Turbulent Boundary Layer dialog box

Operation Name
Sets the name of the turbulent boundary layer (TBL) model node in the Simulation Navigator.
Region Selection
Lets you select element faces to specify the region where the software applies the turbulent boundary layer model. Typically, you select free element faces of the structural mesh where no sharp pressure gradients along the direction normal of the loaded face exist.
Frequency Range
Type	Specifies the type to use in frequency response solutions.Appears also when Type is set to Use Frequencies from User-Defined Auto-Spectrum, which uses the frequencies specified in a field for a user-defined auto-spectrum model.
Frequency List (Hz) box	Appears when Type is set to Individual Frequencies.Lets you specify as many frequencies as you need.Enter the frequencies to include. Separate them by commas or spaces.
First Frequency, End Frequency After, and Step Value	Appear when Type is set to Linear Sweep.Specify the frequency range.Note: When the End Frequency After value does not fit into the sweep definition, the software includes the next valid frequency in the frequency list.For example, if First Frequency is 100, End Frequency After is 200, and Step Value is 75, the software exports 100, 175, and the next valid frequency, which is 250.When the End Frequency After value is greater than First Frequency, the software generates one interval.
First Frequency, Last Frequency, and Number of Logarithmic Intervals	Appear when Type is set to Logarithmic Sweep.Specify the frequency range.
Lower Center Frequency and Upper Center Frequency	Appear when Type is set to Octave, 1/3 Octave, or 1/12 Octave.Let you enter the lower and upper center frequency values of the frequency range.
Correlation Spectrum Definition
Model	Allows you to select correlation spectrum models. You can enter spectrum-related parameters in the Parameters group, after you select one of the following models:CorcosThis model is especially useful for accurately predicting the spectrum convective ridge for high-speed flows, and for its simple formulation. You need to adjust only the Correlation Decay Rate (alpha) and Correlation Decay Rate (beta).Note: This model overestimates the experimental data in the subconvective region, and does not consider boundary layer parameters that can influence the spectrum shape. It considers only the hydrodynamic part of the flow field.EfimtsovThis is the only model in Simcenter 3D that was developed from aircraft instead of laboratory measurements. This model was validated with measurements on an aircraft that was traveling at speeds above Mach 0.41 and below Mach 2.1.ChaseThis model provides a direct formulation for the wall pressure spectrum because it is not defined as a product of a correlation and auto-spectrum model.User DefinedThis model allows you to select your own model and prompts for a .dll file. The software queries your file to obtain parameter names and types, and populates them in the dialog box.Depending on the selected model, you must also select a model from the Auto-Spectrum Definition group.For more information on correlation spectrum models, see Turbulent Boundary Layer Models.
Auto-Spectrum
Model	Allows you to select auto-spectrum models that are one-sided in Simcenter 3D. That is, the software considers only positive frequencies. Therefore, all input and output spectra are one-sided quantities.You can enter spectrum-related parameters in the Parameters group, after you select one of the following models:**Robert (Corcos)**This model is defined as a function of the outer scaling parameters Fluid Outer Velocity and Displacement Thickness, and the Fluid Density.EfimtsovThis model is defined as a function of the Reynolds number. This model applies to zero-pressure gradient boundary layers. It has been calibrated from measurements of TBL wall pressure fluctuations on an aircraft. It is valid over a wide range of Mach numbers above 0.015 and below 4, Reynolds numbers above 6E2 and below 1.5E5, and Strouhal numbers above 0.2 and below 1E4.GoodyThis model is limited to zero pressure gradient flows but considers the effect of the Reynolds number variations through the time scale ratio. This model shows good agreement with experimental data over Reynolds numbers above 1400 and below 23400.SmolyakovThis model is a semi-empirical model and mostly applicable to flat plate surfaces.Cockburn-RobertsonThis model is used for flows at transonic and supersonic speeds. The model was calibrated when investigating the vibration response of spacecraft shrouds to in-flight fluctuating pressures. The effects of the Mach number affect only the mean square pressure, and become negligible at transonic and lower speeds.Smolyakov-TkachenkoThis model is a semi-empirical model and mostly applicable to flat plate surfaces.Chase-HoweThis model is limited to near or below the universal range of a quantity, which is a function of frequency, fluid viscosity, and wall friction velocity.User DefinedThis model allows you to define your own model with a field.Depending on the model you select, the software allows you to specify a field with frequency-related values or additional spectrum-related parameters.For more information on auto-spectrum models, see Turbulent Boundary Layer Models.
Parameters
Lets you enter parameter values for your combination of correlation and auto-spectrum models. Depending on the selected models, only specific parameters are available.Note: You can find valid parameter values in the literature, or obtain them from experiments or previous simulations.The software does not check the parameter values; therefore you must enter only valid values. For example, fluid density, displacement thickness, decay rates, and so on cannot be zero or negative.You must specify convective velocity parameters for any TBL model, even if you use a User Defined correlation spectrum model that may contain information about convective velocity in a user defined .dll file.
Formulation
Lets you select the method to compute the TBL.
Wave Number Domain	Lets you enter minimum, maximum, and delta wave number domain (interval) parameters in the X or Y direction.Applicable when the loading is represented in stochastic terms in wave number domain.
Spatial Cholesky	Decomposes the loading into deterministic components with or without Random Sampling.Applicable when the loading is represented in only stochastic terms.
Scale Loads for Unity PSD Factors	Scales loads so that the power spectral density (PSD) factors will be 1. This modifies the magnitude of complex field values.
Random Sampling
Enable Random Sampling	Lets you specify the number of random samples to reduce the computation time when the model has many random load cases. The solver uses less than the available input loads.
Number of Random Samples	Available when the Enable Random Sampling check box is selected.Specifies the number of random samples. The number of samples you need depends on the model and loading type. It is recommended that you try your case once with different numbers and see if the solution converges from a certain value onwards. You can then use this value for similar cases.

For more information on correlation spectrum and auto-spectrum models, see Turbulent Boundary Layer Models.

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Turbulent Boundary Layer dialog box, Simcenter 3D 2021.1 Series

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