Turbomachinery velocity triangle problem

In summary, the problem involves an incompressible air flow across a rotor, with the absolute velocity increasing from 15 m/s to 25 m/s. The objective is to determine the direction of the absolute velocity at the outlet and whether the rotor rotates clockwise or counterclockwise. Using Euler's torque equation, it is determined that there is no torque on the rotor, indicating that it is a pump rather than a turbine. The velocity triangle can be completed using the Pythagorean theorem to find the angle of the absolute velocity at the outlet.
  • #1
MacLaddy
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Capture.PNG

Homework Statement



Air (assumed incompressible) flows across the rotor shown in the figure such that the magnitude of the absolute velocity increases from 15 m/s to 25 m/s. Measurements indicate that the absolute velocity at the inlet is in the direction shown. Determine the direction of the absolute velocity at the outlet if the fluid puts no torque on the rotor. Is the rotation CW or CCW? Is this device a pump or a turbine?

Homework Equations



Euler's Torque equation

[itex]T=\dot{m}(r_2V_{\theta2}-r_1V_{\theta1})[/itex]

The Attempt at a Solution


[/B]
As torque = 0

[itex]T=\dot{m}(r_2V_{\theta2}-r_1V_{\theta1})=0[/itex]

[itex](r_2V_{\theta2})=(r_1V_{\theta1})[/itex]

[itex]V_{\theta2}=V_{\theta1}*\frac{r_1}{r_2}=15\sin{60}*\frac{1.9}{1.2}=20.57 m/s[/itex]

No idea where to take it from here. I can't tell from the problem statement if the direction of [itex]V_2[/itex] is as indicated.

If there is no torque, as indicated, then I would assume that this must be a pump--as the fluid isn't doing any work on the rotor. However, I believe I need to prove this with velocity triangles and the like.

Any help would be appreciated.
Mac
 
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  • #2
It looks like you found the velocity in the same direction as V1. The problem gives you the full velocity. You can complete the triangle using the Pythagorean thm, and find the angle from that.
 

1. What is a turbomachinery velocity triangle?

A turbomachinery velocity triangle is a graphical representation of the relative velocities and angles of the fluid flow through a turbomachine, such as a turbine or compressor. It is used to analyze and design the performance of these machines.

2. How do you construct a turbomachinery velocity triangle?

A turbomachinery velocity triangle is constructed by drawing a horizontal line to represent the rotor blade velocity, a vertical line to represent the axial velocity, and a diagonal line to represent the relative velocity. The angles and magnitudes of these lines are then calculated using trigonometric relationships based on the geometry of the machine.

3. What is the purpose of a turbomachinery velocity triangle?

The purpose of a turbomachinery velocity triangle is to analyze the performance and efficiency of a turbomachine. It allows engineers to visualize and understand the fluid flow through the machine and make informed design decisions to improve its performance.

4. How is a turbomachinery velocity triangle used to calculate the power output of a turbine?

The power output of a turbine can be calculated using the turbomachinery velocity triangle by first determining the relative velocity and then using the equation P = ρVrelArel, where ρ is the fluid density, Vrel is the relative velocity, and Arel is the cross-sectional area of the relative velocity.

5. Can a turbomachinery velocity triangle be used for both compressible and incompressible fluids?

Yes, a turbomachinery velocity triangle can be used for both compressible and incompressible fluids. However, for compressible fluids, the Mach number must also be considered in the calculations as it affects the fluid properties and flow behavior.

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