Dynamic Analysis of Turbulent Annular Seals Based On Hirs’ Lubrication Equation

1983 ◽  
Vol 105 (3) ◽  
pp. 429-436 ◽  
Author(s):  
D. W. Childs
Keyword(s):  
High Pressure ◽  
Space Shuttle ◽  
Water Pump ◽  
Centrifugal Pumps ◽  
First Order ◽  
Lubrication Equation ◽  
Inlet Swirl ◽  
Main Engine ◽  
Perturbation Solutions ◽  
Annular Seals

Expressions are derived which define dynamic coefficients for high-pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps. Completely developed turbulent flow is assumed in both the circumferential and axial directions, and is modeled in this analysis by Hirs’ turbulent lubrication equations. Linear zeroth and first-order “short-bearing” perturbation solutions are developed by an expansion in the eccentricity ratio. The influence of inlet swirl is accounted for in the development of the circumferential flow field. Comparisons are made between the stiffness, damping, and inertia coefficients derived herein based on Hirs’ model and previously published results based on other models. Finally, numerical results are presented for interstage seals in the Space Shuttle Main Engine High Pressure Fuel Turbopump and a water pump.

Effects of Wall Flexibility on the Rotordynamic Coefficients of Turbulent Cryogenic Annular Seals

1996 ◽  
Vol 118 (3) ◽  
pp. 509-519 ◽  
Author(s):  
B. Venkataraman ◽  
A. B. Palazzolo
Keyword(s):  
Energy Transport ◽  
Space Shuttle ◽  
Element Formulation ◽  
Local Pressure ◽  
First Order ◽  
Rotordynamic Coefficients ◽  
Wall Flexibility ◽  
Main Engine ◽  
Symmetric Finite Element ◽  
Annular Seals

A theory for analyzing the effects of elastic deformations of the seal wall on the dynamic characteristics of high pressure cryogenic annular seals under concentric operation is presented. The bulk flow continuity, axial and circumferential momentum, and the energy transport equations are utilized to determine the pressure distribution in the seal. Thermophysical properties of the cryogenic fluid are assumed to be functions of the local pressure and temperature. The wall deformations are obtained using an iso-parametric, axi-symmetric Finite Element formulation of the seal wall. A perturbation analysis is employed to arrive at the first order solution which yields the rotordynamic coefficients. Results obtained for the case of Space Shuttle Main Engine Oxygen Turbopump (SSME-HPOTP) Preburner Seal show a significant impact of seal flexibility on the dynamic coefficients.

Cold Flow Testing of the Space Shuttle Main Engine Alternate Turbopump Development High Pressure Fuel Turbine Model

1992 ◽  
Author(s):  
Stephen W. Gaddis ◽  
Susan T. Hudson ◽  
P. Dean Johnson
Keyword(s):  
High Pressure ◽  
Space Shuttle ◽  
Rocket Engine ◽  
Performance Model ◽  
Test Article ◽  
Turbine Performance ◽  
Reynolds Number Effects ◽  
Liquid Rocket ◽  
Turbine Design ◽  
Main Engine

The National Aeronautics and Space Administration’s (NASA’s) Marshall Space Flight Center (MSFC) has established a “cold” airflow turbine test program to experimentally determine the performance of liquid rocket engine turbopump drive turbines. Testing of the space shuttle main engine (SSME) alternate turbopump development (ATD) fuel turbine was conducted for “back-to-back” comparisons with the baseline SSME fuel turbine results obtained in the first quarter of 1991. Turbine performance, Reynolds number effects, and turbine diagnostics, such as stage reactions and exit swirl angles, were investigated at the turbine design point and at off-design conditions. The test data showed that the ATD fuel turbine test article was approximately 1.4 percent higher in efficiency and flowed 5.3 percent more than the baseline fuel turbine test article. This paper describes the method and results used to validate the ATD fuel turbine aerodynamic design. The results are being used to determine the ATD high pressure fuel turbopump (HPFTP) turbine performance over its operating range, anchor the SSME ATD steady-state performance model, and validate various prediction and design analyses.

Convergent-Tapered Annular Seals: Analysis and Testing for Rotordynamic Coefficients

1985 ◽  
Vol 107 (3) ◽  
pp. 307-316 ◽  
Author(s):  
D. W. Childs ◽  
J. B. Dressman
Keyword(s):  
Dynamic Pressure ◽  
Momentum Equation ◽  
Computational Method ◽  
Centrifugal Pumps ◽  
Zeroth Order ◽  
Taper Angle ◽  
First Order ◽  
Dynamic Coefficients ◽  
Direct Stiffness ◽  
Annular Seals

A combined analytical-computational method is developed to calculate the pressure field and dynamic coefficients for tapered high-pressure annular seals typical of neck-ring and interstage seals employed in multistage centrifugal pumps. Completely developed turbulent flow is assumed in both the circumferential and axial directions and is modeled by Hirs’ bulk-flow turbulent-lubrication equations. Linear zeroth- and first-order perturbation equations are developed for the momentum equations and continuity equations. The development of the circumferential velocity field is defined from the zeroth-order circumferential-momentum equation, and a leakage relationship is defined from the zeroth-order axial-momentum equation. A short-bearing approximation is used to derive an analytical expression for the first-order (dynamic) pressure gradient. This expression is integrated numerically to define dynamic coefficients for the seal. Numerical results are presented and compared to previous results for straight and tapered seals. The direct stiffness and leakage increase with increasing taper angle, while the remaining dynamic coefficients decrease. An optimal taper angle is shown to exist with respect to (a) the direct stiffness, and (b) the ratio of direct stiffness to leakage. Stiffness increases on the order of 40-50 percent are predicted. Experimental results are presented for seals with three taper angles which show generally good agreement between theory and prediction.

