是否切三角形
* 外圍用`FACE SIZING`，`ELEMENT SIZE` 0.5 m
* 內部平整方型平面用`FACE SIZING`，`ELEMENT SIZE` 0.01 m
* 規則但非方形面用`EDGE SIZING`，`number of division`，切到大約每0.01 m 一個網格
* 其他未特別mesh

### 其他
![image](https://hackmd.io/_uploads/SkMjQYlU-l.png)
![image](https://hackmd.io/_uploads/BJ12mFe8-g.png)
其他都用預設的
![image](https://hackmd.io/_uploads/HkKkEtgLWl.png)
![image](https://hackmd.io/_uploads/BJvWEYx8Ze.png)

## 零攻角
### 機身
![image](https://hackmd.io/_uploads/S1k4eFeUWl.png)
![image](https://hackmd.io/_uploads/HJgrlKx8Wx.png)
![image](https://hackmd.io/_uploads/S1EiZtxUWe.png)
![image](https://hackmd.io/_uploads/r1f-MFg8bl.png)

### 機翼
![image](https://hackmd.io/_uploads/BJ26ZckU-x.png)
![image](https://hackmd.io/_uploads/B1CRWq1UZx.png)
![image](https://hackmd.io/_uploads/HyKVMcJUbe.png)
![image](https://hackmd.io/_uploads/S1xaMq1IZe.png)
![image](https://hackmd.io/_uploads/rJYy7qJ8Zl.png)

### 機翼+tail
![image](https://hackmd.io/_uploads/rkQ-Boy8Wl.png)
![image](https://hackmd.io/_uploads/SJfNHs1L-e.png)
![image](https://hackmd.io/_uploads/S1qI8jkU-e.png)
![image](https://hackmd.io/_uploads/SkUtIjJUZl.png)
![image](https://hackmd.io/_uploads/SyjCLoJLZx.png)

### 整體
![image](https://hackmd.io/_uploads/HJB1qLlUWl.png)
![image](https://hackmd.io/_uploads/H1BecIlLZe.png)
![image](https://hackmd.io/_uploads/HygvCIlIbg.png)
![image](https://hackmd.io/_uploads/HkQFPPlLbe.png)

## 巡航攻角(2.85度)
:::info
cos(5°)=0.998763
sin(5°)=0.049721
:::

### 整體
![image](https://hackmd.io/_uploads/SkL1YNMIbx.png)
![image](https://hackmd.io/_uploads/BkNxYVM8Zx.png)
![image](https://hackmd.io/_uploads/HyqPKNMIWl.png)
![image](https://hackmd.io/_uploads/ry95tEzUbx.png)

### wing
![image](https://hackmd.io/_uploads/HJqWqBMIWl.png)
![image](https://hackmd.io/_uploads/SJvM5SfUbx.png)
![image](https://hackmd.io/_uploads/SkeGejHGLWg.png)
![image](https://hackmd.io/_uploads/B1gXjHz8bg.png)



## 5度攻角
:::info
cos(5°)=0.996
sin(5°)=0.087
:::

### 整體
![image](https://hackmd.io/_uploads/B1vT1--IZg.png)
![image](https://hackmd.io/_uploads/ryZ1g-bL-g.png)
![image](https://hackmd.io/_uploads/B1qUlZW8Zg.png)
![image](https://hackmd.io/_uploads/r1rtgbZL-x.png)
![image](https://hackmd.io/_uploads/BkNtWWW8-g.png)

### 機身
![image](https://hackmd.io/_uploads/Sk-EqcbUWg.png)
![image](https://hackmd.io/_uploads/H1Er9qWUZg.png)
![image](https://hackmd.io/_uploads/SkfNsq-UWg.png)

### 機翼
![image](https://hackmd.io/_uploads/BkjQq3-Lbe.png)
![image](https://hackmd.io/_uploads/BkiV92-8Wg.png)
![image](https://hackmd.io/_uploads/BJNJjnZU-g.png)

### wing+tail
![image](https://hackmd.io/_uploads/HJWs5bzLWe.png)
![image](https://hackmd.io/_uploads/S1xncbGU-l.png)
![image](https://hackmd.io/_uploads/BJ2X3XMLbg.png)
![image](https://hackmd.io/_uploads/ryLq2XfLbg.png)



## 失速情況
### 20°
:::info
cos(20°)=0.939693
sin(20°)=0.342020
:::
![image](https://hackmd.io/_uploads/B1zvxaWI-g.png)
![image](https://hackmd.io/_uploads/BJJOe6b8bx.png)

