滑移可以通过经验模型估算。CFturbo中提供以下模型（不适用于径向流入涡轮机）。2B叶片角度β必须确定，以达到所需的能量传递——即所需扬程/压差——同时考虑滑移速度。2B以下常见叶片角度β的建议基于最佳效率：
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15°...45°，常用20°...27°τ2 in section 2.
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For determination of β2B it is important to be aware about the deviation between flow angle and blade angle. The direction of the relative flow w2 at impeller outlet does not follow exactly with the blade contour at angle β2B. The flow angle β2 is always smaller than blade angle β2B due to the slip velocity. This difference is called deviation angle δ:
The deviation angle should not exceed 10°…14°, in order to limit increased turbulence losses by asymmetric flow distribution.
A reduced flow angle β2 results in smaller circumferential component of absolute speed cu2, which is - according to Euler's equation - dominant for the transmission of energy. Blade angle β2B is estimated by c特定定义 for blade congruent flow (see figure). Therefore an estimation of slip is necessary.
Slip can be estimated by empirical models. The following models are available in CFturbo (not for Radial-inflow Turbines):
• 封闭经验模型
• 输入系数a
• 封闭经验模型
Blade angle β2B must be determined to reach the desired energy transmission - respectively the required head/ pressure difference - under consideration of slip velocity.
The following recommendations for common blade angles β2B exist due to optimal efficiency:
泵 |
15°...45°, commonly used 20°...27° |
风扇 |
不超过50° |
压缩机 |
35°...50°，无罩叶轮可达70°...90° |
Turbines |
取决于半径，详见正弦定理 |
离心机械（径向进气燃气轮机除外）在低比转速nq下，β值通常相近2B此类叶轮的叶片常设计为直后缘（β2B=常数）。对于径向进气燃气轮机转轮和混流式转轮，从轮毂到轮缘的后缘半径差异很大，导致β值差异显著2B并采用扭曲叶片
可能的警告
问题 |
可能的解决方案 |
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后缘叶片角ßB2 < xx° |
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异常低的出口叶片角 可在“首选项”下调整警告级别：警告级别. |
出口角过小表明出口截面过大。需减小后缘尺寸 |
叶片与流动之间的偏转角δ（滑移）较大 |
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出口处叶片与流动方向之间的偏转（滑移）异常高，表明叶片载荷过大 可在“首选项”下调整警告级别：警告级别. |
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后缘叶片角ßB2 > xx° |
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后缘叶片角异常高，可能由叶轮过载引起 可在“首选项”下调整警告级别：警告级别. |
增大后缘尺寸（主要尺寸）和/或滑移系数γ |
无法在@TE处计算合理的热力学状态。请考虑调整叶片角、厚度、主要尺寸或全局设置 [仅适用于压缩机和燃气轮机] |
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几何结构不允许建立物理有效状态。例如，质量流量过高。 |
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无法计算后缘叶片角。请更改叶片形状、叶片角或进出口直径 |
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全局设置、主要尺寸和叶片设置的组合无法计算叶片角。不存在满足所有上述约束的叶片角 |
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叶片角不在有效范围内 |
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CFturbo的使用仅限于0°至180°的叶片角 |
叶片角度计算不可能（见下文），或调整不合适的用户输入叶片角度。 |
无法确定叶片角ßB |
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叶片角度计算失败。 |
尝试增大叶轮直径d2或出口宽度b2和/或滑移系数γ |