Analysis for Rotordynamic Coefficients of Helically-Grooved Turbulent Annular Seals

1987 ◽  
Vol 109 (1) ◽  
pp. 136-143 ◽  
Author(s):  
Chang-Ho Kim ◽  
D. W. Childs
Keyword(s):  
Space Shuttle ◽  
Helix Angle ◽  
Circumferential Velocity ◽  
Surface Pattern ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Small Motion ◽  
First Order ◽  
Rotordynamic Coefficients ◽  
Annular Seals

An analysis for helically-grooved turbulent annular seals is developed to predict leakage and dynamic coefficients, as related to rotordynamics. The grooved surface pattern is formulated as an inhomogeneous directivity in surface shear stress. The governing equations, based on both Hirs’ turbulent lubrication theory and “fine-groove” theory, are expanded in the eccentricity ratio to yield zeroth and first-order perturbation solutions. The zeroth-order equations define the steady-state leakage and the circumferential velocity development due to wall shear for a centered rotor position. The first-order equations define perturbations in the pressure and axial and circumferential velocity fields due to small motion of the rotor about the centered position. Numerical results are presented for proposed grooved seals in the High Pressure Oxygen Turbopump (HPOTP) of the Space Shuttle Main Engine (SSME) and for a water-pump application. The results show that an optimum helix angle exists from a rotordynamic stability viewpoint. Further, a properly designed helically-grooved stator is predicted to have pronounced stability advantages over other currently used seals.

The Space Shuttle Main Engine High-Pressure Fuel Turbopump Rotordynamic Instability Problem

1978 ◽  
Vol 100 (1) ◽  
pp. 48-57 ◽  
Author(s):  
D. W. Childs
Keyword(s):  
High Pressure ◽  
Space Shuttle ◽  
Original Design ◽  
Support Design ◽  
Response Characteristics ◽  
Instability Problem ◽  
Stability Performance ◽  
Improved Stability ◽  
The Stability ◽  
Main Engine

The SSME (Space Shuttle Main Engine) HPFTP (High-Pressure Fuel Turbopump) has been subject to a rotordynamic instability problem, characterized by large and damaging subsynchronous whirling motion. The original design of the HPFTP (from a rotordynamic viewpoint) and the evolution of the HPFTP subsynchronous whirl problem are reviewed. The models and analysis which have been developed and utilized to explain the HPFTP instability and improve its stability performance are also reviewed. Elements of the rotordynamic model which are discussed in detail include the following: (a) hydrodynamic forces due to seals, (b) internal rotor damping, (c) bearing and casing support stiffness asymmetry, and (d) casing dynamics. The stability and synchronous response characteristics of the following two design alternatives are compared: (a) a “stiff” symmetric bearing support design and (b) a damped asymmetric stiffness design. With appropriate interstage seal designs, both designs are shown, in theory to provide substantially improved stability and synchronous response characteristics in comparison to the original design. The asymmetric design is shown to have better stability and synchronous response characteristics than the stiffly supported design.

Experimental and Theoretical Comparison of Two Swirl Brake Designs

2000 ◽  
Vol 123 (2) ◽  
pp. 353-358 ◽  
Author(s):  
K. K. Nielsen ◽  
D. W. Childs ◽  
C. M. Myllerup
Keyword(s):  
Space Shuttle ◽  
Theoretical Data ◽  
Superior Performance ◽  
Swirl Ratio ◽  
Strong Separation ◽  
Inlet Swirl ◽  
Computational Fluid Dynamics Cfd ◽  
Brake Performance ◽  
Main Engine ◽  
Better Than

Experimental and theoretical data are presented for two interchangeable swirl brakes designed in connection with the Space Shuttle Main Engine (SSME) Alternate Turbopump Development (ATD) High-Pressure Fuel Turbopump (HPFTP) program. The experimental data includes rotordynamic data for a extensive variation of test variables. Comparison of the swirl brake performance revealed that a nonaerodynamic swirl brake design proved as efficient and at times better than an aerodynamic design. For this reason a theoretical investigation using computational fluid dynamics (CFD) was recently carried out. This modeling focused on predicting the seal inlet swirl ratio which is the primary swirl brake performance parameter. The nonaerodynamic swirl brake showed superior performance for a variety of test variable conditions. Strong separation vortices within the swirl vanes are the main reason for this finding.

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