![image](https://hackmd.io/_uploads/HksBfT-8bx.png)
翼尖:![image](https://hackmd.io/_uploads/By1tMab8be.png)
翼根:![image](https://hackmd.io/_uploads/BJOcGa-Ube.png)
![image](https://hackmd.io/_uploads/HyWpfpb8Ze.png)

### 18°
:::info
cos(18°)=0.951057
sin(18°)=0.309017
:::
![image](https://hackmd.io/_uploads/B1CP3Z78-g.png)

### 15°
:::info
cos(15°)=0.965926
sin(15°)=0.258819
:::
![image](https://hackmd.io/_uploads/HknLMzXIbl.png)

### 12°
:::info
cos(12°)=0.978148
sin(12°)=0.207912
:::
![image](https://hackmd.io/_uploads/By0qrf7LWx.png)


### 24°
:::info
cos(24°)=0.913545
sin(24°)=0.406737
:::
![image](https://hackmd.io/_uploads/r18o2MX8-e.png)

### 28°
:::info
cos(28°)=0.882948
sin(28°)=0.469472
:::
![image](https://hackmd.io/_uploads/Sku9rIQU-x.png)


### 30°
:::info
cos(30°)=0.866025
sin(30°)=0.5
:::
![image](https://hackmd.io/_uploads/BJG8yImUWx.png)
![image](https://hackmd.io/_uploads/ByDIU8QU-x.png)


|  | Cl |
| -------- | -------- |
| 0° | 0.2628 |
| 2.85° | 0.4199 |
| 5° | 0.5344 |
| 12° | 0.8375 |
| 15° | 0.9161 |
| 18° | 0.9655 |
| 20° | 0.9959 |
| 24° | 1.0544 |
| 28° | 1.0714 |
| 30° | 1.0772 |

![image](https://hackmd.io/_uploads/B1PeOI78Ze.png)

## 高攻角重跑
### 整體
20度
![image](https://hackmd.io/_uploads/H1j5u0uL-x.png)
![image](https://hackmd.io/_uploads/By9o_COIZl.png)


15度
![image](https://hackmd.io/_uploads/HJEHu2r8We.png)
![image](https://hackmd.io/_uploads/H16Y-EUUWl.png)

10度
![image](https://hackmd.io/_uploads/rkxkXJLLZg.png)
![image](https://hackmd.io/_uploads/rkSVbNLIZe.png)

5度
![image](https://hackmd.io/_uploads/Skqcwl8LWx.png)
![image](https://hackmd.io/_uploads/HJMoxN8UZl.png)

2.85度
![image](https://hackmd.io/_uploads/r1jFPWLIWe.png)
![image](https://hackmd.io/_uploads/SypOgEUU-l.png)

0度
![image](https://hackmd.io/_uploads/Hyo_wXUIbl.png)
![image](https://hackmd.io/_uploads/BkcLgEU8Wx.png)


|  | Cl | Cl$\alpha$ |
| -------- | -------- | ----|
| 0° | 0.3071 |  |
| 2.85° | 0.5517 | 4.9174 |
| 5° | 0.7253 | 4.6263 |
| 10° | 1.2002 | 5.4420 |
| 15° | 1.5563 | 4.0806 |
| 20° | 1.8169 | ? |

### 機翼
0度
![image](https://hackmd.io/_uploads/rJ4BqNU8Zx.png)
![image](https://hackmd.io/_uploads/Bkq-j4LL-l.png)

2.85度
![image](https://hackmd.io/_uploads/SJjlNILLZl.png)
![image](https://hackmd.io/_uploads/BJzMVUU8We.png)

5度
![image](https://hackmd.io/_uploads/r17hQ4PL-e.png)
![image](https://hackmd.io/_uploads/BJ4pQNwLWg.png)

### 機身
0度
![image](https://hackmd.io/_uploads/SyOIV4w8-e.png)
![image](https://hackmd.io/_uploads/r1BwE4DUZg.png)

2.85度
![image](https://hackmd.io/_uploads/B1czOVvLWg.png)
![image](https://hackmd.io/_uploads/Hklc7_VvLbx.png)

5度
![image](https://hackmd.io/_uploads/Syeh3NvUWg.png)
![image](https://hackmd.io/_uploads/rkET3NDI-l.png)

### wing+tail
0度
![image](https://hackmd.io/_uploads/r1X4s7uLWe.png)
![image](https://hackmd.io/_uploads/S1PSjm_8-x.png)

2.85度
![image](https://hackmd.io/_uploads/rkLLtEdI-l.png)
![image](https://hackmd.io/_uploads/BJDvFVdU-l.png)

5度
![image](https://hackmd.io/_uploads/HJ4fRBO8-l.png)
![image](https://hackmd.io/_uploads/H1mQCH_8We.png)


