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Photograph of static pressure taps on an turbine blade and the internal
 routing of the pressure tubes to the transducer.

This page shows two photographs of a wind tunnel model of a turbine blade. The model is used for diagnostic testing to determine the pressure distribution around the blade. At the lower right of the figure, we have labeled the pressure taps which are small holes drilled perpendicular to the surface of the blade. Because the flow around the blade is tangent to the surface, the taps are also perpendicular to the local flow direction and are pressurized by the random component of the air velocity. The pressure in the taps is the static pressure as discussed in Bernoulli's equation.

To measure the pressure, long thin tubes connect the taps to a pressure transducer located outside of the wind tunnel model. In this figure, the transducer is shown in a schematic drawing. The transducer measures the difference in pressure between the pressure in the tube and a reference pressure. A typical transducer measures the strain in a thin element using an electronic strain gauge as shown in red on the drawing. The reference pressure is arbitrary, but should be noted in any data report. Possible reference pressures include the external free stream static value, the wind tunnel total pressure, or a static value located somewhere on the model. Either an average, steady state pressure, or a time-varying, unsteady pressure value can be obtained depending on the capabilities of the transducer.

Looking at the picture of the model, on the left, we see that diagnostic models are complex, precise, and normally quite expensive pieces of equipment. The model must be carefully designed to place the pressure taps where they can provide the most information to the engineer. Routing pressure taps to the transducer is obviously a challenging engineering and manufacturing problem.

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Editor: Nancy Hall
NASA Official: Nancy Hall
Last Updated: May 05 2015

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