Rocket Nozzle Plume Heating

Rocket Plume Heat Transfer

Thermal Desktop® is commonly used for thermal analyses of spacecraft and propulsion systems. Less frequently, these tools are used for calculating the temperatures in supersonic exhaust nozzles, such as those in rockets or thrusters.

The temperature of the nozzle wall is an important aspect of rocket design. The exhaust-gas temperature typically exceeds the maximum allowable temperature of the nozzle wall material. The ability to estimate the wall temperature allows the design of a cooling system.

Four types of cooling systems can be modeled in Thermal Desktop: heat sink; thermal radiation; even regenerative (using FloCAD®). A difficult part of modeling the cooling system is approximating the heat transfer from the plume to the nozzle wall. The convective film coefficient can be estimated through a number of methods (Bartz equation, TDK boundary layer technique, etc); the coefficient is highly dependent on the axial location within the nozzle.

Rocket nozzle segments

    C&R Thermal Desktop® Model of a Radiating Nozzle

 

The steady-state solution is presented below. Note the increased temperatures on the front right side of the nozzle caused by variation in the heat transfer coefficient, called streaking. The radiating section of the nozzle shows varying wall temperatures as a result of the changing heat transfer coefficient.

When compared to the actual system, the convective heat fluxes for the radiating portion of the nozzle are underestimated by about 20%. These are reasonable results based on simplification of the geometry (no structural reinforcements were included) and assumptions made within the fluid properties and equilibrium reactions. The correction factor mentioned above could be adjusted to remove this error or provide a safety factor: a key benefit of model parameterization.

Rocket nozzle temperature results with streaking

   Steady-State Results of Plume Convection in a Radiating Nozzle Using the Bartz Equation with Streaking

 

Expansions of the model could be:

  • Adding regenerative cooling in place of the fixed-temperature boundary condition
  • Adding surfaces representing the throat (a torus, perhaps) and the combustion chamber
  • Adding material properties to the inner wall of the nozzle or throat to evaluate recession of the material
  • Adding a second, concentric surface around the nozzle and mapping solid elements between the surfaces to form a heat sink nozzle
  • Mapping the results to a NASTRAN or ANSYS structural FE model

 

flow regimes

Introduction to Two-phase Flow

September 24, 2-3pm MDT

This webinar introduces basic concepts in two-phase flow modeling including quality, void fraction, flow regimes, slip flow, pressure drops and accelerations, and heat transfer.

No knowledge of CRTech software is required. However, references to the corresponding FloCAD features will be made to assist users of that product.

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Introductory FloCAD Training

Class times: September 5, 10, and 12, 2019, 9:00 am to 12:00 pm MDT daily
Cost: no charge (attendees must have an active support contract)

CRTech will be hosting introductory training for FloCAD (Flow Modeling in Thermal Desktop). This is our standard FloCAD class previously hosted in a classroom environment and now restructured for an online teaching environment.

The class will introduce single-phase fluid modeling concepts and how to build fluid models within the FloCAD work environment. Topics covered include an introduction to fluid modeling components, geometric versus non-geometric modeling options, working with FloCAD Pipes, solution control, and an introduction to path and pipe libraries.

The class will be broken into three two- to three-hour sessions held over a 3 day period. The format will be online lecture and demonstration with opportunities to ask questions. Hands-on lab work will be provided to students to work on after each session. To gain the most from this class, students are encouraged to attend all three sessions.

Prerequisites: Attendees must have basic working knowledge of Thermal Desktop as many of its base features will not be covered in this class but their usage is required for FloCAD.

Eligibility Requirement: This class is a service to our customers. All attendees must have an active support contract. If you are unsure of your support status, please contact CRTech.

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