## 縱向穩定
:::danger
先提醒:我並未修正參考座標系
* YZ座標皆會差一個負號
* 機鼻的X座標為0，機尾的X座標為負
:::
### 條件一:0°攻角
![image](https://hackmd.io/_uploads/By_pK8Q8-x.png)
![image](https://hackmd.io/_uploads/HkKe9ImUZl.png)
![image](https://hackmd.io/_uploads/B18M987Ubg.png)
:::success
先進行驗算:
* 兩個旋轉點差了0.5 m
* 其力矩分別為0.4988 與 0.0244，差值為0.4744
* 升力係數為0.2628

**0.2628(升力係數)\*0.5(力臂)/0.277(弦長) = 0.4744**

---
cp點應位於0.5+0.0244*0.277/0.2628=0.5257

![image](https://hackmd.io/_uploads/B16hjLmIWl.png)
:partying_face: 

:::

### 條件二:5°攻角

![image](https://hackmd.io/_uploads/H1yH687Lbe.png)
![image](https://hackmd.io/_uploads/HJe8T8X8bx.png)
![image](https://hackmd.io/_uploads/rJ4KpLm8Ze.png)

### 求解
0.55167439x+0.14097154=0.30714985x+0.1605209
X=0.0799485=0.022146 m
NP點位於0.6707 m

### 驗證
0:
![image](https://hackmd.io/_uploads/SkySCQULbe.png)

2.85:
![image](https://hackmd.io/_uploads/SJgwR7UUZl.png)

5:
![image](https://hackmd.io/_uploads/r1mRC7UIWl.png)


:::info
結論:
NP點在機鼻往後 0.6707 m
以現有重心12%來說，穩定裕度高達45%

avl有更新檔案，NP點在 0.666624 m
xflr5的NP點在 0.716994 m
:::

## 橫向穩定
簡單說我們要跑側滑角為+-5的情況，因為三維角度有點難處理，所以我側滑角是跑0攻角情況。
:::info
cos(5°)=0.996195
sin(5°)=0.087156
重心:0.6140 m
:::

### -5°

cl:![image](https://hackmd.io/_uploads/SJAMJY78bl.png)
![image](https://hackmd.io/_uploads/SJeiJKXUZg.png)

cn:![image](https://hackmd.io/_uploads/SJN41tm8Wx.png)
![image](https://hackmd.io/_uploads/ByctJYmLZx.png)

### 0°
cl:![image](https://hackmd.io/_uploads/HyqIlKQUWe.png)
![image](https://hackmd.io/_uploads/SyRwlt7L-l.png)

cn:![image](https://hackmd.io/_uploads/rJmclKXU-e.png)
![image](https://hackmd.io/_uploads/B1GKlt7L-x.png)

### 5°
cl:![image](https://hackmd.io/_uploads/Hy-dzFQL-l.png)
![image](https://hackmd.io/_uploads/ryDKzKQUZx.png)

cn:![image](https://hackmd.io/_uploads/HkOcGtX8bx.png)
![image](https://hackmd.io/_uploads/ryaozFQIZe.png)

## 橫向穩定重跑
### -5度
cl:
![image](https://hackmd.io/_uploads/SJRcuKPU-l.png)

cn:
![image](https://hackmd.io/_uploads/H1EnuKvUWg.png)
![image](https://hackmd.io/_uploads/BJX6dKD8Wl.png)

### -2度
cl:
![image](https://hackmd.io/_uploads/Sy4Q5qPLbe.png)

cn:
![image](https://hackmd.io/_uploads/HkxMc9P8Zl.png)
![image](https://hackmd.io/_uploads/rJES55w8-l.png)

| 機鼻 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.082 | -0.123 |-| 1.4095 | -0.9397 |-5°|
|-2°| 0.033 | -0.047 |-| 1.3465 | -0.9454 |-2°|
|0°| -0.000 | 0.002 |-|  |  |0°|
|2°| -0.032 | 0.050 |-| 1.3751 | -0.9167 |2°|
|5°| -0.081 | 0.124 |-| * | * |5°|

| 重心 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.082 | -0.049 |-| 0.5615 | -0.9397 |-5°|
|-2°| 0.033 | -0.019 |-| 0.5443 | -0.9454 |-2°|
|0°| -0.000 | -0.000 |-|  |  |0°|
|2°| -0.032 | 0.020 |-| 0.5730 | -0.9167 |2°|
|5°| -0.081 | 0.048 |-| 0.5500 | -0.9282 |5°|

