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Wake Frequency Calculator

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In the realm of fluid dynamics and process engineering, ensuring the structural integrity and performance of instruments exposed to fluid flow is paramount. This is where the wake frequency calculator becomes an essential tool. Designed to predict the natural frequencies of vibration for thermowells in a fluid stream, this calculator plays a crucial role in preventing equipment failure due to vortex-induced vibrations.

Purpose and Functionality

The wake frequency calculator is based on the principles of fluid-structure interaction, where the force of a fluid flow impacts the stability of immersed structures. Specifically, it calculates the wake frequency, or vortex shedding frequency, experienced by a thermowell—a device used to house temperature sensors in industrial processes.

This calculation involves several inputs related to the fluid properties (density, velocity, viscosity), thermowell dimensions (tip and root diameters, length, modulus of elasticity, moment of inertia), and installation parameters (insertion length). By analyzing these variables, the calculator helps engineers design thermowells that can withstand the fluid forces without resonating at dangerous frequencies, which could lead to failure.

The Formula

The wake frequency f is estimated using the Strouhal number, a dimensionless value that relates fluid speed, vortex shedding frequency, and the diameter of the thermowell. The formula simplifies to:

f n = (1 / (2π)) * sqrt((E * I) / (m * L^3))​​

where m represents the effective mass per unit length of the thermowell, considering the added mass due to the fluid dynamics.

Step-by-Step Example

Let’s walk through a simple example:

  1. Given Data:
    • Fluid Density (ρ): 1000 kg/m³
    • Fluid Velocity (v): 2 m/s
    • Fluid Viscosity (μ): 0.001 Pa·s
    • Thermowell Tip Diameter (D): 0.01 m
    • Thermowell Root Diameter (d): 0.015 m
    • Thermowell Length (L): 0.5 m
    • Modulus of Elasticity (E): 200 GPa
    • Moment of Inertia (I): 1.5e-9 m⁴
    • Insertion Length (t): 0.4 m
  2. Calculation:
    • First, calculate the effective mass (m) considering the fluid’s density and the thermowell’s dimensions.
    • Apply the values into the formula to find the natural frequency (f n​).

This simplified example demonstrates the calculator’s process, but remember, real-world scenarios might require more detailed analysis.

Relevant Information Table

Density of the Fluidρkg/m³
Velocity of the Fluidvm/s
Viscosity of the FluidμPa·s
Tip DiameterDmeters
Root Diameterdmeters
Length of the ThermowellLmeters
Modulus of ElasticityEPa
Moment of InertiaIm⁴
Insertion Lengthtmeters


The wake frequency calculator serves as an indispensable tool in the design and analysis of thermowells in fluid applications. By enabling precise calculations of vortex shedding frequencies, it ensures that thermowells are designed to avoid resonant frequencies that could lead to catastrophic failures. Its applications span various industries, including oil and gas, chemical processing, and energy generation, highlighting its significance in ensuring the safety and efficiency of industrial operations. Through its comprehensive approach to calculating wake frequencies, this calculator aids engineers in adhering to standards and achieving optimal thermowell design, ultimately contributing to the reliability and longevity of temperature measurement systems in fluid flow.

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