0度
cl:
![image](https://hackmd.io/_uploads/HyYMkbtU-x.png)

cn:
![image](https://hackmd.io/_uploads/SywVk-F8be.png)
![image](https://hackmd.io/_uploads/BydSJWFIZl.png)

2度
cl:
![image](https://hackmd.io/_uploads/H1U2JZt8bl.png)

cn:
![image](https://hackmd.io/_uploads/SyKT1bKI-l.png)
![image](https://hackmd.io/_uploads/H1pQlbFL-e.png)

5度
cl:
![image](https://hackmd.io/_uploads/SJDZ_MKUWg.png)

cn:
![image](https://hackmd.io/_uploads/SytMOMtUZl.png)
![image](https://hackmd.io/_uploads/rysmuGKLZe.png)



## 統整

### 各部件結果

| Cl | 0° | 2.85° | 5° | 15° |
| -------- | -------- | -------- | -------- | -------- |
| fuselage | -0.0203 | -0.0110 | -0.0023 | x |
| wing | 0.4889 | 0.6997 | 0.8696 | x |
| wing+tail | 0.3892 | 0.6005 | 0.8104 | x |
| all | 0.3071 | 0.5517 | 0.7254 | 1.5563 |

| Cl$_\alpha$ | 0°~2.85° | 2.85°~5° | 0°~5° |
| -------- | -------- | -------- | -------- |
| fuselage | 0.1870 | 0.2318 | 0.2063 |
| wing | 4.2379 | 4.5277 | 4.3625 |
| wing+tail |4.2479 | 5.5937 | 4.8266 |
| all | 4.9174 | 4.6290 | 4.7934 |

| Cd | 0° | 2.85° | 5° | 20° |
| -------- | -------- | -------- | -------- | -------- |
| fuselage | 0.0177 | 0.0167 | 0.0167 | x |
| wing | 0.0346 | 0.0494 | 0.0654 | x |
| wing+tail | 0.0384 | 0.0515 | 0.0676 | x |
| all | 0.0556 | 0.0671 | 0.0767 | x |

|  | Cl | Cl$\alpha$ |
| -------- | -------- | ----|
| 0° | 0.3071 |  |
| 2.85° | 0.5517 | 4.9174 |
| 5° | 0.7253 | 4.6263 |
| 10° | 1.2002 | 5.4420 |
| 15° | 1.5563 | 4.0806 |

### xflr5
| Cl | 0° | 2.85° | 5° | 14.5° |
| -------- | -------- | -------- | -------- | -------- |
| wing | 0.444 | 0.6625| 0.806 | 1.452 |
| wing+tail |0.401 | 0.6399 | 0.801 | 1.517 |
| all | 0.397 | 0.6410 | 0.802 | 1.526 |

| Cl$_\alpha$ | 0°~2.85° | 2.85°~5° | 0°~5° |
| -------- | -------- | -------- | -------- |
| wing | 4.3846 | 3.8242| 3.8961 |
| wing+tail |4.8028 | 4.2932 | 4.3183 |
| all | 4.9053 | 4.2905| 4.3665 |

| Cd | 0° | 2.85° | 5° | 14.5° |
| -------- | -------- | -------- | -------- | -------- |
| wing | 0.025 | 0.0370 | 0.049 | 0.137 |
| wing+tail | 0.027 | 0.0384 | 0.052 | 0.151 |
| all | 0.026 | 0.0383 | 0.051 | 0.153 |

### avl
| Cl | 0° | 2.85° | 5° | 14.5° | 20° |
| -------- | -------- | -------- | -------- | -------- | -------- |
| wing |   |   |   |   |  |
| wing+tail |  |   |   |   |  |
| all | 0.45475 | 0.70309  | 0.88803  | 1.66636  | 2.07718 |

| Cl$_\alpha$ | 0° | 2.85° | 5° |14.5° |20° |
| -------- | -------- | -------- | -------- | -------- | -------- |
| wing |  |  |  |   |   |
| wing+tail |  |  |  |   |   |
| all | 4.452727 | 4.452727 | 4.452727  | 4.452727 | 4.452727  |

![image](https://hackmd.io/_uploads/B1lj2ogKIZe.png)
![image](https://hackmd.io/_uploads/Sy-2slFUZl.png)

:::success
* cfd tail & wing CLA 調到all以下
* body 不要放斜率、cfd wing+tail放平的，其他放兩點
:::



### 縱向穩定
NP點在
* 機鼻往後 0.6486 m
* 翼前緣往後 0.1584 m
* 57.2%的位置

以現有重心12%來說，穩定裕度高達45%



### 橫向穩定
::: spoiler
| 機鼻 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.018781 | -0.054211 |-| 0.6108 | -0.2910 |-5°~0°|
|0°| -0.006614 | -0.000910 |-| 0.6241 | -0.2756 |-5°~5°|
|5°| -0.029328 | 0.054707 |-| 0.6373 | -0.2603 |0°~5°|

| 重心 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.018781 | -0.089905 |-| 1.0161 | -0.2910 |-5°~0°|
|0°| -0.006614 | -0.001232 |-| 1.0310 | -0.2756 |-5°~5°|
|5°| -0.029328 | 0.090045 |-| 1.0460 | -0.2603 |0°~5°|
:::
| 機鼻 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.082 | -0.123 |-| 1.4095 | -0.9397 |-5°|
|-2°| 0.033 | -0.047 |-| 1.3465 | -0.9454 |-2°|
|0°| -0.000 | 0.002 |-|  |  |0°|
|2°| -0.032 | 0.050 |-| 1.3751 | -0.9167 |2°|
|5°| * | * |-| * | * |5°|

| 重心 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.082 | -0.049 |-| 0.5615 | -0.9397 |-5°|
|-2°| 0.033 | -0.019 |-| 0.5443 | -0.9454 |-2°|
|0°| -0.000 | -0.000 |-|  |  |0°|
|2°| -0.032 | -0.020 |-| 0.5730 | -0.9167 |2°|
|5°| * |  * |-| * | * |5°|

### xflr5的橫向穩定 零度攻角
| 機鼻 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.017 | -0.025 |-| 0.3375 | -0.1982 |-5°|
|-2°| 0.007 | -0.010 |-| 0.2889 | -0.1939 |-2°|
|0°| -0.000 | -0.000 |-| 0.2952 | -0.1964 |0°|
|2°| -0.007 | 0.010 |-| 0.2889 | -0.1939 |2°|
|5°| -0.017 | 0.025 |-| 0.3375 | -0.1982 |5°|

| 重心 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.003 | -0.014 |-| 0.1820 | -0.0300 |-5°|
|-2°| 0.001 | -0.006 |-| 0.1532 | -0.0223 |-2°|
|0°| -0.000 | -0.000 |-| 0.1566 | -0.0245 |0°|
|2°| -0.001 |  0.006 |-| 0.1532 | -0.0223 |2°|
|5°| -0.003 |  0.014 |-| 0.1820 | -0.0300 |5°|

### avl的橫向穩定 零度攻角
| 機鼻 | cl | cn |-|cn$\beta$|cl$\beta$| |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°|  | -0.025 |-| 0.3375 | -0.1982 |-5°|
|-2°|  | -0.010 |-| 0.2889 | -0.1939 |-2°|
|0°|  | -0.000 |-| 0.2952 | -0.1964 |0°|
|2°|  | 0.010 |-| 0.2889 | -0.1939 |2°|
|5°|  | 0.025 |-| 0.3375 | -0.1982 |5°|

| 重心 | cl | cn |-|cn$\beta$|cl$\beta$| Neutral point |
| ------ | ------ | ------ |-| ------ | ------ |-|
|-5°| 0.00743 | 0.00142 |-| -0.016107 | -0.084318 | 0.051380 |
|-2°| 0.00299 | 0.00057 |-| -0.016315 | -0.085411 | 0.051390 |
|0°| 0.000 | -0.000 |-|  -0.016355 | -0.085619 | 0.051392 |
|2°| -0.00299 |  -0.00057 |-| -0.016315 | -0.085411 | 0.051390 |
|5°| -0.00743 |  -0.00142 |-| -0.016107 | -0.084318 | 0.051380 |

![image](https://hackmd.io/_uploads/Byy-jxU8Wx.png)


## 總結
1. 要達到最大起飛重量巡航攻角必須大於5度
2. 升力斜率偏小，僅3.1左右，遠低於常規的4.2左右
3. 可以明顯看到翼尖比翼根不容易失速
4. 機身產生的升力為負，且升力斜率不如想像的大，高攻角下無法提供足夠升力

## 存些圖
:::info
v color bar : 10~25
p color bar : +-200
:::
![image](https://hackmd.io/_uploads/By9QP7_UZe.png)
![image](https://hackmd.io/_uploads/H1zaDmuU-e.png)
![image](https://hackmd.io/_uploads/ByVRvQd8-g.png)
![image](https://hackmd.io/_uploads/ByU3umdUbx.png)
![image](https://hackmd.io/_uploads/SJCAuQdIWx.png)

![image](https://hackmd.io/_uploads/HJreqQdLWx.png)
![image](https://hackmd.io/_uploads/rkHZ9mO8Zx.png)
